After the completion of its Plunge Creek Conservation Project, San Bernardino Valley Water Conservation District (SBVWCD) recently reported that its efforts to return water flow to historic channels are successfully restoring natural habitat for endangered species and increasing the area’s natural groundwater recharging capabilities.
In August 2020, the Conservation District completed its project to return a 2.5-mile stretch of Plunge Creek, south of Greenspot Road and east of Orange Street, back to its historic braided-streambed after decades of rerouting the creek’s water flow created a swifter, narrower streambed.
According to Senior Engineer and Project Manager Irwin Fogerson, over the past decades the construction of roads, bridges and other features in the area altered the naturally braided stream to a narrower and more focused flow. The plan was to return Plunge Creek to a braided creek that will slow the stormwater flows as they pass through the area. This will also allow the water to spread over a larger area, which will increase the area’s important streambed habitat and its water recharging surface area.
The project cost approximately $500,000, involved several partnering agencies and included environmental studies for the kangaroo rat and other endangered species.
Santa Ana River Watershed Project Authority and California Department of Water Resources participated in the project, which was completed with funds from the Safe Drinking Water, Water Quality and Supply, Flood Control, River and Costal Protection Bond Act of 2006 (Proposition 84).
Reconstructing the historic creek channels required the digging of five pilot channels to reconnect isolated channels and the creation of six splitter mounds to direct flow into these channels. Many of the isolated channels were graded in preparation to once again receive periodic flows and flooding during rainstorms. The project also constructed a soil berm south of a newly reattached pilot channel in order to prevent overflows from disrupting nearby mining operations.
These improvements were all made using natural materials ⎯ sand and boulders ⎯ from either Plunge Creek itself or the borrow pit left in the Santa Ana River bed during the construction of Seven Oaks Dam. Over 5,850 cubic yards of material was excavated.
“One of the things that I think is so neat about this project is that sometimes you see heavy-handed engineering solutions, but, for this project, this is it,” said SBVWCD Assistant General Manager and Land Resources Manager Betsy Miller Vixie, referring to the re-digging of an old channel. “For this project, there’s no concrete, no steel. We’re using materials that naturally occur out here, which makes it faster. We constructed it in just over four weeks. It makes it cheaper; we already had lots of rocks and sand waiting here. We’re just gently supporting Mother Nature to do the natural work.”
An important habitat
The hydrological project is within and permitted through the Santa Ana River Wash Plan and included efforts to protect and study local endangered species and to restore their habitat in and along the creek.
Particular attention was given to the conservation of the San Bernardino kangaroo rat and the woolly star flower, both dependent on the alluvial habitat created by the periodic flooding of the wash by mountainous floodwaters entering the arid valley.
To protect K-rats living in Plunge Creek from construction activities, an onsite biologist was permitted to trap in the area prior to the construction. A total of 58 k-rats were captured then released following the construction activities. Thirteen of the rats were selected for a special study of their movements within the habitat.
As part of a Safe Harbor agreement, the first awarded in Southern California, the onsite biologist worked with the San Diego Zoo to place radio transmitter backpacks on the participating K-rats. The transmitters were used to track the rats’ movements throughout the creekbeds and gather information on which habitat types they prefer and if and how they migrate during and after seasonal water flows and flooding.
In addition to this, nearly 200 woolly star seedlings were planted within the protected area.
Signs of success
While the recent rain season did not offer any major rain events, the changes to Plunge Creek proved effective during the winter’s numerous small rainstorms, spreading flow into more channels and flooding a wider area of the creekbed.
According to Vixie, although the project’s first winter was one of low rainfall, the project has already recharged an estimated 106 acre-feet of water into the Bunker Hill Groundwater Basin and created 3.25 acres of new wetlands within the district’s property.
While inspecting the channels, Vixie and Fogerson noticed signs of the channels’ widening, slowed water flows and new areas that experienced flooding.
One such sign was the erosion of soil covered by invasive grasses. According to Vixie, these grasses present challenges to K-rats, which prefer the open areas of sand and gravel characteristic of dry river and creek beds.
While the K-rat’s aversion to these grassy areas is still being studied, there are several theories ⎯ the grasses might hide predators or they might attract competing rat species. Conversationalists are seeking methods for removing theses grasses from K-rat habitats, including the use of goats or swift moving water. The erosion of the grasses from the Plunge Creek area and their natural replacement with coarse sand and gravel, dropped from the water as it loses its speed passing through the shallow braids, is a promising sign, Vixie said.
As stormwater periodically traverses the new channels their beds will continue to grow wider, naturally creating more of the sandy, creek bed habitat so important to the K-rat and woolly star.