While Carpinterians have enjoyed a few dry days of sun after the recent flurry of rains, watersheds impacted by the Thomas Fire remain vulnerable to increased runoff, according to a statement released Feb. 19 from Santa Barbara County Public Works. Winter storms continue to bring a significant amount of rocks and sediment into the debris basins above Montecito and Carpinteria. Emergency efforts to clear basins and prevent flooding and debris flows have the County Flood Control District implementing ongoing sediment placement at Carpinteria Beach at Ash Avenue since Feb. 4. The District began depositing sediment at Goleta Beach this week (Feb. 19) as well.
In creating maximum capacity in the watersheds as a safeguard against future storms, the District is placing coarse sediments on Carpinteria’s Ash Avenue beach. Flood control basins located at the base of the foothills protect residential communities from damaging winter storms by trapping trees, boulders and mineral sediment that could cause flooding or deadly debris flows.
Constructed 50 years ago, the Santa Monica Basin is considered the “crown jewel” in the south coast Santa Barbara County system, according to information provided in the City of Carpinteria’s e-newsletter The Current. Its capacity is far greater than the other basins in the system, and it is credited for saving Carpinteria from potentially disastrous flooding and debris flows on Jan. 9, 2018, when an intense rainstorm followed the massive Thomas Fire.
The County is following emergency permit protocol for the sediment removal operation. Most of the material arriving at Ash Avenue has come from the Santa Monica flood control basin, though in the beginning of the operation some sediment was delivered from Montecito. Approximately 7,000 cubic yards of sediment has been deposited at the beach. Dump trucks place the sediment, and bulldozers move it into the tidal area where high tides, surf action and current help to disperse the material.
One challenge related to the operation is the mess. Dozens of daily truck trips cause muddy streets, are noisy and add traffic. These effects are particularly noticeable in the beach neighborhood. In response, the County brought in a fulltime street sweeper and installed rumble plates at the exit of the job site to reduce the mud being transported onto city streets. Additionally, the County is altering its delivery methods to reduce mud on the street and better control truck traffic.
The City of Carpinteria is working to mitigate these nuisances in cooperation with the County, which is responsible for the costs and management of the sediment placement project.
Secondary benefits of sediment placement
Protecting homes and infrastructure from storm damage is the primary purpose of the emergency operation, but the project offers the additional benefit of re-nourishing the beach with materials that would naturally be conveyed to the coastline without the flood control basins functioning as coarse sediment filters, according to the City. Unlike beaches in less mountainous areas, Carpinteria’s coastline should naturally have a steady supply of coarse sediments. High-velocity stream flows in the area would regularly transport coarse sediments to the beach if the flood control basins didn’t act as filters that allow only fine materials to pass through. While the basins play a critical role in protecting private and public assets, over time they contribute to beach erosion that can put coastal homes and beach areas at greater risk of flooding.
Decades of study by the Army Corps of Engineers indicate that Carpinteria’s shoreline is starved for mineral sediments that are necessary for stability and sustainability. As the threat of sea level rise increases, so does the need for re-nourishing local beaches.
The City intends to work with regulatory agencies and BEACON (Beach Erosion Authority for Clean Oceans and Nourishment) to pursue a permanent permit for a regular program to help stabilize the beach with sediment from the flood control basins in the local watershed. Historically, these mineral sediments have been transported to upland disposal sites.
The sediments deposited this year differ dramatically in content from those deposited after the Jan. 9, 2018 storm event. At that time, sediment dredged from the Carpinteria Salt Marsh was deposited at Ash Avenue. The marsh’s fine silt with high organic content is distinct from the coarse mineral sediment currently being removed from the Santa Monica and other flood control basins in the region. Materials from the upper reaches of the watershed are also far less likely to be contaminated by urban and agricultural influences such as fertilizers, pesticides, oil from roadways and pet waste.
Santa Barbara County Environmental Health workers have recently placed warning signs at Carpinteria City and State beaches, informing beach users that recent ocean water testing results exceeded one or more state health standards at those locations. Water testing takes place near the mouth of the Salt Marsh and Carpinteria Creek where inputs from urban and agricultural runoff is likely to be highest. Elevated levels of bacteria have been recorded at various times at Carpinteria beaches during this rainy season prior to the start of sediment placement.
While the sediment placement operation could be a contributor, bacterial levels typically increase in ocean water after storms as a result of outputs from creek mouths and storm drains, and in addition to Carpinteria, four Santa Barbara area beaches are under warning status for bacterial levels that exceed health thresholds during the last weekly test, which took place on Feb. 11.
At this time, all Santa Barbara County beaches are open. At beaches that are under warning status, members of the public are advised to stay at least 50 yards away from creek mouths and storm drains due to probable high bacterial levels in those sources. Water testing results are updated weekly on the Ocean Water Quality Hotline (805) 681-4949 and at sbcphd.org.