The reservoir will have a maximum pool of 2,280,000 acre-feet capacity, a 53,500-acre surface area, and 368 miles of shoreline. The present operational plan provides for a conservation pool having a surface area of 15,700 acres, a shoreline of 112 miles, and a length of 20 miles. BIG BLUE RIVER BASIN Big Blue River and its tributaries, a sub-basin of the Kansas River System, drain approximately 9,600 square miles, of which 2,484 miles are in Kansas (Colby, _et al._, 1956:44). The headwaters of the Big Blue River are in central Hamilton County, Nebraska, near the Platte River (Fig. 1). The stream flows generally south and east for 283 miles to its confluence with the Kansas River near Manhattan, Kansas. Little Blue River, the largest tributary to the Big Blue, rises in eastern Kearney and western Adams counties, Nebraska, and flows southeast for 208 miles to join the Big Blue near Blue Rapids, Kansas (Nebraska State Planning Board, 1936:628). The Big Blue River Basin varies in width from 129 miles in the northwest, to approximately ten miles near the mouth (Colby, _et al._, 1956:44). GEOLOGY OF THE BASIN In Kansas, outcrops of Pennsylvanian and Cretaceous age occur along the extreme eastern and western sides of the Big Blue River Basin, respectively, whereas Permian beds (overlain by Pleistocene deposits) occur throughout most of the remainder of the watershed (see Moore and Landes, 1937). The Big Blue and Little Blue rivers and their tributaries have deeply incised the Permian beds of the Flint Hills in Kansas, exposing limestones and shales of the Admire, Council Grove, Chase, and Sumner groups (Wolfcampian and Leonardian series) (Walters, 1954:41-44). Pleistocene deposits in the Big Blue Basin in Kansas consist of alluvium, glacial till, and glacial outwash from the Kansan glacial stage, overlain by loess deposits of Wisconsin and Recent stages (Frye and Leonard, 1952: pl. 1). [Illustration: FIG. 1. Big Blue River Basin, Kansas and Nebraska.] The Big Blue River was formed "in part on the till plain surface and in part by integration of spillway channels," in the latter portion of the Kansan glaciation (Frye and Leonard, 1952:192). This stream, and the Republican River to the west, carried waters from the areas that are now the Platte, Niobrara, and upper Missouri River basins (Lugn, 1935:153). Drainage was southward, through Oklahoma, until establishment of the east-flowing Kansas River (Frye and Leonard, 1952:189-190). As Kansan ice receded the Blue and Republican rivers retained what is now the Platte River Basin. The lower Platte River developed and the surface drainage became distinct in the Iowan (Tazwellian) portion of the Wisconsin glacial stage (Lugn, 1935:152-153). However, according to Lugn (1935:203) the Platte River Basin contributes about 300,000 acre-feet of water per year to the Big Blue and Republican rivers by percolation through sands and gravels underlying the uplands that now separate the basins.