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<br />Works of Improvement <br /> <br />the upper part. The maximum thickness of these deposits ranges from <br />about 20 feet at the smaller sites to an estimated 50 or '60 feet at the <br />larger sites., At most of the dam sites, bedrock in the abutments is at <br />or within a few feet of the surface. The abutements are mantled by a <br />few feet of silt and, clay which are mainly wind-deposited. At the sites <br />where the depth to bedrock is greater, the abutments are underlain by <br />deposits of firm alluvial clay. ' <br /> <br />The emergency spillway at all of the sites except ss-4 will be excavated <br />into either claystone and siltstone bedrock or into firm alluvial clay. <br />These materials are resistant to erosion. Structure ss-4 spillway is in <br />silt and sand, and will be covered by a thin layer of clay. Adequate <br />amounts of satisfactory borrow materials, mainly silt and clay with some <br />silty sands, are available from within or adJacent to the reservoir area <br />at all of the sites. <br /> <br />Foundation Treatment <br /> <br />Foundation treatment consists of stripping the ground, surface beneath <br />the embankment and construction of a cutoff core into the alluvium. The <br />core will cut through the silty well-graded sand of the upper part of <br />the alluvium to the less permeable silt and clay of the lower part. <br />_ __ -~CoFes-af'e-expeGted---t.o-avel"age-lO-~to-l-5-f'ee.t-i.n depth w'Lth---1.;.Ls.i.da---' <br />slopes. Clearing will be 'done ol)ly where construction necessitates. <br /> <br />Embankment <br /> <br />The embankment for the dams will be zoned fill-section having a center <br />core of impervious material and upstream and downstream zones consisting <br />of the coarse permeable material abundant at the sites. Embankment <br />slopes will be 3:1 upstream and ~.5:1 downstream. <br /> <br />Principal Spillway <br /> <br />Each principal spillway will consist of a standard covered twostage <br />inlet, a 30-inch diameter reinforced concrete pipe conduit placed on a <br />cradle, and an impact basin outlet. Two floodways (I and 2) are planned <br />to take the combined maximum low stage release from nine of the flood- <br />water retarding structures to the South Platte River. Discharge from <br />Structure ss-8.5 wi 11 be conta ined by the Hi gh line Canal.. <br /> <br />37 <br />