Dabus Hydropower Project Summary

FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA
MINISTRY OF WATER, IRRIGATION AND ENERGY
DABUS HPPs
Consultancy Services for Pre-Feasibility and Feasibility Study of the Dabus Hydropower Project
Proairwnent Reference ^umhrr - DHPP/WoWUTOJ/WH
DABUS HPPs
PRE-FEASIBILITY DESIGN
GEOLOGICAL and GEOTECHNICAL REPORT
July 2016
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tel 0632,10,000 to: 06 327?. 276
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Ministry of Water Irrigation & Energy
Haile G/Sdase Road P.O. Box NO.: 5744 Addis Ababa, Ethiopia
t*] I r>f ]
Rome, 01'* July 2Q15
Att.ne:
Mr. GETU TlLAHUN
Email:
getu_tilahun2005@vdtioo.com
Telephone:
+251 11 11 /11 6637222
Telefax:
+251 11 6610710
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DABUS
CorwHancy Servtes for the PRE-FEAS1BILTTY and FEASIBILITY Studies of the DABUS Hydropower Project
PRE-FEASIBILITY DESIGN and EIA BASELINE rev. B- Transmission Letter
Dear Mr. Getu TlLAHUN,
following:
your  comments  to  the  pre-feasibllity  design  report  and  EIA  baseline  report  (reference  is  made  to  the attached matrix);
the workshop held In Addis Abeba on 16 Jone 2016;
r
our meeting neld at your office on IT71 June 2016,
We have updated the following reports:
100 WHO R SP 003 B vol. 1 / 2 - Main Report;
- 100 WHO R SP 003 B vol. 2 / 2 - Drawings;
120 HYD R SP 001 A - Hydrological Report;
130 GEO P SP 001 A - Geological and Geotechnical Report; 140 SEA R SP001B - BASELINE Study.
Yours faithfully
StWto Jhp, a
Antonio PIETRANGEU
Antonio BRASCA
EnOosurps n. 2C hard copes; 2 CO
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WORKSHOP 16 JUNE 2016
Pd<je 1 of 9
___ ____________ _____  _______ _________ coysLt r>yvrs wsacwses ro cwvr ossfr? m ^ovs_____________________________________
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WORKSHOP 16 JUNE 2016
Page 2 of 9
QQfrSU WTT figSTOftSBS TO «ZPV? O6Sf?U4 77OVS
Comments by Client
Answer by Consultant
5AVMW 17 ftw
^^.se i<**fi ctetffc 
nas ciyxivrfFcr on >/* &-105 ftMAf OTjJ or on frWn LA Ownfte bntfy We
sto toe Owe sxw
ch* 15$ (CM _____________
tor pnwsmg of We
Sferrosrtwr      tr^ges      We      -to      fms      Wfa      to      ort^r      to      cooitHf?
r/rcose Wc ovfried ooe Wan onfr
s*7** -*020n ar
A7
AB
ttvWrm -13L ft weft -Vftx* rtafiFflrtffioftS W We iWM* KVW iXT not
conduct on
?n
xzvex^<x«4 ^tmeyoor.
jusfA                 >W7eW?v toe ty/t* />*bc 
Ch /sa
The drone survey was earned out on the ch- 15$ dam area,
This typo will be corrected In Revision 6 of the Prefeasibility Report. ______________________________
AH the topographic  activities  regarding the Pleiades  have been concluded (acquishon and processing). In April 2Q16 a ground survey  was  carried out to acquire Ground Control Points (GCPs) to georeference and orthorectify  the images  Processing to obtain contour lines  has  recently been completed sc  the Pleiades  topographic  database will be usedr instead of the SRTM, for rhe Feasibility Study since it has a much better accuracy.__________________________________________
There were problems finding suitable landing area near PH ch-lOB. The Consultant will start from the PLEIADES images which are sufficient for design purposes at this stage.
AThneotnhaemr deroonf ethsue friveguy rewshill oeualrdneredaodu“tchin 1a5f5u“tuibreis stwailgl ebeoncocerregct ooedd liannRdeinvi gsiaorenaBs ohfatvehebeen
_______________________________
ntofc J.U.- Owed sunein?o tatos toem « no yoond confroi*
r
at Ouw At ChJ$5*tf4r ChJO& w* kkx Asftficafty? <fayfr_
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orftrvi    ?.i>    Osruss    iM?    detey    We    Ope    or    soffw^    awf    meWod    used
tor CHI7>W9 out Wo Awpoo* ftie
energy OToUtoi
«mr < izh<s as a toortkxi </ p^don s/mxAj tx
glpto^r^ haswf on l**6xW ft^tgri^/vc strvej<__________________ _________
4.rzw^> 7TW jarvrtrvi t JJl ft* CtXJSUtant sfajkf
Wff FSttWOtr
otudiftxage    «*w    Mdtewto    Oasw    on    sto?jeor    toeastztvw:    6cX   toe    natxvf
A9
A10
All A12
A13
Aid
PIdreefnetaisi fibeiwdy , Report ____________________  __________ __________ _ ______________ __________  _______________ The Consultant explained that another type of drone (RTK) was used that does not require GCPs.
This drone is currently under testing
A   mathematical   model   created   by   SP   was   used   for   the   reservoir   routing.   Die   model   is   described   at length in the report._____________________________________________________________________________________ Agreed.
In Che Feasibility Study the accuracy will be improved (Plealdes Database More detailed modelling will be done during the Feasibility Study.
>W5 June rw<J un jtiuortxy cCfd from
juaraf toe -rU6l ----------------------
Ctw>me^ pJ/           Mtoty «j*t
Ajoif □/ toe Ktfwftas  flwevteo' as  ay  toe i/w 7O? Av  toaafrWy Aftxft Wrec  tooaf r/ toe xjyxjrtanr sfr *7*wa^ntor»j -xii not OW <W
CTi^aAFto-S 'VVT ftv faasaMfy ifape*
f^ekf
We wAisrs jyiwi to
0U«ng We cvr&or aotf a\senoir i
opto cs  gt/to ftxr fheanc  cevn totxxjW*n msKK-' Ww ^Wess ,on?M¥Ke of xqom oor rorwaered as  mgt*wr tor nert pftase wi atomo-_____________ ____ ___ _____ _—-— ----------------------------L
CwtrucPfen ^ayirx  dHMWMe
1
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stv?X? otVa^ af 4msT -tv                  sf»*gf /QJftNtf c/
A16
The    Consultant    explained    that    Investigation    planning    will    be    done    in    the    near    ruture    in    collaboration wFoitrhtthheesrCtleieanlt ch - 130 the Consultant estimated the quality and the quantity of the quarry 
material (ref. page 86/223).
c/ wi We joniwef
thu
•VdtAnf
{ ^1 7 I or
I tfaoe maZ>
STkr r>/xp
to Ototf or *oc*tc? *7b-?£ti5W?r>‘?
zH-
wsetfcafJOT a wjoortarrf ft fl«wy af Wtf ,
For the site at ch ~ 108, detailed indications were not considered necessary given the abundant
evidence of easily available construction material outcropping everywhere
The    Consultant    pointed    out    that    this    information    was    included    in    the    report    130    GEO    R    SP    001 [Geology Report) of the Prefeasibility Report
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a c&t&n constfud/on fnrtewt |
A17 1
16D627, DABUS, Reply to DBS at PRETEAS Report (Workshop 160615)
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DABUS hpp
WORKSHOP 16 JUNE 2016
Pag^ 3 of 9
cpAgx.q/yrs jg^saotySES to g/evfQfiSCTM ffovs
No.
Comments by Client
Answer by Consultant
At AFr
•jfjfcF
Ih? nxiW nxrft? 4Q7                    house S*e
sud*j as f-TEFxwr®                         f>re/Mp
Q1B
pnopp^ rrjri: WK njdr O^SS ibttctrWftt
/ypst^jo? D/ 4^ /crt(WTKft)9*C ft# or wostxi? to LTyjtftonW                                   S^DTjA be aattsed *e*. 77xa pnxwr pMniwy r>wW*xj </
w/tos-
c^xr   jXtes   fly   ^QCMXtPO^   s/nxitxr-   of   the   nwr«k*m7   <juo>i   «   flto tos nx*s to a                                   v/r ATV Hawton/ vpotjgh to flrt4f M npwx^
/
A10
This will oe addressed in more detail in the Feasibility Study.
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cam hpe setocftv? cttfertt flAen h the report ooto                              are not &*)<** tto nyyt-i rw* wV atoer
Q19
AI9
1
The allemdtfves  studied at site ch - 130 included an RCC dam and a CRT dam. As  may  be read in the report, the cost of the RCC dam and the CRFD are practically  idenocal so the Consultant preferred to adopt a 'safer’ solution and with fewer maintenance cosfc, i.e. an RCC dam.
As   far   as   the   dam   at   ch   -   108   is   concerned,   an   RCC   dam   was   considered   the   only   option   given   the general geological conditions.
The    Consultant    points    out    however    that    the    two    dams    are    completely    different,    so    much    so    that the dam at ch - 130 was presented wrth two distinct solutions
dam with central spillway and ski jump dissipator;
non-crverflow dam with separate spdlwuy
The dam at ch - 108 on the other hand can be overtopped with a stepped spillway
1-----------
Q20
7J5e 4?mx/ o&m aW ^DCXftvw?/ stoxtonre Pta/V 6e €**rfr «watod «i fte
A2d
Noted and agreed.
This will he corrected m Revision 0 of the Report.
0400$ Hf***                             Grfm>
Q21
In yMMr Jfrwm flc*y gcWditon <XKWiyj monthh                                      asa?^w toe 7**?           ftrttv/ s Kft toe d«xij£F*AA? •*y*x* z'^sje *3 <Z 2233
A21
Revision 0 of the Prefeasibility Report will correct this error.
rf
' Q22
Stare  'Xtl   -ho   fl^ank  sotoMTF  are  *sfw  <?  xxz  ore-'feMflWh'  reccvf  to$t  tSSftJ to               cfefa. £mZ toe re-M6*fy•#& qudbty of those aVtaare iy not ^Wjfo*
A22
Pic software used to elaborate the Pre-Feasibility Design was:
either software internationally recognized, or
mathematical models elaborated by 5P,
Jtare iTo Alt of
art toe tox?f page 0< toe XXO ■
. Q23
^mMv> report. TtaMore /(snot «s> to wawto toe ajcon*
A23
Noted and agreed
This wtil be addressed in Revision 0 of the Report.
Oator                Aower Protect* Ctx^n*ot» 07 f*s
Q2-1
fieeptte cornojents  //okjW on toe *9cwy*off flqoort reoreo to toe nwne of top
/Wfl/y  if b not oons/aemd in the preewbon of tfvs  report' ft (x»ts toe
A24
W< ww cS toe At^sfrk 
is Wstot* <X ftotec /mtNton
_
Noted and agreed
This will be corrected in Revision 0 of the Report.
Q2S
Sojibr to toe nxywflf Ao. L towrfint £NW on ta*v too                                    o' £wqsW tycirtpoHer sitoefljffi on toe rriga&cw Atoew                                 to be <**wdpetf h* acmeses.                      nc/taig flay been &w n toe report rented to tox
A25
The     Consultant     points     out     that     Intended     Irrigation     schemes     am     not     wiehm     toe     scope     of     this assignment.
Only the impact on existing irrigation schemes will be considered in the ES1A report
Q26
1
■ jL
to tot? >oc3Ddtxi import ft Has  prtfjtaetf to w 'fSff <Rr»* Ay  fwpMf^ date cc^w bot to toe pre ■'feasrbMy sfuto flow-w* AtfUOfS s*iv*te ropery Aas  d2so taw txsetf to toi sftxj^. toe /tMSww necwts  Mf to we toto of then « Aone^r not stated tn the report
A26
The accuracy of the drone is greater than toe accuracy of the Pleades.
However the areas  that can be surveyed by  drone are in lhe order of a few square kilometres. The PleaWes, on toe other hand, ran be used to survey  areas  of several hundreds  of square kilometres (over LOGO km2 were surveyed for the Dabus project).
For this reason toe drone was used to survey the main works (dam and powerhouse), while the Pleaides images were used for the topography of the remaining .jrts [reservoir, quarries, etc
r
160627, DABUS, Reply to DBS at PRE-FEAS Report (Workshop 160615)
studio pietrangdi, rumeWORKSHOP 16 JUNE 2016
Page *1 of 9
DABUS hpp
coystx Mfr rs ^fyovses to ctJ&tfr osse>?ui wovs          —--------------------- -------------- ■
_____ — ----------------------------- —------ “ ~
No.
Comments by Client
Answer by Consultant
1
Q27
.
^fecfny? of 0&7>s rrvtae br cowdtftng
d axrjcpivrf 4F*e*> w toe                wort ths sfixA  4f* focufttf on nh? s-j/rje -W sfw                     rfM?r cqtrsc l*‘*'=* "
iftjtHw
A27
The entire nvtr course was studied.
As can be                dearly from the longitudinal profile of the river (ref. Fig. 7.2.2), the areas studies were the only ones feasible from a technical-ecooomlr viewpoint.
1----------
| Q2B
fote™              hm rrfaKf on
Tfter/n^otscen^on toeoutor
'
tot* &J< *f*/? eV ronu/rocftw            HoWW. H/totHtf rons«*vaftOT of toe fotoxs -s^jpV ■'©•ter crxvMctod concrete 6^XJ **tf axxrete
A28
The main factors  (geology. quarry, mamtcnaiKe etc,) haw* been considered in this  preliminary evaluation, nwe than adequate far a pre-tesibiiity  design More detailed elements  will be considered in the next stage (Feasibility Design).
| Q29
H/foX! ■XflA J*7'1
_
j>ot x- qu*t>. wfas xr ittwtffatf *n ton itea> ArX no *rcwtf reMtetf ft? q«*r> vto  utVtzrx* ofttje tedtew*’’ to 6e oojmw Aws been & W.
1
429
Reference    is    made    to    quality    and    volume    of    the    identified    quarry    sites    at    Page    86/223    of    the Prefeasibtljry Report,
>Oflft>*09*c**Owow>^ wuroAw 4 imWm ciff^/ihr Zxrec                           H)
1 Q30
7fie sto tx? sW .'dcoaxxtife toe o~tx*v? of tot? /xqpcw«/-hc? s/tas anc toe 7W ■'r'ftyonh to we tor rfsuw^ftbn enw toa^J aAoha mt i'W 2
A30
toed and agreed.
Revision B of the Prefeasibrbty Report will address this.
rttgg JV. ------------------- -------------- ----------------- -------;----- to  c&Ateatex?  pnxwss&s  o»Tsr  cwvre-rf  c»O  iprecotaarw  ancr atatodte? autej. >oo used a 3                 <**<»         (J96S-196?), nA>? 3ninM' Ax kitorfXX? f/969 <JW J9?2-J9MJ. f^ge S4              5S
Q31
A31
Periods  spanning Jan 1965, Dec  1967 and Jan 1972, Dec  1974 provide the more complete mH of Significant dally  discharge measurements  at the station of Dabus  near Assosa and were therefore selected (or calibration and valldatjon purposes  Different periods  were selected to perform the calibration and the validation of the model In order to guarantee that the calibration resulting from one period was  actually  efficient for the application of the model to another period, in other words in order to guarantee the generalisation to other penod of the calibration performed on a specific period.
to sfofetW teste fAjpotte®* iwtoyiX /wxtenyre«x *x*w»o(w
toteogOTety *«■ *teto>*7iy wtoocA >K*o jcxxfwr W -Xrf snoyo
stXf/F^JrtrtW ■'esr/b' of edCb test fMrntf ftW7 tW iteftcVKy^p teste
.^rt-Tw*.             tests are *jte*red -» nc^rtw ffrenctl *xf
use r> prtciKe (tt» sntmrvy lesti <kk? tour £09B 56 *W 67
to
1
| Q32
A32
A   table   presenting   the   results   of   the   performed   tests   in   terms   of   the   specific   statistics   used   by   each test Is Included m the revisea version of the report.
The assumption of neglecting the observed trend stems  from the observation that the trend Is negative, i.e. the observed maxima lend to decrease in the spanned period (1961-2008). The analysis  of the extremes  considering the sample as  a not-stabonary  sequence, i.e. considering stabsbeal models whose parameters are dependent on time (e.g. Reiss and Thomas, 2007, Coies,
2000,     Fawcett,     2013),     would     have     produced     a     not     conservative     decreasing     in     time     of     the discharge quintiles.
toss, R D. and Thomas, M (2DQ7). SMfrsf/Cdf 4Od(k$X3 of frfreme I^Zues 
/rxstxeXKii /frxjqce. T^ohxbg^                        Other Aptatf. Birkhauser Third Edition Coles, S. (2000). Air ^Footcfw to statist^/noa^tfrqg
to
wye^s Springer.
---------------- ---------------- ——  . ---------------------  ---------------------- ---- --------------
Fawcett,      L      (2013).      Topics      in      Statistics.      Environmental      Extremes.      Lecture      Notes.      University      of Newcastie.
Q33
rtrMsn  avrecf  prqww>  toe  bWvrrjefrt  sfatton  mm   0/  Dfassw  ■'iw  4jo "TsftsxJ c/ 4rb tototpdo^ toe obox^rfs.
A33
Noted and agreed.
Fhls will be corrected in Revision H of the Report
1
;7                             1
j
Q34
On papt- <Z i^w ? otof 00 feff </               ■nc^tNes-'  SJrrj&fy f^^vi Dag-
A34
Noted and agreed
This will be corrected In RewSJOn 0 of the Report.
160627, DABUS, Repty to 0<t$ rt PR£-fEA5 Report (Workshop 3 £43615 J
Mudio pietratyieil. ram?DABUS hpp
WORKSHOP 16 JUNE 2016
Page 5 of 9
cpysu frwrs x?6sffovsgs zu g/fjyr 0&sCTk4 zrovs_________
No.
Comments by Client
Answer by Consultant
Q35
G«wa/  cot/otC  *>  W-3  S^port  Due*  ft  ts  ftof  a  gooc  *c*w  to  xxX  **  Me OB&i US pfffltw W or fifaH/HjOh&r W ft* wwtfk ^WSQOi
A35
Noted
Thts will be removed Prom Revision B of tbe Prefeasibility Report.
Dew/opmeflf •**#              ^eAhM^»Cn»r*GO &*vctorwfv
JAtougft CTOf fCltoj*to                       GT*w tawJ 
fl ooe of Ite Most
Zisuefl Ax fMum to                            ift enwryy^tat Meoc/k- «x*w^
pruivM   *1   parPTL^r   rtx*   to   Me   fort   IW   I^wrwo^er   a-   ow   (/   Me   ptfxs   Ax Me wtcoienteboo of Ww sto+togy- ft fl                           07 Me W' JTxa Me
stai&JteK? tecto ^LSLieXx/ ■o/  i»e^<w*getfto fie report
Agreed to discuss the CRGE to the final repent
_
/XDHKW Afe FM*q>*? /wtMXTr
/rorfaMdtoXT
Agreed to incorporate the proclamation 197/2000 and Regukjtron (115/2005) in the final report
Q36 L
192/200Q rXJtf
ijrp             to                 assnciMoO
constouTw    of    (&n    for    paw    gewabon    ate    not    mcorporafra    «7    Me
rtyzyf.
1--------
Q37
/>*■ to Me toe t Mrf Me*e M *p M< ^7^ &
r
9^*^
Agreed to address Proclamation 513/2007 In the final report
