5.2A – Managing Hydromodification Impacts – Streambank and Shoreline Erosion Control
- Stabilize eroding streambanks and shorelines by using indirect or vegetative methods over structural methods.
- Protect and conserve streambank and shoreline features with the potential to attenuate polluted runoff.
- Plan and manage activities within water bodies adjacent to, or on streambanks and shorelines so that erosion is limited or eliminated.
Stream channels and associated riparian areas function to transport water, energy and sediment from upland sources within their respective watersheds to depositional basins, typically wetlands, lakes, estuaries, and oceans. Some erosion and deposition is naturally occurring and beneficial to ecosystems, however, excessively high erosion (especially of fine-grained sediments and clays) into receiving waters can increase sediment oxygen demand - depriving aquatic life of necessary dissolved oxygen; and can physically cover shellfish beds, aquatic vegetation, and riffle pools (important for native fish spawning). Depending on the geography of the site (adjacent land-use and geologic material) sediments may transport various hydrophilic nutrients and chemicals attached (sorbed) to the soil organic matter and/or cations located on the edges of clay minerals. Therefore, sedimentation causes not only physical damage to aquatic ecosystems; it also exposes aquatic life to harmful concentrations of chemicals and nutrients. Nutrients, especially phosphorus, reduce dissolved oxygen and promote algae blooms. In extreme cases this process may cause eutrophication and/or harmful algae blooms. In addition to phosphorus, sediment can also contain harmful organic chemicals sorbed to the soil organic matter. The solubility for many of these toxic chemicals is increased along with increasing temperature. Therefore, in addition to metabolic stress, increased water temperatures can also cause aquatic organisms to suffer from toxic stress.
Streambank protection and stream channel stabilization practices, including various types of revetments, grade control structures, and flow restrictors, have been effective in controlling sediment production caused by hydromodification activities. Bioengineering techniques reduce flow velocities and scour by increasing sediment deposition along the shoreline. Bioengineering includes planting vegetation that forms dense mats of flexible stems such as willow to protect or rehabilitate eroded streambanks. Streambank protection using vegetation is probably the most commonly used practice, particularly in small tributaries. Structural practices, both direct and indirect, protect or rehabilitate eroded streambanks and are usually implemented in combination to provide stability to the stream system. Indirect methods include grade control structures or hydraulic barriers installed across streams to stabilize the channel and control upstream degradation.
Vegetative methods should be used in conjunction with or over structural methods because vegetation is relatively easy to establish and maintain, is visually attractive, and is the only streambank stabilization method that can repair itself when damaged. Other advantages to using vegetative erosion control over structural control include increased pollutant attenuation and nutrient uptake capacity, habitat for fish and wildlife, and added cultural resources. Additionally, hardening the banks of streams and rivers with shoreline stabilization protection such as stone riprap revetments can accelerate the movement of surface water and pollutants from upstream, thus degrading water quality in depositional areas downstream.
Appropriate native plant species should be used preferably collected from stock within the same watershed as the revegetated site. Use the following bioengineering and other non-structural controls over structural controls to restore damaged habitat and protect shoreline and streambank erosion:
- Live staking involves the insertion and tamping of live, rootable vegetative cuttings into the ground.
- Live fascines are long bundles of branch cuttings bound together into sausage-like structures. When cut from appropriate species and properly installed, they will root and immediately begin to stabilize slopes.
- Brush layering consists of placing live branch cuttings in small benches excavated into the slope. The portions of the brush that protrude from the slope face assist in retarding runoff and reducing surface erosion.
- Brush mattressing involves digging a slight depression on the bank and creating a mat or mattress from woven wire or single strands of wire and live, freshly cut branches from sprouting trees or shrubs.
- Branch packing consists of alternating layers of live branch cuttings and compacted backfill to repair small localized slumps and holes in slopes.
- Joint planting involves planting live cuttings of rootable plant material into soil between the joints or open spaces in rocks that have previously been placed on a slope.
- Live cribwalls consist of a hollow, box-like interlocking arrangement of untreated log or timber members. The structure is filled with suitable backfill material and layers of live branch cuttings, which root inside the crib structure and extend into the slope.
