Understanding the Complicated Relationship of Hydrology and Geology
By Anna Rogers, Sanctuary Forest, Inc.
Since 2002, when the community called upon Sanctuary Forest to help address low-flow problems in the upper Mattole, we’ve been busily applying ourselves, trying different strategies to reduce the effects of drought and legacy impacts. We’ve worked closely with the community over the years to reduce direct human impacts on water use through our growing Storage & Forbearance Program, officially launched in 2007. Our participants now number 34, and they store approximately 2 million gallons annually, and there are also many community members who participate unofficially. When conserving the water above the surface wasn’t enough, we realized that we must also try to improve the water we don’t see—the groundwater. What goes on beneath the surface is inextricably related to the river and all that we see above the surface.
Groundwater is just that—water in the ground. For something that is invisible, we depend on it a lot: 51% of drinking water for the U.S. population comes from groundwater, and 99% of the rural U.S. population relies on groundwater for their drinking supplies.1 If you get your water from a spring or an aquifer, you’re using groundwater. But sometimes groundwater gets depleted from overuse or being unable to “refill” due to drought, and the conditions that normally retain some of that sponginess can affect how well the ground recovers. This is what we see in the Mattole River watershed: the capacity of the land to hold water has been deeply affected by legacy land-use impacts such as logging, road building, and the removal of wood from the streams. The loss of wood in the river has caused streambeds to become incised (downcut to bedrock) and disconnected from floodplains. All of this affects the way that water moves across the landscape and at what speed. For groundwater recharge to occur, “we need to teach running
water how to walk,” to paraphrase Jasper Oshun, Assistant Professor of Geology at Cal Poly Humboldt.
Groundwater recharge is a term we use a lot around the Sanctuary Forest office. In order to recharge groundwater levels and restore salmonid habitat, we have been adding wood back into the streams. Unanchored and anchored log structures, log and boulder weirs, and beaver dam analogs help to slow down the movement of the water, raise the level of the water, and spread it out onto the historic flood plain where it can sink into the groundwater. We have also been using another strategy to help improve groundwater storage—off-channel ponds that are lined with a mixture of clay and native soil so that the water naturally seeps out throughout the dry season.
Big Things start with Small Steps
The thing about accomplishing big things is that it almost always starts with small steps. For Sanctuary Forest, we’ve found success in our restoration projects by implementing what are called “pilot projects.” These are small-scale projects that are used to show how effective a particular strategy might be on a larger scale. We monitor the effectiveness of the project, weigh the success, and make changes based on adaptive management needs. Of course, we want to implement projects that are going to be effective, but more importantly, we want to make sure that we are aiding the natural processes already in place, and when possible, assessing how the landscape might have looked before. If a historic floodplain can be reconnected to the stream by raising the level of the water and associated groundwater level, then we’re repairing a natural system that is already in place—and we’re more confident of the success of the project.
We’ve completed several pilot projects in Lost River, and in Baker and McKee Creeks, and have seen small successes. But what we’re attempting now is what we’re informally referring to as “stacking”—using multiple strategies in one project in order to have a bigger impact. The North Fork Lost River Flow and Habitat Enhancement Project, funded by the Wildlife Conservation Board for $2 million, does just that. This project will utilize two important strategies: 1) increased runoff detention and groundwater storage, providing streamflow benefits that mimic the natural hydrologic cycle, improving late spring and early summer flows; and 2) increased surface water storage with metered flow to augment late summer flows. Increased groundwater storage is achieved through raising the streambed and connecting floodplains. A total of 3,055 linear ft. is designed with channel-spanning structures, including beaver dam analogs and log and boulder weirs, with the objective of increasing groundwater storage in the streambed and banks, increasing pool depth and area, and generally enhancing habitat complexity.
Flow augmentation is achieved through construction of two terrace ponds with metered flow directed to the creek during the critical dry months (August through October). The ponds will be sealed to minimize leakage through installation of a clay keyway in the berm that also extends below the berm, connecting with a natural subsurface restrictive layer of blue clay or bedrock. They will be filled by surface runoff and retention of shallow groundwater, and water will be diverted to the creek via a siphon pipe and valve.
Several of the strategies planned for this project are ones we’ve used before, but two are new: the use of Stage 0 (“zero”) and the use of ponds with metered release into the creek.
Stage 0 is a fairly new restoration concept, described as “a valley-scale, process-based approach that aims to reestablish stream depositional environments to maximize connectivity at base flows and facilitate development of dynamic, self-formed, and self-sustaining wetland-stream complexes.”2 So, what does that mean? Basically, we are aiming to create a wider floodplain with complex, multi-channel conditions. Realizing Stage 0 conditions can be a complex journey, and it can be achieved in different ways. The project designer, Joel Monschke of Stillwater Sciences, has tailored the design of the project to fit the planned site. He writes: “This site offers a low-risk opportunity to experiment with a modified Stage ‘0’ channel restoration approach. This approach is different than the Stage 0 approach utilized in Oregon where entire wide valleys have been reshaped. Instead we are proposing to reshape narrower valleys extending from the base of one hillslope to the opposite side, generally 15’–70’ in width, filling the existing incised channel and adding a combination of grade control and roughness that will direct flows along a more sinuous route.”3 Because we have extreme dry seasons and can’t rely on snow melt here in the Mattole watershed, we must incorporate subsurface clay barriers into the weir design so that the flow doesn’t immediately go subsurface.
Using ponds with metered water release is also a relatively new approach to assisting streamflows in the dry season. Unfortunately, the need for it underlines the severity of the drought. Initially, upslope groundwater recharge ponds were planned for this site—similar to the groundwater recharge ponds we implemented upslope of Baker Creek. But the dry seasons of 2020 and 2021 taught us “that for instream flow-enhancement projects to be successful in extreme drought years, a significant incoming source of water with some pressure head is needed. Options with enough pressure head to provide flow into the stream include upslope instream and off-channel ponds as well as piping directly from upslope springs.”4 The total groundwater storage for both the instream and terrace ponds project is estimated at 2.65 million gallons (1.65 million from groundwater storage and 1 million from pond surface water storage).
Thank you to our community, our watershed partners, collaborating organizations, and the state agencies and foundations who have taken these small steps with us as we learn how to store more water on and in the landscape—for fish, people, and wildlife. Using stacked strategies and a larger-scale approach, we’re hopeful this project can be a model for how to make a big impact to improve the water shortage problem in the Mattole River watershed and beyond.
For more information: sanctuaryforest.org
1 Source: www.groundwater.org 2 Executive Summary, River Restoration to Achieve a Stage 0 Condition Workshop, Oregon Watershed Enhancement Board, Institute for Natural Resources at Oregon State University. 3 Stillwater Sciences. 2020. Basis of Design Report for North Fork Lost River Streamflow and Habitat Enhancement Project. Prepared by Stillwater Sciences, Arcata, California, for Sanctuary Forest, Whitethorn, California. 4 Stillwater Sciences. 2020. Basis of Design Report for North Fork Lost River Streamflow and Habitat Enhancement Project. Prepared by Stillwater Sciences, Arcata, California for Sanctuary Forest, Whitethorn, California.