The Rio Grande Valley National Water‐Quality Assessment study unit encompasses about 45,700 square miles in Colorado, New Mexico, and Texas upstream from the gaging station Rio Grande at El Paso, Texas, and includes surface‐water closed basins east of the Continental Divide in New Mexico, and the San Luis Closed Basin in Colorado. The mean annual precipitation ranges from less than 6 to more than 50 inches; potential evapo‐transpiration ranges from less than 35 to more than 80 inches per year. Land use is mainly rangeland, forest land, and cropland. Total irrigated acreage in 1990 was about 914,000 acres and water use was about 3,410,000 acre‐feet. Two structural settings are found in the study unit: alluvial basins and bedrock basins. The alluvial basins can have through‐flowing surface water or be closed basins. The discussion of streamflow and water quality for the surface‐water system is based on four river reaches for the 750 miles of the main stem. The quality of the ground water is affected by both natural process and human activities and by nonpoint and point sources. Nonpoint sources for surface water include agriculture, hydromodification, and mining operations; point sources are mainly discharge from wastewater treatment plants. Nonpoint sources for ground water include agriculture and septic tanks and cesspools; point sources include leaking underground storage tanks, unlined or manure‐lined holding ponds used for disposal of dairy wastes, landfills, and mining operations.

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Urban storm-runoff data, collected from 1975 to 1977, on three catchment areas in the Denver metropolitan area are presented in this report. The catchments are predominantly a single-family residential catchment area in Littleton, a multifamily residential and commercial catchment area in Lakewood, and a high-density residential and commercial catchment area in Denver. Precipitation, rainfal1-runoff, snowmelt-runoff, water-quality (common constituents, nutrients, biochemical oxygen demand, coliform bacteria, and solids, trace elements, and pesticides), and catchment-area data are necessary to use the U.S. Environmental Protection Agency's Storm Water Management Model II. The urban storm-runoff data may be used by planning, water-management, and environmental-protection agencies to assess the impact of urban storm runoff on the hydrologic system.

Runoff characteristics and washoff loads from rainfall-simulation experiments on a street surface and a native pasture in the Denver metropolitan area, Colorado.

No abstract