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2007 Ground Water Summit |
Monday, April 30, 2007 : 9:50 a.m.
Importance of a Properly Conceptualized Shallow Flow System on Ground Water Availability Estimates for Regional Flow Systems Near Coastlines With Dipping Stratigraphy
From a groundwater management viewpoint, groundwater recharge is particularly important because it is sometimes used by policy makers to estimate sustainable yield. For large regional models, accurate representation of recharge can be difficult to achieve because of problems associated with using large grid cells to model relatively short groundwater flow paths that connect shallow groundwater systems to surface water bodies. With aquifers consisting of dipping strata near coastlines, the problems with representing a shallow groundwater flow system are aggravated. In this situation, the model layers are often layered at the dip angle of the geological strata – with the end result being that the model does not explicitly contain a shallow groundwater system. Historically, MODFLOW-based regional groundwater flow models for coastal areas in Texas have been developed without an explicitly define shallow groundwater system. Recently, we have developed a MODFLOW-based regional groundwater model for the Texas Gulf Coast that explicitly represents the shallow aquifer system as a continuous and single model layer. We have successfully calibrated the new model prototype and compared it to the results from previous models. To develop the new model we have implement a method to “pinch out” the up-dipping strata below and into the shallow aquifer system. The new model design provides recharge estimates that are over 10 times greater than previous models and also provides significantly better matches to the estimated exchange between groundwater and surface water as determined from baseflow analyses of field data.