Update on the Use of the RORA Program for Recharge Estimation

Abstract

An update on the use of the RORA program is provided to supplement information given in the initial description of the program in Ground Water in 1994. The method estimates ground water recharge on the basis of streamflow records. Important considerations in the use of the automated approach are described that should improve the reliability of recharge estimates and avoid misapplication of the technique. Topics include the recession index, errors caused by direct surface runoff, the time scale for reporting results, comparisons with results of manual calculations, and errors caused by gradual recharge and discharge. The use of ground water levels for independent assessment of results from RORA is also described. RORA results are compared and contrasted with results from other base flow separation techniques.

Assessment of aquifer properties, evapotranspiration, and the effects of ditching in the Stoney Brook watershed, Fond du Lac Reservation, Minnesota, 2006-9

“…The amount and percentage of total precipitation areally recharging shallow groundwater generally increased from 2006 to 2009, resulting in groundwater-level rises. Below-normal precipitation in 2006, 2007(National Climatic Data Center, 2013 caused smaller-than-normal groundwater recharge and low groundwater levels that gradually rose. Recharge estimates from groundwater-level analysis for wells close to the ditches are large because water levels in those wells rose in response to water inflow from the ditches as well as areal groundwater recharge following precipitation.…”

“…The recession-curve displacement method estimates recharge for each peak in a streamflow record (Rutledge, 2007). The RORA program uses a median recession index of a streamflow record to estimate groundwater recharge after each precipitation event.…”

“…The RORA program uses a recession-curve displacement method to estimate groundwater recharge on a watershed scale using streamflow (Rorabaugh, 1964;Rutledge, 2007). The recession-curve displacement method estimates recharge for each peak in a streamflow record (Rutledge, 2007).…”

“…The RORA program uses a median recession index of a streamflow record to estimate groundwater recharge after each precipitation event. The recession index for a recession period is the time required for groundwater discharge to recede by one log cycle after the recession becomes linear on a semilog hydrograph (Rutledge, 1998;Rutledge, 2007). The RECESS computer program (Rutledge, 1998), a program that determines a median recession index from water-level hydrographs, was used to determine a median recession index from daily streamflow at the Stoney Brook streamgage.…”

“…The RORA program was used to (1) identify the segments of the streamflow record that represent groundwater discharge, (2) identify recharge events, and (3) extrapolate procedures for determining recharge (Rutledge, 2007). The drainage area of the Stoney Brook watershed above the streamgage (101 mi 2 ) was used to specify the part of the stream-discharge record that represents groundwater discharge using the following equation:…”