Comparison Of Distributed Versus Lumped Hydrologic Simulation Models Using Stationary And Moving Storm Events Applied To Small Synthetic Rectangular Basins And An Actual Watershed Basin

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2008-04-22T02:41:24Z

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Civil & Environmental Engineering

Abstract

The purpose of this investigation is to compare simulations using several artificial rectangular basins and a real drainage basin for distributed and lumped hydrologic models via results obtained with the U.S. Geological Survey Modular Modeling System (MMS). Impervious watershed conditions were assumed for each simulation. A critical objective of this investigation is to assess the performance of a physically-simple lumped model compared to a more physically-complex distributed model for various storm events. Knowledge gained from this investigation may be applied to the practical problem of determining when either a distributed or lumped model may be expected to function well given a set of hydrologic conditions.

 The MMS was configured to simulate both distributed and lumped hydrologic models, and then combined with a kinematic wave technique to simulate overland and channel flow.  Synthetic rectangular basins and a real drainage basin (Cowleech Fork Sabine River near Greenville, Texas) were investigated.  Highlights of the methodology employed include:  (1) synthetic rectangular drainage basins using three overland flow plane slopes and one channel slope developed based on a range of shape factors; (2) a real drainage basin for comparison of results; (3) specification of Manning's n coefficients which represent both natural overland flow and channel flow conditions; and (4) stationary and moving storm events applied to each drainage basin using the same total rainfall volumes.

 Significant results for stationary rainfall events follow.  Peak flow simulations were very similar for distributed rainfall applied as individual cases to the upper, middle, and lower part of each basin.  However, peak flow magnitudes were much greater for the distributed cases when compared to the lumped cases.  As for timing differences, downstream rains yielded earlier peak outflows when compared to peaks resulting from upstream rains.  Peak flow comparisons for the distributed versus lumped cases generally ranged from 2.5 to 3.0 for the synthetic rectangular basins and 2.1 to 2.3 for the Greenville basin.  These values dropped to 1.3 when the Greenville basin reached equilibrium conditions.  Overall shapes of the dimensionless hydrographs differ when comparing distributed versus lumped cases.  For the Greenville basin, the overall shapes of the dimensionless hydrographs also differ for equilibrium versus non-equilibrium conditions.

 Significant results for moving storm events follow.  For the synthetic rectangular basins, peak flows computed for both distributed and lumped rainfall scenarios were very similar.  For storm systems moving upstream to downstream, peak flow magnitudes were slightly greater for the distributed cases when compared to the lumped cases.  However, for storm systems moving in the opposite direction (downstream to upstream), peak flow magnitudes were slightly less for the distributed cases compared to the lumped case.  For Greenville, this same general pattern occurred except the degree of magnitude between the distributed and lumped cases were either higher or lower for the upstream to downstream or downstream to upstream storm systems, respectively.  Peak flows occurred later in time for storm systems moving from upstream to downstream when compared to storm systems moving in the opposite direction.  Overall shapes of the dimensionless hydrographs were also different when comparing distributed versus lumped cases.

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