Two-Dimensional Applications

Application 2: Rainfall-Runoff Model

The DHM can be used to develop a runoff hydrograph given the time distribution of effective rainfall. To demonstrate the DHM runoff hydrograph generation (Hromadka and Nestlinger, 1985), the DHM is used to develop a synthetic S-graph for a watershed where overland flow is the dominating flow effect.

To develop the S-graph, a uniform effective rainfall is assumed to uniformly occur over the watershed. For each timestep (5-seconds), an incremental volume of water is added directly to each grid-element based on the assumed constant rainfall intensity, resulting in an equivalent increase in the nodal point depth of water. Runoff flows to the point of concentration according to two-dimensional diffusion hydrodynamics model.

The 10 square mile Cucamonga Creek watershed (California) is shown, discretized by 1000-foot grid elements, in figure 17. A design storm (figure 18) was applied to the watershed and resulting runoff hydrographs are depicted in figure 19 for DHM model and synthetic unit hydrograph method. From figure 19, the diffusion model generates runoff quantities which are in good agreement with the values computed using synthetic unit hydrograph method derived from stream gage data.

Next, the DHM is applied to three hypothetical dam-failures in Orange County, California (see figure 20). Applications of the DHM illustrates its use in a municipal setting where flood flow patterns are affected by railroad, bridge undercrossings, and other man-made obstacles to flow.

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