OWE? toe CDOSftoCPXZ >176. rf fl to|MXf<W to UQtTf&S Me flSUC tyrff) rvg&tf
to Soto fy&te
f+tx&oabop (513/200? J
1
Q38
4wMJt   11   ofpage/JZ   ft   v   stated   tM   HpooDoterpus   aOjpn&wk   a    one   of Me n/ta                    tatojr ff> Me stoo^ aw fw MqqsA tots- mV <kw>^ a
riMTrtjbrf   to   toe   /U7V   mU   fat   Me   coasx/toof   wxf   cfces   xxMto   Mtt   fact   On Mt? otoe* band tow                 ZVwtened <W ram vwto jrx^ -wuted to Me TXxyf          tMe          fSM&wapwijs          (Loooml          fiWhera          Leo          (Honl GBCTtatonepxc&ta     /Z«¥>kV     nxfwset     AMoftcms.     OxixuM^jsnrfoflous     fVte
As  per the TOR, this  is  an EIA Baseline Study  phase, therefore, the resource and the potential impacts  are discussed. However, detailed mitigation measures  will be presented In the Full F-SLA report
Owm>?2 «xid dtnw not ina^tv
to pm/pcf Me
I
■--------
Q39
4m*jt2 ftedfej of xwge 132 Thxr <xv Ast of P&&                                  *xe tow to Me dflrecf   rwxT   yw   fiLC   Me   tar   c*xs   not   seefn   ctyzpWr   x   MtotfUsAve.   j^x fastened toor* fl ao a sangto cfojder *to A/rn                               ah toe tai Ooes
txsx^ Mere *s ■*» c^toer *n toe art*d?
Yes,    the    list    Is    not    complete    or    exhaustive.    Detailed    sampling    and    kfentitartxjri    of    plants    will    be earned out during full EIA
Q40
fitoflW w w.taerjbritV fl rwX M^owmbed.
Once   detailed   sampling   and   identification   of   piants   is   done   during   full   ElA,   we   will   gwe   information on species vulnerability using [IKN RED LIST Of ETHIOPIA
1—
*H*A*  QUrf^fr  «3J0S5F?7enC  it  fl  W  £*M^  iJeSVMet  Me  MtMTtoOCT
txstw to ra«Wi Me wte ftr
taw Me -TuMbtx of s&wte n
Agreed   to   discuss   how   the   sampling   sites   are   selected   and   the   technique   used   to   collect   the   sample in the final report
Q4i
stotKafy (tow* and oMer tato-xa/ /taoes Me                                       p^noa (Cry/w? season)           swte (fsirvtxjboo                  nor *ve^ ■Wrasetf n Me ^wri. fbe
rwrt sfjotAl
teen jXTOntocf to jzxti
to dtatraft? Me stdtoAtaj1
r^xwen/dfruw of Me Me r-aftix»A“ 6eVw Me otiMjctoon of Me
$aoy>*s  Me ^xMoa of af^dfysis  ww* the ^abffiry of the ohtpuf
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160627, DABUS, Reply to DBS at PRE-FEAS Report (Workshop 160615)
StuOiij pwtiangfMi. r<yne■
ft ft k l
l I
lWORKSHOP 16 JUNE 2016
Page 6 of 9
.
No.
Comments by Client
Answer by Consultant
/? s oof <^M aW                                   **ter sf-s^xter*             used to eiaAeto toe |
r
Agreed to elaborate in the final report
I Q42
I
/irtittoysTtf* Of KJft* 90^ (Tlfbfft* Dfsso^jp sMl
etc. 1 -Moreoirt rter/X^ p*"dWft*T
not
uiTk* tens brto&Gif rtsww                                to Hator qt»W> -*r
□KvtootWX
1-
[
Q^3
TAe   4«**f*^W   of   Dabus   *tm    *   storxtf   a?   trtt   fc?ond   f6fc   toe   cws^t twtoM to                     fi -*i             ftw, srxb c0rrfxr^rf port of hw 4A*to
fiyyotovj.
According to CBPWDG (Comrnunry  Bused Participatory  Watershed Development Guideline), the watersheds  size ranges  6,000*20,000 ha Is  used to identify  communities  and ranges  of community where watershed planning can start at this  level. However, before implementation starts  an in depth study will be expected to do based on the Guideline
I
Q44
4s to*A»<W to toe report                           of so-' kas a rqM & tJSLt
£ *”xs
rof   -.TXW*^   fa£s$*   1*00}   £O*es   *>tf   ni<v-   tente   h/to6   suzwe   to   irt*r the <xw*n*y? of toe                 tots, it s ^-/yre^ to tocwx^
otoe^ cwton-gt*               A&bs to oonsx*r toe tose                     by gg**s W "V*
tents
RUBLE is  used for soil loss  estimation- The main soil loss  part and cause for Gully  formation is  the untreated or unmanaged part of big watershed. So that focusing on assessing soil loss  from the First phase of erosion 1$ essential al this  stdge Therefore, that is  why  this  assessment does  not consider losses from gullies and river bank.
0,5
tosfew of tang t&,£ it wuto tew teen tetor ft) txse toe
1
ste Ase fA’OStO n/wto w toepr«fc*x«sy (xStf.
(zn-ers^
RUSLE ts used for soil loss estimator. Please see the collected data
p
' Q46
1
AxiiM ctnoy toftxi* /and use 4xw cow- cteoges of a WV itetx?                       AmW on toe    jwtuxx    Mw    teff    an    n^ssa-e    importance    for    a    proper    n^na^^rt    of a  Wersterf  *r  h/wto  ts  higher  associated  to  zyufm*  a  te<n  fttrn  sctf  erosw  > 7/FCAXie/  SrtXhcof  atXVZjOCsftCto  Ox»  Wy  (X  tor  Other.  trt&Sten&ng  (V  Hie
The current land use and land cover has  already  been done and shown in the document. However, assessing the dynamics  or change of land use Is  not covered In the TOR and beyond the scope of this assignment
rate of patterns or change of toe h^ftr jAm» jtu t
^rprttant to
dWwwe tw o<toe <^> S& tout toe cOTs^/w^teuto* tew w* toe
■tend  use  tancf  row-  cteopf  &rO*tes  watershed  area  in  a  manner  to  steiv  toe ituft* tteue ext*) cflwryrs
TO*D*Cf
Q47
tor     consufttof     Orf     not     stocoy     to*«v     the     Myt^upon**     Aocfccftcn 7Mq3pcrfabon 4n& Ftatote/W guiuefine (lOfr? F^W.
As   per   the   TOR   dirs   is   an   ELA   Baseline   Study   phase   Therefore,   during   the   next   phase   the   Full   ESIA will strktly address all the Issues as per the ERA Guideline.
Q48
*r po-Woo fOpgracfapbQ &r quaaty by oust ancf wteM« emtssfons)
The same as above
Q4$
—-------- L
Sasrt pcAjborf (fyxhrts «te crashers, coxwto
?ww® to ambient ntrsr /**■ toe sutetaitonsj
cAwtws off,
The same as above
Q50
H«ftv PodUw fCbWwa^ of surface and trN^rp>wxf HOteto tewooos
The same as above
tfMH, OABLS, Reply to DBS at PW-FfAS Rpport (workshop 160615}
stud«o pietrangeii, ronicDABUS hpp
WORKSHOP 16 JUNE 20 IS
CCfi&Jt WrS WSPQtfSFS 70a/fiVr05SfX?k4Z7OVS
Page 7 of 9
No.
Comments by Client
Answer by Consultant
So' poA/w                        of wvsnOW rjowfwfiwn af t*K> (&ty Serf rotorjdcflcvi
QSl
1
^pqtjctor *) io ifert^iy. -Storf
&s a            tZ                               of
Yes    there    will    be    sal    erosion    during    construction    and    this    impact    will    tie    elaborated    and    mitigation measures ■dentrfied and recommended to the Full ESIA,
acrf eTXjf^toaOcm tfwi stVisfofroosJ <#T ■'XV             assrccsw
(Z ffw fXKUWVW tVjI^OOW^
tost toe nyisotont 6sM cemW*^ fly 
notary TryftfFH?
M cnUSf d
!TWjf*-rtt<xs     dtocxxZ     of     c»smndm     an     toe     ^Kcmjwf.     ^wtevw.     toe <wsufant r^cnn/rjc^Oitton <XW cwW^ iZwto                                      no w’wwtt
not to pn»c«* toe zytjtxjftxl £M£KA" W wms «?
.Tgjftf A) toe toss xomfrfiK? Ay toe ronHirt>W- Ooes to«Z >7?e^i
vto
toe
mwroretocvZa/   te   re   oototoff5     O   tftf   toe   rnnsr/iW   rtvxKxf   toe   stotv   Ax sate or procKMxe?
Based on this  EIA Baseline Study, there will be both posits  and unavodabie negative impacts associated with the Implementation of this  Project. These potential benefioaJ  as  well as  significant adverse impacts on the physical, biological and sooo economic environment are Identified
However, based on this  baseline survey  result, it is  concluded that there an? no environmental grounds  for not proceeding the Proporsed Dabus  Hydropower project to the next phase and therefore, it is  recommended to proceed with the feasibility  Phase of the Project This recommendation s consistent with EPA's EIA Guideline.
"-----------
Q52
1
xltte^too   .Zwota   de   g/w   fly   to/s   zsma?   ano    toe   nnstrffrif   re   ftwectata   to tor orosr totfyj’fctxr iTxwwxe                           yj oo                             *?v^' to
toe ziesw^*                       stpoose to de reOxetf to xn^rxA-hhZ LKtoojtog to f^wwwtef zx^cr «Z fhW»tJ <799/1 Auc<Widtay? on
NTjoacf aHmsTxxrf f?»94?0O?JL Gbcfc^Te flx »tos aw
wwz i'?i JEX.1
3
as per ERA'S FLA Guideline requirements, a full Environmental and Social Impact Assessment will be prepared during the Feasibility  Study  and all relevant matters  related to the potential environmental impacts identified in this Study will be fully addressed
The        significant        environmental        impacts        require        avcwlance,        mitigation        and/or        compensation measures. These measures will be Identified and eWxrated further in the next phase.
QftWnWlW
Q53
Afott cZtoe tabtat
.7>rre eta to toe f■*> -w n&bta fbre
Will be corrected in the Tmal version of the EIA Basdioe report,
otxt/wtf             Sc oseo1 tor flxtoere- ston>« #*7 TOferooce tor toe tofore.
Q54
ZJnpAto^MQ- (¥|M*wneO&#Z .Oyrwrfe ra4/Jng flXftGt fl?Soi/n« AO toe ;>nvect <xea toouta  de stotftta jW mxwwfitf to toe rqpcyf These
■'nrtoqe togMtf on jfjoidc Ktutytffems. ftyrwtoZ ecwston^ (Ze Aura ant?
j^ewJh tonre/ Mx^wcsbc- tom#                 c>u^* r? up<&v to
1
tor ■•ectocho'i <Z            cw*vgc ixw  e^ <*W tevW cok* jtafltams- fsuto cU lANTtonjFtot flytsst wgetohix* rot+s eto7
1
Preliminary  environmental impacts  including forest resources  in the project area was  described. The existences  of unique riparian and wetland vegetation were discussed and the recommcndatxxi re to avoid any damage on these resources
However,   as   d   compromise,   it   was   also   recommended   to   asses   areas   m   the   Oabus   drainage   system as a substitute that is going to be tost by the dam
—
'WTO?*vf*
iALt^y focatotf to .jrrws h^to fonwfc,
1
Q55
■jrvris date dem cfcared tor w *s <j*>i toosfrurton and *hZ?t wkx
TA&n&tore toe preta^ftxy ^urootoetfa/ OjflpOfrXr WJyw *w rosfs tor
rryfr^kZtoS Axts/ tass aW otoer ^ZrcvM-jeoRZ /sates ot nof 6r*A- rqcxxfW to toe                           5tooy (Z toe Zxbus >iH*Q»‘*er                   Y
During    the    next    phase,    the    Full    ESIA    will    identify    and    recommend    mitigation    and/or    compensation measures for forest losses and estimate all costs to implement these measures.
Q56 |
4s 0^ toe JW (ZsecMx? J. ft toe pre^wnry ayr^
fTe^ves aou
costa           ^neWerwt suncort tend and toahv^/ /ukm. and
The   TOP.   requires   an   EIA   Basdlne   Study   lor   this   phase   and   a   detailed   and   Fulr   ESIA   in   the   next phase. Therefore, during rhe next phase the Full ESIA will strictly address all the Issues as per the
16O627 DABUS, Rtpfy to DBS al PRE-FEAS Report (Workshop 160615)
r
studio [wrtrangei, ramcrj
Page 8 of 9
WORKSHOP 16 JUNE 2016
OABUShpp
consul x?fSAavsgs to a^roBs^Mno^
Comments by Client
Answer by Consultant
nor            dKCflbetf -n         zxe fw&ty rqoort.
FPA     Guideline,     This     will     Include     all     environmental     miogatxxi     and     management,     buffer     zones     and watershed development, environmental monitoring, capacity building and training costs.
the
Die same as above
Q6/
pre^^tn^ry 
nor Arjritow t6e costs ts noT
soctf evtf reto to
cast win&j
and sdcm/ rarfr «•
am? and acroun/w for rfa?
<qcoY Tfw ftyo? ev>i*W7jento/ joc/ j»o^' rtparr. Zh? ftvn, cw wiwnenf*'
ewnto* IM X* tantf paid aWcr
/■nK«4fi7>eofff and <xx*.»aw c/
_________ Oiwrtwyeof ____________________ _________
7b aoOnsff              suc^ gsugh foage 65 2/ J A*e
4 Mtscwrtoa
4
xx* ocxVKVh*1 proftto CM 2002 ^gpert«
•W^rmd Th/s hM true fix rfysxtf &szb*ty rjfr i rwye w Hoff if not PQ£96^ to rvfiy figure os/wcr ofi te+Jhp o<Z<WW
health wi^astrurtlirp
<r to A#4re u*Qi*vfr<cz
None out of the five TaWes  and Charts  below that are based on CSA can be updated because of lack  of up to date and disaggiegated data - disaggregated such as  urban/rural, male/female, region/zone/woreda, etc  Such comprehensive and disaggregated data can only  t>e obtained from the CSA and the next national population census  Is  yet to be conducted In the absence of such datar another source is  administrative data compiled by  the woredas. In addition to its  limited reliability, very  often, administrative data is  either not comprehensive. or not disaggregated by gender and the rest of variables, or unavailable altogether.
Despite these limitations, efforts  will be made during the upcoming ES1A fieldwork  to gather, where possible, data and information required updating those Table? and Charts  (1 to 5 below) that are based on CSA's outdated data
Q58
1.
2.
Table    2.4:    Literacy    Rates    of    Population    of    the    Project    Area    by    Sex    and    Urtaan/Rural    Residence {CSA 2007)
Chart     2.1:     Proportions     of     Major     Ethnic     Groups     Living     in     the     Proposed     Dabus     Hydropower Project Areas (West WoNega Zone and Asossa Zone) (CSA 200/
3.    Chart     2.4:     Proportions     of     Populations     by     Religious     Affiliations     m     Dabus     Hydropower     Project Areas (Based on CSA:2007)
4,
Chart    2.5:    Economic    Acnvty    Rate    of    Population    (Aged    10    Years    and    Above)    in    the    Proposed Dabus Hydropower Project Area by Urban-Rural Residence and Sex (CSA: 2007)
5.     Chart     2.9:     Physical     Disability     Rates     (Per     10,000     People)     among     Populations     in     the     Proposed Project Area (Based on CSA: 2007)
On (.t..h.e....O..t.h..e..r...h..a..n..d.....T..a..b.l.e...5. .2..0.. t.s ...co....r.r.e..ct . ..e..xce ......p..t..t.h..a..t..t.h..e...ye...a...r..(.2..0..0..7..)..].s ...m...i.st...a..ke...n..l.y ...w...r.i.t.t.e..n...m......  _ ____________ r
...
4r
sooo-eeoww- «Mr**rtv*«s*s tfi* OaAvs 6^«ooh<v
onw an? oof va/wr r> the nm-•nsoxr. Ais/tne «*$ ne# as 
rM$k>ffVe SD0iD-W3OGW /Qp*-f5 to 6? cKTHX*? (HjP to ffe pfQ/T<f ft?
Etfnopwn     calendar     Instead     of     Gregorian     Therefore,     the     year     2007     will     be     converted     Gregorian
2014/15-
Yesr      due    to    field    constraints    the    socio-economic    aspects/nsks    of    the    Dabus    Hydropower    project    are 1  not clearly stated in this EIA Baseline Survey report.
fa?
flyhoyaofre
<?>v Mff^n
!bD6?7 DABUS. Reply to 065 at PFtE-FEAS Report (Workshop 160615)
rDABUS hpp
to a^roBs^^Tto^s 
WORKSHOP 16 JUNE ?O16
Page 9 of 9
No.
Comments by Client
Answer by Consultant
____
vkj/fv Qt4Wk ana6®s forest ohnenoiW ert/w dctrnttes, at/mct
on 6cx7>ao              *V ecoooo>r staOfi. ffxwncp fZ n<ft* rented cfix&s&s.
reteMteffan and TO^nR$0O7» /ywyan/rr cZfoe protect e/r.
However, detailed field survey will be earned out dunng the full ESLA
160627, DABUS, Reply to DBS at PRE-FEAS Report (Workshop 160615)
tfufri fMPtnvijeli, romeDABUS HPPs PRE-FEAS
GEOLOGICAL and GEOTECHNICAL Report
INDEX
page i of ii
1       CONTENT.......... ................................. ....................................... .................... ................ ....................... ........... .... 1
2       REGIONAL GEOLOGY................................................................................................ ........................................... 3
2.1
INTRODUCTION......................................................... ..................................................................3
2.2
REGIONALSTRUCTURAL EVOLUTION................................................................................................... 6
2.3
REGIONALTECTONICS.............................................................................................................................7
3 LOCAL GEOLOGY.............................................................................................................................................. 8
4       CH- HO: DAM SITE................................................ ............................................................................................... 11
4.1
MORPHOLOGICAL FEATURES............................................................................................................... 11
4.2
INVESTIGATION CARRIED OUT DURING THE PREVIOUS STUDIES................................................ 11
4.3
ACTIVITIES CARRIED OLTT DURING THE VISIT.................................................................................. 12
4.4
GEOLOGY OF THE DAM SITE.................................................................................................................13
4.5
GEOTECHNICS OF DAM SITE................................................................................................................. 15
4.6
QUARRY FOR CONSTRUCTION MATERIALS....................................................................................... 16
5       CH - 130: WATERWAYS and POWER HOUSE.....................................................................................................16
