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Title:   Author  item
                                            CHAPMAN, TOM - UNIV. OF NEW SOUTH WALESitem
                                            Malone, Robert

                                                         - *Rob*
  Submitted to: International Congress on Modeling and Simulation Proceedings
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 12/6/1999
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary: Recently developed computer models determine groundwater recharge using complex equations that require difficult to determine input parameters.  Simple models are available and there is little evidence that the more complex models are superior.  The purpose of this study is to compare the performance of 11 of these simple  groundwater recharge models using 11 years of Coshocton weighing lysimeter data.  The results indicate that one model named the generalized SFB model performed superior to the other models and performed satisfactorily compared to the natural spatial variability of recharge.  However, it did not succeed in matching large peaks in the recharge hydrograph.  This research will assist model developers by providing evidence that the relatively simple SFB model may simulate groundwater recharge adequately  under certain circumstances.  This in turn may help simplify hydrologic models because the more simple approaches require less difficulty to determine input parameters.
                                Technical Abstract: Most conceptual models of catchment hydrology include algorithms for estimation of recharge to groundwater, which is then routed to stream base flow and/or deep regional groundwater.  In recent complex models, these algorithms take the form of solution of the Richards equation for vertical flow in the soil column above the water table, while other models  treat the transformation of excess soil water into base flow as a single process.  However, the majority of models have an algorithm for simulation of the process of percolation to groundwater from an overlying soil water store, which may be conceived as a single store or a series combination of stores.  The purpose of this study is to compare the performance of 11 of these simple models selected from the literature, using an 11 year daily record from a weighing lysimeter 2.4 m deep at Coshocton, Ohio, supporting a pasture grass.  The percolation data are measured directly, while the  volume of water in the soil column is measured by weighing the monolith every 5 minutes.  The quality of the data has been verified by comparing monthly measurements of soil water in the column with estimates from the daily water balance of the lysimeter.  The data also provide an opportunity to assess the spatial variability of groundwater recharge, as the weighing lysimeter is located in a nest with three non-weighing lysimeters, in each of which the percolation is measured on a daily basis.  The results of the study show that the recharge algorithm in the generalized SFB model is unequivocally superior to any of the other models tested, and that it achieves a satisfactory standard relative to the natural spatial variability of recharge.  However, it does not succeed in matching large peaks in the recharge hydrographs.


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