A program of water-quality sampling to define the relationships between land use, watershed characteristics, and the quantity, quality, and timing of runoff has been started for the Twin Cities metropolitan area of Minnesota. Ten major watersheds were chosen as representative of conditions in the metropolitan area. Each will be sampled at one location near the outlet. Six of the watersheds are agricultural and range in size from 14.3 to 82.9 square miles. The four remaining watersheds are urbanized and range in size from 1.22 to 31.7 square miles. In addition, seven urban subwatersheds, which range in size from 0.12 to 0.47 square miles and reflect a dominant land-use type, will be sampled.
Data collection is designed around the hydrologic conditions expected for each site. Sixteen of 17 sites are instrumented to define stream discharge, and 12 sites have automatic water samplers and recording rain gages. In addition, six sites will have automatic wetfall/dryfall precipitation collectors.
Samples for analysis of 32 chemical, physical, and biological constituents will be collected at varying frequencies, with emphasis on storm sampling for suspended solids and nutrients. A data-management system being designed for the U.S. Geological Survey Urban Hydrology Studies Program will facilitate data processing. Data interpretation will be aimed at defining the quantity and quality characteristics of runoff from study watersheds. These findings will be extrapolated to unsampled watersheds in the metropolitan area.
