(5) Problem . A reach of the James River just upstream from the 

 James River Bridge is the major source of seed oysters for the $5 million 

 per annum Chesapeake Bay oyster industry. Plans to dredge a deeper channel 

 would probably need revising if deepening would adversely affect hydraulic 

 or salinity conditions over the seed oysterbeds, 



(6) Purpose of Model Study . A comprehensive model of the James 

 River was used to determine the probable effects of a proposed 10-foot 

 increase in the depth (from -25 to -35 feet MLW) of the navigation chan- 

 nel between Newport News and Richmond on salinities and currents in the 

 estuary as a whole and especially over the seed oysterbeds. 



(7) The Model . The model (Fig. 3-48), constructed to linear 

 scales of 1:1,000 horizontally and 1:100 vertically, was about 550 feet 

 long and 130 feet wide at its widest point. 



(8) Test Procedures . The model tests involved reproduction of 

 low, medium, and high sustained freshwater inflows into the James River 

 and its principal tributaries, together with reproduction of an average 

 ocean tide. Measurements of salinities and currents were made throughout 

 the problem reach at hourly and 1/2-hour intervals, respectively, over a 

 complete tidal cycle; the results were generally averaged (time and depth) 

 to determine the average velocity and average salinity values. These data 

 were intended to demonstrate the effects of the proposed channel deepening 

 on the entire estuary, as well as in areas used for seed oysterbeds. 



(9) Summary of Test Results . Figure 3-49 shows the effects of 

 the 35-foot channel on time- and depth -averaged salinities at sampling 

 stations located in and immediately adjacent to the navigation channel 

 for the three inflow conditions tested. The figure shows that the effects 

 were negligible for a river discharge of 11,500 cubic feet per second, 

 that average channel salinities were increased by about 0.1 to 0.8 part 

 per thousand for a discharge of 3,200 cubic feet per second and that 

 average channel salinities were increased by about 0.1 to 0.4 part per 

 thousand for a discharge of 1,000 cubic feet per second. Figures 3-50, 

 3-51, and 3-52 show the changes in time- and depth-averaged salinities 



at stations in the seed oysterbeds for the various river discharges. 

 Over the entire seed oysterbed area, average salinity was decreased by 

 0.2 part per thousand at 11,500 cubic feet per second, and was increased 

 by 0.2 and 0.4 part per thousand at 3,200 and 1,000 cubic feet per second, 

 respectively. Similar information developed for the effects of the en- 

 larged channel on velocities in the problem area indicated that average 

 flood and ebb velocities over the entire area would be changed on the 

 order of ±0.2 foot per second. 



It was concluded that the proposed 10-foot deepening of the channel 

 would have no significant effects on tides, currents, or salinities in 

 the James River in the reach between the James River Bridge and Fort 

 Eustis, which includes the important seed oysterbeds. 



33 



