5C DIRT Program: Direct Inventory of Roads and Treatments
It
is commonly recognized that erosion and migration barrier problems associated
with road systems represent a threat to salmonid population recovery. Roads
modify natural hillslope drainage networks and accelerate erosion processes.
This can have biological consequences that affect virtually all components
of stream ecosystems (Furniss et al. 1991)*. However, road systems are one
of the most easily controlled sources of sediment production and delivery
to stream channels. Within the Five Counties, there are 4,790 miles of County
roads and approximately 16,600 culverts. 5C has committed to a long-term,
systematic, prioritization-based, sediment reduction program on County roads
to improve the quality of water and salmonid habitat.
The Program has performed road erosion inventories in Del Norte, Humboldt, Mendocino, Siskiyou and Trinity Counties under numerous grant sources including SB 271, Proposition 204 and the CDFG Fisheries Restoration Grant Program.
The goals of the 5C road erosion inventories are to: identify specific sites along county roads and facilities that are contributing sediment to waterways; prioritize implementation treatments to assure economic, biological, management and physical effectiveness; and identify sites where excess material (spoils) generated from construction and maintenance projects can be stored with minimal potential for sediment delivery into watercourses.
Methodology:
The Pacific Watershed Associates
(PWA) protocols for forest and ranch road inventories were used to develop
the base model for inventorying County roads, Direct Inventory of Roads and
Treatments (DIRT). The PWA model was modified to reflect the differences between
private forest and ranch roads and public roads. PWA completed an intensive
field-training program for all crew members and was responsible for quality
assurance and control (QA/QC) of inventory crews, assessments, and data collection.
For the field inventory, field technicians visit each site and enter data
(i.e., physical characteristics) into the DIRT database which is then processed
by the program to provide specific figures on how much erosion can be produced
- both chronically in one year and episodically during a major storm or event
- by that particular site. Other considerations, such as whether a site is
a fish migration barrier are also noted. The field technician then prescribes
specific treatments to fix the site and recommends a level of immediacy. Major
factors considered in the field-based prioritization process include treatment
immediacy, erosion activity, total potential sediment yield, complexity, and
controllability. For spoils disposal sites, size, ownership, and suitability
are recorded. All inventory sites are located using map coordinates and GPS
points and regularly downloaded into an ArcGIS platform.
Final prioritization is based on various factors obtained directly from DIRT -- treatment immediacy, potential sediment delivery volumes, and likelihood of delivery to a stream – and factors not entered into the DIRT database: biological considerations of anadromous salmonids (habitat quality and quantity), current water quality violations, TMDL criteria, cost effectiveness, subsequent scheduling of county capitol improvement and maintenance projects, management, public input, complexity and design, and other professional considerations. These factors are entered into a Simplified Prioritization Ranking Model for final prioritization.
Results: To date, more than 2,455 miles of County roads have been inventoried in Del Norte, Humboldt, Mendocino, Siskiyou and Trinity Counties under several grant sources: California Department of Fish and Game's Fisheries Restoration Program, State Water Resources Control Board's Proposition 204, and the Trinity County Transportation Commission. The inventory of the Scott and Salmon River watersheds, completed in March 2008, examined 342 miles of County maintained roads in Siskiyou County for potential sediment sources.
The inventoried roads have been estimated to produce potentially 6 million yd3 of sediment delivery to streams over a ten year period. The majority of this delivery comes from deficient stream crossings. The 5C Roads Sediment Reduction Program is a direct result of the DIRT inventory and is in full implementation phase. Sixteen projects have been completed, minimizing or preventing approximately 72,181 cubic yards of potential sediment delivery to a stream. Additional implementation proposals have been and will continue to be submitted for funding. DIRT results have proven especially valuable to County Road Departments as over 600 maintenance activity sites have been highlighted during the inventory and can be treated immediately to reduce sediment potential.
Read About Completed Inventories in the Following Final Report Documents:
Final Report: Scott & Salmon River Road Erosion Inventory. Prepared for Siskiyou County and the California Department of Fish and Game's Fisheries Restoration Grant Program, June 2008.
Final Report: Trinity, Del Norte, Humboldt County Road Erosion Inventory. Prepared for the California Department of Fish and Game's Fisheries Restoration Grant Program, Trinity, Humboldt and Del Norte Counties, 2005.
Final Report: Trinity River Watershed Five Counties Road Erosion Inventory. Prepared for the State Water Resources Control Board Proposition 204 Program.
Final Report: Five Counties Road Erosion Inventory, Del Norte, Humboldt, and Mendocino Counties. Prepared for the California Department of Fish and Game's S.B. 271 Coastal Fisheries Recovery Program.
For more Information on DIRT, contact Sandra Pérez at (530) 623-3967 Ext. 112 sperez@5counties.org