|Shields Jr, Fletcher|
Submitted to: American Society of Civil Engineers Water Resources Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/2/2003
Publication Date: 3/1/2004
Citation: Zhu, T., Jia, Y., Shields Jr, F.D. 2004. Water quality modeling of lake using cche2d. American Society Of Civil Engineers Water Resources Conference Proceedings. p. 306-315.
Interpretive Summary: Lakes in agricultural watersheds sometimes have the water quality problems due to soil eroded from fields that enters the lake with runoff. Fine sediment suspended in the lake water can affect ecological cycles in the lakes. For example, water made turbid by suspended sediment will transmit less light to lower levels in the lake, hindering photosynthesis by simple plants (algae). Various best management practices (BMPs) may be employed to reduce fine sediment load leaving agricultural lands, but methods are needed to link BMPs to improvements in receiving water quality. A computer program to simulate lake water quality was developed and coupled with an existing computer program that simulates the movement of water and sediment. The latter model was adjusted to match actual conditions in Deep Hollow Lake, an oxbow lake in the Mississippi Delta, using data from two dye tests conducted in 1999. During the dye tests, a fluorescent dye was pumped into the lake with well water to simulate a runoff event. Mixing of the dye with the lake waters was observed and measured for 24 hours. After adjusting the computer model, lake water quality was simulated using actual weather conditions for 1999. Computer outputs were compared with water quality measurements. The computer program reproduced observed levels of chlorophyll with acceptable accuracy. The impact of hypothetical changes in the fine sediment concentrations entering the lake on chlorophyll concentrations were estimated using the model. A series of numerical experiments showed how the water quality in the lake was improved due to hypothetical sediment load reduction.
Technical Abstract: Some oxbow lakes in North Mississippi have the water quality problems due to the sediment loads from the upland runoff. Fine sediment can affect the light attenuation and adsorption /desorption balance thus playing an important role in the ecological cycles in the lakes. Various best management practices (BMPs) may be employed to reduce fine sediment load, but methods are needed to link BMPs to improvements in receiving water quality. A water quality module was developed and coupled with a two two-dimensional depth-averaged hydrodynamic model, CCHE2D, which has includes a sediment transport module. The transport capability was first calibrated and then verified using filed data of data from two dye tests. Physical parameters, temperature, chemical and bio-chemical parameters, such as dissolved oxygen, suspended solids, phytoplankton and nutrients were simulated. The impact of the fine sediment on chlorophyll concentrations were estimated using the model. A series of numerical experiments showed how the water quality in the lake was improved due to hypothetical sediment load reduction.