Abstract
Total maximum daily loads (TMDLs) are used to protect water bodies based on their assimilative ability and are transferred as a maximum allowable load, which is the sum of all pollution emissions in a watershed that cannot be exceeded. This allowable load is calculated from a target water quality concentration and a flow state. The target water quality concentration is typically consistent with water quality standards; however, it is difficult to determine which flow state to use, especially for lakes and reservoirs. In this study, an exceedance probability method is established for determining the TMDL for reservoirs. The SWMM (Storm Water Management Model) was used to understand the pollution loads from the watershed, and the Vollenweider model was used to simulate the total phosphorous (TP) concentrations in the reservoir. Using the validated Vollenweider model, the relationship between pollution loads and the target TP concentration is illustrated. This relationship is associated with real changes in the reservoir water volume and is presented as the exceedance probability. In the study area (i.e., the Shiman Reservoir in Taiwan), an exceedance probability of 50% is suggested, and the allowable TP load is 22,209 kg/year when considering a target TP concentration of 20 μg/L. When considering effective management, the pollution sources in three hot spots are priorities, and controlling their point and nonpoint pollution sources can decrease TP from 25 to 22 μg/L.
Highlights
Total maximum daily loads (TMDLs) were originally developed for the Clean Water Act in the United States, which was passed to protect waterbodies based on their assimilative abilities or carrying capacities
This study focused on reservoir TMDL and required a reservoir water quality model and a watershed model
We used the exceedance probability to demonstrate the relationships between water quality and allowable loads
Summary
Total maximum daily loads (TMDLs) were originally developed for the Clean Water Act in the United States, which was passed to protect waterbodies based on their assimilative abilities or carrying capacities. Wastewater effluents are required to comply with specified discharge pollution concentrations and total emission loadings. The TMDL provides complete protection at the watershed scale and includes point and nonpoint pollution sources. The TMDL considers water quality management from effluent-based control to ambient-based management [3], accounting for relationships between pollution sources and water quality conditions in the waterbody. The TMDL has been widely accepted and applied in the U.S [4] It has been applied in other countries; for example, Kang et al [5] considered the TMDL in a small watershed in
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