Xiaobo Chao

Three-dimensional numerical simulation of water quality and sediment-associated processes with application to a Mississippi Delta lake

A three-dimensional water quality model was developed for simulating temporal and spatial variations of phytoplankton, nutrients, and dissolved oxygen in freshwater bodies. Effects of suspended and bed sediment on the water quality processes were simulated. A formula was generated from field measurements to calculate the light attenuation coefficient by considering the effects of suspended sediment and chlorophyll. The processes of adsorption-desorption of nutrients by sediment were described using the Langmuir Equation. The release rates of nutrients from the bed were calculated based on the concentration gradient across the water-sediment interface and other variables including pH, temperature and dissolved oxygen concentration. The model was calibrated and validated by applying it to simulate the concentrations of chlorophyll and nutrients in a natural oxbow lake in Mississippi Delta. The simulated time series of phytoplankton (as chlorophyll) and nutrient concentrations were generally in agreement with field observations. Sensitivity analyses were conducted to demonstrate the impacts of varying suspended sediment concentration on lake chlorophyll levels.

Numerical modeling of surface flow and transport phenomena with applications to Lake Pontchartrain

Abstract This article presents the capabilities of a numerical model, CCHE2D, by using its application to study the response of a highly complex water system, Lake Pontchartrain, Louisiana, under extreme conditions of Hurricane Katrina in 2005 and the flood water release from Bonnet Carré Spillway in 1997. The numerical simulations were validated using the field data collected by the US Geological Survey and US Army Corps of Engineers, as well as satellite imagery obtained from National Oceanic and Atmospheric Administration. The close agreements obtained with technically acceptable accuracy in both field properties and trends of their spatial and temporal variations fully demonstrated this models usefulness in predicting the hydrodynamics, sediment transport, and salinity distribution of lakes under extreme flood forcing. This model provides a useful tool for lake water quality management.

Numerical Modeling of Flow and Sediment Transport in Lake Pontchartrain due to Flood Release from Bonnet Carré Spillway

Lake Pontchartrain is a brackish estuary located in southeastern Louisiana, United States. It is the second-largest saltwater lake in U.S. The lake covers an area of 1630 square km with a mean depth of 4.0 meters. It is an oval-shaped quasi-enclosed water body with the main east-west axis spanning 66 km, while the shorter north–south axis is about 40 km. It is con‐ nected to the Gulf of Mexico via Rigolets strait, to Lake Borgne via Chef Menteur Pass, and to Lake Maurepas via Pass Manchac. These lakes form one of the largest estuaries in the Gulf Coast region. It receives fresh water from a few rivers located on the north and north‐ west of the lake. The estuary drains the Pontchartrain Basin, an area of over 12,000 km2 situ‐ ated on the eastern side of the Mississippi River delta plain.

Application of Advanced Remote Sensing Techniques to Improve Modeling Estuary Water Quality

Estuaries, the interface between terrestrial and coastal waters are an important component of complex and dynamic coastal watersheds. They are usually characterized by abrupt chemical gradients and complex dynamics, which can result in major transformations in the amount, chemical nature and timing of the flux of material along these river–sea transition zones. The ecological functioning of these areas is considered to be of major concern, as estuaries offer the last opportunity to manage water quality problems before they become uncontrollable in the coastal waters.

Three Dimensional Numerical Modeling of Cohesive Sediment Transport in a Shallow Oxbow Lake

This paper presents the development and application of a three-dimensional numerical model for simulating the cohesive sediment transport in water bodies where both currents and wind-driven waves are important. The model was verified by a simple test case with an analytical solution (nonconservative tracer in a prismatic channel with uniform flow) and applied to Deep Hollow Lake, a small oxbow lake in Leflore County, Mississippi. The model produced predictions within 2% of the analytical solution. The bottom shear stresses induced by currents and waves were calculated, and the processes of resuspension, deposition and settling were considered. The primary forces associated with sediment transport were caused by wind-induced currents and waves. Simulated sediment concentrations were compared with limited field observations available, with generally good agreement. Simulated concentrations for a scenario with wind-driven waves were about one to three times greater than for a simulation without wind-wave processes.

Numerical Modeling of the Phosphorus Cycle i n a Shallow Oxbow Lake

A three-dimensional model was developed for simulating the phosphorus concentration in a shallow oxbow lake. The processes of mineralization, settling, adsorption, desorption, bed release (diffusion), growth and death of phytoplankton, etc, were considered, and the concentration of organic phosphorus, orthophosphate and phytoplankton were simulated. The adsorption and desorption of phosphorus from suspended sediment particles, as well as its release from bed sediment were verified using results obtained from laboratory experiments. The model was calibrated and applied to Deep Hollow Lake in the Mississippi alluvial plain. Simulated trends and magnitudes are generally in good agreement with field observations. Simulation indicates strong interactions between sediment-related processes and phosphorus concentration.