Westhaven Community Services District Disinfection Byproduct Reduction Project (Lake or Streambed Alteration Agreement No. EPIMS-HUM-54138-R1C, Westhaven Commun

Westhaven Community Services District Disinfection Byproduct Reduction Project (Lake or Streambed Alteration Agreement No. EPIMS-HUM-54138-R1C, Westhaven Commun

Full Title: Westhaven Community Services District Disinfection Byproduct Reduction Project (Lake or Streambed Alteration Agreement No. EPIMS-HUM-54138-R1C, Westhaven Community Services District Stream Remediation) The Project is limited to three (3) encroachments for habitat enhancements associated with the Disinfection Byproduct Reduction Project. The Westhaven Community Services District (District) is proposing to remove an obsolete Humboldt crossing over the south branch of Two Creek, a locally named spring-fed stream. Currently, the crossing impedes flows in Two Creek, causing incising, bank erosion, and increased sedimentation. Work includes removing the crossing and grading a new descending flow line. The newly exposed stream bank at the Humboldt crossing site would be graded to have side slopes of no more than 2:1. Six-inch-deep redwood bark mulch would be installed on the recontoured creek slope, and five-gallon sword ferns (Polystichum munitum) or other similarly sized native vegetation would be planted at ten feet on center spacing. CDFW has recommended this action to the District in order to improve biological conditions within Two Creek. In addition, drainage from a hillside north of the District's water treatment ponds is currently diverted to a roadside ditch, which extends over 1,000 feet before it enters Two Creek. CDFW has recommended that the flow be directed to Two Creek via a new culvert that would discharge into the creek near the existing Humboldt crossing. This would put the water in the upstream reach of Two Creek and enhance the biological value of this upper stream reach. An earthen dam would be installed in the roadside ditch on the north side of the District's Water Treatment Plant (WTP) access road to divert flows to a new 18-inch-diameter corrugated metal pipe (CMP) culvert that would extend ~70 feet to the creek. The culvert inlet would be armored with six-inch crushed rock, while 12-inch crushed riprap would be installed by hand on the banks at the culvert outlet to dissipate flows. Lastly, rock slope protection (RSP) is proposed to be added to 12 lineal feet of Two Creek at the culvert outlet of the District's water treatment pond, which drains into Two Creek. The additional RSP would address ongoing erosion at the culvert outlet. Removal of the Humboldt crossing over Two Creek would restore the topography of the creek to natural conditions that existed prior to construction of the crossing and would improve the aquatic habitat at this location. Redirection of flow from the ditch to the stream would improve aquatic habitat within a ~1,000-foot reach of Two Creek, while addition of riprap at the existing culvert outlet would minimize the potential for further erosion and sedimentation of Two Creek.

Westhaven

Humboldt

Northern California

Humboldt