Discrete‐Storm Water‐Table Fluctuation Method to Estimate Episodic Recharge

Abstract

We have developed a method to identify and quantify recharge episodes, along with their associated infiltration-related inputs, by a consistent, systematic procedure. Our algorithm partitions a time series of water levels into discrete recharge episodes and intervals of no episodic recharge. It correlates each recharge episode with a specific interval of rainfall, so storm characteristics such as intensity and duration can be associated with the amount of recharge that results. To be useful in humid climates, the algorithm evaluates the separability of events, so that those whose recharge cannot be associated with a single storm can be appropriately lumped together. Elements of this method that are subject to subjectivity in the application of hydrologic judgment are values of lag time, fluctuation tolerance, and master recession parameters. Because these are determined once for a given site, they do not contribute subjective influences affecting episode-to-episode comparisons. By centralizing the elements requiring scientific judgment, our method facilitates such comparisons by keeping the most subjective elements openly apparent, making it easy to maintain consistency. If applied to a period of data long enough to include recharge episodes with broadly diverse characteristics, the method has value for predicting how climatic alterations in the distribution of storm intensities and seasonal duration may affect recharge.

Groundwater recharge amidst focused stormwater infiltration

“…Storm event pulses of recharge were expected to be more diffuse in time and depth for wells with thicker unsaturated zones. Storm‐generated water table responses of these wells were generally more subdued and more autocorrelated over longer lengths of time, with lesser representation of high‐frequency components. Four wells in our study area (Wells 3–6) were analysed with the EMR method for water table fluctuations (Nimmo et al, ). We found that these wells had significantly different RPR (Figure b).…”

“…A continuous approach for analysing water table fluctuations was presented by Crosbie et al (), but we will use an event‐based approach, called the EMR method (Nimmo, Horowitz, & Mitchell, ). The EMR method combines the water table fluctuation approach (Equation ) with a reproducible process to define and separately estimate recharge for individual storm events (https://wwwrcamnl.wr.usgs.gov/uzf/EMR_Method/EMR.method.html).…”

Precipitation Intensity Effects on Groundwater Recharge in the Southwestern United States

“…[76] studied episodic recharge in the Murray Darling basin, later identifying the nature of episodic recharge across the region [26]. Limited studies [26,28] have assessed in situ groundwater data to characterize changes in recharge. This study evaluated groundwater elevations within the arid southwestern United States to understand potential changes in recharge which may have led to decreases in groundwater storage which Castle et al [31] and Konikow [67] identified within the Lower Colorado River basin and Arizona, respectively.…”

“…Nimmo et al [28] extend the MRC approach to account for episodic recharge events. In that study, selected episodic recharge events from wells were used to estimate recharge.…”

“…Because of the episodic nature of recharge in arid environments, small changes in precipitation intensity have been suggested to influence groundwater recharge [26,27]. Recent studies have sought to quantify episodic recharge [28] or identify regional groundwater recharge [10,11,23]. Such evaluations, however, did not identify influences in observed groundwater recharge as a function of precipitation, the primary goal of this study.…”