Use properly designed and constructed structural controls in conjunction with bioengineering controls for shorelines and streambanks that require heavy armoring. Maintenance of structural controls is necessary to repair any damage to the structure itself and to address the effects of flanking and/or offshore profile deepening of the land surrounding the structure.
- Breakwaters are wave energy barriers designed to protect the land or nearshore area behind them from the direct assault of waves. Bulkheads and seawalls are primarily soil-retaining structures designed also to resist wave attack. Both bulkheads and seawalls may be built of many materials, including steel, timber, or aluminum sheet pile, gabions, or rubble-mound structures.
- Revetments are armored structures build to protect shorelines and streambanks from erosion. These structural erosion controls usually take the form of a stone apron installed at the base of the vertical structure or levee to reduce wave reflection and scour. Such revetment designs contain several layers of randomly shaped and randomly placed stones, protected with several layers of selected armor units or quarry stone. The armor units in the cover layer should be placed in an orderly manner to obtain good wedging and interlocking between individual stones. The cover layer may also be constructed of specially shaped concrete units. Another option is installing gabions (stone-filled wire baskets) or interlocking blocks of precast concrete along eroding banks. In addition to the surface layer of armor stone, gabions, or rigid blocks, successful revetment designs also include an underlying layer composed of either a geotextile filter fabric with gravel or a crushed stone filter and bedding layer.
- Groins are structures that are built perpendicular to the shoreline or streambank and extend into the water. Groins are generally constructed in series along the entire length of shore to be protected and are commonly referred to as a groin field. Groins trap sand in littoral drift and halt its longshore movement along beaches. The sand beach trapped by each groin acts as a protective barrier that waves can attack and erode without damaging previously unprotected upland areas.
Plan and manage activities within water bodies adjacent to, or on streambanks and shorelines so that erosion is limited or eliminated.
- Setbacks should be established to minimize disturbance of land adjacent to streambank and shorelines. Setbacks most often take the form of restrictions on the siting and construction of new standing structures along the shoreline or streambank.
- Plan and design all streambank, shoreline, and navigation structures so that they do not transfer erosion energy or otherwise cause visible loss of surrounding streambanks or shorelines.
- Many streambank or shoreline protection projects result in a transfer of energy from one area to another, which causes increased erosion in the adjacent or downstream area. Property owners should consider the possible effects of adjacent and upstream erosion control measures on other properties located along the shoreline or streambank.
- No-wake zones should be established and enforced. No-wake zones should be given preference over posted speed limits in shallow waters so that erosion potential of boat wakes on streambanks and shorelines is minimized.
- Minimize loads on top of streambanks or shorelines.
- Upland drainage from development should be directed away from bluffs and banks so as to avoid accelerating slope erosion.
Protect and conserve streambank and shoreline features with the potential to attenuate polluted runoff, refer to MM 6A – Wetlands/Riparian Areas/Vegetated Treatment Systems, Protection and Conservation for more information.
- California Tahoe Conservancy has undertaken a comprehensive program to reduce the sources of soil erosion and the amount of sediment and algae-encouraging nutrients that reach Lake Tahoe.
- Department of Boating and Waterways, Beach Erosion Control Program is dictated in beach erosion control statutes, Sections 65 through 67.3 of the Harbors and Navigation Code, which authorizes the Department to study erosion problems; act as shore protection advisor to all agencies of government; and plan, design and construct protective works when funds are provided by the Legislature.
- California Department of Fish and Wildlife (DFG) has jurisdictional authority over wetland resources associated with rivers, streams, and lakes under California Fish and Game Code sections 1600 to 1607 (City of Palo Alto, 2001). The DFG has the authority to regulate work that will substantially divert, obstruct, or change the natural flow of a river, stream, or lake; substantially change the bed, channel, or bank of a river, stream, or lake; or use material from a streambed. Typical activities regulated by DFG under sections 1600–1607 authority include rechanneling and diverting streams, stabilizing banks, implementing flood control projects, river and stream crossings, diverting water, damming streams, gravel mining, and logging operations. The DFG requires completion of a Streambed Alteration Agreement, which is a mutual agreement between the DFG and the project proponent. After the Department receives a complete notification package, it will determine whether you will need a Lake or Streambed Alteration Agreement for your activity. An agreement will be required if the activity could substantially adversely affect an existing fish and wildlife resource. If an agreement is required, the Department will conduct an onsite inspection, if necessary, and submit a draft agreement to you. The draft agreement will include measures to protect fish and wildlife resources while conducting the project. If you are applying for a regular agreement, the Department will submit a draft agreement to you within 60 calendar days after your notification is complete. The 60-daytime period will not begin until your notification is complete. The 60-day time period does not apply to notifications for long-term agreements.
