Problems Associated with Estimating Ground Water Discharge and Recharge from Stream‐Discharge Records

Abstract

Ground water discharge and recharge frequently have been estimated with hydrograph‐separation techniques, but the critical assumptions of the techniques have not been investigated. The critical assumptions are that the hydraulic characteristics of the contributing aquifer (recession index) can be estimated from stream‐discharge records; that periods of exclusively ground water discharge can be reliably identified; and that stream‐discharge peaks approximate the magnitude and timing of recharge events. The first assumption was tested by estimating the recession index from stream‐discharge hydrographs, ground water hydrographs, and hydraulic diffusivity estimates from aquifer tests in basins throughout the eastern United States and Montana. The recession index frequently could not be estimated reliably from stream‐discharge records alone because many of the estimates of the recession index were greater than 1000 days. The ratio of stream discharge during base flow periods was two to 36 times greater than the maximum expected range of ground water discharge at 12 of the 13 field sites. The identification of the ground water component of stream‐discharge records was ambiguous because drainage from bank‐storage, wetlands, surface water bodies, soils, and snowpacks frequently exceeded ground water discharge and also decreased exponentially during recession periods. The timing and magnitude of recharge events could not be ascertained from stream‐discharge records at any of the sites investigated because recharge events were not directly correlated with stream peaks. When used alone, the recession‐curve‐displacement method and other hydrograph‐separation techniques are poor tools for estimating ground water discharge or recharge because the major assumptions of the methods are commonly and grossly violated. Multiple, alternative methods of estimating ground water discharge and recharge should be used because of the uncertainty associated with any one technique.

Measuring methods for groundwater – surface water interactions: a review

“…Hydrograph separation is based on the assumptions that stream discharge can be directly correlated to groundwater recharge. Several factors are neglected in this approach, such as evapotranspiration and bank storage, leading to considerable uncertainties (Halford and Mayer, 2000). Tracer-based hydrograph separation further assumes that preevent water and event water are clearly different in isotopic or chemical composition and that the composition is constant in space and time; both being conditions that are often not met (Genereux and Hopper, 1998).…”

“…Furthermore, in cases where drainage from bank storage, lakes or wetlands, soils, or snowpacks contributes to stream discharge, the assumption that baseflow discharge represents groundwater discharge may not hold (Halford and Mayer, 2000). The limited number of stream gauging stations constrains the resolution of this method.…”

“…The validity of the underlying assumptions of the separation techniques is critical for the performance of hydrograph separation as a tool to determine groundwater-surface water interactions (Halford and Mayer, 2000). Furthermore, in cases where drainage from bank storage, lakes or wetlands, soils, or snowpacks contributes to stream discharge, the assumption that baseflow discharge represents groundwater discharge may not hold (Halford and Mayer, 2000).…”

Evaluation of outputs from automated baseflow separation methods against simulated baseflow from a physically based, surface water-groundwater flow model

“…The reviews of Hall (1968), Smakhtin (2001) and Schwartz (2007) provide a history of methods for baseflow separation, and discuss the problems related to the definition of baseflow, as well as the underlying assumptions of the different separation methods. In the context of identifying groundwater recharge from streamflow records, the underlying assumptions that underpin many methods were examined by Halford and Mayer (2000). They concluded that identifying the groundwater contribution from streamflow records can be ambiguous due to drainage exponentially decreasing from other sources, such as bank storage, wetlands and the unsaturated zone.…”

Are streamflow recession characteristics really characteristic?

“…More often streamflow recession analysis methods are adjusted for a specific case of application or a distinct set of catchments. However, when storage-outflow behavior is solely analyzed with streamflow data, multiple-methods approaches have been suggested to overcome potential biases of a single recession analysis method (Halford and Mayer, 2000).…”