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Lake Okeechobee is a large, shallow subtropical lake, located in south Florida. Over the last several decades, Lake Okeechobee has experienced accelerated eutrophication due to excessive phosphorus loads from agricultural run-off. Recycling of phosphorus from bottom sediments through resuspension is critical to addressing eutrophication of the lake and for water quality management. The present study investigates the impacts of wind waves on sediment transport in Lake Okeechobee, using measured data and the Lake Okeechobee Environmental Model ( LOEM). The LOEM was fully calibrated and verified with more than 10 years of measured data in previous studies. Analysis of the measured data indicates significant wave height (SWH) and suspended sediment concentration are closely correlated to the wind speed in the lake. The nonlinear interaction of high-frequency wind waves with relatively low-frequency currents in the boundary layer plays a key role in sediment deposition/resuspension. Without considering the effects of wind waves, the bottom shear stress can be greatly underestimated. The spatial variations of key variables for sediment modelling, including SWH, water depth, orbital velocity, current velocity, bottom shear stress and sediment concentration, are discussed. In general, the near-bottom wave velocity (and the associated bottom shear stress) is greater than or the same order of magnitude as the near-bed current velocity (and the associated bottom shear stress) in this shallow water system. Although the sediment zones of Lake Okeechobee were described in previous studies, few published papers discussed its formation mechanisms. The findings of the present study include that the multiyear averaged bottom shear stress with wind-wave effect plays a key role in forming the spatial patterns of the sediment zones. The study results are currently being used in lake management and in developing strategies for reducing phosphorus in the lake. [ABSTRACT FROM AUTHOR]

Three hurricanes (Frances and Jeanne in 2004 and Wilma in 2005) passed over Lake Okeechobee causing a number of changes in its sediment and environment. The unconsolidated sediment atop the mud sediments in the central region of the lake became thicker due to the settling and deposition of resuspended sediments after the hurricanes passed. The increased unconsolidated sediment layer was more easily resuspended, and resulted in sustained higher solids and nutrient concentrations and lower light transparency in the water column for more than 4 years after the hurricanes passed. Hurricanes Frances and Jeanne disturbed consolidated sediments to a depth of 7-15 cm from the surface while Hurricane Wilma extended the disturbance to a depth of 25 cm. Concentrations of total suspended solids (TSS) in the water column increased four to sixfold after the hurricanes. The high concentration of TSS was continuous and maintained 2-4 times higher than a normal situation in the lake until present. Hurricanes contributed to a decrease of submerged aquatic vegetation (SAV) density from 4-34 g dw/m2 to 0.1-4 g dw/m2 primarily through scouring. SAV recovery was very slow due to the increasing turbidity and reduced light transparency. [ABSTRACT FROM AUTHOR]

There are increasing demands for reliable engineering tools for sediment modeling and water resources management. The Lake Okeechobee environmental model (LOEM), which was calibrated and verified to simulate sediment resuspension and transport in Lake Okeechobee, Florida, is a dependable tool to meet those demands. The LOEM contains 2,126 horizontal grid cells and 5 vertical layers. The primary hydrodynamic and sediment transport driving forces are wind waves, surface wind stresses, and inflows/outflows. The LOEM was calibrated and verified, using two sets of observed data from May 16 to June 13, 1989 and January 17 to March 3, 2000, respectively. The model results indicate that sediment solids are resuspended primarily by wind–wave action and transported by lake circulation. The strong relationship between significant wave height and suspended sediment concentration in the lake indicates that sediment resuspension is primarily driven by wind-induced waves. To simulate this sediment resuspension, the processes of wind–wave- and current-induced bottom shear stresses on the lake bed were added to the LOEM. Once resuspended, the suspended sediment is transported to different areas of the lake by wind-induced currents. The importance of wind-wave, currents, and their interactions to sediment transport is included and discussed. By using the comprehensive data set for model calibration and verification, the LOEM model is proven to be a useful tool to water sources management in the lake. [ABSTRACT FROM AUTHOR]