INITIAL OBSERVATIONS ON DAM REMOVAL EFFECTS ON ASSOCIATED WETLANDS FOR A MAIN STEM DAM ON THE ROGUE RIVER, JACKSON COUNTY, OREGON

As water was emptied from Tolo Slough on Oregon’s Rogue River on the morning of August 11, 2010, a narrow spit between the main stem of the Rogue River and the slough gave way upstream of a temporary coffer dam connecting the spit to the center of Gold Ray Dam. The breach was accidental, occurring a week before the scheduled breaching of the coffer dam. Within hours the major sloughs (Kelly and Tolo) were emptied, their reservoirs adding to a spike in total discharge on the Rogue past the partially-deconstructed dam. Five piezometer nests had been established in the Kelly Slough area prior to dam removal and monitored both pre- and post-removal. Two upstream piezometers nests indicate likely groundwater gaining conditions in the upper Kelly Slough. The three downstream indicate losing conditions in the slough. Temperature data also support a spring-fed source of water in the upper Kelly Slough. Geomorphic analysis through use of ArcView GIS indicates a net wetted area decrease on the main stem of the river (through development of new bars and islands) of approximately 30% in the near-upstream reach. The wetted area decrease in the slough areas is more pronounced: a decrease in Kelly Slough of -252%, and nearly an order of magnitude decrease in Tolo Slough (-810%, essentially dewatering the slough). Future work remains on volumetric analyses of the water bodies, groundwater contributions, and channel reactivation. However, significant hydrologic and habitat changes are likely in the upstream wetlands environment.