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|USGS Virginia Water Science Center|
Streamflow characteristics are used to indicate the ability of a stream to supply sufficient streamflow for waste disposal, municipal supplies, irrigation, ground-water recharge, and maintenance of natural conditions. These characteristics can be used to estimate water budgets, which are necessary for the Commonwealth’s requirement for local and regional water-supply planning. Also, evaluation of low- and base-flow characteristics can provide valuable insight into the availability of surface and ground water and aquifer properties within a watershed.
Low-flow characteristics (7Q10 and 7Q2) have been determined from daily discharge records for approximately 300 continuous-record sites in Virginia. Low-flow values have been estimated at an additional 400 partial-record sites from relations developed between partial-record sites and continuous-record sites (Hayes, 1991). Base-flow characteristics have been determined for 212 continuous-record sites and 192 partial-record sites in the Piedmont, Blue Ridge, and Valley Ridge Physiographic Provinces of Virginia (Nelms and others, 1997). The period of record covered by both of these investigations ended in 1984. Over the past 20 years, additional data have been collected and the extended drought from 1998-2002 has occurred. Richardson (1994) determined annual and seasonal ground-water discharge rates for 16 continuous-record sites in the Coastal Plain of Virginia.
Recently, these relations have become increasingly important to State regulatory agencies and U.S. Geological Survey (USGS) cooperative studies, where additional streamflow information is needed at a partial-record site or for a general area and for determining water-budget components for water-availability purposes. Currently, the Virginia Department of Environmental Quality (VDEQ) is using these relations to determine streamflow characteristics for wasteload allocation, toxic loads, and instream-flow requirements. Requirements extend to flows other than the 7Q10 and 7Q2 values previously determined. These relations also have been used for estimates of ground-water recharge, base flow, and recession indexes by individual localities.
Throughout the history of the USGS and the VDEQ, data have been collected at partial-record sites for special study requirements. Data collection at these sites was intense for short periods of time and small areal extent. Once sufficient data were collected at the sites to meet the requirements of a study and relations were developed, much of the analytical work was filed in boxes, lost, or destroyed. Additionally, data were sporadically collected over wide areas of the State during extreme events with little continuation of the data collection during other streamflow conditions. Presently, it is difficult to determine what data have been collected in a specific area of the State, and where the data are located. Attempts to reconstruct past work or quickly review the data to determine additional data needs are almost impossible.
Publish existing low- and base-flow characteristics of streams in Virginia (Hayes, 1991; Richardson, 1994; Nelms and others, 1997) to a Web-based application for use in regulatory flow and water-supply planning activities.
View Existing Data:
Revise these characteristics by incorporating data collected over the past 20 years at gages used by Hayes (1991); Richardson (1994); and Nelms and others (1997) and at gages established since 1984 by using spatial and hydrograph separation techniques that were not available at the time of these investigations.
The investigations conducted by Hayes (1991) and Nelms and others (1997) were designed to be companion studies that considered streamflows for the period of record up to 1984. This proposed investigation will consider both low- and base-flow characteristics simultaneously in order to minimize duplication of effort and resources. The proposed approach will consist of four main categories: 1) low-flow characteristics, 2) base-flow characteristics, 3) geographic information system (GIS) spatial analysis, and 4) Web-based applications.
Low-flow and base-flow characteristics for Virginia streams
developed by the U.S. Geological Survey, Water Resources Division, Richmond, Va.
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