Assignment 6

Behera, P, Papa, F., Adams, B (1999) “Optimization of Regional Storm-Water Management Systems” Journal of Water Resources Planning and Management, 125(2) pg. 107-114.

Summary

This essay is an expansion of a previous study, authored by the same individuals. It introduced design of ponds that will follow constraints of runoff control along with quality control. There is always a problem of designing multiple storm-water management ponds in a site that will outfall to the same point. The writers extended their previous study’s methodology by introducing a dynamic programming model to three parallel catchments, each of which had their own detention pond.

Obviously, the objective function of this model was to minimize cost of the ponds in each catchment, which included initial construction cost, operation cost, and maintenance costs. The variables that were optimized were the storage volume, location, pond depth, and release rate. The major constraints of the model were the runoff control constraint and the pollution control constraint.

The cost of the individual SWM pond was the sum of pond surface area multiplied by the land value and the product of the volume of the pond and value of construction and OMR costs. Furthermore, this cost was a function of the active storage volume of the pond, the pond depth, and the surface area of the catchment.

The performance (runoff and pollution) constraints were that the trunk sewer (discharge point) was required to meet or exceed a certain level of both quantity and quality control. The authors chose to optimize the blend of catchment controls in the multiple catchment system, compared to providing uniform control. The runoff control constraint was a function of storage and release rate, and the pollution control constraint was dependent on the settling velocity and the mass of suspended solids. This constraint was a function of the three decision variables: pond depth, release rate, and storage volume. Since these two major constraint equations were quite complex in the sense of isolating the decision variables, “isoquants” were generated to find the optimal solution for the three ponds.

Discussion

This paper was significant due to the large interest in designing storm-water management ponds in optimized fashions. Land developers wish to maximize the developable land, leaving little to be used for detention ponds. Therefore there is a high interest in minimizing the cost of the pond, and furthermore minimizing the storage volume (volume is proportional to cost). There is often pollution constraints set on an outlet that will be released back to the rivers, and many designers just choose to design the individual pond to follow that constraint. These authors decided to implement a model that would allow each pond to have a lower runoff and pollution control percentage; however the entire system (at the outfall point) will reach the minimal value. The authors proved that this methodology in fact decreased the cost, as shown in their example.

The assumptions that were made for the model were meteorological conditions, and that the ponds all outfall to eventually the same location. It is important that someone building research on this model understand that a multiple catchment pond design cannot be designed with this methodology if these assumptions are not satisfied. The authors did a great job on this research, and I cannot find any faults. If I were to build on this research, I would look into incorporating land use patterns with the model, creating the most developable land.