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levels, while the well grids provided a three- dimensional view of the groundwater levels at <br />each site. Three of the grid wells at each site were equipped with Stevens Type F recorders <br />for continuously monitoring groundwater levels since the start of the study. Two additional <br />wells were equipped with recorders at the Crane Meadows site in 1990 (CM35BBB in May, <br />and CM26CDA in mid September). The National Audubon Society also maintained four <br />additional recorders (Rowe West LO and HI, and Rowe East LO and HI) at the Rowe <br />Sanctuary, but their continuous data were not included in our analysis. The remainder of the <br />cross - valley transect wells and the grid wells were measured at least once a month, with <br />supplemental weekly measurements taken by the National Audubon Society. The cross -valley <br />transect wells were installed by the U.S. Bureau of Reclamation and were cased with 11 /a inch <br />pipe (iron or PVC). Most wells in the grids were new, although some previously existing <br />wells were also used. New wells were constructed of 2 inch, schedule 40 PVC pipe with the <br />lower 3 feet perforated. In 1990, the U.S. Bureau of Reclamation tied the coordinates of the <br />grid wells into the 10,000 -foot grid of the Nebraska coordinate system, south zone. Surface <br />profiles were surveyed for the Rowe Sanctuary and Crane Meadows cross -valley transects. <br />Elm Creek's surface profile was surveyed within the study area, and distances between wells <br />outside the study area were estimated from 1:24,000 topographic maps. All transect and grid <br />wells were surveyed to elevations above mean sea level. <br />River stage was monitored at each site with a continuous Stevens Type F recorder. The <br />Elm Creek site had an additional recorder installed at the west end of the groundwater drain in <br />June of 1990, and an additional river -stage recorder was installed on the northwest comer of <br />Crane Meadows in June of 1990. A stilling well was used at each gage to reduce fluctuations <br />caused by wave action. Additional staff gages were installed to monitor surface water <br />elevations surrounding each site. Staff gage readings were taken when the well grids were <br />sampled. All gaging stations and staff gages were surveyed to elevations above mean sea <br />level. <br />10 <br />