The Chowan River system in Southeast Virginia consists of three rivers that form two confluences before flowing into Albemarle Sound in North Carolina. This study investigated, by means of numerical simulation, the river's water quality problems related to excessive algal growth. A computer program was developed to determine flow rates, velocities, and depths at 51 computer stations by routing flows through the river system. The output of this flow program provided the input for calculating the concentrations of biochemical oxygen demand (BOD), chemical oxygen demand (COD), dissolved oxygen (DO), and four nitrogen parameters (organic, ammonia, nitrite-nitrate, and algal) at each of the computer stations. The four nitrogen parameters were solved for simultaneously. Measured field data collected in 1974. were used to calibrate the model. The program was then used to simulate algal growth for 1974 and 1975 and was compared with measured data for verification of the program.

The program was also used to study management strategies for water quality control. The first such plan was to measure the effects of reducing the concentration of nutrients from overland runoff on algal concentrations at the mouth of the river. Another application of the program assumed the watershed to consist only of forests and nutrient runoff from the forests to be the river's only nonpoint source of pollution. This primeval condition resulted in roughly half the concentrations measured in 1974.