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Title:   Author  item
                                            CHAPMAN, T - U. OF NEW SOUTH WALESitem
                                            Malone, Robert

                                                         - *Rob*
  Submitted to: Computers and Mathematics in Simulation
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/15/2000
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary: Recently developed computer models determine groundwater recharge using complex equations that require input parameters that are difficult to determine.  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 several simple groundwater recharge models using g11 years of Coshocton weighing lysimeter data. The results indicate that 5 models perform well in simulating recharge, but did not perform as well in simulating variations of total soil water in the column, particularly during periods of high evapotranspiration.  In addition, all the models tend to underestimate the sharp peaks in recharge that may occur in extreme events.  This research will assist model developers and users by providing evidence that the relatively simple models may adequately simulate groundwater recharge under many circumstances.  This in turn may help  simplify hydrologic models because the simple models use data that are easier to collect than are the data for the complex models.
                                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.  The majority of models attempt to simulate 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.  However, these models have seldom been tested against field observations, and therefore the purpose of this study is to compare the performance of 13 single store and two store 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 neutron probe  measurements of soil water in the column with lysimeter measurements of rainfall, runoff, evapotranspiration and percolation.  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 5 models perform well in simulating recharge to a level consistent with spatial variability over a scale of a few metres, but did not perform as well in simulating variations of total soil water in the column, particularly during periods of high evapotranspiration.  All the models, however, tend to underestimate the sharp peaks in recharge which may occur in extreme events.


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