5.1             MORPHOLOGICAL FEATURES............................................................................................................. 18
5.2           ACTIVITIES CARRIED OUT DURING THE VISIT.....................................................................................IS
5.3           GEOLOGY and GEOTECHNICS............................................................................................................... 19
6       CH - 106: DAM SITE........................ ................................... .................................. .................................................20
6.1
GEOMORPHOLOGICAL and GEO5TRUCTURAL FEATURES............................................................... 20
6.2
ACTIVITIES CARRIED OUT DURING THE VISIT..................................................................................... 23
6.3
G EOLOGY OF THE DAM SITE................................................................................................................ 23
6.4
GEOTECHNICS OF THE DAM SITE......................................................................................................... 24
6.5
QUARRY FOR CONSTRUCTION MATERIALS........................................................................................ 27
7       CH - 108: WATERWAYS and POWER HOUSE..................................................................................................... 28
7.1           GEOMORPHOLOGICAL FEATURES........................................................................................................ 20
7.2           ACTIVITIES CARRIED OUT DURING THE VISIT..................................................................................... 29
7.3           GEOLOGY and GEOTECHNICS................................................................................................................29
8       SEI5MIC ASSESSMENT......................................................................................................................................... 30
8.1           INTRODUCTION........................ .................................................................................................................30
8.2           SEISMICITY OF THE AFRICAN EASTERN RIFT VALLEY....................................................................... 30
8.3           DETERMINISTIC SEISMIC HAZARD APPROACH................................................................................... 33
8.3.1    INTRODUCTION............................................ ................................................................................... jj
8.3.2    GROUND MOTION PREDICTION EQUA TIONS (GMPES)............................................................34
83.3     SEISMIC SCENARIO................................................................................................................................J#
8.4           PROBABILISTIC SEISMIC HAZARD ANALYSIS....................................................................................... 36
ft < J   IN TRODUCTION ............................................................................................................................ 3$
8.4.2    SEISMIC RISK.................................................................................................................................... „„ 57
130 GEO R 5P001A (GEOL and GEO’’ Report).docx              no GEO R SP0C1A
studki pielrangdi, fomeDABUS HPPs ^E-FEAS
GEOLOGICAL and GEOTECHNICAL Report
page II of it
Rtf flrawjpr_________ ___ ________________________
-      130 GEN DSP001 Plan 500k
-      130GEN DSP002 Legend
-      130 GEN D SP 004 DAM ch- -130, Plan 6k 130 GEN D SP 005 DAM ch. -108, Ran 6k
-</Wer
- ANNEX A
130 GEO R 5P001A (GEOL and -SECT R«pdt).ito
130 GEORSPDOIA
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I
■
■
I
■
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I II
■
II li n
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□ABUS HF*s
PRE-FEAS
GEOLOGICAL and GEOTECHNICAL Report
ABBREVIATIONS ACRONYMS
DSHA             Deterministic Seismic Hazard Approach EARS             East Rift Valley of Africa
GMPES Ground Motion Prediction Equations GSHAP Ground Hazard Assessment Program GSI Geological Strength Index
MER               Main Ethiopian Rift
PGA               Peak Ground Acceleration
PS HA            Probabilistic Seismic Hazard Approach RMR               Rock Mass Rating
RQD               Rock Quality Designation
SASW Spectral Analysis of Surface Waves SRTM Shuttle Radar Topography Mission
130 GEO R SPOOIA (GE01 and GEC^ Report).cto
UOGfORSP 001A
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GEOLOGICAL and GEOTECHNICAL Report
page 1 rtf 40
PRE-FEAS
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1 CONTENT
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This   report   illustrates   the   preliminary   geological   and   geotechnical   characteristics   evaluated   for   the   project area of the following hydropower projects:
-     Dabus CH - 130;
-     Dabus CH - 108.
The preliminary geological analysis was based on:
analysis of the existing geological maps and precedent studies;
pbotomterpretation of the satellite images and drone aerial photos;
- site visit, preliminary geological survey and site investigations.
The following project component sites were surveyed during the geological investigation:
Dam sites;
Waterways;
Power houses;
Quarries.
Based on the collected data a preliminary geological model was developed In the areas of these main works.
This model is based on the photo-interpretation of the satellite imagery, on the geological analysis of the
rock outcrops observed during the site visits.
In  addition,  a  seismic  assessment  was  carried  out  over  the  Dabus  project  area  aimed  at  evaluating  the  Peak Ground Acceleration at different return periods.
The report Is divided into the following chapters:
CONTENT
This chapter shows the scope of the present study,
-     REGIONAL GEOLOGY
Illustrates the regional geology.
~ LOCAL GEOLOGY
Illustrates the geology of the project area.
-     CH-130; DAM SITE
Descnbes  morphological  features  of  the  Dam  area  and  the  activities  carried  out  during  the  site  visit. Geological and geotechnical characteristics of the dam site were specified.
BO GEO R SP001A (GEOL and GEOT Rec^nj.docx                  BO GEORSPOOJA
sTurf fl
flDABUS HPPS
PRE-FFAS
GEOLOGICAL and GEOTECHNICAL Report
P»QC 2 nMO
CH - 130: WATERWAYS and POWER HOUSE
Describes  morphological  features  of  the  Waterways  and  PH  area  and  the  activities  carried  out  during the site visit. Geological and geotechnical characteristics of the examined areas were specif ed,
- CH - 108: DAM SHE
Describes  morphological  features  of  the  Dam  ares  and  the  activities  earned  out  during  the  site  visit. Geological and geotechnical characteristics of the dam site were specified.
CH - 108: WATERWAYS and POWER HOUSE
Deschoes  morphological  features  of  tine  Waterways  and  PH  area  and  the  activities  carried  out  during rhe site visit. Geological and geotechnical characterise Hi of the examined areas were specified.
- SEISMIC ASSESSMENT
Illustrates  the  seismic  assessment  for  the  project  a^ea  to  evaluate  the  peak  ground  acceleration  at different return periods
130 GEO R SP001A (GEOL and GfOT
doot
llOGEO RSP 001*.
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PAE-FEA5
GEOLOGICAL and GEOTECHNICAL Report
2 REGIONAL GEOLOGY 2.1 INTRODUCTION
NQt 3 of 40
Three main physiographic  provinces  characterize the Ethiopian region: the highlands  (represented by the northern and southern Ethiopian plateaus  and the Somali plateau), the Afar depression, and the Mam Ethiopian Rift" M ER' (Figure 2.1.1).
The birth, evolution and present-day  morphology  of these provinces, although not achieved at the same time, are linked to the uplift and nftmg of the Afro- Arabian plate since tine Oligocene.
These physiographic  features  derive from a long geological history  that started with the closure of the Mozambique ocean, between West and East Gondwana, and the development of the Ethiopian basement (Paleozoic  rocks) ranging in age from 900 to 550 Ma. This  folded and tilted Proterozoic basement underwent Intense erosion, which lasted 100 million years.
ftpurf ! J. /VAf ofEttwpw
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The beginning of the breakup of Gondwana gave rise to the Jurassic  transgression and deposition of Cretaceous  continental deposits, after that the Ethiopian region was  an exposed land for a period of about seventy  million years. Concomitant with the first phase of the nfting of the Afru/Arctblan plate, an intense outpouring of the trap flood basalts took place predominantly during the OUgocene.
PRECAMBRIAN METAMORPHIC and associated intrusive igneous  rocks  are exposed in many  parts  of the country  and have a fundamentally  important tectonic  position. The Precambrian shield is  situated between the predominantly  gneissic  rocks  of the Mozambique Belt to south and south-eastern Afnca and the volcarxi- sedimentary-p4utonic complexes to the north, bordenng the Red Sea (Arabian-Nubian Shield).
The Ethiopian Precambrian shield Is  formed by  dominantly  north-trending linear belts  of low-grade volcano- sedimentary  rocks  and mafic-ultramafic  rocks, sandwiched between medium- Co high-grade gneisses  and rmgmabtes. The high-grade gneisses  and migmatites  are referred to as  Lower Complex, which is  parL of the Mozambique Orogenic  Belt and generally  consist of amphibolites  facies  (locally  granulite facies) orthogneissesr paragneisses, migmatites, and amphibolite with bands  of marble. The lowgrade volcano- sedimentary  rocks  with associated mafic  to felsic  mtrusjves, which Is  referred to as  Upper Complex, belongs to the Pan-Afncan Arabian-Nubian Shield.
130 GEO R SP001A (GE CL and GECT RepartJ.dooe
130 GEO R5P0GLA
studio j]ie£rang?U1 frxiieGA8U5 HPPs PRE-FEAS
GEOLOGICAL and GEOTECHNICAL Report
page 4 of <n
figure 2. 12 SrnpWtxJ geotopfC.* map of t ttucpia, from Tefera ef X fl 996}. modrfied by Abbate rf > (2015)
Referring to the project area, the tract of western land along the Ethiopian-Sudanese border Is  underlain by gneiss  and miqmatite known as  the Baro Group. It is  flanked on the east by  a large tract of land underlain by the relatively low grade volcano sedimentary succession known as the B<rt>r group.
2f-
2.1.3           SmpMted map of western ftroocva inset map shows the spaoat dtstnbutton of the Arabian -Hutvan Savst (A HS) ana the Murambique fie* <r. /mc* Africa fatter ften.e' MrVy-v^, .AweAeand Qyuteht Shrnjo, 2005}
The MESOZOIC SEDIMENTS are represented by  three distinct sedimentary  basins: the Ogaden Basin, the Abay  (Blue Nile) Basin, and the Mekeie Basin. They  do not cover the western region of Ethiopia directly involved m the Dabus project.
I3< StO R SPOOLA (GEOL and GEOT Report).doo
530 GEORSPCXJIA
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GEOLOGICAL and GEOTECHNICAL Report
P4g« 5 of 40
CENOZOIC VOLCANIC ROCKS and related SEDIMENTS cover 50% of the country's  landmass, and range in age from the late Eocene up to historical times. Volcanism started during the Eocene’late Oligocene with the eruption of flood basalts  that have generally  been related to either one or two mantle plumes  Impinging the base of the lithosphere under Afar or Afar-Northern Kenya nfts.
The volcanic  rocks  have been subdivided into five major provinces  on the basis  of their lithological development, type of activity, frequency  of volcanic  centres  and age of effusion (Abbate and Saqn 1980):
(1)  vofcanltes  of  the  northern  plateau;  (2)  volcanltes  of  the  southern  plateau,  (3)  volcamtes  of  the  Somali plateau; (4) Afar volcan Ites; and (5) Main Ethiopian Rift (MER) volcanites.
In the northern Ethiopian plateau, huge Miocene shield volcanoes  were superimposed on the flood basalts. Following the end of the Oligocene, the volcanism shifted toward the Afar depression and successively moved between the southern Ethiopian plateau and the Somali plateau in correspondence with the
formation of the Main Ethiopian Rift (MER).
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130 GEO R STOC1A (GEOL and GEOT Report),doot               L3G GEO R SR 001ADABUS HPPs PRE FEAS
GEOLOGICAL and GEOTECHNICAL Report
2.2 REGIONAL STRUCTURAL EVOLUTION
page  6 o*4O
The region was affected by a complex tectonic history that can be summarized in two broad phases'
J. Compression stress regimes - orogenic cycle: (Pre-Cambrian time, 870 to 550 Ma)
2. Tensional stress regimes - rifting: (Triassic-Cretaceous and Neogene-Quaternary time)
COM PRESS ION AL STAGE (870 to 550 Mai
The rocks were affected by the Pan-African event, a tectond-thermal event, some 500 Ma ago, during which a number of mobile belts formed, surrounding older cratons.
This  thermal  event  constitutes  the  final  part  of  an  orogenic  cydc,  leading  to  orogenic  belts  which  are currently believed the result of continental domain amalgamation during the period &70 to 550 Ma.
The  Pan-African  event  is  a  protracted  orogenic  cycle  reflecting  the  opening  and  dosing  of  large  oceanic realms, as well as the accretion and collision of buoyant crustal blocks. Pan-Afncan events culminated in the formation of the Late Neo-Proterozoic superconttnent Gondwana (Figure below).
Il
III
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IV
SesAocr spreading, arc and
bttfc-wc bufri lormaion,
and terrane accretion
-a70-630 Mt
Confcnenlai ooMsJon and tormaton
of th* East African Oregon
■^30-600 Ma
Continued tfiorlenlng. escape
lactones, and orogene coAapea
-600-540 Ma
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□unrig rifting and seafloor spreading, several forms of sed’mentation have occurred: arc and back arc oasrn formations,  epicontinental   basins   with  sedimentary  deposition  (sandstones  and  pelites),  chemical  and sedimentary deposition (limestone, calcareous sandstones and mad), volcanic matenal deposition.
During the compressive stage, continued shortening arid tectonic  escape occurred. All residual oasement components (gneiss granulate and amphibolite) tom from the edge of the escarpment have mixed with the epicontinental volcano sediments  forming the thrust belt. The temperature and pressure generated by  the overlap and the thrust movement caused metamorphism in the Igneous rocks and volcanic rocks.
IENSIi^ALJTAGE^IFTING
Along  with  the  initial  breakup  of  Gondwana,  an  Early  Jurassic  regional  marine  transgression  invaded  the Hom of Africa from the northeast (Paleotethys) and east (India/ Madagascar nascent ocean).
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The sea covered the NS-trending block-faulted structures  connected to the Karoo nft system in southern Ethiopia (Ogaden region), and the NW trending rift basins linked to the Central Africa shear zone in central Ethiopia (e,g.r the Blue Nile rift). The Jurassic  marine sedimentation was  preceded by  deposit of the continental Adigrat Sandstones.
After the Jurassic marine regression and deposition of Cretaceous continental deposits, the Ethiopian region was an exposed land affected by tectonic deformation and regional uplifts for a period of about 70 Ma,
From the Ohqocene started the first phases of rifting m the Afro/Arabian plate, with intense volcanic activity predominantly in the Hom of Africa and southern Arabia which were at that time connected.
These volcanic rocks, mainly represented by basalts and traditionally referred to as the trap succession, have estimated to have covered an area in Ethiopia not less than 750,000 km  before erosion (Mohr 1983).
J
2.3       REGIONAL TECTONICS
Two different tectonic phases can be distinguished: Precambrian and Phanaerezorc tectonics.
tn Precambrian, lithotectonic terranes that comprise high-grade gneisses of the Mozambique Belt and low- grade metavoicano-sedimentary sequences of the Arab<an-Nublan Shield are juxtaposed along north-south sheared thrust contacts, which are marked by arc-llke ophiolite sequences.
The tectonic  evolution of the country  during Phanerozoic  can be thought of as  relating to the polyphase break-up of Gondwanaland. The Phanerozoic  tectonics  can broadty  be divided into: (i) Late Paleozoic  to Cretaceous, and (II) Cenozoic tectonics.
The  first  is  related  to  earty  rifting  of  Afnca  from  East  Gondwana,  which  led  to  formation  of  multiple  rift basins and deposition of terrestrial and marine sediments In central and eastern Africa.
