Mount Diablo State Park: Mitchell Creek Riparian Restoration

Abstract:

This project will restore the natural riparian corridor of Mitchell Creek in Mount Diablo State Park (MDSP).  Mitchell Creek is one of the only perennial streams in MDSP, and is a tributary to Mt. Diablo Creek, which eventually flows to Suisun Bay.  Riparian restoration will include the removal of barriers to restore fish passage, improvements to channel stability, removal of fill from an old earthen dam and old roads along the creek bank, and re-countouring of the bank in some locations to help riparian vegetation become re-established.  Fish passage barriers include two cement dams, and two culverts.

Purpose: The purpose of this project is to remove fish passage barriers along Mitchell Creek as part of a comprehensive effort to return steelhead to the Mt. Diablo Creek watershed, and to restore the riparian ecosystem along Mitchell Creek to improve critical habitat for wildlife, as well as improve water quality. Mitchell Creek and Mt. Diablo Creek, together with Donner Creek, comprise the most pristine watershed remaining in the Concord/Walnut Creek region. They are the focus of a recently formed community watershed group, and potentially home to steelhead trout. The headwaters of Mitchell Creek originate on the north side of MDSP, and contains some creek stretches with healthy riparian habitat, and a number of degraded sections. The creek is severely incised in areas where fill from old road beds and a large earthen dam is perched on the creek banks. These steep fill slopes continually erode and deliver sediment directly into the creek, degrading trout habitat and water quality. This project seeks to restore the natural hydrologic function to Mitchell Creek, thus helping to improve the health of the entire Mt. Diablo Creek watershed. Mitchell Creek is extremely valuable for native wildlife, being home to listed species such as the Alameda whipsnake and California red-legged frog, as well as over 100 species of both resident and migratory birds. In addition, Mitchell Creek has supported a population of rainbow trout, which haven't been seen in the park in recent years. The 1989 Mount Diablo State Park General Plan states, "Mitchell Creek supports a small, remnant population of rainbow trout suspected of being native, and known to be the only remaining wild rainbow trout population in the Walnut Creek drainage basin. The present population in Mitchell Creek is very small, and the total population of fish probably does not exceed 500 individuals." This project is needed to remove fish passage barriers, so that the rainbow trout can return. This project is part of a watershed-wide effort with the goal of improving habitat to restore steelhead populations, improve water quality, and enhance restore habitat for all wildlife species. If this project is not implemented, then the fish passage barriers will remain in place, prohibiting rainbow trout from returning to high-quality habitat in upper Mitchell Canoyn. Fill from old roadbeds and the earthen dam will continue to erode, degrading water quality and habitat downstream. The steep creek banks along the creek at these locations will continue to be barren, since riparian vegetation has not been able to become established in these areas. If this project does not happen, one of the most significant creeks in the 20,000-acre Mt Diablo State Park will continue to be in desperate need of restoration activities.

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