Engineer Metropolitan Water District of Southern California
The Metropolitan Water District of Southern California (Metropolitan) is a regional water wholesaler that imports, treats, and delivers water to its 26-member public agencies, serving approximately 19 million people living in Southern California. Metropolitan’s conveyance and distribution system includes 830 miles of almost exclusively large-diameter pipelines, and these pipelines are routinely dewatered either for scheduled maintenance or emergency repairs. As part of environmental permitting requirements, it is usually required to identify the discharge flow paths and the potential impact on any receiving water body. In order to protect environmentally sensitive habitat areas or to prevent invasive species from entering the downstream water bodies, Metropolitan has begun to utilize a two-dimensional (2D) surface water modeling tool to predict the dewatering flow boundaries for the planned shutdowns of its pipelines under various flow, soil, and weather conditions. In addition to the typical hydraulic modeling of overland flows and hydraulic structures, the tool accurately models the losses through infiltration processes and surface depressions. Two case studies will be discussed where the model-predicted flow boundaries were verified in the field. In the study, the 2D model was extended to predict sediment mobility and erosion potential for the dewatering flow paths. As part of the study, a simple quadratic equation has been derived to estimate the distances of dewatering flows, and the calculated results reasonably match the 2D model results. The findings of the study provide a reliable framework for evaluating the potential impact due to the release of a large amount of water in a receiving water body.
