Mar 25, 2022

Chorro Creek Ecological Reserve Floodplain Restoration Project Performs Well During Storms


Members of the California Conservation Corps planted thousands of native plants at the Chorro Creek Ecological Reserve floodplain restoration project site.

With the help of project partners and funding from the California Department of Fish and Wildlife and the State Coastal Conservancy, the Estuary Program completed a 4.8-acre restoration project at the Chorro Creek Ecological Reserve project in fall of 2019. The project included grading close to a half mile of side channel habitat to widen the floodplain on Chorro Creek, installing large woody debris, and planting diverse native shrubs and trees. To learn more about the implementation of the project and history of the site read this blog or watch a video presentation here.

January 2021 storm conditions and hydrograph

During the first rainy season after project completion, there wasn’t enough precipitation to flood Chorro Creek and activate the channels. Then, in January of 2021, a large rainstorm brought almost eight inches of rain to the Morro Bay area over a three-day period. This storm was large enough to be classified as a ten-year-storm, which means that we can expect to get a storm of this size once every ten years. The storm caused Chorro Creek to overflow into the newly restored floodplain, putting the project to the test.

Hydrograph of Chorro Creek monitoring site at Canet Road during storm of January 2021
The figure above is referred to as a hydrograph and illustrates the height of water at a particular spot in a creek over time. This hydrograph shows the height of the water in Chorro Creek during the January 2021 storm at a monitoring site near Canet Road, which is close to the restoration project site. Estuary Program staff use the data from this site to estimate when and for how long the floodplain restoration site will activate. This data is available through the San Luis Obispo County website.

January 2021 floodplain activation videos

Estuary Program staff can’t always be on site to watch the creek rise during storms, so we use technology to help us gather data. Time lapse videos have helped us capture what the project site looks like during peak flows.

Given that water levels are relatively low during typical weather conditions for much of the year, the amount of water that flows through our watershed during these large storm events looks dramatic.

Watch this timelapse video of the floodplain activating during the ten-year storm event in January 2021. You can see that the full floodplain is activated and, as the flows dissipate, a large gravel bar appears. This gravel bar is made of sediment that was washed into the creek during the storm and deposited here.

This video shows the high flows within the side channel of Chorro Creek from another vantage point, showing side channel changes after the January 2021 storm event.

This video shows high flows along the upper side channel that was constructed as part of the restoration project. Flows had receded from the peak during this video.

How did the site respond to these high flows?

Water is a powerful force, and the storm in January 2021 changed the project site. The high, rushing water carved out new deep pools in some places and deposited excess sediment in others, creating new gravel bars.

Experts at Environmental Sciences Associates (ESA), the firm who designed the restoration project, have conducted repeat geomorphic surveys including a drone flight, cross-sections, and profiles of the side channels. These surveys track changes in the landscape and the ways in which water flows over it.

The data shows that much of the restoration site held up well, given that these high flows came so early in the post-restoration life of the project site. There was some erosion resulting in a net loss of 1,318 cubic yards of sediment. However, if the floodplain hadn’t been excavated during the project implementation period, much more sediment would have eroded and washed downstream from the site with these large stormwater flows.

Map of elevation changes on CCER project site after January 2021 Storm
Change in elevation along the two side channels (1,200 ft.) adjacent to Chorro Creek using drones. Data provided by Environmental Science Associates.

Eighty-three of the 1,415 new plants added to the site were lost during the storm, and many cages needed to be cleaned from debris. Despite this, the site still meets the project target for plant health with 90% of the plants having survived the storm.

More stormwater flows in December 2021

The floodplain also activated for an extended period of time in December 2021. Flows filled much of the constructed floodplain area. The rushing water deposited additional sediment at the project site and created a low flow channel within the large gravel bar deposited during the January storm, almost a year earlier. Water has also remained in the channel, providing wildlife habitat.

Gravel Bar created during January 2021 storm at Chorro Creek Ecological Reserve Project Site
Flooding conditions at the Chorro Creek Ecological Reserve in December 2021 showing a gravel bar that formed in January 2021 and then continued to evolve this year.

This timelapse video shows floodwaters flowing through the project site during multiple rain events in December 2021.

Log found on top of plant protection cage at CCER
After a storm recedes, you can usually find debris collected along the bank (similar to a high tide wrack line along the estuary). We were surprised to see this tree branch perched on top of one of our six-foot-tall plant cages after the waters receded.


As you can see in the two pictures above, reconnecting the creek to the floodplain has allowed the excess sediment to be deposited at the project site. This has reduced the amount of sediment flowing into the Morro Bay estuary, which has historically filled in at an unnaturally fast rate.

Monitoring continues at the project site

We will continue to track the evolution of the side channels and growth of the native plantings. These types of restoration projects are many years in the making and it is encouraging to see the project site taking form and beginning to show ecological benefits.

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