MODELING OF THE GENESEE RIVER WATERSHED USING SWAT 2000 Introduction The Genesee River is a major tributary to Lake Ontario and has a watershed area of about 2500 square miles. At its mouth the river flows thru the City of Rochester and the federal navigation channel in the city. The watershed is primarily agricultural (52%), closely followed by forest (40%). About 4.6% of the land area is classified as urban. The remaining land is split between water and wetlands (2%). Water quality concerns of the watershed include the amount of sediment that is present in the river. Average annual volumes of dredge material from the federal channel approach 250,000 cubic yards. Disposal of this material occurs at an open lake site located approximately 1.5 miles northeast of the harbor. Two beneficial use impairments for the area of concern are the degradation of the benthos and restrictions on dredging. The degradation of benthos is primarily the result of excessive sedimentation.. The restrictions on dredging activities are, in fact, simply a mandate against overflow dredging for the purpose of reducing the impact of the release of sediment into the navigation channel. Section 516e of the Water Resources Development Act of 1996, as amended (WRDA96) directs the United States Army Corps of Engineers to develop sediment transport models for tributaries to the Great Lakes that flow into Federal navigation channels or areas of concern. The purpose of the program is to evaluate the impact of land use and other management practices on the production and delivery of sediment on a watershed scale. Development of the model will assist the Genesee/Finger Lakes Regional Planning Council (GFLRPC) and State and local watershed managers with a tool to aid in their evaluation, prioritization, and implementation of alternatives for soil conservation and non-point source pollution prevention in the watershed. Methodology The Soil and Water Assessment Tool (SWAT) is a river basin, or watershed scale model developed by Dr. Jeff Arnold for the USDA Agricultural Research Service (ARS). SWAT was developed to predict the impact of land management practices on water, sediment, and agricultural chemical yields in large complex watersheds with varying soils, landuse, and management conditions over long periods of time. SWAT has been used extensively in the United States for TDML applications. SWAT has been incorporated into the US EPA’s BASINS (Better Assessment Science Integrating Point and Nonpoint Sources) system, developed for watershed and water quality based assessment and integrated analysis of point and nonpoint sources BASINS integrates a geographic information system (GIS), national watershed and meteorlogical data, and state-of-the-art environmental assessment and modeling tools into one convenient package. The SWAT modeling work in this study was conducted within the BASINS system (version 3.0). The Soil and Water Assessment Tool (SWAT) is a physically-based, continuous simulation erosion model designed to simulate water and sediment yield from watersheds. It was developed by the USDA-ARS to provide a tool for predicting the impact of land management practices on water, sediment, and agricultural chemical yields in large complex watersheds with varying soils, land use and management conditions over long periods of time. The model contains components of both the Universal Soil Loss Equation (USLE) and the Modified Universal Soil Loss Equation (MUSLE). The model can be applied to large watersheds and complex landscapes. It uses a grid-cell characterization of the landscape to represent the spatial variability across watersheds or regions. Input information is grouped into categories consisting of weather or climate, land cover, soil, and land management. It has the capability of analyzing the above categories for sub-watersheds, ponds/reservoirs, groundwater, channels, or reaches. The model can be extended to include nutrients and pesticide loadings. SWAT has been integrated into Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) suite of models developed by the United States Environmental Protection Agency (USEPA) Description of the Watershed The Genesee River drains about 2500 square miles in states of New York and Pennsylvania. Its drainage area encompasses parts of nine counties in New York and one in Pennsylvania. The basin is roughly elliptical in shape, with a major north-south axis of about 100 miles, and a maximum width of about 40 miles. The basin lies generally between 41o 45’ and 43o15’ North Latitude and between 77o25’ and 78o25’ West Longitude. The basin is split into two hydrologic units at Mount Morris Dam, built and operated by the Corps of Engineers. The drainage area above the dam is about 1080 square miles. A location map of the watershed is