Assignment # 66

Article Reference:
Pradeep Kumar Behera, Fabian Papa, Barry J. Adams, Optimization of Regional Storm Water Management Systems, 1999, Journal of Water Resources Planning and Management

Summary:
The paper focuses on the optimization methodology to determine the detention pond storage volume, release rate and pond depth for a single storm management pond, to meet the environmental regulations of runoff quality and quantity. The above mentioned methodology was extended to evaluate the storm management parameter for multiple catchments using dynamic programming.

With the increase in urbanization the importance of dealing with the uncontrolled discharge of runoff which results in adverse impacts like bank erosion, flooding and increasing the chances of pollution. Best management practices (BMP) are considered to attenuate the peak flow, control the runoff volume and control runoff quality, so as to maintain the predevelopment runoff conditions or meet the environmental regulations for runoff quality and quantity. The present study focuses on using detention pond as the storm management control measure. Volume and quality of runoff controlled is largely dependent on the storage volume of the detention pond. Though Storm water management pond (detention pond) is considered as the measure to mitigate the adverse effects, land developers and municipalities consider such ponds to be loss of developable land and added cost of construction and maintenance. The objective of such developers is to minimize the cost associated to the SWM ponds with satisfying the environmental regulations. Typical cost of concerns associated to these SWM ponds are cost of land occupied by the ponds, operation, maintenance and repair (OMR) costs. The present study is to optimize the geometry of the SWM pond to meet the runoff volume control and pollution control to a single catchment, further the problem was formulated for a multiple catchments to optimize design the parameters such that they meet the overall runoff control and pollution control.

The model was formulated considering three parallel catchments having similar metrological characteristics and with SWM ponds which are located upstream of the outlet into the common collection system. Different levels of quality and quantity control was considered at different catchments such that the final or overall control of quality and quantity at the outfall was met according to the environmental regulations. By considering the above mentioned methodology it will be easy to optimize the solution for minimizing the cost of implementing the SWM ponds for all the catchments by providing optimal blend of individual catchments controls than considered uniform control. Both runoff quantity and quality control constraint at the outfall are considered to be greater than the area-weighted average level of pollution/volume control at each catchment. In the study they have not considered the local conveyance cost as normally the SWM ponds are situated in close proximity to the collection system and they did not consider differential cost associated to different rates of release from the pond. In the present work, SWM ponds is considered to be extended detention dry pond type which stores catchment runoff until the entire volume is used. Decision variable in the optimization of the problem are the storage volume, release rate and the pond depth which estimates the extent of runoff quantity and quality.

For carrying out optimizing of SWM pond in a single catchment they have considered 90% runoff control isoquant and 50% pollution control isoquant with constant pond depth to study the strategy of how the release rates and storage volume of the pond vary. As pond depth is also a decision variable in optimizing the solution, a range of depths are analyzed to produce corresponding optimal storage volume and release rates. Therefore by considering the relationship between pond cost and pond depth, an optimal pond depth is estimated which meets the pollution and runoff control constraints.

For optimizing a SWM pond for multiple catchments, DP is considered as the optimization tool which divides the multiple catchment problem into series of individual problems, then combining the solution of each small(stages) problem to the overall (multiple catchment) problem. Overall pollution and runoff control is not violated even if we decompose the model into simpler stages. After the computation of each stage is carried out, track back procedure is followed to find the least cost of the SWM pond considering the design variables.

Discussion:
I found the paper very informative as it gives an idea on how a single catchment SWM optimization and multiple catchment optimizations are done. I could not find any particular problem of concern. But it would be interesting to carry out further research by considering all the assumptions they made in the present study.