Application of Unit Hydrograph Technique to the Discharge Record at Big Spring, Carter County, Missouri

In the Ozark region, karst aquifers are an important source of fresh water. To effectively manage the water supply, a predictive model of groundwater flow and solute transport is necessary. The linear systems approach holds potential for use as a predictive model. One drawback to this approach is the lack of an easy-to-use method to derive a transfer function that can be used to model the response to individual storm events, multiple-day events, and year-long series. In this study, we determine the transfer function relating excess precipitation to discharge from Big Spring, Carter County, Missouri by using unit-hydrograph technique. We calculated the discharge from Big Spring over a range of hydrologic conditions and evaluated the range of applicability of the unit hydrograph technique. We found that the unit hydrograph technique provided a simple and quick method of obtaining the transfer function of a large spring basin to recharge events without the inherent problems of deconvolution and without concerns about errors in the input series. The unit hydrograph technique was successfully used to calculate the discharge from Big Spring generated by large isolated storms, multiple-day events, and a year-long series. However, for a hydrologically open basin, such as Big Spring, the use of a scaling factor was necessary to obtain a closed water budget. Therefore, true prediction of the discharge was not possible. A better means of determining the temporal and spatial distribution of recharge to the groundwater basin is needed before a closed water balance can be obtained and the scaling factor eliminated.