Santa Cruz, CA
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ag-flood

Client: Coastal San Luis RCD, County of San Luis Obispo

In 1959 the lower three miles of the mainstem Arroyo Grande Creek were converted to a trapezoidal flood control channel to reduce flood risk to high value farm land. Sedimentation, vigorous riparian growth and changes in the watershed due to urbanization have altered the flood control channel to the point where it provides very little in the way of flood protection. In addition, environmental regulations that protect sensitive species have limited the ability of the County to perform channel maintenance work. In 2001 a high intensity storm event caused levee failure, resulting in millions of dollars in damage to adjacent farmland and residential properties. In response, the Coastal San Luis Resource Conservation District (RCD) commissioned Waterways staff, in conjunction with SH+G, to evaluate potential alternatives to improve flood protection along this reach of Arroyo Grande Creek. Identified alternatives included levee raising, environmentally appropriate vegetation and sediment management, and erosion control and flood detention projects in the upper watershed to reduce sedimentation in the flood control reach.

Habitat enhancement elements were also recommended to provide mitigation for project impacts. The alternatives were evaluated using a HEC-RAS model to determine the level of flood protection afforded each alternative and their respective costs of implementation. Following selection of a preferred alternative, Waterways has worked with SWCA on the regulatory permitting and environmental review phase of the project and are currently contracted with San Luis Obispo County to provide bid ready documents for the levee raise and sediment management components of the projects and provide construction-phase support. Waterways staff also prepared the long-term management plan for the flood control channel that included a comprehensive monitoring plan that addresses vegetation and accumulation of sediment in the channel.

Client: South Coast Habitat Restoration

Waterways provided design and construction support services to South Coast Habitat Restoration to improve fish passage conditions and vehicular access at a private bridge that crosses Carpinteria Creek. The project site had a concrete-lined channel with drop structures that impeded the upstream migration of salmonids and an undersized bridge that could be overtopped during flood events. Site improvements included removing the concrete-lined channel, recontouring the banks, and revegetating the riparian area. The redesigned channel will provide hydraulic conditions conducive to fish passage. Waterways designed a 55’-span vehicular bridge to replace the undersized bridge. The new bridge can convey floods greater than the 100-year storm event. The construction phase of the project was funded by the Fisheries Restoration Grant Program through the California Department of Fish and Wildlife.

widdoes1 webClient: South Coast Habitat Restoration

South Coast Habitat Restoration contracted with Waterways to provide design services for the improvement of fish passage conditions at Widdoes Crossing, a private road crossing on Gobernador Creek. Fish passage conditions at the site were severely impacted by incision of the streambed below a concrete and boulder ford which created an 8 foot hydraulic drop.

 

The design for fish passage improvements consisted of replacement of the existing ford with a clear-span bridge and construction of a roughened channel to transition. The channel was reconstructed for approximately 240 feet using native rock salvaged from the site to provide a smooth transition in the stream profile and hydraulic conditions conducive to fish passage. The design incorporated three pools and installation of woody debris structures in the channel to provide resting area, refuge, and aquatic habitat. Boulder weirs were placed to maintain pool scour and grade control through the project area. Additionally, the project included bank protection and the the site was revegetated with willow, sycamore and other native vegetation.

 

DSC01634 webClient: Coastal San Luis Resource Conservation District

The primary objective of this project was to develop a planning document to restore and enhance aquatic habitat conditions for steelhead trout in the Morro Bay watershed. Specific tasks included oversight and review of field data collection by Resource Conservation District programs, organization and review of existing and historical data, field reconnaissance of potential limiting factors, interaction with agency staff and members of the public, and development of the Restoration Planning document. Recommendations and restoration priorities were developed based on the results of the limiting factors analysis and input from agencies and the public. This project was funded by the Morro Bay National Estuary Program, California Department of Fish and Game, and the California Coastal Conservancy.

IMG 2471webClient: Coastal San Luis Resource Conservation District

NOAA Fisheries Recovery Plan for steelhead populations lists Pismo Creek as a high priority system for the recovery of the South Central California Coast Steelhead ESU.  Limiting factors to their continued survival in the Pismo Creek Watershed are water withdrawals and fish passage barriers.  One of the most significant fish passage barriers in the lower portion of the system is a Union Pacific Railroad Crossing that blocks all life stages of steelhead under all flow conditions.  Incision downstream of the concrete culvert railroad crossing has resulted in a 12 foot drop over the concrete structure along with a broad concrete apron through the culvert itself that creates shallow flow under most discharges.  A series of Denil fish ladders was installed at the site in the 1980's but has proven to be ineffective at providing fish passage and requires constant maintenance from debris and bedload. 

RodriguezClient: County of San Luis Obispo

Waterways was contracted by the County of San Luis Obispo Public Works Department (Utilities Division) to provide assessment, design and construction observation services for the improvement of fish passage conditions and the protection of a waterline in Arroyo Grande Creek at the Rodriguez Bridge crossing. Our work also included preparation of a design report and response to comments from NMFS fish passage engineers.


Just upstream of Rodriguez Bridge there was an exposed concrete encased water supply line within the bed of Arroyo Grande. Channel scour on the downstream side of the encasement had nearly undermined the encasement, potentially leading to structural failure of the pipeline, and leaving a 3 foot hydraulic drop that created a partial barrier to fish passage.
The designs for fish passage improvements and pipeline included installation of a roughened channel. The channel was reconstructed for approximately 250 feet, using imported rock to provide a smooth transition in the stream profile and hydraulic conditions conducive to fish passage. Two pools and a woody debris structure were incorporated into the project to provide resting and rearing habitat. Additionally, boulder weirs were installed to maintain pool scour and grade control through the project area.


Steelhead were not found in the project reach during pre-construction field surveys. However, steelhead were observed both upstream and downstream of Rodriguez Bridge, and near the installed woody debris structure during post-construction monitoring. The project has greatly improved fish passage conditions and is meeting established success criteria.

P7080089 webClient: Coastal San Luis Resource Conservation District

Channel and riparian conditions along Tally Ho Creek within the project area look much different today than they did several hundred years ago. Pressure to utilize flat valley bottoms for agriculture and, later, suburban development, resulted in removal of much of the riparian vegetation, filling of wetlands, road building, and straightening and deepening of Tally Ho Creek. Cleared portions of the valley bottom now consist of single family homes and Tally Ho Road, and Tally Ho Creek has been confined to the eastern edge of the valley floor.