The need for information on the interrelationship of ground water and surface water is causing a growing interest in methods used for direct measurment of seepage to and from surface-water bodies. Instruments developed for measurement of seepage date from about the mid 1940's largely in response to the need for knowing the quantity of seepage loss from canals. This bibliography includes abstracts, summaries, or conclusions from papers describing seepage measurement devices. Illustrations of the instruments are included.

Because of growing interest in the role of lakes and wetlands in the hydrology of the prairie environment, a group of wetlands in the Cottonwood Lake area, Stutsman County, are being instrumented for long-term hydrologic studies. The study site is on a regional topographic high near the eastern edge of the Missouri Coteau and is underlain by more than 400 feet of glacial drift, largely clayey, silty till. Long-term climatic data indicate the study area is in a water deficient area mean annual evaporation exceeds mean annual precipitation by about 18 inches. Different methods are being used for comparison of measurements and estimates of each hydrologic component interacting with the lakes and wetlands. For example, for 3 months during 1979, estimates of precipitation for the study site using data collected at Nationa] Weather Service stations differed from that measured by a recording gage at the study site by several tenths of an inch for 14-day totals and differed by more than 0.5 inch for individual storms. Numerical-simulation analysis of regional groundwater flow systems show the study site is situated in a regional recharge area, but local groundwater flow systems can discharge to lakes and wetlands within the recharge area. Instrumentation at the study site shows a complex interrelationship of wetlands and ground water. Based on data for 1979 only, some wetlands appear to recharge ground water, some are flow-through types and some are discharge points for ground water. These interrelationships vary throughout the year.

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