Cenozoic tectonism In Ethiopia is related to the final stage of Gondwanaland rifbng that took place between Late Eocene and the Early Miocene, and is generally associated with continued rifting at their margins and within the Afncan-Arablan plate.
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3  LOCAL GEOLOGY
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Hie preliminary geological analysis was based on:
analysis of the existing geological maps and precedent studies;
- photomterpretation of the satellite Images and drone aerial photos;
site visit, preliminary geological survey and site Investigations.
The first step in the analysis of the dam areas was carried out by using remote sensing data, including the SRTM digital terrain model at 30 m cell size, landsat IM Images  were processed in order to obtain Information about vegetation coverage and rock  outcrops. The processing of the digital terrain models allowed a morpho-structural analysis of the area.
The following table summarizes the remote sensing data that was used
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Taking into account the data provided by  the geological maps  at a scale of 1:250,000 published by  the Geological Survey of Ethiopia, the study of satellite images and the on-site geological survey allowed us to define the geology In the project area.
Most of the study area is mduded in the geological sheet NC 36-12 "Gimbr, while only a small part of the catchment area In the south is mduded in sheet NC 36*16 and only the power house site of the dam at Ch 109 is included In the sheet NC36-8 - Kunnuk Asosa (see drawing 130 GEN D SP 001).
According  to  the  geological  maps  published  by  the  Geological  Survey  ol  Ethiopia,  the  following  lithologic units constitute the project area.
SOIL COVER (Pan
This consists of alluvial and latentic soil cover. The fine-grained soils are found in flat laying plains and along the nver meanders. Alluvial deposits have several gradings, from cobble’pebbte size to sandy*gravel to silt size.
130 GEO 4 SPOGIA (GEOL and GEOT Report).doo
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The  flanks  of  the  valley  and  the  plateau  are  generally  formed  by  thick  lateritic  and  other  types  of  sod developed by intense weathering of rocks.
This unit affects, In particular, the proposed site at Ch. 130,
TE5HARY BA$ALUW
Pie lower fkwd basalt unconformably overlays the basement composed by Precambrian rocks.
Pilckness and extension of lava flows vary depending on local morphology and tectonic factors. Because of their rheology  and large volume, basaltic  lava flows  have filled paleo-depresslons  creating a wide, flat topography. Large outcrops of basalt form also ridges end elongated hills-
This unit, although rt is widespread in the study area, does not directly affect the works. It outcrops on the plateaus and forms a large part of the reservoir area of the Ch, 130 - Dam and the relative catchment area.
PRE‘TECTONIC INTRUSIVES (Pad t Poti)
According to the geofogical map NC 36-12 "Girnbl*, two unrts were identified In the project area. The first one (Pgdt) is granodiorite-tonalite with minor gabbrolc pods. The rocks are described as light gray to dark gray, medium grained to rarely  fine and coarse grained, and slightly  to strongly  deformed and sheared. Modally, rocks  of this  unit range from rare diorite/gabbrc, through dominant quartz-diorite, tonalite and granodiontes. This unit represents the bedrock of the dam site at Ch. 13Q and the reservoir area of the dam at Ch. 108.
The second unit (Pgtl) Is  described as  gramte-granodlorlte. The rock  is  pink  to grayish pink, medium grained, foliated and sheared. This  unit has  been mapped tn the northern part of the project area and constitutes [almost in part) the bedrock of the dam site and power house at Ch. 108.
The geological map NC 36-16 (which covers the power house site of the dam at Ch. 109) describes a slightly different interpretation because the rocks  are reported as  metatonalite (tn) and metagranodionte (gd), corresponding to the unit "'Pgdt” of the Geological sheet NC36-L6, and as metagranlte (gti), corresponding to the unit ’PgrT.
The prefix -meta indicates that a metamorphic process has been identified in these rocks. Variability In the degree of deformation and metamorphism is reported as a charactenstlc feature of these intrusive rocks. At places these rocks show gneissose structure with clear segregation of mafic minerals; elsewhere they are massive or weakly foliated.
The survey  earned out on site confirmed this  latter interpretation: strongly  deformation, iso-oneotation of crystals, foliation and metamorphic alteration of the original structure have been recognized In most of the outcropping rocks, particularly »n the dam-site at Ch. 108. This evidence was confirmed also by petrographic analysts conducted on thin section derived from some samples collected on site. For this reason the prefix - meta is used in this report where a metamorphic process has been recognized. The term "orto-gneiss* is 
130 GEO R SP001A (GEDL and GEDT Repeat),too-
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used where a strong orientation and "fluid* structure are evident. In some places the outcrop shows also a typical migmatite structure.
As  already  described in the Geological Notes  of sheet NC36-16, several rock  types  are found intimately associated: metagranite, metagranodlorite, metatonalite (and several other types  ranging in the same rock family); the rocks are probably comagmatk In origin. On the geological map only the dominant rock type Is shown in any given area.
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4  CH - 130: DAM SITE
4.1  MORPHOLOGICAL FEATURES
11 o<40
In this stretch of valley the river Hows with a straight course, from SW to ME. The nver bed has a width of
250-300 m and splits Into various channels seoarated try elongated islands covered by vegetation.
The dam axis  is  located m a very  gently  U-shaped symmetric  valley. Both the flanks  have two different sections: the upper part has a slope of about 15% (<10% while the lower section, at the foot of the slope, has a very gentle morphology with a slope of 2-3%. This lower section represents the alluvial plain, blended to the detrital talus of the slope.
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Both the flanks are crossed by some creeks, slightly Incised in the upper pan of the slope and terminating in the lower part with a very gentle slope; In some places this part of the slope is fan-shaped, indicating a past process of transportation and sed»mentation along the creeks (alluvial fan).
4.2  INVESTIGATION CARRIED OUT DURING THE PREVIOUS STUDIES
Sub-surface investigation was carried out during the Reconnaissance Level Study conducted by the Client in 2002. Ten test pits and trenches were executed at the Dabus II dam site, which is located very dose to the Ch. 130 dam site proposed in this study. Test pits were dug along two possible axes and the proposed spillway, at the coordinates listed In the following table (extracted from Reconnaissance Level Study report).
Almost all the pits dug on the banks encountered the bedrock at shallow depth, except pits No. 5  6,
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the right and pit No. 10 on the left bank (located on the upper part of the slopes).
130 GEO R SP001A (GEOL arvd GEOT Repon) doo
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Or- lhe right bank, a thick residual alty-day layer was encountered at pits No. 5 and 6 (depth >6 m)r  while on the left side the maximum soil depth exceeds 4.5m at pit No. 10.
Outcropping of bedrock was reported along the riverbed.
LABORATORY ANALYSIS
A tew d sturbed soli samples were collected from pits for laboratory classification. Test results conducted on reddish., residual silty day soils, depicted that most of the samples are dom-nated by highly plastic soils (with ranges from medium to highly plastic).
4.3   ACTIVITIES CARRIED OUT DURING THE VISIT
Tne following activities were conducted:
geological  survey  with  examination  of  No.  15  rock  outcrops  {photographic  documentation was collected of each outcrop);
coll lection of No. 8 rock samples;
thin  sections  of  No,  5  samples  with  petrographic  analysis  by  microscope  (realised  by  the University of "Roma Tre\ Department of Geology);
No, 7 geostructural stations, with a total of almost No. 130 joint measurements; No. 4 tnal pits, ranging In depth from 0.6 m to 3.2 m;
No. 6 seismic lines with SASW technique.
The results of these activities (pnmo documentation, stereoplots pit
f
logs, etc.) are inducted in Annex A.
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4.4       GEOLOGY OF THE DAM SITE
page 13 of 40
From the results of the on-site activities, the following geological situation can be summarized.
Both the flanks of the dam site are Formed by  residual soil coven Trial pits (Nos. 1 and 4, respectively on the right and the left abutment) were excavated In red silty-dayey  soils, with medium plasticity, stiff and dry, At the bottom of both the pits, the sod contains fragments (millrmetnc to cenbmetric) of very weathered rocks,, which form a sort of"skeleton" in the soil matrix. This lower part of the excavation can be interpreted as the top side of the "C* layer of the classic soil horizon, known as "parent rock" or substratum.
This evidence may lead to the hypothesis that weathered bedrock should be encountered around a range of 4^6m, while the fresh (or slightly weathered) rock in the range 5-10 m of depth. This Is In accordance with d>e results of previous pits which encountered the thickest layer of soil on the upper part of the slopes.
Comparable results were obtained by the seismic tests earned out with SASW technique on the right side, at the lower part of the slope. The results of the SASW tests confirm that in this a^ea a soil layer thicker than 3-4m covers the bedrock,
4, 4. J. >45'4' taf r.mW ort right ban*
On the right side of the alluvial plain, the bedrock is covered by alluvial soils. Tria! pit No. 2 (1.2 m deep) shows  greyrsh to light brown alluvial soils, medium to highly  plastic. Large outcropping of rocks  in the riverbed suggest that bedrock m this area should not exceed the depth of some metres.
Outcropping of meta-granites (with a strong foliation and gneissic structure, as showed by thin sections) has been surveyed along the creek on the right bank, just downstream the dam axis (Outcrop No. 52).
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On the alluvial plain, left side, the bedrock (granite and meta-granlte to rneta-granodiorite, as Indicated by the microscopic analysis on ttiin sections) is frequently outcropping in scattered or wide areas (see Outcrops No. 55 and from 57 to 63). Tnal pit No. 3 (on the alluvial plain at the foot of the slope) shows that very weathered rock underlies a thin sandy soil cover.
Several oiitcrops of rock were surveyed on the river bed: on the right (Outcrop No. SO, 50/A, 51 along the dam axis, No. S3 upstream and other outcroos downstream) and on the left side (no. 54 downstream and No. 56 upstream). All these outcrops  are made of meta-granodionte and meta-tonalite with several meta- lavic intrusions, in form of dykes, these intrusions are ve*y frequent in Outcrops No. 50, 50/A and 51 (thin section indicates a probably trachiUc origin of this metamorphosed lavic intrusion),
rvvre■¥.<.?; Left: meta tevic intrusions, nvvrhed ieft (OC5Q). Right or^nodionfe, nverbcti ngtR (OC V? 56)
The intrusions  form very  inclined layers  (dykes) which cross  almost transversally  the river bed. The joint measurements  show a similar orientation of these structures, which is  around E-W (strike), sub-vertical or dipping around 60-70° toward North. These orientations  were measured in almost all the geostructural stations  realized In the dam site (see Annex  A). The following figures  show the stereoplot of all the measurements  taken in this  dam site and two representative geostations. All the the plots are reported in Annex.
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4.5  GEOTECHNICS OF DAM SITE
Rock outcropping m the dam site is slightly weathered or very slightly weathered (almost fresh in the meta- lavic intrusions). In same places a higher level of weathering can be reported, particularly where the grain Is medium to coarse and where the metamorphism created a strong lamination structure.
The rock Is strong to very strong up to extremely strung in the fine grained meta-favic intrusion,
Due to the small extension of rock outcrops, joint spacing is not evaluable from a statistical point of view. A moderate to low density of joint can be estimated at this stage of the study.
In order to obtain more geotechnical data, considering the abovementioned geologic situation, a field and laboratory investigation is necessary,
Rock Mass Classification will be developed mainly from geomechanical survey of cores, RQDr number of joints, joint frequency, roughness, joint condition and other parameters will be collected on drill cores. The GSI procedure (Geological Strergth Index, by Hock) will be followed for the Rock Mass Classification.
Regarding the reservoir's  waterbghtness, at ths  stage of the study, considering the presence of a oroad silty-clayey soli cover on the flanks of the reservoir, a low risk of water loss can be assumed. More in-depth analysis wJl be developed to evaluate a potential water loss through fractures and linealions in the bedrock.
Regarding slope stability, no significant landslides on the flanks of the reservoir have been reported in the previous studies, nor have been Identified by photo aerial analysis and recent surveys.
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GEOLOGICAL and GEOTECHNICAL Report
4.6 QUARRY FOR CONSTRUCTION MATERIALS
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Suitable material for rockfill and granular materials should be constituted by strong, not
weathered/weatherable rode Both the basaltic and the Intrusive rocks, which form the bedrock of rhe project area, should be suitable for this purpose. Basaltic rocks are preferable for concrete aggregates.
A specific investigation is necessary to confirm the availability o this material in terms of volume and quality. Specific tests will be earned out also lo verily the suitability of this material for concrete aggregates.
Due the presence of basaltic rocks near the dam site, a specific survey was executed during the last visit in order to identify suitable quarry sites to be investigated in depth during the next phase.
Three possible sites have been identified.
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Site No. 1 is located along the track which leads to the Nekempt-Asosa road, about 4 km south-east of the dam site. This is a flat area with outcrops of vesicular basalt scattered In an area of almost 4 hectares. Investigation will be needed to verity if massive, fresh basalt underlies the vesicular layer.
Site No. 2 is a most evident and surtabte quarry area. The site is located 2.5 km south o* the dam site, where a basalt elongated hill prosecutes east of the hills of the first site,
The rock 1$ widely outcropping m an a'ea of almost 650x250 m, forming rock walls up to ten metres high. Fhe rock  is  dark  grayish, fine-grained, very  strong aphanitic  basalt, which could be suitable for the
embankment dam and also for concrete aggregates. This represent the first quarry choice.
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The volume Qt basaltic rock available in this area is estimated in some hundreds of thousands cubic metres, to be directly excavated without sol covering.
The third site i$ located along Nekempt'Asosa road (7km south-east to the dam site}. In this place there is an existing quarry area In vesicular and sconaceous basalt.
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Also if this site is furthest from the dam site compared with the other two sites, rt could be exploited for lower Quality material (being easy to excavate by excavator and ripper, and not by blasting) anrl also to obtain sand and tiller (by crushing) for concrete aggregates (difficult to obtain by crushing strong basalt). No natural sand quarry sites are available around the site.
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GEOLOGICAL and GEOTECHNICAL Report
5 CH - 130: WATERWAYS and POWER HOUSE
5.1   MORPHOLOGICAL FEATURES
18 o* 40
1
