Glen Canyon Sloughs Conceptual Design

An upper and lower backwater slough located on the Colorado River in Glen Canyon roughly 12 miles upstream of Lee’s Ferry (RM -12) and 3.5 miles downstream of Glen Canyon Dam currently provides habitat for invasive fish species through increased water temperatures; annual efforts are needed to remove the non-natives. In a 2016 Long-Term Experimental and Management Plan Biological Opinion, Reclamation was directed to alter the sloughs to make them unsuitable or inaccessible to warmwater nonnative species. The goal of the project is to cool water temperatures so that non-native Green sunfish and other invasive warmwater fish do not find favorable conditions that allow them to propagate in these off channel areas and impact the native and endangered humpback chub population.

A two-dimensional depth-averaged hydraulic model (SRH-2D) was utilized to evaluate the existing conditions, and in 2018, seven design options were developed focusing on the central design criteria of the elimination of the nonnative fish habitat. To meet this design criteria, either the water needs to be drained from the upper slough, the upper slough needs to be filled in, or a water temperature reduction goal needs to be met. The conceptual designs were evaluated and compared amongst each other using criteria such as constructability, level of operations and maintenance, cut/fill volumes, and area of disturbance. General recommendations were made for each option, but a preferred alternative was not selected. Since 2018, the reservoir (Lake Powell) level has dropped significantly and water temperatures in the mainstem Colorado River are much higher. Therefore, in 2022 a request was made to update the previous work through the development and analysis of additional conceptual designs given the changing environmental conditions. This effort is ongoing.