shown on Figure 1. The Genesee River has a total length of about 157 miles. It rises in the Allegany Mountains in Potter County, Pennsylvania, at an elevation of about 2500 feet. It flows generally northwest to approximate river mile 106 near Houghton, New York, and then shifts to the northeast to its mouth on Lake Ontario at an elevation of about 247 feet. The topography of the southern portion of the basin (Upper Basin), upstream of the dam, is steep and rugged, while the northern portion (Lower Basin) is gently rolling. Geologically, the upper basin is in a stage of young maturity, while the lower basin has reached a geologically old stage with much meandering, a wide flood plain, and numerous oxbows. In Letchworth State Park, just upstream of the Mount Morris Dam, the river drops from an elevation of about 1080 feet to 768 feet, over three successive falls, flowing through a deep gorge cut in rock. It then flows through narrow valleys and gorges to enter the broad lower Genesee Valley in the village of Mount Morris. From this point to the City of Rochester, the river valley is a flat alluvial plain up to three miles wide and was subject to frequent flooding before the construction of the dam in 1952. At Rochester, the river drops over three falls from elevation 513 to 247 feet. Between Letchworth State Park and the headwaters, the average stream slope is 8.9 feet per mile, while between Rochester and Mount Morris, the average stream slope is 0.8 feet per mile. Figure 1 Location Map The largest tributary of the Genesee River is Canaseraga Creek. It has a drainage area of 334 square miles and joins the Genesee River near Jones Bridge, just downstream of Mount Morris at approximate river mile 62. It resembles the Genesee River in that its upper reaches, above the Village of Dansville, are steep and rugged, while its lower valley is a flat alluvial plain which is frequently flooded for long durations of time. Above Dansville, the main stem of the creek has a slope of about 40 feet per mile, while from Dansville to its mouth, it has a slope of about 3 feet per mile. The Canaseraga Creek basin is roughly square in shape, about 20 miles on a side. The main stem, which rises at an approximate elevation of 1900 feet, has a length of 42 miles and joins the Genesee River at approximate elevation 548. Other tributaries of the Genesee have a wide range in size and topographic characteristics. For example, Angelica Creek, located in the upper basin, has a drainage area of 85 square miles and is topographically rugged, with a main stream slope of 38 feet per mile. Conversely, Black Creek, located in the lower basin, has a drainage area of 214 square miles. Its basin is relatively level and marshy with a main stream slope of 6.5 feet per mile. There are numerous artificial controls in the Genesee River basin. The major one is the Mount Morris Dam and Reservoir which was completed in June 1952. It is a concrete gravity dam with an uncontrolled ogee spillway 550 feet long, and a crest elevation of 760 feet, 175 feet above the streambed. The dam has an overall length of 1028 feet and a maximum height of 215 feet. Reservoir control is provided by nine 5 x 7 foot rectangular conduits, each controlled by a vertical hydraulic slide gate. The reservoir is contained within the deep, narrow valley between Mount Morris and the Lower Portage falls. At the op of the flood control pool, the reservoir has a total length of about 17 miles and a maximum width of about ½ mile. The total storage at the spillway crest (elev. 760) is 337,400 acre-feet, of which 610 acre-feet is dead storage, leaving 336,790 acre-feet or 5.86 inches of storage for flood control. The reservoir is regulated for flood control most frequently in the winter and spring months and has resulted in significant benefits in the lower basin. Other artificial controls in the Genesee River basin include the following: A series of run-of-river structures for hydroelectric power, developed in the falls reaches of Rochester by the Rochester Gas& Electric Company. Run-of –river structures are those that utilize the natural flow of the river and contain little or no storage capacity. A state operated gated dam in Rochester for regulation of the elevation of the New York State Barge Canal, which crosses the Genesee River at grade just upstream of Rochester. Its elevation is maintained at approximately 513 feet during the navigation season, and it is provided with guard gates on either side of the river to prevent high flows from entering the canal. A dam and reservoir operated by the Rochester Gas & Electric Company, on Caneadea Creek, an upper basin tributary which enters the Genesee at about river mile 108 on the main stem. Power is not produced at this dam, its purpose being to augment low flows downstream.