A 6.5 km long headrace tunnel will be excavated along a series of gentle hills on the left bank of valley. The Intake will be located in a gentle slope, about 1500 m upstream of the dam axis, while the exit of the tunnel will be about 1340 m a.s.l; from this point, a 1.9 km long penstock will link the tunnel to the power station.
The penstock will cross a wide and gentle valley, with dark grey to brownish gray alluvial silty-clayey soils, with Traces of swampli>g.
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The power house will be located at about 1250 m a.s.l, dose to a creek. This creek has a very Irregular course, with many curves, and flows into the Dabus River at about 1235 m a.s.l..
5.2   ACTIVITIES CARRIED OUT DURING THE VISIT
The following activities were conducted:
-      geological  survey  of  waterways  and  power  house  site,  with  examination  of  No.  2  rock outcrops along the tunnel axis. No. 4 rock outcrops in the power house; other geological observations points were recorded where deep soil was surveyed;
collection of No. 3 rock samples;
-      thin sections  of  No.  2  samples  for  petrographic  analysis  by  microscope  (realized by  the University of ’Roma Tre* Department of Geology).
The results of these activities are Included In Annex A.
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5.3       GEOLOGY and GEOTECHNICS
p.lge 19 of 10
According to the geological data, the tunnel should be excavated in Precambrian rocks,
Only a few outcrops were surveyed along the tunnel: one is represented by pegmatite intrusion (crystalline basement) found inside a creek. (Outcrop Mo. 64) and one by  effusive lava (dolite type, Outcrop No, 69) which presumably forms a thin cover of the crystalline basement on the top of the bilL
More than 4-5 m of soil cover was surveyed in the intake area.
Large rock outcrops were surveyed in the power house area (OC Mo. 6&) and along the creek which flows from the PH area to the Dabus River (OC No. 65, 66 67).
r
In this area the rock Is basic intrusive, dark grey, ranging from tonalite, to diorite and gabbro. Some pods of basic  granulite are inducted. Low traces  of metamorphism have been reported in this  area. Microscopic analysis of thins sections on two samples (OC No. 65), classifies this rock as a tonalite (rich in felcfcpar5r plagioclases and amphibote).
The rock  Is  very  strong to extremely  strorg (specimen can only  be chipped with a geological hammer). A moderate to low density of joints was surveyed on the outcrops. The degree of weathering is very low In the outcropping rock.
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GEOLOGICAL and GEOTECHNICAL Report
6  CH - 108: DAM SITE
6.1 GEOMORPHOLOGICAL and GEO STRUCTURAL FEATURES
In this site the river has a rectilinear course flowing NW along a very narrow riverbed, ranging from 30 m to about SO m In width.
The dam axis Is located in a V-shaped asymmetric valley The left flank Is steep, wrth an average slope of about 60%, but with two different sections: the upper part has  a gentle slope of about 15-20% (~ 10°), while the lower section is  very steep, with a slope of 100% and more. Some deep creeks (approximately perpendicular to the river) c^dss the bark, forming veiy  steep scarps  ana isolating large boulders  (see following figures).
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The foot of the slope has a very irregular morphology due to the presence o* large ooulders.
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The nght bank  has  an average slope of around 20-25%- The abutment is  modelled by  some ver/ gently areas which separate other steeper sections of the slope. A wide flat and very gentle slope area Is located around level 1220 m a sd. (see following photo). The slope is crossed by some creeks incised in rock.
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The  bedrock  of  this  site  is  formed  by  Precambnan  rocks,  here  constituted  by  meta-granlte  and  rneta- granodmnte. Large outcrops of rocks are vistole on the plateaus, on the banks and along the riverbed.
The project area is affected by some tectonic lineatons well discernible on aerial photographs. Several sub parallel fractures aligned in direction SE-NW are recognizable from high resolution drone images, mainly on the river bed; this feature represents the mam trend of this site. Another joint set (direction SW-NE) can also be recognized on the nver bed and on the banks, GeostructuraJ surveys conducted on site have confirmed these trend5 (see geotechnical features).
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The 11 neatton system discernible by drone Images are similar to those ones viable m the larger scale satellite images. From these Images is evident that the river course Is dominated by tectonic features.
Upstream the dam axis, the nver flows  for several kilometres  in direction SSW-NNE. About one km upstream the dam site, a 90° curve to the left changes abruptly the direction of the river as to be "captured" by tectonic alignments (a rectilinear gully, which prosecutes the river alignment SSW*NNE, represents a hint of this hypothesis), Downstream this curve, the nver flows with a rectilinear course for some kilometres in the same direction of the main tectonic lineatlons visible on the river bed (SE-NW),
More generally, the satellite images show other evidences of these phenomena known m literature as "river elbow capture". Other examples  of river captures  related to tectonic  structures  are recognizable in the stretch of valley downstream the dam axis, as showed in the following figure.
On the basis  of aerial-photograph interpretations, supposed by  on site geostructurd surveys, the mam tectonic  features  of the dam site are represented in the simplified geostructural map (drawing 130GENDSP00S).
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The following act vibes were conducted:
-     geological survey with examination of No. 30 rock outcrops, 14 of them located in the dam and intake area (for each of them a photographic documentation has been collected);
-     collecting of No. 8 rock samples;
thin  sections  of  No.  3  samples  for  petrographic  analysis  by  microscope  (realized  by  the University of "Roma Tre", Department of Geology);
No. 18 geostrudural stations, with a total of almost No. 4SD joint measurements.
The results of these activities are included in Annex A.
6.3       GEOLOGY OF THE DAM SITE
As already described, bedrock outcrops widely m both flanks of the dam area.
All the outcrops  can be classified as  meta-granite and meta-granodionte rocks. Differences  in terms  of petrographic characteristics and metamorphlc/texture grade can be appreciated in the same outcrop and rn between different areas. Nevertheless, these differences appear as gradual transitions from one type to the other, without the evidence of a real dominance of one petrographic type and/or metamorphic grade.
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As already desen bed in the Local Geology chapter, several rock types are found intimately associated, in the range of granite and granodiorite (up to tonalite), as a symptom of a comagmatic origin,
In almost all the outcrops  a strongly  deformation, Iso-orientaton of crystals, foliation and metamorphic alteration of the original structure have been recognized. Tins structure has been Identified and confirmed by microscope analysys conducted on thin sections. For this reason the prefix -meta has been used for the rocks of this dam-site. In same outcrops the term *orto-gneiss ' seems to be more appropriate.
1
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fi.4 GEOTECHNICS OF THE OAM SITE
Considering the abovementioned geologic situation, the main technical issues to be studied are represented by the geostructural and geomechanical conditions of the dam site.
During the last visit, several pint sets  were measured. The results  are shown in Annex  A (all the measurements  and two representative stations  are shown in the stereoplots  of the following figure)- In almost all the geostructural stations, three main joint sets were identified.
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The first set is measurable In all the stations: plunge (dip direction) is in the range from 190° to 720c  with a
dip of 25 r40 . The second set
ca
Is less frequent than the first but often measurable; it is almost "conjugated"
to  the  first  set,  having  a  similar  strike  but  an opposite dip direction  (dip  is  mainly in the range 65-B0°}. A third set is mainly sub-vertical, with a stnke of about 20-40°,
The First joint set plays a role In the morphological and stability feature of the valley. This joint orientation Is effectively against slope stability on the right bank (dip direction of the sliding plane lies approximately ±20& of the dip direction of the slope) and the opposite for the left bank. This  aspect is  very  dear on site, as shown in the following photos. The first joint set provokes some sliding phenomena on the right bank and, in some cases, when associated with other joints, some toppling on the left bank. This geo-structure is also the reason, of the different morphology of the two banks, with the right one less steep than the left ore.
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^Vurr 6 4. 4. Scwit* frjfums of the tfxrr mjrr? joint sets
From a geomechanlcal point of view, the following preliminary observations were recorded.
The  rock  strength  can  be  assessed  as  “strong"  to  “very  strong'*  (according  to  Hoek  &  Brown  criteria  for practical estimates of rock mass strength).The weathering grade Is generally low to ver/ low.
For the first joint set an average spacing ranging fmm 50 to 100 cm (locally  up to 20-30 cm) can be estimated; the discontinuity surface is rough and undulating with very high persistence; joints are generally dosed or with small aperture (^1 mm).
Pie second joint set has  an average spacing of 100 cm (but with local venations), slightly  rough or shckensided surfaces, generally  closed or with small aperture, persistence is  difficult to estimate, but generally more than a few metres.
The third joint set (sub-vertical) has  a metric  spacing (3 to 5 m), with local higher frequency, high persistence (several metres); discontinuity  surfaces  are rough and planar; frequently  high aperture was noticed up to several centimetres, with a silty soil filling.
In the following phase, a complete Rock  Mass  Classification will be developed according to the GSI procedure: evaluation of GSI rating will be specifically  studied for the dam site context, referring also to
other rock mass classifications (RMR  Q) and considenng that
r
several authors published new developments 
of Rock Mechanics theories (Palmstrom, Diedtrichs, etc.). This approach will allow us to collect a complete geomecharxal data base of rock masses.
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Regarding slope stability, no significant landslides on the flanks of the future reservoir have been Identified, at this stage of the study, by photo-aerial analysis. Local sliding on the right bank and some toppling on the left bank  of the dam site are provoked by  the particular geo-structural condition above commented. These slides are, in any case, of relatively small dimensions and they should not affect the feasibility of the dam; they will have to be taken into consideration in the following design stage.
On the left bank  the slope is  covered by  vegetation and many  boulders  were surveyed: detailed on-site survey and geophysical investigations will define the real fractu ration grade of this bank, which could affect the foundation excavations.
6.5 QUARRY FOR CONSTRUCTION MATERIALS
The presence of several outcrops of rocks in the whole area suggests that It should be possible to obtain rockfill material and concrete aggregates from a quarry area to be located dose to the dam site. The exact location will also depend on the work site needs, In order to optimize excavations and transportation works.
A  specific  investigation  campaign  will  assess  the  quality  of  the  rock  for  both  concrete  aggregates  and granular material.
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7 CH - 108: WATERWAYS and POWER HOUSE
7.1   GEOMORPHOLOGICAL FEATURES
A 6 km long headrace tunnel will be realized on the right bank of the river; a 0.9 km long penstock will join the tunnel to the powerhouse, located on the right bank of the over.
According to geological information, this  area is  constituted by  Precambrian rocks  (meta-granite and meta* granodiorite). The morphology  along the tunnel alignment Is  very  rough, dominated by  outcrops  of rocks, steep elongated hills frequently rounded by scarps and deep gullies.
The powerhouse will be located on a small hill on the right bank of the river; this area is characterzed by a gentle morphology. No outcrops of rocks were surveyed in this area, while large outcrops are visible on the river bed.
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From a geostructural point of view, the same features  described for the dam site are recognizable also m this  area. Also m this  stretch of valley  several llneations  (mainly SV;-ME) were created "nver captures", as illustrated fn the previous chapter.
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The following activities were conducted:
geological survey  of waterways  and power house site, with examination of No. 20 rock outcrops  along the tunnel alignment, the penstock  and in the nverbed dose to the power house;
- No. 6 geostructural stations along tunnel and penstock, with almost No. 100 joint
measurements.
The results of these activities are included »n Annex A.
7.3   GEOLOGY and GEOTECHNICS
According to the geological data, the tunnel will be excavated In Precambrian rocks, mainly meta-granite and meta-granod ion te. Several outcrops  were surveyed, recording similar conditions  (from a geological and geomechamcal point of view) comparable with those of the dam site.
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Very similar joint sets were recorded also in these sites (at some km distance from the dam site} suggesting that the three mam joint sets are dominated by regional tectonic features. Small differences are recorded In terms of dip and dip direction. Also a fourth joint set is recognizable in this area.
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L
8 SEISMIC ASSESSMENT
1
8.1 INTRODUCTION
The scope of the present chapter Is to illustrate the seismic assessment, earned out over the Dabus project area aimed at evaluating the Peak Ground Acceleration at different return perods.
In particular, the foltowing two approaches were used In order lo estimate the value of the PGA related to its return period.
OSH A ■ Deterministic seismic hazard approach, and
PSHA Probabilistic seismic hazard approach.
The main source of information, containing well-documented studies on toe probabilistic seismic hazard for Eastern and Southern Africa, and involving the surrounding areas indudmg the Dabus project srte, were the following documents:
c Mavonga T., (2010). Seismic hazard assessment and volcancgenic seismicity tor the Democratic Republic of Congo and surroundings areas, Western Rift Valley of Africa;
o Chorowicz J. (2005). The East African rift system;
o Abdalla JA, Mohamedzeln Y. EA, Wahab AA (2001). Probabilistic Seismic Hazard Assessment of
Sudan and its Vicinity.
Midzi, V. et al.r (1999). Seismic hazard assessment in Eastern and Southern Afnca.
Twesigomwe E. (1997). Seismic hazard In Uganda, Journal of African Earth Screrces 
o Jonathan F. (1996). Some aspects of seismicity in Zimbabwe and eastern and southern Africa.
Moreover,  die  reference  guidelines  underlying  the  definition  of  the  seismic  hazard  and  adopted  in  the present study are:
o 1999, "Manual EM 1110-2-6053’ by USACE (U.S. Army Corps of Engineers);
o 1989, ” I COLD BULLETIN n. 148’ by International Commission of Large Dams;
o 2003, Eurocode 8 (Design of structures tor earthquake resistance) by Technical Committee CEN.
8.2 SEISMICITY OF THE AFRICAN EASTERN RIFT VALLEY
The  occurrence  of  earthquakes  in  the  project  area  is  mainly  controlled  by  the  East  R  ft  Valley  of  Africa (EARS).
The East A to can nft system represents the most extensive cumently active zone of continental rifting on the globe. The extensional nature of the rift system, deduced from focal mechanism studies provides convincing evidence that East African rift system is a developing constructive plate bounda^.
