The target for construction is 2021 or 2022 depending on funding. The public comment period will likely begin in October 2020.
Marshall Ranch FAQ
The water will be drawn out of the bottom of the reservoir, and the depth will keep that water cool.
There is also a nearby downstream reach where approximately 30 gallons per minute flow below gravel, which will cool the water further.
The WCB project will likely protect or contribute to an increase in property values due to a stream flow enhancement that keeps Redwood Creek wet when it otherwise might be dry. Property values will benefit from the aesthetic or amenity of a flowing creek. The proposed project is a highly-engineered reservoir with modern safety considerations that will enhance streamflow and improve the ecological function of the creek. Many ranches and riverside properties across the western U.S. typically have an appreciable increase in fair market value most directly attributable to their frontage and instream flow. Specific examples include ranching properties that historically diverted from and dewatered the entirety of a creek for hay or other livestock feed production that switched diversion practices to accommodate an enhanced stream flow and continued ranching diversion and use of water.
Additionally, the reservoir water would be available for fire suppression, extending an added measure of safety for the community and these same downstream homes and properties.
The project goal is to provide measurable improvements to Redwood Creek habitat conditions by increasing instream flows.
This reservoir is designed to release 50 GPM (gallons per minute) during the dry season. This would allow for fish migration and sufficient instream flows to support juvenile salmonids. Reducing the target GPM releases would not decrease project costs but it would diminish the results.
15.5 million gallons (the total reservoir volume) is much lower than consumptive use on Redwood Creek (approximately ½ to ⅔ of human consumptive use). SRF and our project team are trying to indirectly mitigate for water use in Redwood Creek while also providing community benefits of fire suppression and improved water quality.
The proposed project includes a fire hydrant that’s gravity fed from the bottom of the pond, so the whole pond can be used for fire suppression in case of wildfire.
Additionally, helicopters could dip a bucket into to the pond, and fire trucks will be able to access it.
Over the last 9 months, the project team has done major revisions to address safety concerns. The project is located on a flat terrace, and 90% of the water storage will be in a hole excavated into the terrace. The design revisions have lowered the pond elevation and the pond footprint. The bottom of the pond will be covered with a plastic and gravel liner that has a French drain that will lower the groundwater table. The designs and all of the technical studies will all be part of the public record and be made available on the SRF website as they are finalized.
Once it is sent to the state clearinghouse, there will be 30-day public review period. The designs will be available there for anyone to access.
Stillwater Sciences has conducted two main types of safety analysis.
1. Slope stability analysis
The first consists of a 2-dimensional analysis that models soil properties and shows where slope instability could happen. The key to the stability design features is small berms that will retain the top portion of the water, which are set back at considerable distance from slopes. There are no plausible failure mechanisms since the berms are far from steep slopes. Groundwater levels are the drivers of slope instability. Maintaining low groundwater levels are key to maintaining slope stability.
2. Hydrological analysis
Stillwater engineers conducted a seismic stability analysis to determine spillway size, so it has the capacity for 100 year storm flows. In the worst case scenario, which they do not think is possible, the simulation showed that all the water would go into Redwood Creek.
Unlike most large ponds, which are onstream and have a higher degree of instability (because they have creek water running into them during storm events), this engineered reservoir is fed by rainfall and is located entirely off-stream.
Additionally, the design includes multiple sensors associated with this project to monitor groundwater levels. There will be sensors on the pond berm to alert the project team to any changes.
This project includes a solar array component that will provide back-up power for operations and will provide a long-term revenue source for long-term maintenance and monitoring of the project. The solar array component is approved and would constitute the largest grid intertie system in Southern Humboldt. The solar array will be a straightforward system that is selling power back to the grid.
This is the first step to making a system that could be made available to the community with some modifications to the grid, including a storage system of batteries. In the future, as those types of systems become more efficient and desirable, there might be grant funds available to set up a local power option.
The solar array is a separate backup power system for the project itself including valves, sensors, internet connection, etc. that will be operational in a power outage.