5.1B – Stream Channel Modification – Dams and Levees Construction
- Reduce erosion and, to the extent practicable, retain sediment onsite during and after construction.
- Prior to land disturbance, prepare and implement an approved erosion and sediment control (ESC) plan or similar administrative document that contains erosion and sediment control provisions.
- Develop and implement a program to manage construction activities that limit the application, generation, and migration of chemicals (including herbicides/pesticides and nutrients) and ensures the proper storage and disposal of toxic chemicals.
The construction of dams and levees has a high potential for adversely impacting the hydrology and quality of surface waters in rivers and streams as well as bordering riparian habitats. For the purposes of this management measure, dams are defined as constructed impoundments that are either (1) 25 feet or more in height and greater than 15 acre-feet in capacity, or (2) 6 feet or more in height and greater than 50 acre-feet in capacity. Levees are embankments or shaped mounds constructed for flood control or hurricane protection (USACE, 1981). Floodwalls or slurry-walls are longitudinal structures used to reduce flooding. Setback levees are levees set back a distance from the banks of a river or stream, these flood control structures can be constructed without disturbing the adjacent natural channel vegetation (riparian habitat), and cross section of the stream or river channel. Levees act like small earthen dams but are typically not subject to constant hydrostatic forces that dams are built to withstand. This is due, in part, to the changing hydraulic head behind levees, especially in California’s Mediterranean climate. Channelized rivers are typically contained between levees. Dams provide economic and societal benefits such as, hydropower, water storage, flood control, and recreational boating opportunities. However, some recreational opportunities are lost from the creation of dams, especially those reliant on wild and scenic rivers.
After dams are constructed they alter the hydrology of the watershed. Some changes to watershed hydrology can be mitigated for using appropriate management practices, however depending on the size of the dam; the riverine ecosystem is likely to be changed indefinitely as a result. The construction of new dams and their resulting impoundments, inundate stream channels and adjacent wetland and/or riparian soils and vegetation. Dams cause habitat fragmentation by impeding the mobility of spawning fish and the migration of other species. Habitat fragmentation and habitat loss from dam construction can cause some species populations to decline to the point of becoming threatened, endangered, or extinct. Dams alter stream channel-forming processes by trapping course-grained sediments and allowing only very fine grained-sediments and clays to be transported in the water column, downstream of the dam. Levees have a similar effect as dams in that they reduce the course-grained sediment inputs into the stream by preventing the stream from overtopping its banks (see MM 5.1A for more information). This loss of course-grained sediment causes a "sediment starved" stream that "eats" the sediment along its banks, often resulting in stream channel degradation. Refer to MM 5.2A, Streambank and Shoreline Erosion for more information on how to manage hydromodification effects from the construction of dams and levee-constrained rivers.
Planning and Design
- Dam siting and design needs to be done on a site-by-site basis, professional services are recommended. Two studies are used to help determine siting for a new dam, 1) a cost/benefit or economic analysis; and 2) an Environmental Impact Statement or Report through the California Environmental Quality Act process.
- Use set-back levees where appropriate. Set-back levees promote the enhancement of some riparian ecosystem functions by allowing over-bank flooding. Depending on the width of the levee set-back, some functions that can be maintained include sediment recharge and nutrient attenuation.
- Avoid driving in stream beds or constructing temporary stream crossings during construction activities. Management practices that address planning for dirt and temporary road construction activities are discussed in the Forestry land-use category, under MM 2A, Preharvest Planning.
- Management practices that address planning for paved road construction activities are discussed in the Urban land-use category, under MM 3.1B, Planning and Design of Land Disturbance and Development.
Recommended practices to control erosion and sediment include the following:
- Develop and implement an erosion and sediment control plan (ESC plan) for the dam. These plans describe how a contractor or developer will reduce soil erosion and contain and treat runoff that is carrying eroded sediments. Plans typically include descriptions and locations of soil stabilization practices, perimeter controls, and runoff treatment facilities that will be installed and maintained before and during construction activities. In addition to special area considerations, the full ESC plan review inventory should include topographic and vicinity maps, a site development plan, construction schedule, erosion and sedimentation control plan drawings, detailed drawings and specifications for practices, design calculations, and a vegetation plan. Areas with steep slopes, unstable soils, inadequate drainage, and other conditions that give rise to a high erosion potential should be avoided. If areas with high erosion potential can’t be avoided, then use measures to minimize disturbance. Changes to an ESC plan should be made based on regular inspections that determine whether the ESC practices were appropriate, properly installed, and maintained.
- Provide education and training opportunities for designers, developers, and contractors. One of the most important factors determining whether erosion and sediment controls will be properly installed and maintained on a construction site is the knowledge and experience of the contractor.
