Dynamic optimization of detention storage in urbanizing areas
Flores, Alejandro C.
Bedient, Philip B.
Master of Arts
Rapid urban development in many areas has increased stormwater runoff and outdated traditional open channel drainage systems. Stormwater management alternatives such as channel enlargement are often difficult to implement in developing urban areas due to downstream land use restrictions. Detention storage in upper watershed areas is an effective stormwater control, but random or unplanned placement can significantly reduce its effectiveness and in some cases aggravate potential flood hazards. Earlier approaches to size and locate detention storage in a watershed have generally relied on trial-and-error methods. The purpose of this research is to develop a method to optimize the size and location of detention storage in a watershed. Hydrologic models were used in the method including two existing models, HEC-1 a flood hydrograph package and STOREME a single reservoir routing. DBOPTE, a multiple detention basin and channel network routing especially developed for this research, was used to optimize the size and location of detention storage. The method was applied to a one and a ten square mile hypothetical watershed with typical rainfall, physiography, soils, drainage patterns and land use data for the Houston area. The general methodology developed can he applied to any watershed where local data are available for runoff hydrograph prediction. Results for the one square mile watershed showed that the 25 year detention storage design is very effective in the peak runoff reduction for any flood frequency. For the ten square mile watershed, several physiography shapes were studied and results showed a higher peak runoff response for concentrated shapes than for elongated under developed conditions. Detention storage is more effective when located in the upper portion (67-8%) of the watershed rather than the downstream portion. For the 1 year flood frequency, detention storage volumes were .5 Acre-ft per acre of development and land requirements for a 5 ft basin depth were less than 1% of the watershed area. Land use distribution affects the detention storage volumes; for example, developing areas from downstream to upstream can require 28% more detention storage volumes than developing in both directions with undeveloped land in the middle.