Introduction
RECESS is a group of six computer programs (RECESS, RORA, PART, TRANS, CURV and STREAM) for describing the Recession of GroundWater Discharge and for Estimating Mean GroundWater Recharge and Discharge from Streamflow Records. These programs develop a mathematical expression for recession of groundwater discharge and estimate mean groundwater recharge and discharge. RECESS is intended for the analysis of the daily streamflow record of a basin where one can reasonably assume that all, or nearly all, groundwater discharges to the stream except for that which is lost to riparian evapotranspiration and regulation and diversion of flow can be considered to be negligible. The RECESS programs utilize extended memory.
RECESS Components
The program RECESS determines the master recession curve (MRC) of streamflow recession during times when all flow can be considered to be groundwater discharge and the profile of the groundwaterhead distribution is nearly stable. The program uses a repetitive interactive procedure for selecting several periods of continuous recession, determines a bestfit equation for the rate of recession as a function of the logarithm of flow and uses the coefficients of this equation to derive the MRC which is an equation of time as a function of the logarithm of flow. RECESS thus allows for the possibility of nonlinearity in the relation between time and the logarithm of flow.
RORA
The program RORA uses the recessioncurvedisplacement method to estimate the recharge for each peak in the streamflow record. This method also called the Rorabaugh Method, is based on the measurement of the change in the total potential groundwater discharge as estimated at critical time after the peak by extrapolation from the prepeak and the postpeak recession periods. RORA is applied to a long period of record and gives an estimate of the mean rate of groundwater recharge.
PART
The program PART uses streamflow partitioning to estimate a daily record of base flow under the streamflow record. The program scans the record for days that fit a requirement of antecedent recession, designates base flow to be equal to streamflow on these days, and linearly interpolates the daily record of base flow for days that do not fit the requirement of antecedent recession. PART is applied to a long period of record to obtain an estimate of the mean rate of groundwater discharge.
TRANS
The program TRANS translates data into a format that can be read by the above three programs. TRANS may be used to convert 2 and 3card format daily mean streamflow data from a USGS database.
STREAM
The program STREAM allows the user to screen the dailyvalues data file for periods of continuous record.
CURV
The program CURV reads an output file from program RECESS and creates a simple file that can be used as input to separate graphical software from which an MRC can be drawn.
RECESS Methods
The methods described herein are intended for the analysis of the groundwaterflow system of a basin for which a streamflowgauging station at the downstream end can be considered the only point of outflow. For most applications, it should be reasonable to assume that all or nearly all ground water in the basin discharges to the stream except for that which is lost by evapotranspiration. The area of contribution in the groundwater system is equal to the surfacedrainage area for the purpose of expressing flow in units of specific discharge (for example, inches per year). Regulation and diversion of flow should be negligible.
It is preferable, but not required, that the record of daily mean streamflow is at least several years in duration. Results are most useful if the programs are executed to give longterm (at least yearly) results. Interbasin comparisons should be made only when the programs are executed for a uniform time period because of climatic variations. The programs work on the basis of the calendar year. In the application of the methods for estimating recharge or discharge, the record should be complete for each year in the period of analysis (365 or 366 daily values per calendar year).
The procedure for defining the recession of groundwater discharge selects several individual periods of continuous streamflow recession (periods during which each pair of subsequent daily values must meet the condition that the first value exceeds or is equal to the second). Periods of reduced precipitation must be long enough that the profile of the groundwater head distribution is nearly stable and groundwater discharge will plot with characteristic linearity or nearlinearity on the graph of the logarithm of flow as a function of time. This condition may not be met for groundwater flow systems of very low diffusivity (transmissivity divided by storage coefficient).
The procedure for defining streamflow recession allows for the possibility of nonlinearity in the relation between the logarithm of groundwater discharge and time when the profile of the groundwater head distribution is nearly stable. Nonlinearity can result from variation in saturated thickness, geologic heterogeneities, and attrition of ground water to leakage or evapotranspiration.
The methods for estimation of recharge or discharge are intended for the analysis of flow systems that are driven by areallydiffuse recharge events that can be considered to be roughly concurrent with peaks in streamflow. The stream is the sink (discharge boundary) of the groundwater flow system. Results of these methods may not be reliable for flow systems dominated by leakage to or from regional flow systems, snowmelt runoff, recharge from losing streams, or groundwater withdrawals. The methods for estimating recharge or discharge should be used only if the drainage area is larger than one square mile so that the time base of surface runoff will exceed the time increment of the data (one day). The upper limit of drainage area may depend on the degree of nonuniformity of weather systems. It has been suggested that the unit hydrograph concept should not be applied for basins that are larger than 2,000 square miles and that the upper limit may be much smaller where convective rainfall predominates. The upper limit for the unit hydrograph concept may also apply to the methods described here for estimating recharge and discharge.
In addition to the above, the user should assess the validity of the mathematics described in the study area. For example, the procedure for defining streamflow recession uses the assumption that the recession index is linearly related to the logarithm of flow, and the methods for estimating groundwater recharge and discharge use an empirical equation for determining the time base of surface runoff to estimate the number of days after a peak in streamflow when most flow can be considered groundwater discharge. Output of the programs allows for some degree of adjustment for variation between the real problem and the default mathematics of the programs.
Source, executable codes, and technical support are included with the package.