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The rift valleys form two main lines, the eastern and western branches of the EARS. A third, south-eastern branch is In the Mozambique Channel. The eastern branch runs over a distance of 2200 km, from the Afar triangle m the north, through the main Ethiopian rift, the Omo Turkara lows, the Kenyan (Gregory! rifts, and ends In the basins of the North.'Tanzanian divergence in the south.
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The  following  image  snow  the  epicenter  of  earthquakes  with  magnitude  M>4,  recorded  in  the  previous centuries up to today; the Rift Valley is ctearly visible and marked by the setting of the epicenters;
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20’
30’
40’
50‘
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Figure  8,2,2  shows  a  concentration  of  epicenters  following  the  nft  structures,  starting  from  Red  Sea  and terminating in southern Malawi.
The Warn Ethiopian Rift (MER) is a roughly NE trendy sector of the East African Rift system 80 km wide in its  central portion and 1,000 km long. It separates  the southern Ethiopian plateau to lhe west from the Somali plateau to the east. Northward, the MER progressively  widens  out into the complex  Afar tnple junction, while at Its  southern end, a 200-300-km tectonically  disturbed area marks  the transition to the Kenyan Gregory Rift in the Turtana depression. The MER is characterized by active extensional tectonics.
The following figure shows a distribution of earthquakes m Ethiopia since 1900 with magnitude M > 3.
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Figure 8.2.3.             Distribution of twTftqujiANi epicentres in
ftfwcpe uMrfry sz.nce J TO? iwZ/i .**>.?
It  may  be  seen  that  me  project  area  does  not  appear  to  have  Deen  hit  by  earthquakes.  The  nearest earthquake occurred on 26 July 1991 at a distance of about 390 km with a magnitude of 4.4.
The most important seismic event in Ethiopia occurred on 25 August 1906 In the central area of the region, with a magnitude of 6.5.
8.3  DETERMINISTIC SEISMIC HAZARD APPROACH
8.3.1    INTRODUCTION
In the deterministic  approach (DSHA), the seismic  parameters  are estimated from a definite seismic scenano, assumed to occur at the closest possible distance from the siter and for the maximum credibfe earthquake (MCE),
It is  worth pointing out that there is  no generally  accepted deterministic  seismic  hazard analysis  that is suitable for all the zones  of the worldr because of the difficulty  m selecting a suitable attenuation relationship. This  relationship defines  either the manner whereby  the earthquake magnitude decreases  with distance and how It is transformed in the Peak Ground Acceleration (PGA) parameter,
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The main limitations of DSHA are:
•     Recurrence of earthquakes is not explicit;
•     Uncertainties in the selection of the earthquake scenarios;
•     no standard approach for the regions where it is difficult to define an earthquake scenario.
However the concept of the design maximum earthquake is generally straightforward and easily understood.
By adopting an appropriate degree of conservatism in the definition of earthquake magnitude, source
distance and the resulting site ground motions, the design for the MCE provides a high level of safety,
8,3.2      GROUND MOTION PREDICTION EQUATIONS (GMPES)
Attenuation is the reduction in amplitude or energy of seismic waves caused by the physical characteristics of the transmitting media or system. It usually Includes geometric effects such as the decrease in amplitude of a wave with increasing distance from the source.
It Is worth pointing out that there is no generally accepted deterministic seismic hazard analysis which is suitable for all of the world zones, because of the difficulty in selecting a suitable attenuation relationship. This relationship defines either the manner whereby the earthquake magnitude decreases with distance and how it is transformed in the Peak Ground Acceleration (PGA) parameter.
As attenuation relationships the following three commonly used formulas were utilized:
-
Inf^) = -3.864 + 1.03 M - 1351 In K - O.OOOH R
Jonathan (1996)
-
In( —)------- V.057 4- 0.866 M - In fl - 0.0025 R
Tweslgomwe (1997)
-
In(^) = -6.539 + 1.43 M - 1.5 + ln(R + 1)
Mavonga {2003}
where
PGA Is peak ground acceleration (g)
M Is the earthquake magnitude (in moment magnitude scale) R is the hypocentral distance (km)
8.3.3    SEISMIC SCENARIO
DSHAs were performed adopting the following two seismic zoning of the region:
• zoning deriving from the Global Seismic Hazard Assessment Program (GSHAP) project, (see Figure 8.3.1);
■ zoning deriving from the work of Adbaila 2001 (see Figure 8.3.2).
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83.2:              Seismic /otvng w Region by Abd^a er ai (2001)
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Tables 8.3.1 and 8.3.? list the ground accelerations computed witfl the classical DSHA foe the two seismic zonings  shown above. For each zonation the name of the source, the maximum magnitude, the shortest distance from the GERD-site, and tne three individual estimate of each attenuation (unction (84= percentile) and the weighted ground acceleration according to the adopted ranking scheme, are reported.
FaWp ft. 1; ■             cxrxnrf aerttfavtions (P&Vy} computes wa DSHA foe the GSha p-project serwic sourm.
Source
Mnui
RflMn         Tweslgomwe Jonathan         Mavonqa    Average
Red Sea
67            906              0,001                0.001            0.001             0.001
Yemen
7.1           97B              0.001
0.001             0.001              0.001
Afar
6.8
506              0.003
0.003
0.002              0.003
East Ethiopian Rift
6.8
419              0,005
0.003
Western Rift
1 78
529
0.007
0.005
0.009
0.008
0.004
0.008
East Kenya Rift             1 ™                  587
0.004
0.005            0.004
0.004
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Source
2: Central Sudan
Hmm
Rum In
Twesigomwe Jonathan
6.4
159
0019
0.014
Mavonga
0.007
Average
0.013
3: SW Sudan
6.6
260
0 013
0.010
0.006
0.010
4: South Sudan
7.2
403
0.008
0.003
0.005
0.007
6: Central Ethiopia
6.8
191
0.020
0.016
0.009
0.015
7: Afar ft Gulf of Aden
7.5
542
0.005
0.006
0.005
0.006
T?>e seismic  zoning from Abdalla et a!. (2001) Is  more conservative since It locates  the seismic  source boundaries  closer to the Dabus-site than the GSHAP seismic  zoning. The maximum average ground acceleration is 0.015g deriving from the Central Ethiopian seismic source (Region 6 of Abdalla et al.).
8.4   PROBABILISTIC SEISMIC HAZARD ANALYSIS
8.4.1 INTRODUCTION
The main scope of Probabilistic Seismic Hazard Analyses (PSHA) is to quantify the probability of exceedance of various ground motion levels, at a selected ate, given all possible earthquake scenanos.
The data necessary to perform this analysis mdudes:
- earthquakes within a radius of five hundred kilometers from the site;
seismtectonic features of the region;
geological features of the region;
local soil conditions;
ground attenuation characters!its.
The advantages of using a PSHA over a DSHA include;
contributions from ail earthquake magnitudes (within equal weight);
contributions from all sources at all distances;
uncertainties in location, magnitude and rate of recurrence of earthquakes are taken into account.
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PRE^EAS ______________________ _________________________ ___ ____________________ __ _______ __________
The  results  provide  the  means  to  select  design  parameters  related  to  a  degree  of  risk  (/.&  the  possibility  to choose the suitable Return Period).
On the basis  of seismic  hazard analysis  methodology  developed by  Cornel I-McGuire (1968, Cornell, 1976, McGuire), Abdalla (2001) evaluated seismic  hazard assessment of Sudan and its  vicinity. The results  are reported as maps showing PGA with a 10% probability of beng exceeded during time spars of 50, 100, 200 and 250 years.
This procedure is based on following main assumptions:
-       occurrence   of   earthquakes   is   random   and   follows   the   Poisson   distribution   (the   events   are Independent and constant over time);
-     probability of exceedance P(Z>z) of a specified ground motion level z, in an exposure time or design
time period t at a site, is related to the annual activity rate of ground motion exceedance (y):
earthquake attenuation with distance follows a selected law;
-    seismicity is uniformly distributed In each seismic region.
The mam steps of the procedure established by Cornell are:
-      STEP 1: definition of  seismotectomc  sources. Sources may range from small faults (linear) to large seismotectonlc provinces (aerial};
-      STEP  2:  definition  of  earthquake  parameters  for  each  source,  where  each  source is  defined by an earthquake  probability  distribution  or  earthquake  recurrence  relationship.  A  recurrence  relationship indicates the chance of an earthquake of a given size occurring anywhere inside the source during a specified  period.  An  upper  boundary  for  the  earthquakes  for  each  source  Is  estimated,  and  this ^presents the source characteristic maximum possible earthquake magnitude;
-     STEP 3: estimation of the earthquake effects, using several GMPEs, each relating to a ground mobon parameter, such as PGA with distance and earthquake magnitude;
STEP 4: determination of the hazard at the site. The effects  of all earthquakes  of different sizes occurring at different locations  in different earthquake sources  at different probabilities  of exceedance are Integrated Into one hazard curve that shows  the probability  of exceeding different levels of ground motion (such as PGA) at the site during a specified period of fame.
8.4.2 SEISMIC RISK
The following maps show the seismic risk according to the Abdalla study, expressed In terms of peak ground acceleration for some relevant return periods:
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Tilt? following table summarizes the PGA values which can be read from the above maps:
r-PGfl siwvnj.iy
RP               PGA/g
Lrt-.wrJ                       U
475
950
1900
2370
0.05
0.08
0.09
0.10
The following figure portrays the PGA/q vs Tr Interpolation curve based on the PGA values read from the above maps.
ntflJV 8. < 5?
LXap/j lV fA- T - fl£J4
far £W*cr* /VO/i-cf jftM
The PGA values follows a time-depending law according to an expression of type:
o PGA/g - A * LN (T+l) + C
By Interpolating the above values by means of the least squares fitting procedure, the following A  B and C
r
parameters can be founo:
o A = 0.00046
o B = 2.62
a C = 0.0007
The following table summarizes the PGA values at different Return Period according to the above mentioned relationship:
S.4.2.
PGA vjAjW x Jrfflcvwf ftp
RP
1^?
475
950
2500
10000
PGA/q
0.05
0,07
0.10
0.15
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DRAWINGS
* 130 GEN D SP 001 Plan 500k
4 130 GEN D SP 002 Legend
■4 130 GEN DSP 004 DAM di,-130 Plan 6k 
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4 130 GEN D SP DOS DAM ch. IOS, Plan 6k
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____      ____ DAM chj.30
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GEOLOGICAL Mid GEOTECHNICAL Report
ANNEX A. page 1 o' 4fi
PRE-FEAS___________  _________ __________________________ DAM CH 130____________________  _______________
Project: Dabus HPPs
Date: 2016-04-12
Location: Dam Ch. 130 Riverbed right side
OUTCROP Mo. 50
Coord.: 705403E - 1087305N
Note: Geostructural Station DAB 50 Petrographic exam by microscope
Lithology:    Granodiorite    with    lavic    intrusion    (deformed).    Slightly    weathered,    strong    to    very strong. Low to moderately jointed.
Oi Annex A,
DAM eti lJO.doot
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ANNEX A, page 3 of 46
- teas
DAM CH 130
Project: Dabus HPPs
Date: 2016-04-12
Location: Dam Ch. 130 River bed RX - 100m upstr
Geostrurtural Station no.: DAB 50
Coord : 705403E - 1087305N
No. of records: 9
N
S
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Project: Dabus HPPs
GEOLOGICAL and GEOTECHNICAL Report DAM CH J30
Date; 2016-04-24
ANNEX A. p*;b4 of«
Location: Dam Ch. 130 River bed RX
Coord.: 705403E - 10B7305N
Components: Feldspars (20-30%) and plagioclase (40-50%)
Petrographic exam by microscope on sample DAB50 (OC n. 50)
Preliminary    classification:    magmatic    rock,    with    effusive    structure,    but    deformed    and
recrystallzed (near the field of andesite). Two different grain size are evident
2x. Normal and cross polarization view
4x. Normal and cross polarization view
01 d, Antwh A,
DAM ch 130. doo
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GEOLOGIC4L and GEOTECHNICAL Report
ANNEX A, 5 at 43
pre  peas____________________ _____________ DAM CH 130 ____________
Project: Dabus HPPs
Date: 2016-04-12
Location: Dam Ch. 130 Riverbed right side
OUTCROP No. 50/A
Coord.: 705424E - 1087273N
Note: Geostructural station DAB 50/A
Lithology: Granodiorite with lavic intrusion (deformed). Slightly weathered, strong to very strong. Low to moderately jointed.
Ol_a Ai”iex A, Geology, DAM rti 1343 dua
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GEOLOGICAL and GEOTECHNICAL Report
DAM CH 130
ANNEX A. page 6 nf 40
Project: Dabus HPPs
Date: 2016-04-12
Location: Dam Ch. 130 River bed RX- 100m upstr
Geostructural Station no.: DAB 50/a
Coord.: 705424E - 1087273N
No. of records: 9
N
01 A, Annex A , Geology, DA*i cb 130 Joo
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ANNEX A, r.mr 7 :f «
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______________ DAM CH 130_______________ ______________ _
Project: Dabus HPPs
Date: 20160412
Location: Dam Ch, 130 Riverbed right side
OUTCROP No. 51
Coord.: 70S29SE- 1087244N
Note: Geostructural station DAB 51
Lithology:    Granodiorite    with    lavic    intrusion    (deformed)-    Slightly    weathered;    strong    to    very strong. Low to moderately jointed,
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Project: Dabus HPPs 
GEOLOGICAL and GEOTECHNICAL Report
DAM CH 130
ANNEX A. owe 8 nr 4B
____  ______ ]_
Date 2016-04-12
_______
Location: Dam Ch. 130 River bed RX- 200m upstr Geostructural Station no.: DAB 51
Coord.: 705295E - 1067244N
No. of records: 24
01 .a, AnnF/ A Llrokw. 0AM rh 130 dco
Stud-c pietrangpli, rome1
ANNEX A page 9 of 40
P/WCW W
Project: Dabus HPPs
Date: 2016-04-12
Location: Dam Ch. 130 Right bank (O/S creek)
OUTCROP No. 52
Coord.: 705912E - 1OB7125N
Note: Geostructural station DAB 52
Lithology: odogneiss (metagranite strongly deformed and sheared). Moderately to highly weathered. Strong to medium strong. Moderately to highly jointed.
DL_a, Arirex ft, Geokxjy, DAM ch 130 doot
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.*-v cSOTKWOU                                 ANNEX A. |W 10 L,r >1tl
Qi a. Annex A, Gcot^y. DAM cfr 13D Oc<x
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DAM CH 130
AN N EX A page 13 of 4B
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Petrographic exam by microscope on sample DAB52/a (OC n. 52)
Coord/ 705912E - 1087125N
Components: Quartz (30-40%), feldspar (30-40%), plagioclase (20-30%) Preliminary classification: Ortogneiss, fine grained (metagranite deformed and sheared)
2x. Normal and cross polarization view
4x. Normal and cross polarization view
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Location: Dam Ch. 130 Right bank Dam site (creek)              Petrographic exam by microscope on
sample DAB52/b (OC n. 52)
Coord.: 705912E-1087125N
Components: Quartz (30-40%), feldspar (30-40%), plagioclase (20-30%)
Preliminary    classification:    Ortogneiss,    fine    grained    (metagranite    strongly    deformed    and sheared)
2x. Normal and cross polarization view
i
01_s, Annex A. Geohxjv. DAM ch 130 docx
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DAM CH 130
ANNEX A, W 16 c< q8
_________
Project: Dabus HPPs
Date: 2016-04-13
Location: Dam Ch. 130 Riverbed right side US
OUTCROP No. 53
Coord.: 704923E - 1086487N
Note: Geostructural station DAB53
Lithology: : Granodiorite (low deformed). Slightly weathered, strong to very strong. Low to moderately jointed
01„a, Annex A, Geology. DAM l li [ 30 rico
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ANNEX A. Mge 18 l'4B
01 a, Anret A. Geology, DAM l’O.dntx
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ANNEX A. im* 19 of 48
pre ■ FEAS__________ _______ _______ ______ DAMCH 130_ _              ___  ______________________
