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<br />----------- <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The flow-net method, described in Reference-7, consists of estima- <br /> <br /> <br />ting the flow lines and equipotential lines (line of equal pressure) in <br /> <br /> <br />accordance with certain physical laws. Then, using the material per- <br /> <br /> <br />meability and the flow-net results, the quantity of seepage can be <br /> <br /> <br />estimated uSing the following equation: <br /> <br />Nf <br />q ~ kH <br />Nd <br /> <br />where <br /> <br />q ~ seepage quantity per foot of length (cfs/ft) <br /> <br /> <br />k ~ soil permeability (f/d) <br /> <br /> <br />Nf = number of flow lines <br /> <br /> <br />H ~ total head on the dam (feet) <br /> <br /> <br />Nd ~ number of equipotential drops <br /> <br />The embankment and foundation materials were assumed to be homogenious <br /> <br /> <br />and therefore the horizontal and vertical permeabilities were approx- <br /> <br />imately equal (see Figure-III). The range of <br /> <br /> <br />silty clays is reported (Reference-7) at 10-5 <br /> <br /> <br />the loose state of the embankment, a value of <br /> <br />permeability for sandy <br />-6 <br />to 10 em/sec. Due to <br />-5 <br />10 em/sec. (0.03 ft/ day) <br /> <br />was used for estimation purposes. Field permeability tests Here not <br />performed for this study. <br /> <br />since the seepage is through a dam embankment, then the flow is <br /> <br /> <br />unconfined and the phraetic line is unknown. The phreatic line was <br /> <br /> <br />estimated using the Cassagrande Method (Reference-8). For the first <br /> <br /> <br />approximation, condition IIA", the embankment was assumed to be homo- <br /> <br /> <br />genious (no soil stratifications) with equal horizontal and vertical <br /> <br /> <br />permeabilities. The seepage quantity estimated for condition "A" was <br /> <br /> <br />from 1 to 5 AF/year. The veriation was due mainly to the confidence <br /> <br /> <br />level of the permeability coefficient and to the yearly variation in <br /> <br />the reservoir water surface. <br /> <br />For condition liB", the embankment was assumed to have a soil layer <br /> <br />with a permeability coefficient (k~10-3 em/sec.) at least 10 times as <br /> <br /> <br />large as the coefficient for the remaining embankment. The pervious <br /> <br />-21- <br />