Development of best management practice (BMP) placement strategies at the watershed scale

This dissertation has developed and demonstrated a holistic approach and framework to analyze and objectively determine the cost-effective placement and design of structural BMPs based on continuous and “long-term” evaluations at the watershed scale. The methodology involves the coupling of a comprehensive watershed simulation model with an optimization technique. Specifically, it consists of three interacting functional components, i.e. a watershed simulation model (AnnAGNPS), a BMP simulation module (the impoundment routine), and an optimization model (the scatter search).; A conceptual “homogeneous” watershed was used to examine the discretization effect on topographical perspectives. Based on results of several numerical experiments using six homogenous test watersheds, it was concluded that: (1) For homogeneous watersheds, due to the effect of channel storage and transport, the peak flow is attenuated and delayed when the cell sizes is reduced, while the magnitude of the effect decreases as the cell sizes are further reduced; (2) the sediment load at the watershed outlet also varies with different cell sizes, but the trend cannot be easily predicted due to the existence of two competing factors, i.e. the delivery ratio and the transport capacity.; A new impoundment module was developed to account for sediment accumulation and resuspension. The modified impoundment module was able to reasonably simulate the effect of sediment accumulation and resuspension on sediment removal on a long-term basis, thereby potentially improving the reliability of the system optimization results.; The significance of the optimization scheme developed lies with its ability to efficiently identify the near optimal stormwater pond implementation plan based on the evaluation of candidate solutions using an “on-line” long-term simulation approach. The scatter search was proven to be a superior optimization algorithm for computing-time intensive complex systems. Furthermore, the sensitivity of the optimal solution to water quality goals, the effect of different cost functions (static and dynamic), as well as the effect of different impoundment routines (with and without considering sediment resuspension) on the optimization results were examined through a series of numerical experiments. By analyzing the optimal or near optimal pond design strategies for a hypothetical case, it was observed that when the water quality goal becomes more stringent, ponds are selected, in order of preference, according to the sequence of regional, sub-regional, and on-site, as long as space is available for pond construction at all of the potential sites. (Abstract shortened by UMI.)...