1 Project: Dabus HPPs
Date: 2016-04-13
Location: Dam Ch. 130 Riverbed Right-900m upstr
Geostrxjctural Station no.: DAB 53
Coord/ 7O4923E - 10B6482N                                            No, of record?: Ifi
N
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DAM CH 130
ANNEX A natur 20 of«
Project: Dabus HPPs
___
Date; 2016-04-14
Location: Dam Ch. 130 Riverbed left side D/S
OUTCROP No. 54
Coord.: 7054641= - 1087642N
Note: Geost ructural station DAB54 Petrographic analysis by microscope
Lithology: : Granodiorite and tonalite (deformed). Slightly weathered, strong to very 
strong. Moderately jointed.
OLa, Annex A Geology, DAM ;b UC doc*
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dam ch jjo
Location: Dam Ch. 130 Riverbed left side D/S
Petrographic exam by microscope on sample DAB54/b (OC n. 54)
Coord.: 705464E - 1087642N
Components: Amphibole (40-50%), Plagioclase (30-40%) sheared Preliminary classification: Meta-tonabte, deformed and sheared
01_a Annex A, Geology,. DAM ch 130. docx
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GEOLOGICAL art GE07FCHMCAL Report
DAM CH 130
Date: 2016-04- 14
ANNEX A pa?e 23 nl «
____
Location: Dam Ch. 130 Riverbed ieft- 150m D/S
Coord.: 705464E - 108764IN
______
Geostructural   station   no.;   DAB   54
No. of records: 21
N
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S
Ql_a, Anm A, beoksgv, DAM ch 130 tto
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A N NEX A, pane 2a. of *h
PRE- FEAS_______________  _______________________ DAM CH J JO __________________ _____ _____ _ __
Project: Dabus HPPs
Date: 2016-04-14
Location: Dam Ch. 130 left bank
OUTCROP No. 55
Coord.: 705324E - 1087519N
Note:
Lithology:    Granodiorite    and    tonalite    (deformed).    Slightly    weathered,    strong    to    very    strong. Moderately jointed.
ai.d Anr*ex A Geotogy. DAM ch 130-doo
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GEOIOGICAl And GEOTECHNICAL Report
ANNEX A. pngr 26 n'-W
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VI
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Date: 2016-04-14
ANNEX A page 2 7 uf«
| Project: Dabus HPPs
Location: Dam Ch. 130 Riverbed left side
OUTCROP No. 56
Coord.: 705310E - 1087464N
Note:
Lithology: Granite/granodiorite. Slightly weathered, strong to ver/ strong. Moderately 
jointed.
Cl_a, Anne* A, Geotogy. 0AM di 130 oocx
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ANNEX A page 28 nf<e
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DAM CH 130
ANNEX A skjp 30 of 4H
________
Project: Dabus HPPs
' Date; 2016-04-14
Location; Dam Ch. 130 Left bank
OUTCROP No. 57
Coord.: 705277E - 1087686N
Note:
Lithology: Granite/granodiorite. Medium to highly weathered, strong. Scattered outcrop
Jl a, Annex A, Geoicgy. DAM ch 130 door
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ANNEX A 31 Of 40
01 d, Arnex A, lieocgv. DAM ch llO.dinjc
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MM CH J 30
ANNEX A. W 32 of -w
_____ ______ ___ ____ _ _________
Project: Dabus HPPs
Date: 2016-04-14
Location: Dam Ch. J 30 Left bank
OUTCROP Mo. 58
Coord.: 705234E - 1087597N
Note:
Lithology: Granile/granodiorite. Medium to highly weathered, strong. Scattered outcrop
DI a, Annex A, Geotogy, DAM ch l30,dB>
sliXl’U pietrangell, nyneGEOLOGICAL and GEOTECHNICAL flenwr
ANNEX A. taste 33 of-IS
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DAM CH 130
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GEOLOGICAL ana GEOTECHNICAt Report
ANNEX A p*J« 34 of <a
PRE FEAS
DAM CH J30 _______  _____  ________ _______  ____
Project: Dabus HPPs
Date: 2016 04-14
Location: Dam Ch. 130 Left bank
OUTCROP No. 59
Coord,: 705289E - W87496N
Note:
Lithology: Granite. Medium weathered, strong. Scattered outcrop
OJ ■) Annex A Geology, Dav c h j?r doo’
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DAM CH 7_?0_______________________________ ___ ______________
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Project: Dabus HPPs 
GEOLOGICAL and GEOTECHNICAL Report MM CH 130
Date: 2016-04-14
ANNEX A paq* 36 of a?
Local ion: Dam Ch. 130 Left bank
OUTCROP No. 60
Coord.: 70532IE - W87506N
Note: Geostructural station DAB60 Petrographic analysis by microscope
Lithology: Granite. Medium weathered, strong.
01A Ainet a Geotoqy, tWM ch 1 ~0 door
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G1 j. Anne« A, r^fogy, 2AM ch lJO.docx
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GEOLOGICAL and GEOTECHNICAL Report
DAM CH 130
ANNEX A, pa<X 38 of 48
Location; Dam Ch. 130 Left bank
____ ___ ____________
Petrographic exam by microscope on sample DAB60 (OC n. 60)
Coord : 7053215- 1087506N
Components: Quartz (40-50%), feldspar (30-40%) Preliminary classification: Granite with large feldspars
2x. Normal and cross polarization view
4x. Normal and cross polarization view
01 _a. Annex A. Geology, DAM ch BD.docx
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- FTAS
GEOLOG/CAL and GEOTECHMCAL Report
DAM CH 130
ANNEX A, page 39 ul1 4£
'"Project; Dabus HPPs________ _____________ Location; Dam Ch. 130 Dam site riverbed left Coord.: 705321E- 1087506N
Date; 2016-04-14
Geostructural Station no.; DAB 60 No. of records: 13
01 d, Annex A, (kotogy, DAM cm 13O.dnrx
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ANNEX A 40 <
Project: Dabus HPPs
_DAMCH13O _ _ _ ___
1 Date: 2016-04-14
Location: Dam Ch, 130 Left bank
OUTCROP No. 61
| Coord.: 705321E - 1087506N
1 Note:
Lithology: Granite. Medium to moderately weathered, strong.
01 _a, Annex A. Geology, DAM m 130 docx
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GEOL OGICAL *r*f GEOTECHNICAL ReooH
DAM CH ISO
ANNEX A paje 41 n*«
C l a. Annex A, Geology. DAM cP 13Q dooc
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MM CH 130
ANNEX A, paoc 42 of 48
____ ______  _______     ___
Project: Dabus HPPs
Date: 2016-04-14
Location: Dam Ch. 130 Left bank
OUTCROP No. 62
Coord.: 705374E - 1087669N
Note:
Lithology: Granite. Medium to moderately weathered, strong.
01.3, Annex A Geology, DAM tri l JO docx
studio pwtrarHjeJi, romeG7-i*i%,7OU and GEO7TCHMCAL feDtrt
annex A Pillj*? 43 I-' *>
DAM CH 130
01_a, Anrei? A 'jK^og-^ DAM ch 120.dcx.ji
studio petTar^rli ^meDALi'JS HPP\i PRE - FEAS
GEOLOGICAL and GEO TECHNICAL Report
DAM CH 130
ANNEX A. p.wr 44 40
Project: Dabus HPPs Location: Dam Ch. 130 Left bank
Date; 2016-04-14
OUTCROP No. 63
_
__
-—
Coord.: 7Q5444E - 10B7680N
Note:                                              „____
Lithology: Granite. Medium to moderately weathered, strong.
01 .!, Annex A Geology DAM Ch ISO.ESCKX
r
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Ot j. Annti a. *Seoh/K. CAM m 140. doo
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GEOLOGICAL and GEOTECHNICAL Report
ANNEX A 46 of 40
PIU FEAS
DAM CH 130
Project: Dabus H P PS
Date: 2016 04-15
Location Dam Ch. 130 Left bank Above abutment
OUTCROP No. 69
Coord.: 7OW88F ■ 108B34N
Note:
Lithology. Granite. Medium to moderately weathered, strong.
31_a.. Annex A.                   DAM ch i30Jdcx
studio ptfirangeh. rcnwGEOLOt^CAi w SfOTfCHMCAl Report
ANNE* A. pw 47 c-r 4S
DAM CH 130              ,
01 a, A?inejt A Geology, DAM rh 130 ifco
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GEOLOGICAL and GEOTECHNICAL Revert
ANNEX A. ;    1 n' *
W - fits
DAM CH 130
Project: Dabus HPPs
Date 2016-04-12/13
Location: Dam Ch. 130 Right Bank - Foot of the slope
TRIAL PFT no TP1
I Coord : 705B77E - 108M76N
Depth; 3.2 m
0.0' O-?rn Top soil, reddish-brown, silty.
0 2- 2.3m Res.dual red sol, silt to clayey silt. Moderately plastic Stiff, dry.
2.3 - 3.2m Residual red soil, silt to clayey silt, with small fragments (mm to 1cm) of completely weathered rock (black probably basic rock); probably top of the very weathered bedrock.
01 b. Annei A. Geolog? JAM ch 130. Thtl PHs.doo
studio piftningeli iTXTii*GEOLOGICAL and GEOTECHNICAL Repnd
DAM CH J JO
ANNEX A, pjqr 2 of 4
Project: Dabus HPPs
Location: Dam Ch. 130 Right Bank - Alluvial plair^ Coord.: 705739E - 1087197N
0.0 0.1m         Top soil, brownish, silty.
Depth: 1.2 m
0.1 -0.8m
Alluvial soil, clayey silt, greyish in colour. Moderately plastic. Stiff/biocky, dry.
U.S - 1.2m        Alluvial  soil,  clayey  silt,  light  brown  to  greyish  in  colour.  Moderately  plastic  Stiff,  slightly humid
01 Annex A
i?AM ch 130, frial Atsdoo
------------------  ----------------- -------------------------- ----------------- -— Stlldki l'ii"trri.Tce.|? torhr&40IJS HPPs 
w - ffas
^Project: Dabus HPPs
GEOLOGICAL artf GEO TECHNICAL Report
DAM CH 130
AN N LX A. p«<- 3 or *
Date: 2016-04-14
Location; Dam Ch. 130 Left Bank - Foot of the slope
TRIAL PTT no.: TP3
Coord.: 705269E    1087692N
Depth: 0.6 m
0.0 - 0.1m Top soil, brownish, sandy-silt.
0.1 - 0 4 up to >0.6m Residual soil, silt to sandy silt, light brown to yellow in colour. Stiff, dry.
0.4 up to >0.6m Very weathered granitic rock, yellow to whitish m colour, decomposed in S'lty &aridy soil. The profile of the contact (rock-soil) is very irregular, deeping toward West.
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DAM CH 130
ANNEX A. |Mge 4 <if <
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MM Ch 130 __________
Date: 2016-04-17 ____ Coord.; 70582OE~1087015N
ANNEX A, IM9S 1 ore
Project . Ddbus HPPs
Location: Dam Ch. 130 Right Bank, dam axis
GDS INSTRUMENTS LIMITED
J7 Mutrail Graen Buiainnf Park
London Road. Nooii
Hampahira RG27 ogr
Tai +44 125*302450 Fa* *44 1256 333451
Surface-Wave Test
ZKltfr        12/04/20 tB
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DaExrs ch^130 RS
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Dam ami
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11 iHa*1 1 rr
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MtyWlJO _________  ____
ANNEX A pagr 2 of 6
GDS INSTRUMENTS LIMITED
32 Murrell Grew BuSi-wss Park Lcndon Road Hook
Hampshire RG27 9GR Tel *44 12S6 332A50 Fas -44 1255 382451
Surface-Wave Test
Date             12/04/2016
Site              Dabus cn 130, RS locator Dam ms
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________           _
_____
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Location: Dam Ch, 130 Right Bank-Tunnel
______________________ ______ _____
Date: 2016-04-15__________________________ OUTCROP No. 64
Coord.: 702937E - 1O91537N
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1 Project: Dabus HPPs
Date: 2016-04-15
| Location: Dam Ch. 130 Power house area
OUTCROP No. 65
Coord.: 705254E - 1094460N
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L ______________
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Lithology: Tonalite with gabbroic pods. Fresh to slightly weathered, extremely strong. Slightly jointed
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Date: 2C164M-24         _
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Components;  Amphibole  (20-30%),  Feldspar  (10%),  Plagioclase  (40-50%);  metal  oxides C<5%), few biotite (<5%)
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Location: Dam Ch. 130 Power house area Coord.: 705254E- 109446CN
Petrographic exam by microscope on sample OC65/b (OC n. 65)
Components: Amphibole (20-30%), Feldspar (10%), Plagioclase (40-50%); metal oxides (<5%), few biotite (<5%)
Preliminary classification: Tonalite
2x. Normal and crass polarization view
2x. Normal and cross polarization view
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__________ J^ofe;_____ _ _ _
Lithology:    tonalite    with    gabbroic    pods.    Fresh    to    slightly    weathered,    extremely    strong.
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i Coord.: 705193E - 1094174N
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1 Lithology: Tonalite/diQnte. Scattered outcrnD
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______
Project: Dabus HPPs
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Location: Dam Ch. 130 Power house area
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Coord. 705153E - 1094319N
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L'thology: Diorite and Tonalite with gabbroic pods (low deformed, locally migmatite structure). Fresh to slightly weathered, extremely strong. Slightly jointed
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Location: Dam Ch. 130 Tunnel alignment
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__  DAM CH IOS __________ __________________ __
Project: Dabus HPPs
Date: 2016-04-08
Location: Dam Ch. 108 Right Bank - Tunnel
OUTCROP No. 7
Coord.: 709875E - 1104174N
Note: Geostructural station DAB 15
Lithology: Metagramte. Slightly weathered, strong to very strong. Low jointed.
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Location; Dam Ch, 108 Right Bank - Tunnel axis
Geostructural Station no.: DAS IS
Coord.: 709895E - 11M187N
No. of records: 44
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Coord : 709675E - 110-W57N
Note: Geos I ru ct oral station DAB 14
Lithology: Meta granodiorite. Slightly weathered, strong to very strong. Low jointed
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Location: Dam Ch. 108 Right Bank - Tunnel
OUTCROP No 11
Coord.: 7096O6E- 1103432N
Note:
Lithology: Meta-granite. Slightly weathered, strong to very strong. Low to moderatefy jointed
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Coord.: 708933E - 1103215N
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Coord _708926E - U03223N
| Na of records: 42
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DAM CH 108____________
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Components: Quart H0-50%j7reFdspar 30-40%), phyllosilicates (biotite and others) (10%)
Preliminary classification: quartz-feldspatic
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Location: Doni Ch. 108 Right Bank
ODTCROP No .17
Coord.; 708953E - 11O325ON
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Lithology:   Mete-granodiorite.   Slightly   weathered,   strong   to   very   strong.   Low   to   moderately jointed.
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1 1                     _Lgatiqn:_Dam Oi. 108 Right Bank - Dam site ; Geostnxtural Station no.: DAB 10 (PC no. 17) ;
Coord : 708953E - 11O325ON
” j No?of records: 53_____________________________________
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Project: Dabus HPPs
Date: 2016-04 08
Location: Dam Ch. 108 Left Bank Upstream                     OUTCROP No. 18
Coord : 708985E - 110296IN
Note: Geostructural station DAB11 Petrographic exam by micrscope
Lithology: Meta-qranite and quartzite. Slightly weathered, strong to very strong. Low to moderately jointed.
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Project: Dabus HPPs
Date: 2016 04-08
Location: Darn Ch. 108 Riverted Left- 300m upstr.
G^csCrbctural Station no.: DAB il OC18
Coord.: 7Q898SE “ 1102959N
No of records: 35
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Location: Dam Ch. 108 Left Bank Coord.: 708933E - 1103215N
PAM CH IOS __________________ ____________
Date: 2016-04-24
Petrographic exam by microscope on sample DAB1 la (OCn. 18)
Components: Quartz predominant (70-80%), feldspar (10-20%)
Classification: Quartzite, slightly deformed
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Date: 2016 04-06
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OUTCROP No. 19
| Coord,: 709547E - 110 3 246N
1    Note: Geostructural station DAB 12
Petrographic exam by microscope
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Date: 2016-04-08
Location: Dam Ch. 108 Right Sank - Intake area
Geostructurai Station no.: DAB 12 (OC IS)
Coord : 708457E- 1103246N
No. of records: 30
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Date: 2016-04-24
Location: Dam Ch. 108 Right Bank
Petrographic exam by microscope on sample DAB12 (OC n. 19)
Coord.: 708457E - 1103246N
Components:  Quartz  (40-50%),  feldspar  (30-40%),  phyllosilicates  (biotite  and  others)  (10- 15%)
Preliminary classification: quartz-feldspatic meta-granite, deformed
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Date: 2016-04-08
Location: Dam Ch. 108 Right Bank Tunnel
OUTCROP No. 20
Coord.: 7O9530E - 1103350N
Note: Geostructural station DAB13
Lithology: Granodiorite, deformed, Slightly weathered, strong to very strong. Low to
1 moderately jointed.
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Date: 2016-04-08
Geostrudural Station no.: DAB 13 (OC20)
i Coord.: 7O9530E - 11D3350N
No. of records: 27
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ANNEX A cage 33 of 45
DAM CH 108___________________
Project: Dabus HPPs
Date: 2016-04-09
.Location: Dam Ch. 108 Right Bank upstream
OUTCROP No. 21
Coord.: 709085E - 1102913N
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Summery

