A model for understanding and managing the impacts of sediment behavior on river water quality
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A mathematical model (Sediment-Transport-Associated Nutrient Dynamics – STAND) has been developed for the study of sediment-associated water quality issues. The model is intended to simulate changes of water quality constituents associated with sediment behavior. It has a 3-level structure. The first level accounts for the hydraulics of open-channel flow. The second computes sediment transport potential and actual rates based on the information provided by the first level. A non-equilibrium approach is used. In the third level, changes of nutrient concentrations along a studied river are computed with the consideration of nutrient transport, adsorption/desorption, and interstitial water release. In order to calibrate the model, field data were collected from the Oconee River, a major tributary of the Altamaha River in Georgia. Two stations, approximately 17 km distant from each other, were established along the river for the purpose of data collection. Observations of the river's hydraulics, suspended sediment, and water quality (mainly ortho-phosphate, nitrate, temperature, specific conductivity, oxidation-reduction potential, dissolved oxygen, and pH) were collected at the two stations. Another data set collected along a major tributary of the Yellow River in China was also used for calibration and evaluation of the model's hydraulic and sediment transport parts. Calibration and evaluation results are encouraging, which suggests that STAND is a useful tool for the thorough study and understanding of water quality issues associated with sediment behavior. A semi-hypothetical river has been mathematically constructed and the model has been applied to the river for the study of sediment and nutrient behavior under the influence of hydrological conditions, pattern of upstream release, the roles of peak flow and base flow, and lateral inflows of sediment and nutrients.