M&T Chico Ranch / Llano Seco Rancho Fish Screen Facility Long-Term Project – Evaluation of Rock Removal on the Sacramento River
M&T/Llano Seco Pumping Plant and Fish Screen Facility (Facility) provides water to agricultural lands on the M&T Chico Ranch, Llano Seco Rancho, U.S. Fish and Wildlife Service (Service) conservation easements, Service Wildlife Management Area Lands and California Department of Fish and Wildlife (CDFW) lands in Butte County.
Recent changes in the channel morphology upstream of the pumping plant, including accelerated bank erosion and gravel bar expansion, have compromised the function of the pumping plant and the City of Chico’s waste water diffusion point. A joint NEPA/CEQA (EIS/EIR) document has been initiated to evaluate alternatives for a long‐term solution for protecting the pumping plant, which may include permanently rocking portions of the riverbank in the vicinity of the pumping plant. Permanent rocking will likely require mitigation in the form of removal of rock that is no longer serving its design purpose along this stretch of the Sacramento River. These measures will be required to meet mitigation requirements for bank swallows and anadromous fish by allowing for natural river processes to ensue.
This study includes a long‐term geomorphic evaluation of the Sacramento River to quantify the impact of the removal of antiquated rock and revetment within the study reach between RM 194 and 187. The objectives of this project are to develop a thorough understanding of hydrologic and geomorphic processes within this project reach for various rock removal alternatives, with the goal to apply this understanding to the selection of a preferred rock removal alternative, and quantify any potential long‐term impacts.
To meet these goals and objectives, cbec utilized the predictions of a meander migration model to develop future (2060) channel planforms for the project reach assuming rock removal for three (3) sites located at RM 191‐192R, RM 190.5‐191L and RM 189L. cbec coordinated with the US Fish and Wildlife Service for the selection of the three sites and the formulation of five rock removal alternatives. The five future (2060) channel planforms/alternatives include no rock removal (no action), rock removal at each of the three proposed sites, and rock removal at all proposed sites. For existing conditions and each of the future (2060) alternatives, the bankfull and 100‐year events were simulated using the SRH‐2D model to quantify potential impacts to the reach‐scale hydraulics. Output from the hydraulic model was then used to infer probable impacts to the sediment regime as a result of the revetment removal.