Austin Creek Gravel Extraction and Fisheries Habitat Enhancement (Lake or Streambed Alteration Agreement No. EPIMS-SON-42631-R3)

Austin Creek Gravel Extraction and Fisheries Habitat Enhancement (Lake or Streambed Alteration Agreement No. EPIMS-SON-42631-R3)

The project is limited to the aggregate mining of gravel bars 1, 2, 3, and 4 (Exhibit A) using the horseshoe skimming method. The upstream end (4:1 slope) and outer edge of the gravel bar (5-foot buffer) will not be disturbed, which will allow the bar to grow with future recruitment of gravel. The remaining portion of the bars will then be skimmed down to an elevation equal to one foot above the groundwater table at the time of excavation. In addition to skimming to reference elevation, the downstream one third of the bar’s skimmed area will be excavated to a depth of six feet below the groundwater table (or until clay layer depth is reached) to create an alcove feature. The project includes the removal of up to 50,000 cubic yards of sand and gravel per year over a five-year period, not to exceed a total of 250,000 cubic yards in five years, from the lower reach of Austin Creek. Over the last five years , the gravel extracted has been in the range of 0 to 15,000 cubic yards per year under Streambed Alteration Agreement No. 1600-2018-0135-R3, which has expired. The material removed is the natural sands and gravels from the bed of the channel. Access to bars 1, 2, 3, and 4 is from existing access roads on either side of the creek, and via temporary bridge crossings between gravel bars 1 and 2 and 2 and 3, above the wetted channel, to allow access for annual gravel harvest (when required by wet years). The crossing will be installed with an excavator, using logs or portable precast concrete blocks as abutments on each side of the wetted channel, with the portable bridge deck placed on top, approximately two feet above the water level. No concrete will be poured onsite. Ramps to the bridge then will be created with harvested natural creek gravels. No work will be performed in the wetted channel. The abutments/bridge will be removed when harvest of the accessed bar is completed. As mitigation for this project, the placement of one piece of large woody debris per year to facilitate gravel accumulation and provide pool habitat features will be required. Removal of invasive giant reed (Arundo donax) is also required within the project site (gravel bars and stockpile area).

Unincorporated area

Sonoma

Northern California, San Francisco Bay Area

Sonoma