Simulating Material Movement through the Lower Altamaha River Estuary Using a 1-D Box Model
Sheldon, Joan E.
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1-D optimum-boundary box models were used to simulate the movement of dissolved pollutants or other conservatively mixing constituents through the Altamaha River estuary. Tracers were introduced into the models as point sources at various locations within the estuary and as a non-point input to the entire system. In each case, models were run at four different river flow rates and were used to simulate both the movement of tracer within the estuary and its rate of removal. When tracer was introduced at head of tide, it moved rapidly (from 1-2 d, depending on flow) to the head of the mixing zone 30 km downstream. Tracer released anywhere in the estuary, including farther downstream at 2 km, moved toward an area 4-6 km upstream of the mouth, where it remained centered as overall removal continued. Movement toward this zone was observed regardless of flow rate. Introduction of tracer as a non-point source also resulted in distributions centered at 4-6 km, suggesting that this area is a potential convergence zone in the Altamaha River estuary. Maximum exposure to tracer, measured as the amount of time that concentration exceeds a given threshold, depends on where in the estuary tracer is released. When released at head of tide, maximum exposure is experienced at 6-10 km. Simulations of the type presented here are useful for evaluating the conservative movements of both point and non-point-source constituents in the estuary.