Tajiguas Creek Restoration and Bridge Installation

Location: Santa Barbara County, California
Partners: South Coast Habitat Restoration, Rancho Tajiguas

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Tajiguas Creek once supported Federally endangered Southern California steelhead. The construction of numerous low-water crossings across the channel for agricultural purposes had blocked access for upstream fish migration, causing substantial sediment aggradation, and leading to bank erosion.

Michael Love & Associates (MLA) performed a geomorphic assessment of 8,000 feet of stream and completed engineering plans, specifications and cost estimates, for the removal of five low-water crossings with drops over the roadway ranging from 4 to 10 feet.. The geomorphic assessments identified the stable natural profile of the historical channel, extent and volume of accumulated sediment behind crossings, location of streambanks susceptible to scour and erosion, and the stable natural channel dimensions and streambed material gradations.

The extent of sediment accumulation upstream of each crossing made excavation to the native channel cost prohibitive. Rather, MLA used the results of a topographic survey and geomorphic to ensure the bulk of aggraded sediment was removed while designing over-steepened channel reaches upstream of crossings that self-adjust, thus reestablishing the stable grade while providing fish passage during the channel adjustment period.

MLA prepared hydraulic and hydrologic analyses to design the channel and a new channel-spanning bridge. The analyses used HEC-RAS and FHWA methods to size the opening of the bridge to provide the required freeboard during a 100-year flow event, and to perform a scour analysis for the new bridge crossing. MLA designed rock scour countermeasures to protect the bridge abutments from contraction scour as well as anticipated channel incision through remaining stored sediments.

The project design incorporated numerous restoration techniques prescribed by California Department of Fish and Wildlife to stabilize the steep channel banks and bed following removal of the stored sediments. These included rock vanes and rock deflectors, willow wattle fences, willow mattresses, live stakes, and willow fascines. MLA staff provided on the ground construction oversight working directly with the owner and contractor for the 3-months of construction, and conducted the post-project survey.