Appraisal of stream sedimentation in the Susquehanna River basin

The Susquehanna River presently transports about 3.0 million tons of sediment annually (110 tons per square mile). Only about 1.8 million tons of sediment enters the head of Chesapeake Bay annually because some sediment is trapped behind the power dams on the lower Susquehanna. Measured annual sediment yields from subbasins in the Susquehanna range from 40 to 440 tons per square mile. The highest yields are from parts of the glaciated section of the basin, in the anthracite coal region, and the Piedmont province. The lowest yields are from parts of the glaciated section of the basin and the Appalachian high plateau. Available data indicate that there has been a downward trend of sediment discharge in recent years. In the future, the high sediment yields associated with urbanization may offset this present downward trend. INTRODUCTION The Pennsylvania Department of Forests and Waters, the Baltimore District of the U.S. Army Corps of Engineers, and the Pennsylvania Department of Agriculture cooperated with the U.S. Geological Survey in a reconnaissance study of fluvial sedimentation in the Susquehanna River basin. The project is part of a study by State and Federal agencies to provide a comprehensive plan for the development and conservation of the water and related land resources of the Susquehanna River basin. Adequate stream-sedimentation information is one of the many requirements for proper utilization of water and related land resources. Stream-sedimentation information is used to predict the usable life of on-stream reservoirs, to aid design of future domestic and industrial water supplies, to guide the selection of good waterFl F2 HYDROLOGIC EFFECTS OF LAND USE recreation sites, and to help define the suitability of the aquatic environment for fish. This report describes the sediment yields throughout the basin, the variability and characteristics of sediment, the suspended-sediment concentrations, potential reservoir-sedimentation problems that may occur in the basin, and trends in sediment discharge. The report also points out potential problem areas where extensive sediment studies may be required. Geologic, hydrologic, and other environmental controls over stream sedimentation are considered. Each physiographic province in the basin is considered as a separate entity which has unique erosion and resultant stream-sedimentation characteristics. Much of the data used was collected between 1962 and 1967 at longterm U.S. Geological Survey stream-gaging stations having drainage areas of 100-800 square miles. In addition, data from independent studies in the basin were used to supplement data obtained during the reconnaissance study. PREVIOUS SEDIMENT INVESTIGATIONS The results of stream-sedimentation studies conducted in terrains similar to the Susquehanna River basin are included in reports on the Potomac and Delaware River basins by Wark, Keller, and Feltz (1961) and Wark and Hall (1959) respectively. The Potomac and Delaware River basin reports discussed average-annual sediment yield of streams, some of the variables causing excess stream sedimentation, and the particle-size distribution of suspended sediment. Reservoir-sedimentation surveys for 16 reservoirs (U.S. Department of Agriculture, 1969) are included in this report to show storagecapacity losses in reservoirs in and near the Susquehanna basin. Culbertson (1957) and Jones (1964 and 1966) reported on the sedimentation characteristics of several small agricultural basins in the central and north-central parts of the Susquehanna River basin. These studies evaluated the effects of conservation practices on hydrology and sedimentation in these basins. McCarren, Wark, and George (1964) presented evidence of the effects of coal mining and processing on sediment yields from a small area in the upper Swatara Creek basin. That report describes the long-term changes in stream-sediment concentration that took place as coal mining and processing decreased in the early 1950's. Schuleen and Higgins (1953) reported sedimentation rates in the Safe Harbor Reservoir and discussed the quantity and nature of sediment transported by the Susquehanna River into the reservoir during the period from 1948 to 1953. STREAM SEDIMENTATION, SUSQUEHANNA RIVER BASIN F3 Williams and George (1968) presented a progress report on sedimentation in the Susquehanna River basin using data collected through September 1965. Measurements of suspended-sediment discharge obtained during other studies were available for several sites in the Susquehanna River basin. The longest continuous record was for the Juniata River at Newport, Pa. , where daily measurements of suspendedsediment discharge were begun in January 1951. These data were collected as a part of the U.S. Geological Survey program to define the long-term variation of stream sedimentation in selected river basins throughout the United States. All available suspendedsediment data for the Susquehanna River basin appear in the annual series of U.S. Geological Survey water-supply papers entitled "Quality of Surface Water of the United States" or in "Water Resources Data for Pennsylvania Part 2, Water Quality Records," (available from U.S. Geol. Survey, Harrisburg, Pa.) which replaced the water-supply papers in 1964. DEFINITION OF TERMS Bedload. Sediment that moves along in almost continuous contact with the streambed. Individual particles move by sliding, rolling, or skipping. Bed material. The sediment mixture of which the streambed is composed. Clay. Sediment particles with a mean diameter smaller than 0.004 mm (millimeter). Fluvial sediment. Fragmentary material that originates from the weathering of rocks and is transported by, suspended in, or deposited from water. Sand. Sediment particles with a mean diameter between 0.062 and 2.0 mm. Sediment discharge. The quantity of sediment, expressed as dry weight, that is carried past a stream cross section in a unit of time. The unit of time may be a short measurement interval, a day, a month, a year, or some other period. Although some sediment is not sampled in the zone near the bed, the unmeasured component of the total sediment discharge is assumed to be small. Sediment load. The sediment that is being moved by a stream. Load refers to the material itself and not to the quantity being moved. Sediment yield. The sediment outflow from a drainage basin at a given location in a specified period of time. The sediment yield is the average-annual sediment discharge from the drainage basin, expressed in tons per square mile per year. F4 HYDROLOGIC EFFECTS OF LAND USE Silt. Sediment particles with a mean diameter between 0.004 and 0.062 mm. Specific weight. The ovendry weight of sediment per unit volume of deposit in place. Suspended-sediment concentration. A ratio of the sediment to the water-sediment mixture, expressed as milligrams per liter. Trap efficiency. The percentage of inflowing sediment that is retained in a reservoir. THE BASIN The Susquehanna River, which empties into the Chesapeake Bay, drains the largest basin along the east coast of the United States. The river drains an area of 27,500 sq mi (square miles) in the States of New York, Pennsylvania, and Maryland. Four physiographic provinces lie within the Susquehanna River basin (fig. 1)': (1) the Appalachian Plateaus, (2) the Valley and Ridge, (3) the Blue Ridge, and (4) the Piedmont (Fenneman, 1938). The Appalachian Plateaus can be divided into a low section in the northeast and a high section in the southwest. Continental glaciation on the northeastern section (the low plateau) of the Appalachian Plateaus has produced well-rounded hills and broad flat valleys. Much of the southwestern section (the high plateau) was not glaciated and is characterized by flat-topped mountains having deeply incised narrow stream valleys. The plateau is underlain by horizontal strata, as only minor folding and faulting occurred in the area. The Valley and Ridge province, which encompasses most of the middle third of the basin, is characterized by steep mountains and ridges separated by broad valleys. The structure in the Valley and Ridge province is the result of extensive folding, faulting, and crushing of the formations, followed by erosion that cut valleys in the soft formations and left the hard strata as mountains. Only a very small part of the mountainous Blue Ridge province lies within the Susquehanna River basin. The Piedmont province, which begins about 10 mi south of Harrisburg, Pa. , contains terrain that is gently rolling to hilly. It consists of both upland and lowland. The lowland is underlain by limestone, sandstone, and shale, and the upland is underlain by crystalline rocks. CLIMATE AND PRECIPITATION The climate in the Susquehanna River basin is considered to be moderate. The length of the growing season ranges from about 120 to 200 days, and the average is about 150 days. The growing season STREAM SEDIMENTATION, SUSQUEHANNA RIVER BASIN F5