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This report gives information on the physical characteristics of Whitehead Watershed and on the characteristics of the suspended sediment transported into and discharged from the reservoirs. Selected periods of significant runoff and outflow from April 1955 to September 1956 are discussed. Particle-size distribution of inflow and outflow samples indicates that all the sand entering reservoir 1 is trapped and that most of the sand entering reservoir 2 is trapped. Results of chemical analyses of water samples and a comparison of suspended-sediment size analyses in native water and in distilled water with dispersing agent indicate that significant sediment flocculation may occur in the reservoirs. INTRODUCTION The study of fluvial sediment in Whitehead Watershed is part of a nationwide investigation of the trap efficiency of detention reservoirs. The Geological Survey is cooperating with the Soil Conservation Service in the work. The sediment investigation in Whitehead Watershed was directed by P. C. Benedict, regional engineer. D. M. Culbertson, area engineer, supervised field operations, compilation of data, and preparation of this report. Records of water discharge were furnished by D. D. Lewis, district engineer. Records of precipitation were obtained in cooperation with the U. S. Weather Bureau. PHYSICAL CHARACTERISTICS OF THE WATERSHED Whitehead Watershed is in the central part of Otoe County, Nebr. (Seefig. 1.) The watershed is part of the dissected till plains of eastern Nebraska. The drainage area is approximately 495 acres. Total relief within the drainage area is about 95 feet. Slopes generally are 4 to 12 percent and range from 100 to 800 feet in length. Figure 1 shows the shape of the watershed and the locations of dams 1 and 2, stabilization structure s, two precipitation gages, and sediment sampling points. Deposits of Pleistocene age mantle the watershed. Peorianloess, of late Pleistocene age, forms ?i nearly continuous mantle over the eastern half of the area and is on divide areas and upper slopes in the western half of the area. Loess of the Loveland formation, which underlies the Peorian loess stratigraphically in this southeastern Nebraska area, is not exposed to any significant extent. Kansan till, also of Pleistocene age, is generally exposed on moderate to steep slopes in the western part of the watershed. The Kansan till, which is stratigraphically lower than the Peorian loess and the Loveland formation, generally is found topographically lower than these formations. Late Pleistocene to Recent alluvium mantles the small, narrow bottomland areas. Soil development in the watershed varies mainly with parent material, physiographic position, and slope. Because climate and vegetation in this small drainage basin are homogeneous, they are relatively unimportant determinants of profile differences. Soils developed on loess are predominant in the eastern half of the area and grade into mainly glacial-till soils in the western part of the area. Slope, infiltration rate, soil p er m eab il i t y, and parent material may vary within small areas. Severe erosion has exposed the B horizon in small areas of steeply sloping land. A soil survey of Otoe County, Nebr., jiy indicates that 61. 6 percent, or about 305 acres, of the watershed is occupied by soils of the Sharpsburg series, which are developed on Peorian loess. Of the 305 acres, about 155 acres is Sharpsburg silty clay loam; 112 acres is Sharpsburg silty clayloam, rollingphase; and 38 acres is Sharpsburg silty clay loam, eroded rolling phase. About 29. 3 percent, or 145 acres, of the watershed is occupied by soils of the Carrington series, which are developed on glacial till. Of the 145 acres, about 5 acres is Carrington clay loam; 125 acres is Carrington clay loam, eroded rolling phase; and 15 acres is Carrington loam, eroded rolling phase. Soils of the Burchard-Carrington complex, developed on glacial till, occupy about 2. 0 percent of the watershed. The Judson-Wabash complex, developed on colluvial-alluvial material, occupies about 7. 1 percent of the watershed. Figure 2 shows the relation between soils, parent material, physiographic position, and slope in Whitehead Watershed. Most of the drainage area is under cultivation; corn, sorghum, oats, and wheat are the main crops. Much of the steeply sloping land is in native grass or is seeded to grasses and legumes, and small areas of native grass are along the major channels. Nearly all the minor drainageways have been seeded to grass to prevent gully formation. _!/ U. S. Department of Agriculture, survey of Otoe County, Nebr. 1950, Soil N R .I IE . R .I 2 E . ^N o n re c o rd in g O Ti p re ci p ita tio n

Fluvial sediment in Whitehead watershed and Whitehead reservoirs, Nebraska, April 1955 to September 1956