Indian Slough Channel Capacity Restoration Project

The purpose of the project is to restore the capacity of the engineered channel, so irrigation runoff or stormwater runoff does not spill over the top of the channel onto the Mokelumne Aqueduct right-of-way, thereby limiting access to critical raw water infrastructure. The project will remove vegetation along the length of the channel, in addition to a beaver dam that is contributing to the vegetation overgrowth by restricting the water flow within the channel. See Attachment A for additional information. Overview and Background Indian Slough Channel (Channel) is an engineered channel that collects irrigation runoff and stormwater runoff from local farmland. The Indian Slough Capacity Restoration Project (Project) will restore the capacity of the channel by removing vegetation, in addition to removing an identified beaver dam. The confined Channel is choked with vegetation, creating low water flow conditions that are compounded by a beaver dam that controls the upstream water surface elevation. The Channel's manmade cut slopes were likely designed to handle transient increased water elevation and high flows but were not likely designed to sustain the current loading and saturation The volume of impounded water has increased the overall wetted perimeter and saturated zone of the Channel reach. Additionally, as storm runoff occurs, the Channel's reduced remaining free board would result in a greater likelihood of overtopping at or above the beaver dam. Over time, the upstream pool will also capture additional sediment, which would further decrease the channels overall capacity. The presence of the beaver dam is also increasing bank erosion at all flow levels as the flow is constricted and the water is accelerated around the perimeter of the dam. The project will remove vegetation growth along the length of the south side of the Channel. The beaver dam will be removed as part of the vegetation removal. The work will be performed using an excavator staged and operated from the gravel access road on the Aqueduct right-of-way. The Project is located on East Bay Municipal District's (EBMUD) Mokelumne Aqueduct rightof-way, near Bixler in Contra Costa County, see Figure la through Figure 1 b. Project Purpose and Objectives The purpose of the Project is to protect the Aqueduct right-of-way critical raw water infrastructure by preventing flooding of the right-of-way and collapse of the edge of the gravel access road through erosion of the bank of the Channel. The Project will restore the capacity of the Channel and reduce further erosion of the Channel bank. Project Location The Project is located on EBMUD's Mokelumne Aqueduct right-of-way near Bixler in Contra Costa County Project Characteristics The project will remove vegetation growth along the length of the south side of the Channel, approximately 1,300 linear feet. The extent of the vegetation removal from the bank to the Channel bed will be up to 30 feet, excavator's arm extent, for a total of 39,000 square feet. Identified trees within the project area will also be removed as they are contributing to the restricted water flow. The beaver dam will be removed as part of the vegetation removal. The work will be performed using an excavator staged and operated from the gravel access road on the Aqueduct right-of-way. Permits All work will be conducted on EB MUD property, so no encroachment permits are necessary. Jurisdictional permits will be obtained from the Army Corp of Engineers, the Central Valley Regional Water Quality Control Board, and the California Department of Fish and Wildlife. Schedule Work is scheduled in two phases. Phase One will be conducted after the 2026 nesting bird season, mid-September through October 31st. pending issuance of the required jurisdictional permits. Phase Two will be conducted in 2027 after the nesting bird season, mid-September through October 3 ist. The Project is expected to be completed within six to eight weeks over the two-year period. Work hours will be limited to weekdays with standard business hours of7:00 a.m.to 3:00 p.m. EBMUD Practices and Procedures Standard construction environmental and safety practices applicable to all EBMUD construction projects have been incorporated into the Project and will be implemented accordingly. A qualified biologist will clear the site prior to start-up of construction. All work will be monitored by the biologist, and in accordance with the jurisdictional permit requirements.