Simulated velocity magnitude and direction.

The Cougar Wetlands are part of a larger broad-based effort to restore and safeguard the integrity of the Cosumnes River, the last undammed river flowing from the Sierra Nevada to the Central Valley.

cbec was contracted by Ducks Unlimited and the US Bureau of Land Management to analyze proposed habitat enhancements. Proposed restoration actions at Cougar Wetlands include the breaching of existing levees and the creation of tidal channels in the unit. A two dimensional hydrodynamic model was developed for the area, including portions of the Cosumnes River, Bear Slough, Grizzly Slough, and floodplain areas adjacent to these channels in order to assess potential scour and deposition resulting from these proposed topographic modifications.

Once constructed, the model was used to simulate typical tidal conditions and flood events of varying return intervals. Simulation results were used to calculate the temporal and spatial distribution of Shields Stress (a metric indicative of the amount of sediment movement likely), with an emphasis on the river channel and the areas surrounding the proposed breaches. The analysis showed that the proposed breaches at the Cougar Wetlands will function differently than the existing breaches on the western side of the Cosumnes River, and that sediment splays are less likely to form due to the proposed breaches because of much lower hydraulic gradients as well as bi-directional flow in the proposed Cougar breaches.