- California Environmental Resources Evaluation System (CERES) is an information system developed by the California Resources Agency to facilitate access to a variety of electronic data describing California’s rich and diverse environments. The goal of CERES is to improve environmental analysis and planning by integrating natural and cultural resource information from multiple contributors and by making it available and useful to a wide variety of users.
- CALFED Bay-Delta Program aims to improve the quality and reliability of California’s water supplies and revive the San Francisco Bay-Delta ecosystem. Its Web site contains information about water supply, water quality, and ecosystem restoration.
- Clean Water Act Section 401 Certification Program administered by Regional Water Quality Control Boards (RWQCBs), review projects that require a federal permit under CWA section 404 or that involve dredge or fill activities that may result in a discharge to waters of the United States. This is to ensure that the State’s interests are protected on any federally permitted activity occurring in or adjacent to waters of the State. Detailed information about CWA section 401 in California, including a description of the program, resources, legal background information, proposed projects, and links, are described on the SWRCB Web site.
- US Army Corps of Engineers 404 Permitting Program, Sacramento District / Regulatory Program administers and enforces Section 10 of the Rivers and Harbors Act of 1899 and Section 404 of the Clean Water Act. Under Section 10, a Corps permit is required for work on structures in, over or under navigable waters of the United States. Under Section 404, a Corps permit is required for the discharge of dredged or fill material into waters of the United States. Many waterbodies and wetlands in the nation are waters of the United States and are subject to the Corps' Section 404 regulatory authority.
- US Fish and Wildlife Service, National Fish Passage Program uses a voluntary, non-regulatory approach to remove and bypass barriers. The Program addresses the problem of fish barriers on a national level, working with local communities and partner agencies to restore natural flows and fish migration. The Program is administered by National and Regional Coordinators, and delivered by Fish and Wildlife Management Assistance Offices, with their 300 biologists located across the Nation.
- California Coastal Commission, Beach Erosion and Response Document The Beach Erosion and Response Guidance Document, or BEAR, is now available by request from the California Coastal Commission. This document provides general information about types of shorelines and seawalls, as well as guidance for analyzing shoreline activities. To receive a copy, call the Technical Services Unit in the Headquarters Office (Telephone: 415-904-5240).
- Resources Agency of California, Draft Policy on Coastal Erosion Planning and Response and Background Material. The draft policy on coastal erosion planning and response focuses on responding to erosion at the coastline with actions that will cause the least environmental damage, while protecting existing coastal infrastructure. The draft policy outlines a tiered approach that proposes the following broad policy goals: (1) increasing sand supply to the coast; (2) avoiding the construction of new structures in hazardous areas; (3) if structures are threatened, considering the feasibility of re-locating them; (4) using beach nourishment (placing sand on or near eroding beaches) as the first priority for stabilizing beaches, if feasible; (5) using hard protective structures (seawalls, revetments, breakwaters, etc) only if other less environmentally damaging alternatives are deemed infeasible. The draft policy and background material .
- USDA Forest Service FS-683 guide - A Soil Bioengineering Guide for Streambank and Lakeshore Stabilization, provides information on how to successfully plan and implement a soil bioengineering project, including the application of soil bioengineering techniques. Basic principles and background information on ecology and the stream dynamics needed before attempting a restoration project are also presented.
- Washington State Dept. of Transportation, M 23-03.01, 2007. Hydraulics Manual, Chapter 4 provides information on calculating flow rates or channel velocities.
Federal Interagency Stream Restoration Working Group (FISRWG). 1998. Stream Corridor Restoration: Principles, Processes, and Practices. PB98-158348LUW. Federal Interagency Stream Restoration Working Group, Washington, DC.
USEPA. 2007. National Management Measures Guidance to Control Nonpoint Source Pollution from Hydromodification. EPA 841-B-07-002. U.S. Environmental Protection Agency, Washington, DC.