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Technical Announcement: USGS Issues Revised Framework for Hydrogeology of Floridan Aquifer

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Regional Groundwater Availability Study Geospatial Data

Press Release: USGS Assesses Current Groundwater-Quality Conditions in the Williston Basin Oil Production Area

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Recession-Curve Displacement Method for Estimating Groundwater Recharge In Humid Regions

Effect of the Requirement of Antecedent Recession

"Before RORA begins making calculations of recharge for each peak, it designates days that fit a requirement of antecedent recession (sometimes referred to as the "time base of surface runoff"). The requirement is equal to basin area raised to 0.02 power, rounded upward to the next larger integer."

"The program allows the user to override the default value. It can be increased by 1, 2, or 3 days. The increase in this variable causes a reduction in the number of peaks detected and a change in the estimate of recharge (see figure). Because RORA is approximating recharge as a complex series of instantaneous events, the reduction in the number of peaks can induce errors."

"The program user might consider increasing the requirement of antecedent recession by a small amount, such as 1 or 2 days. It is evident, however, that as the requirement is increased, errors caused by the reduction in the number of peaks detected may greatly outweigh all other errors." The result of raising the basin area to the 0.02 power… "might be a guide for determining whether RORA can be applied to a particular hydrologic system. If the time of surface runoff is considered to exceed the result of this equation by a large margin – which may be the case in regions of low relief – then the program may not be appropriate for use." (Rutledge, 2000)

The work of Mau and Winter (1996) showed the substantial sensitivity of the RORA program to changes in the requirement of antecedent recession in a small watershed. They found during wet years, results from RORA agreed best to manual application of the recession-curve displacement method by increasing the antecedent recession requirement by 3 days. However, during dry years the default value provided better results.

Change in the number of peaks detected and the change in the estimate of recharge from RORA that results from increasing the requirement of antecedent recession above its default value (from Rutledge, 2000 fig. 14)