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<br />. <br /> <br />. <br /> <br />Ii <br /> <br />. <br /> <br />'. <br /> <br />COIU'ARISON Of CHARACTERISTICS OF NARIlOiIS AND TETON IlM1SITES <br /> <br />The prillcipal,similarity of the two structures is that Teton "as a <br />zoned, rolled earthen embankment structure and a similnr embankment <br />is planned for the Nnrrowtl s:Lt{~e lIu\o/(~vHr, thl! topogr;:lphy ':JOel <br />foundation conditions arc entirely different resulting in design <br />requirements much simpler and more straightfoI'\"ard for NarrOl"s Dam <br />than Was the case for Teton. <br /> <br />The NarrOl",s location is in a wide, flat alluvial valley with <br />extremely gentle slopes); while Teton is located in a narrow, deep <br />eroded canyon . The canyon ",aIls consist of rhyolite and basalt with <br />extensive jointing, ",hile the Narrows site has shale near the <br />surface on the left abutment and up to 300 feet of alluvium <br />consisting of eolian soils over silts,. sands, and gravcls over the <br />shale on the right abutment. <br /> <br />IHth reuard t.o the rCllatIve watertightness of the foundntIon, drill <br />hole water loss in the abutment rock at Teton before grouting was <br />performed was as much as 400 to l,50 gallons per minute, ",hile the <br />loss at Narrows in shale is a mnximuT:l of 32 ga.llons per minute and <br />averages JA gallons per r.lLnute in the alluvllil'. Teton Ilam is about <br />3,000 feet in crest length ,dth a height of nbout 300 feet, ",hUe <br />Narrows Dam will be about 145 feet h1Ch and 4-1/2 milbs long. The <br />total seepage cstlmatad at Teton Dam on final designs \.ltlS <br />7':> cubic feet per second after extensive grout treatment. <br /> <br />Total esCi.mated seepage at lIarrOl"s is 30 to 60 cubIc feet per-second <br />and will be widely d ispcrs,'d th rOllghout the g ranula r valley fill <br />,~ithollt any high velocity or concentnition of Elm" as could be <br />expe rienced whe re the fOllndat ion is jointed. No rmally, the re ,wuld <br />be no tendency to move the material. in the allUVium. <br /> <br />A study of the ground-",ater conditions adjacent to the proposed <br />reservoir has,'been completed, by the Geolor,icnl Survey and its <br />results published in an open file report 76-379, dated May 1976. <br />This study assumes steady state conditions hased on rcse.rvoir conserva- <br />tion water surface clcvat:iol!-' '~!~Ol~, tlnd concludes that resulting <br />ground-'~ater slopes upstream of the dam ",ill be te)\"ard the reservoir <br />and reservoir seepage can be expected to be some\lhat less than our <br />estimate of 30 to 60 cllhic feet per second ",ith a slurry trench as <br />outlined belO\". <br /> <br />.... <br />