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22 I I I I I I I I I I I I I I I I I I I flooded bottomlands and grow for several weeks before re-entering the river. There is some indication that flooded areas need to be available to the larval fish from four to six weeks to provide a meaningful contribution to their life history. Current conditions may not allow this to occur. The 1993 water year was the largest since 1986, yet the period of high water was quite short and peak flow was not particularly high. Only one day had flows exceeding 20,000 cfs. Prior to 1963, a water year such as this may have produced two to four weeks of flows exceeding 20,000 cfs. Flows which would have flooded the wetland area of the project site occurred for approximately three weeks in 1993, but prior to dam construction flows in this range may have lasted four to seven weeks (Cooper and Severn 1994b). To be of benefit to larval razorback suckers, developments at this site will need to be designed to provide regular, extended periods of flooding. Wetland Hydrology - The hydrology of the wetlands on this site is extremely complex and will require additional study to fully understand the processes at work. However, preliminary investigation indicate that water levels within the wetland area are currently controlled by groundwater. The Green River dike, which was constructed sometime in the 1800's, is currently the only water control structure for the bottomland and wetland area. The presence of the dike and incision of the river channel effectively prevent and surface flow from the Green River. There are apparently four major sources of groundwater supplying the wetlands. The Green River influences areas near the river in the southern portion of the site. springs occur at three sites on the northeast, east and southeast portions of the site. These four sources allow standing water to occur on the site throughout the year. However, the extent of standing water dramatically decreases in the late summer and fall. There are approximately 24 surface acres of open water within the existing wetlands during high water in the spring. It appears that the irrigation groundwater seepage is insufficient to sustain a constant wetland water surface level during the year. A connection to the river may be required to maintain the wetland water levels required by the developments proposed in this plan. Water levels in the wetlands are two to five feet lower than the Green River in the spring and are either equal to or a few feet lower than the river through the summer. Ground water elevation declines at some sites studied in 1993 were similar in magnitude and timing to those of the Green River, indicating that a connection occurs (Figure 13). All of these sites are located in the western portion of the site indicating that sites closer to the Green River are under a greater influence of the river system.