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• Executive Summary Flooding enhancement activities have been implemented at eight floodplain habitats along the Green River near Vernal, Utah. These sites, as a result of restoration activities, now flood at a greater frequency under the existing flow regimes. The restoration activities have provided fish access to what is believed to be important nursery habitat at tower flooding discharges. Since the restoration activities have been implemented, the erosion and sedimentation processes have been monitored. This report presents the results of monitoring activities. The objectives of this study were to determine 1) The as built configuration of the sites; 2) The magnitude of erosion and sedimentation at the bottomland opening; 3) The magnitude of sedimentation in the bottomland after restoration activities; and 4) The effect of restoration activities on local channel morphology. These objectives were met by performing the following: • Topographic as built mapping of the restoration sites after construction activities. • Cross-section monitoring of the inlet/outlet locations, the river channel adjacent to the site, and of the bottomland where possible. • Topographic mapping of the manipulated areas after each runoff season. • Written and photographic documentation of the erosion/sedimentation and vegetation growth occurring. Two years worth of data collection is presented in this report. Topographic mapping is presented with the text for each individual site, and all cross section plots are appended. • Initial results have indicated that these sites have maintained their as built floodability, more or less. In many cases, future flooding will initiate at lower discharges than they did as built. This is due to scour channels that have developed in the openings as the sites drained. The scour channels lower the flooding elevation of the openings. The development of scour channels was more pronounced during the 1998 runoff season. This was due to the fact that the Green River peak flows receded quickly during the 1998 runoff season. When the river drops several thousand cubic feet per second in a matter of days, as it did in 1998, the river stage drops 1-2ft. The difference in hydraulic head between the filled bottomland and the river causes the bottomland to drain more rapidly, scouring channels through the reworked bottomland opening. For -most of the sites, this resulted in 0.5' to 1.0' of scour in small channels. However, at the Leota-7A outlet, the scour was much more drastic. The configuration of the Leota site, which was designed to fill at an inlet approximately one mile upstream of the outlet, a greater difference in hydraulic head was experienced. Therefore, as the site drained in 1998, 2' to 3' of down cutting was experienced and a 20' wide channel scoured at the outlet. Erosion control mitigation measures have been implemented at this location. Protective geowebbing material has been placed along with a concrete pad where the flows were concentrated. This should reduce further erosion in future years, and provides a channel crossing so vehicle access is maintained along the Leota riverbank. The 1997 runoff season saw a longer sustained connection of the bottomlands to the river, for approximately 50 days. This induced a lot of deposition at the mouths of the openings. Flows circulated around the mouths of the openings, and deposited sediment, up to 2' at some sites, in the center of the openings. This has reduced the full surtace connection floodability at some of the sites. However, at the same time, scour channels along the upper or lower edges of the openings, have maintained the initial flooding elevation. Flooding will initiate through the channels at the design discharge or a lower discharge, but a greater flow (approximately 14,000 cfs- 15,000 cfs versus 13,000 cfs) will be required to develop the full surface connection providing the full width of fish access. The scour at the openings was less pronounced in 1997 because the river mows receded ai: a s~uwer rate: The hydraulic head between river and bottomland was less; therefore, there was less scour experienced in 1997. •