- To reduce or eliminate any runoff, schedule projects so clearing and grading are done during the time of minimum erosion potential. In California, this is the 6-month dry season from May 1 to October 31.
- Plan to use construction phasing to minimize the area of land disturbance. Construction site phasing involves disturbing only small portions of a site at a time in order to prevent erosion from dormant parts.
- Quickly, retain any sediment on-site using both structural and vegetative sediment capturing devices. Runoff should be diverted away from areas of high erosion potential, then captured and treated on-site.
- Management practices that address streambank and shoreline erosion are discussed in MM 5.2A, Managing Hydromodification Impacts, Streambank and Shoreline Erosion Control.
- Management practices that address sediment control from construction sites are discussed in MM 3.1E – Planning and Design, Land Development and 3.2D – Construction Practices, Grading/Excavation.
Practices to control chemical pollution from dam and levee construction sites include the following:
- Develop and implement a spill prevention program. Spill procedure information should be posted, and persons trained in spill handling should be onsite or on call at all times. Materials for cleaning up spills should be kept onsite and easily available. Spills should be cleaned up immediately and the contaminated material properly disposed of.
- During construction activities at dams and levees, equipment and machinery can be a potential source of pollution to the surface and ground waters. Control pollutant runoff from equipment by storing equipment away from water, sensitive habitats, and away from steep slopes.
- Establish fuel and maintenance staging areas. Proper maintenance of equipment and installation of proper stream crossings further reduces pollution of water by these sources. Vehicles need to be inspected for leaks. To prevent runoff, fuel and maintain vehicles onsite only in a bermed area or over a drip pan.
- Store, cover, and isolate construction materials such as: cement, lime, refuse, garbage, sewage, debris, oil and other petroleum products, mineral salts, industrial chemicals, and topsoil to prevent runoff of pollutants and contamination of ground water.
- Management practices that address chemical pollution control from construction sites are discussed in 3.2B – Construction Practices, Groundskeeping/Chemical Control.
- Mix, transport, load, and apply pesticides, and dispose of their containers in accordance with the label. Fertilizers should be handled and applied properly; refer to MM 1D – Agriculture, Pest and Weed Management for more information.
- 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.
- Department of Homeland Security, Federal Emergency Management Agency, National Dam Safety Program (NDSP) is a partnership of the states, federal agencies, and other stakeholders to encourage individual and community responsibility for dam safety. Established by the Water Resources and Development Act of 1996, three components include grant assistance to States, and Dam Safety research and training.
- Clean Water Act Section 401 – Certification and Wetlands 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 Website.
- 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 or 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 (USFWS) Section 7 of the Endangered Species Act directs all Federal agencies to use their existing authorities to conserve threatened and endangered species and, in consultation with the Service, to ensure that their actions do not jeopardize listed species or destroy or adversely modify critical habitat. Section 7 applies to management of Federal lands as well as other Federal actions that may affect listed species, such as Federal approval of private activities through the issuance of Federal permits, licenses, or other actions.
- Association of Engineering Geologists, Dams Technical Working Group has the responsibility of reviewing geotechnical questions relating to dam siting, construction and safety, which should be brought to the attention of the membership. The group makes recommendations to the Board for consideration, with respect to position or policy statements on dam-related matters. Committee activities include informing the membership of state-of-the-art procedures in site investigation for dams, improving public awareness of the geotechnical implications of dam safety, and providing input into local or Federal regulations as required.
- California Storm Water Quality Association, Construction Handbook: The Construction Handbook provides general guidance for selecting and implementing management practices that will eliminate or reduce the discharge of pollutants from construction sites to waters of the State. The practices for erosion and sediment control are included in Section 3 of the handbook.
- Congress via the National Dam Inspection Act (P.L. 92-367) of 1972, authorized U.S. Army Corps of Engineers (USACE) to inventory dams located in the United States. The Water Resources Development Act of 1986 (P.L 99-662) authorized USACE to maintain and periodically publish an updated National Inventory of Dams (NID). The Water Resources Development Act of 1996 (P.L. 104-303), Section 215, re-authorized periodic update of the NID by USACE, and continued a funding mechanism.
- USACE, Environmental Design of Waterways (ENDOW) is an expert system or knowledge-based computer program intended to aid planners and designers in learning about and selecting environmental features for stream channel alteration projects based on key project parameters and specific environmental goals. This program aids in environmental protection by allowing input and output for soil stabilization, levees, drainage, runoffs, water erosion, erosion resistance etc. when designing for construction projects.
- Walnut Creek Energy Park, Drainage, Erosion, and Sediment Control Plan (draft).
USACE. 1981. Low-cost shore protection, final report on the shoreline erosion control demonstration program (Section 54). U.S. Army Corps of Engineers. 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. (http://www.epa.gov/owow/nps/hydromod/index.htm)