Pump Sizing for Dewatering a Levee-Protected Rural Area Using Combined 1D-2D Modeling

Rob James and Karen Finney


The Sonoma Land Trust (SLT) aims to protect and restore natural spaces in Sonoma, California. The Sears Point Restoration project, initiated by SLT, encompasses 2, 327 acres and includes the restoration of tidal and diked wetlands and upland habitats near the intersection of Lakeville Road and State Highway (State Route) 37. Agricultural fields south of Hwy 37 are to be dewatered during and after large events to prevent Hwy 37 from overtopping and to remove ponded water from the fields. Ditches constructed across the fields help drainage, however pumps are required to remove standing water.

SWMM5 was originally developed to solve one dimensional problems, making it difficult to represent rural low lying storage and overland flow. To size the de-watering pumps the Sears Point Valley was first modeled and calibrated using a strictly 1D approach. In this approach the surveyed transects were computed to overtop making the storage volume on the fields difficult to approximate as a single storage unit.

Thus a 2D mesh was then incorporated into the Sears Point SWMM5 model using PCSWMM 2012. The mesh had a 300 ft. resolution and cell elevations were estimated by sampling the DEM layer at a 10ft. resolution. An overland 2D mesh comprising 555 links and 216 nodes better predicted the extent and duration of overland flow. This paper compares the two approaches and summarises findings for a computationally efficient 2D finite mesh for the Sears Point restoration project.

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