Physical Setting And Hydrology

The James River is a typical coastal plain estuary draining to the Chesapeake Bay. The variation of depth, cross-sectional area, and tidal velocity in the James River from Richmond to the Chesapeake Bay is significant. For example, the cross-sectional depths vary from about 10 feet in areas with shallow side embayments to 25 to 30 feet in the deepwater channel. The river generally widens in the downstream direction, although natural constrictions occur at several locations. Cross-sectional area varies markedly, from the deep, narrow channel in the upstream section to broad, shallower profiles downstream.

Upstream freshwater flow to the study area is monitored at the USGS gaging station near Richmond, Virginia, on the James River. The freshwater flow to the James River is contributed by runoff from 6,758 square miles of woodland and agricultural areas upstream of the city of Richmond. A relatively small additional flow enters the study area via the Kanawha Canal, bypassing the USGS gage near Richmond. The combined average annual flow in the river at the gage is 6,946 cfs (1937-1998). A

Figure 9-1 Hydrologic Region 2 and the James estuary watershed.

relatively small intervening drainage area provides a nominal increase in in-stream flow between Richmond and the confluence with the Appomattox River. Water is withdrawn from the James River for both municipal and industrial purposes and then returned to the river. Treatment is provided by all users except those who use the water solely for cooling purposes. Long-term interannual and mean monthly trends in streamflow for the James River near Richmond, Virginia, are shown in Figures 9-3 and 9-4.

Figure 9-2 Location map of the James River basin. (River miles shown are distances from Chesapeake Bay at the mouth of the James River.)

Figure 9-3 Trends of mean, tenth, and ninetieth percentile statistics computed for summer (July-September) streamflow for the James River (USGS Gage 02037500 near Richmond, Virginia). Source: USGS, 1999.

0 0

Post a comment