Project Overview

Project Name: Dabus Hydropower Project (HPP)

Location: Ethiopia

Client: Ministry of Water, Irrigation and Energy, Federal Democratic Republic of Ethiopia

Consultant: Studio Ing. G. Pletrangeli S.r.l.

Report Date: July 2016

Document Type: Pre-Feasibility Design - Geological and Geotechnical Report

Project Components

The project consists of two hydropower components:

Dabus CH-130: Includes dam site, waterways, and power house
Dabus CH-108: Includes dam site, waterways, and power house

Key Findings

Geological Characteristics

The project area is characterized by:

Precambrian metamorphic and intrusive igneous rocks (meta-granite, meta-granodiorite)
Tertiary basalt formations
Alluvial and lateritic soil cover

Dam Site CH-130

U-shaped symmetric valley with gentle slopes (15%)
Bedrock covered by 4-6m of residual soil
Rock types: meta-granite, meta-granodiorite with meta-lavic intrusions
Three potential quarry sites identified for construction materials

Dam Site CH-108

V-shaped asymmetric valley with steep left flank (60% slope)
Bedrock exposed in many areas with meta-granite and meta-granodiorite
Three main joint sets identified affecting slope stability

Seismic Assessment

Peak Ground Acceleration (PGA) values:

Return Period (years)	PGA (g)
475	0.05
950	0.07
2500	0.10
10000	0.15

Recommendations

Further detailed investigations required for feasibility study phase
Additional geotechnical surveys needed for dam foundations
Detailed assessment of construction material quality and quantity
Comprehensive environmental impact assessment to be conducted

Client-Consultant Workshop Notes (June 2016)

Key discussion points and responses to client observations:

Report structure improvements to be implemented
Drone survey clarification (conducted on CH-155 dam area)
Sediment measurement methodology to be enhanced
Construction material analysis to be expanded
Environmental and social impact assessments to be completed in next phase