CCHE2D/3D Water Quality Model

Environment quality can be compromised in exchange to more products of agriculture. Excessive nutrients, pesticides and other agro-chemicals are washed or carried into surface waters resulting in eutrophication, fish kill, environment degradation and disturbance on water supply. The water quality models are designed for studying environmental water quality problems in water bodies such as rivers, lakes and oceans. CCHE_WQ models have been developed to simulate temporal and spatial variations of environmental water quality variables in water bodies.

Four major water quality processes are simulated, including phytoplankton kinetics, nitrogen cycle, phosphorus cycles, and dissolved oxygen balance. The processes in the bed sediment layer are taken into account. Three major sediment-associated water quality processes are simulated, including the effect of sediment on the light intensity for the growth of phytoplankton, the adsorption-desorption of nutrients by sediment and the release of nutrients from bed sediment layer.

The transport and mixing of sediment and water quality constituents in water bodies are simulated by CCHE Flow and Sed models.

Beasley Lake watershed located in Sunflower County, Mississippi, was one of the three watersheds of the Mississippi Delta Management Systems Evaluation Area project (MDMSEA) for developing and assessing alternative innovative farming for improved water quality and ecology in the Mississippi Delta. In 2004, the lake was selected as one of the Conservation Effect Assessment Project (CEAP) benchmark watersheds to assess environmental benefits derived from implementing USDA conservation programs.

Beasley is an oxbow lake with a surface area of between 0.25 to 0.30 km2 and average depth of 2 m. Wind is the major driving force for its flow circulations. The flow fields are also affected by runoffs from the surrounding watershed. CCHE hydrodynamic and water quality models were applied to simulate the flow fields and water quality distributions in Beasley Lake. The figure shows the measured and simulated long-term variation of chlorophyll in this lake.

In order to prevent the city of New Orleans from flooding, the high floodwater of the Mississippi River is diverted into the Lake Pontchartrain via the Bonnet Carré Spillway. During a flood release, a large amount of freshwater, nutrients, sediment, etc. is discharged into the Lake and causes environmental problems.

To evaluate the environmental impacts of the floodwater on lake ecosystems, CCHE hydrodynamic and water quality models were applied to simulate the flow circulation, sediment transport and the water quality process in the Lake Pontchartrain. The effects of nutrients and suspended sediment concentration on the growth of algae were considered. The figure shows (a) the observed algal bloom distribution obtained from remote sensing imagery acquired on June 13, 1997; and (b) simulated chlorophyll a concentration. The general distribution of the chlorophyll a concentration is found to be consistent with that of the algal blooming imagery.