Basin Boundary Delineation and Annual Flood Peaks of Streams in Virginia

The Need

Economic growth, development, and management of Virginias natural resources require planning for new construction or modification of existing transportation infrastructure. Extensive hydraulic analysis and design are needed to reduce the environmental impact of highways and bridges on the drainage basins which they cross. Effective design and placement of structures near streams and on flood plains requires an understanding of the peak discharge and basin characteristics of those streams. Knowledge of the magnitude and frequency of peak discharge is needed to construct highway bridges and culverts; to locate transportation infrastructure on flood plains; and to design flood-control structures. Knowledge of basin characteristics is needed to transfer station peak-discharge characteristics to ungaged locations.

Since 1949, the USGS, in cooperation with the Virginia Department of Transportation (VDOT), has maintained a network of partial-record peak-discharge gaging stations, combined with continuous-record gaging stations to provide annual peak-discharge data for more than 550 gaging stations throughout Virginia. Most of these gages have 10 years or more of peak-discharge data.

Objectives:

The objectives of the study are (1) to develop digital basin boundaries at approximately 550 current and historic surface-water gaging stations and (2) to update annual flood-peak data for these gages in preparation for a flood frequency analysis study.

Relevance and Benefits:

This project will produce flood records needed to determine flood frequency of streams at gaged locations across Virginia, and the basin information necessary to develop methods for estimating flood frequency at ungaged locations. Although the flood records and basin information described herein have been published in various USGS reports, a single-volume summary compilation is needed. Digital basin boundaries stored in a geospatial database can be related to other Geographic Information System (GIS) databases, which will allow accurate, consistent determination of basin characteristics, such as area, slopes, elevations, soils, geology, land use, and precipitation. Digital basin boundaries have several advantages over traditional delineations on paper maps: digital basin boundaries are portable to other datums and projections, can be combined with other geospatial databases, produce more accurate and consistent determination of basin characteristics, and facilitate revisions.

Virginia streams approaching flood stage