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Press Release: Study Explores Groundwater and Geothermal Energy in Drought-Stricken Eastern Oregon and Neighboring States

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

Press Release: High Plains Aquifer Groundwater Levels Continue to Decline

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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Water-Table Fluctuation (WTF) Method

MRC Approach of Delin and others (2007)

The Master Recession Curve (MRC) approach of Delin and others (2007) used in the WTF method is an automated procedure for calculating DH(t_j) from daily water-level data. The antecedent recession curve is determined from a nonlinear regression equation of the log of the difference in altitude between the water level and the “pour point,” the water-level at which no discharge occurs. Development of a MRC begins by generating a list of recessions (periods during which ground-water levels continually decrease) for a given well using a program called FALL ( A. Rutledge, U.S. Geological Survey, written commun., 2003). A minimum recession duration needs to be chosen (a value of 10 days is typical). Once a list of recessions is tabulated for the entire period of record, statistical analysis software S-Plus® is used to estimate the MRC recession parameters d and RR from the following nonlinear relation:

ln(H_t - d) = ln(H₀ - d) + RR * t,      (1)

Master recession curve approach (Delin and others, 2007) to the water-table fluctuation method for estimating recharge.

where H_t is water level at the end of the recession (cm), d is the water level or pour point at which no discharge occurs (cm), H₀ is the water level at start of recession (cm), RR is the recession rate (which is negative); and t is the time of the recession (days). The negative reciprocal of RR is the time in days for a decrease of one natural log cycle in the water table above d. With a MRC thus derived, the MRC is applied to the daily water levels. The MRC is projected from the first water-level value in the record. If the subsequent ground-water level rose above this projected recession, recharge was measured as the distance from the projected MRC to the shallower water level. From this point, a new MRC is drawn, and the process repeated.

Even though multiple steps are required, the MRC approach is straightforward and easy to apply. The approach avoids subjectivity after the estimation of the MRC parameters, but there remains the possibility that water-level rises that were not due to recharge may be improperly included in the calculations.