SEEPAGE METERS TO MEASURE GROUNDWATER FLOW: AN HISTORICAL PERSPECTIVE

Until about 40 years ago, groundwater discharge to surface waters was an unappreciated and un-quantified component of the hydrologic cycle. Limnologists generally thought lakes were sealed off from the groundwater system. Israelsen and Reeve (1944) performed the first seepage-meter measurements in their efforts to identify areas of water loss from irrigation canals. Pioneering work by Meyboom (1966, 1967) showed that groundwater was connected to lakes. Lee (1972) devised an inexpensive seepage meter and measured groundwater discharge in Lake Sallie, MN. McBride and Pfannkuch (1975) used Lee's measurements to "confirm model results by demonstrating that both the near-shore seepage band and the exponential decrease in seepage velocity actually exist." Subsequent investigators found that spatial variations in hydraulic conductivity cause deviations from the exponential distribution postulated by McBride and Pfannkuch.

Working in Great South Bay, NY, Bokuniewicz (1980) used seepage meters to perform the first detailed investigation of submarine groundwater discharge. He concluded that groundwater "may contribute a substantial amount of water to the coastal zone." Johannes (1980) showed that even though the volume of groundwater discharge in coastal waters near Perth, Australia, was small relative to surface water runoff, the ratio of nitrate in groundwater to nitrate in river water was three to one. Johannes cited evidence for dependence of marine flora and fauna on groundwater discharge. Similar dependence was later found in lakes and streams.

While there is nothing quite so convincing as direct measurement, there are limitations and problems with seepage-meter measurements. These include improper procedure, failure of the seal and difficulties related to current, water depth and bed material.

Seepage meters have been used to obtain continuous records of temporal variation in flow rate and to measure groundwater/surface-water exchange in wetlands, rivers and coastal environments. There have been at least 6 automated meters and 2 patents. Seepage meters are being used for teaching and in groundwater remediation.