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310G . Geological Survey USGS requested further discussion of the reservoir impact upon the geologic conditions of the project area. The most significant impact the reservoir will have upon the geological conditions are related to erosion; above the reservoir, an additional average annual 69,200 acre feet of water will come down the Arkansas River for storage and regulation. This water is in addition to normal Arkansas River flows and will come from diversion and collection features of the Fryingpan-Arkansas Project. The additional flows will increase the erosive forces of the river and accelerate the degregation rate. Much of the crystalline bed- rockaxurring in the Arkansas valley above the reservoir is resistant to erosion. Reaches of the river which cross less resistant bedrock and alluvial deposits will undergo slight to moderate degree of cutting. The material carried down the Arkansas River above the reservoir will be deposited upon the thin mantle of gravel, sand, silt, and clay underlaid by layers of cretaceous age sandstone, shale and limestone. The impact would be the establishment of layers of nutrient rich silt and clay to the existing overburden in the upper end of the reservoir. . Below the dam, the reduction of stream volume should not have any significant effects on the stream channel. The ability of the reservoir's clear water to erode should be offset by the reduction of the maximum flows. The valley and the reservoir walls are shale and limestone with a thin (0 to lO feet) covering of unconsolidated materials. These walls are presently stable, and there will be no ancient or active landslide areas which will be in contact with reservoir waters. Both the shale and limestone are insoluh1e and considered erosion resistant. These rock characteristics eliminate problems of bank undercu t.t ing which would result in the development of small land- slides or slumps. Some surface bank erosion will occur; it will be accelerated by the wave action at all reservoir levels. Groundwater conditions should not change by the construction of the dam and reservoir. The highly impermeable shale and limestone which border and underlie the reservoir will prevent any lateral or vertical movement of water from the reservoir. Normal releases from the reservoir will recharge the downstream alluvial aquifer. Water quality of the surface flow and downstream should increase as a result of the construction of the dam and reservoir, . 70