Management of flood control sumps and pollutant transport

Levee sump systems are used by many riverine communities for temporary stor age of urban wet weather flows. The hydrologic performance and transport of stormwater pollutants in sump systems, however, have not been systematical ly studied. The objective of this paper is to present a case study to demon strate development and application of a procedure for assessing the hydraul ic performance of flood control sumps in an urban watershed. Two sumps of h ighly variable physical and hydraulic characteristics were selected for ana lysis. A hydrologic modeling package was used to estimate the flow hydrogra ph for each outfall as part of the flow balance for the sump. To validate t hese results, a water balance was used to estimate the total runoff using s ump operational data. The hydrologic model calculations provide a satisfact ory estimate of the total runoff and its time-distribution to the sump. The model was then used to estimate pollutant loads to the sump and to the riv er. Although flow of stormwater through a sump system is regulated solely b y flood-control requirements, these sumps may function as sedimentation bas ins that provide purification of stormwater. A sample calculation of remova ls of several conventional pollutants in the target sumps using a mass bala nce approach is presented.