The County's stream restoration program uses a variety of techniques to stabilize stream banks, reestablish aquatic ecosystems and habitat for fish and aquatic life, and prevent erosion and sediment pollution of streams and watersheds.
In areas where the stream is set away from urban property lines, natural materials and "soft" techniques are used. Soft techniques include the use of natural materials such as rocks, logs, and native vegetation to:
Reduce pressure on eroded banks
Prevent down-cutting of the streambed
Restore the natural meander pattern found in stable streams (such as an S-curve or a sine curve)
Long-term protection is provided by reforestation of the stream buffer zone around the stream or river.
In areas where the stream is closer to the street and in dense urban areas, "hard" solutions such as riprap and rock walls can be used to protect and reinforce stream banks.
"Soft" Stream Restoration Techniques
Stone toe protection: Stone installed at the base of the stream bank protects it from heavy storm flows and prevents erosive flows from undermining the base of the stream bank.
J-hook: Rock is placed in streams in the shape of a J to channel the flow of water away from eroding stream banks. The hook or curved tip of the J has slots that allow fast-flowing water through to dissipate energy and form scour pools, which add habitat.
Cross vane: Lines of stone are carefully positioned at an angle to help turn the flow of water toward the center of the stream. These vanes help to keep fast-flowing water away from the banks to prevent erosion and maintain the streambed elevation.
Grading and planting: Steep stream banks are graded into a series of gently sloping steps. During high-flow events, the stream has a channel with a wider fit and more surface to spread out along the mini-floodplains. Plants and vegetation roots help to stabilize the banks and hold them in place.
Log vane: Logs are placed and anchored to divert stream flow away from eroding stream banks toward the center of the stream. The concentrated stream current forms scour pools below the vane, adding pool habitat. Vanes can also be constructed with rock.
Step pools: Rocks are placed in front of storm drain outfalls to form a step pool system that dissipates the energy of high-velocity stormwater runoff before it enters the stream. Step pools allow stream flow to lose erosive energy by gradually lowering the elevation of the stream in a series of steps.
Brush layering: Layers of live branch cuttings are installed horizontally. These cuttings sprout new plants, which then stabilize eroded stream bank slopes.
Root wads: Tree trunks with attached roots are anchored in stream banks to provide cover for fish, amphibians, and aquatic insects. The tangled root mass slows the flow of the stream, armors the bank, deflects energy away from the bank, and forms scour pools, providing habitat for aquatic organisms.
Woody debris: Woody debris includes logs and woody material, which can be used to provide spaces where fish can live and reproduce. Large tree limbs and woody materials are anchored along stream banks to reduce erosion and to buttress terraces and pools.
Mulch planting: Lengths of stream bank are planted with vegetation to stabilize the banks and hold sediment in place through the roots of the plant.
Shallow wetlands: Creation of a shallow wetland below a local storm drain allows water quality treatment through infiltration, nutrient uptake, and limited detention. Shallow wetlands also provide habitat for balanced aquatic plant and animal communities.
Coir logs: Made from biodegradable coconut fibers, coir logs provide a medium for vegetation, protecting less erosive stream reaches by holding the bank in place and trapping eroding material.
Rock pack and flush cut: Stream bank trees seriously undercut by erosive storm flows can be protected with supportive rock packing. If undercut too far, they can be flush cut, which allows the roots to remain in the bank for stabilization and erosion protection.
Imbricated Riprap: Overlapping stones help protect stream banks from erosion or potential failure. Riprap is typically used along stream reaches where eroding stream banks threaten private property or public infrastructure, or where the stream is highly confined and subject to particularly erosive storm flows.
Three major methods used to restore our local streams and prevent urban stormwater from blowing out stream channels are presented by Mark Wilcox, Stream Restoration Engineer. Double click the image above to launch a bigger view.
