Road systems are a significant source of sediment in streams and can be easily controlled. Erosion prevention and “storm-proofing” of road systems has immediate benefit to stream and aquatic habitats. Road storm-proofing helps ensure that the biological productivity of the watershed’s streams is not impacted by future human-caused erosion. Proper storm-proofing is accomplished by dispersing road surface drainage, protecting stream crossings from failure or diversion, and preventing failure of unstable cut-banks or fill-slopes from delivering sediment to a stream.
As roads are driven in the dry season, fine sediments accumulate on the road surface. With every rainfall that produces runoff, the road surface erodes and is carried away by the runoff. When the road surface is hydrologically connected (runoff drains directly or via ditches) to a creek, these road sediments are delivered to the stream system. In a post-fire situation it is especially important to minimize the amount of sediment being delivered to streams as this can lead to debris and mudflows.
Note: Do not perform any work within the creek bed or bank without first consulting the appropriate agencies.
Storm-proofed stream crossings
- Ensure that culvert inlet, outlet, and bottom are open and in sound condition.
- Ensure that any plastic culverts have not melted due to exposure to heat.
- Ensure that culverted stream crossings have no diversion potential (functional critical dips are in place).
- Ensure that culverted stream crossing inlets have low plug potential (single-post trash rack). You should expect streams to flow with more debris than has been previously observed.
- Ensure that bridges have stable, non-eroding abutments. Check the decking as well as the underside of wooden bridges for any significant damage.
Storm-proofed cut-banks and fill-slopes
- Monitor cut-banks and fill-slopes for slumping, rock falls, or other land sliding. These areas may become more unstable due to lack of vegetation.
- Excavated soil should be placed in locations where it will not enter a stream.
- Excavated soils should be placed where it will not cause further slope failures or landslides.
- Unstable soils may be too saturated to excavate during the rainy season so treatments may have to wait until a dryer time of year.
Road surface drainage
- All road surfaces can be storm proofed by implementing a variety of surface drainage techniques including construction of rolling dips and/or waterbars, and berm removal.
- Ditches and cut-banks can be storm proofed by frequently draining them with rolling dips or waterbars and/or ditch relief culverts. Ensure that these features do not discharge to streams or onto active (or potentially active) landslide areas.
- Monitor outflow from rolling dips, waterbars, and ditch relief culverts during the rainy season.
- Watch for gully development along the outside edge of the road throughout the rainy season. If gullies do develop, dewater them to best extent possible.
- Understanding Napa County Watersheds – Watershed-friendly Roads – Napa RCD
- After Wildfire – Road and Trail Treatments
- After Wildfire – Post-fire Treatments Comparisons Table
- Unpaved Road Storm-Proofing
- Watershed and Wallet Friendly Roads – Napa County Watershed Information and Conservation Council
See the Post-Fire Watershed Recovery Frequently Asked Questions for more information.
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