Modeling floodplain flow on Lower Deer Creek*

Michael L. MacWilliams, Robert L. Street, and Peter K. Kitanidis

There is increasing recognition that channelization and other river control efforts on Lower Deer Creek have been detrimental to aquatic and riparian habitat and have been expensive to maintain. Currently, flood management alternatives are being considered by California DWR that will change the style of flood management to set levees back, permit overbank flooding, and incorporate natural distributary channels back into the floodplain system. These actions would help to restore the reliability of the flood control project, help natural stream processes to occur, and would also be the most effective ecological strategy to restoring the terrestrial and aquatic habitats of Lower Deer Creek.

The implementation of these flood management alternatives requires a detailed analysis of the hydraulic characteristics of the floodplain during flood events. To accomplish this objective, a three-dimensional hydrodynamic code, UN-TRIM, was applied on an unstructured grid developed using available topographic and hydrologic data for Lower Deer Creek, and used to simulate flow on the Lower Deer Creek floodplain.

To validate this model, the January 1997 flood on Deer Creek was simulated. During the 1997 flood, Deer Creek breeched its levee and flowed across the floodplain for several miles. The results of the UN-TRIM simulation for the 1997 flood were compared with available observation data and a conceptual model of the flood event developed by DWR.

We will present a description of the UN-TRIM code and discuss the approach used to apply it to Lower Deer Creek. Preliminary results of the simulation of the 1997 flood and model validation will also be presented. These results demonstrate the important features influencing flow on the Lower Deer Creek floodplain and can be used to help guide the planning and implementation of future flood management strategies.

The collaboration of Stacy Cepello of the California DWR on this project is gratefully acknowledged.

* MacWilliams, M. L., R. L. Street, and P. K. Kitanidis, Modeling Floodplain Flow on Lower Deer Creek, CALFED Science Conference 2003: Advances in Science and Restoration in the Bay, Delta and Watershed, Abstract Volume, p.109, January 2003.