The proposed Rainbow Water Quality Improvement Project, which is located in the unincorporated community of Rainbow in northern San Diego County, would install structural Best Management Practices (BMPs) in the form of subsurface wetland channels and pre-treatment channels to help attain Total Maximum Daily Load (TMDL) compliance for nutrients in the Rainbow Creek watershed. The existing roadside ditches receive runoff and stormwater flows with high nutrient loads from adjacent land uses and discharge directly into Rainbow Creek, which converges with the Santa Margarita River. The existing concrete-lined and earthen roadside ditches would be converted into subsurface wetland channels that would filter and treat stormwater runoff. Adjacent to the subsurface wetland channels would be pre-treatment channels that would remove sediment from the surface water prior to flowing into the subsurface wetland channels. Additional improvements include driveway reconstruction, new sidewalk, and curb and gutter in deficient areas.
The project is located along portions of Fifth Street, Huffstatler Street, and Rainbow Valley Boulevard between the road shoulder and adjacent residential or commercial developments, and consists of Sites 2, 3, 4, and 5. The two proposed subsurface wetland channels, which are currently functioning as maintained roadside ditches at Site 2, are identified as Sites 2A and 2B. Site 2A is located along the west side of Huffstatler Street, south of Fifth Street, and would include improvements for a lined subsurface wetland channel with a pre-treatment channel. Site 2B is located along the north side of Fifth Street between Rainbow Valley Boulevard and extends past Huffstatler Street and would include improvements for a lined subsurface wetland channel with a pre-treatment channel. Site 2C is located south of the intersection of Fifth Street and Huffstatler Street and would include sidewalk, curb, and gutter improvements. Site 2D is located within Rainbow County Park and would include swale improvements.
Site 3 is located south of Chica Road along the west side of Rainbow Valley Boulevard and would include improvements for lined subsurface wetland channels with a pre-treatment channel. Site 4 is located along the west side of Rainbow Valley Boulevard between Rainbow Valley Boulevard West and Rainbow Creek Road and would include improvements for lined and unlined subsurface wetland channels. Site 5 is located along Huffstatler Street, approximately 335 feet south of Second Street to approximately 625 feet north of Second Street and would include improvements for lined subsurface wetland channels with a pre-treatment channel.
The existing roadside ditches are within County right-of-way and six of the roadside ditches are within the County’s Regional General Permit-53 (RGP-53) permit program which are subject to maintenance by the County Department of Public Works (DPW). The six maintained facilities are numbered; Facility 57-015 is the existing 5-foot wide concrete-lined channel along the north side of Fifth Street; Facilities 57-110, 57-016, and 57-017 are the roadside ditches along Huffstatler Street; and Facilities 57-012 and 57-013 are the roadside ditches along Rainbow Valley Boulevard. County DPW maintains these facilities by removing sediment, vegetation, and debris. Once the roadside ditches are improved, they will continue to undergo regular maintenance for flood control and water quality. The total quantity of cut for the project is approximately 11,000 cubic yards and the total quantity of fill is approximately 4,300 cubic yards. Construction is anticipated to last approximately 8 months.