3.1B – Planning and Design – Flood Control
Management Measure
- Limit, reduce and/or mitigate for impervious surfaces throughout the watershed.
- Conserve and protect areas for groundwater recharge. Utilize conjunctive management to enhance groundwater storage: in some instances, diversions of surface water for groundwater infiltration could enhance flood management by reducing peak flows.
- Limit or restrict development of impervious surfaces and urban infrastructure within FEMA certified 100-year floodplains and areas adjacent to streams.
- Promote groundwater recharge and pollutant attenuation by removing concrete flood-control channels and exposing the underlying native sediment.
Traditional urban flood control focused on constructing networks of concrete conveyance channels that funnel and transfer urban stormwater runoff into the closest receiving waterbody, i.e. bays, ocean, rivers and lakes. Traditional urban flood control structural water quality management practices (MPs) include detention basins and other devices used to store volumes of runoff in order to reduce peak flows. Unless flood detention basins are highly engineered to provide adequate flow duration control they 1) do not adequately protect receiving waters from accelerated channel bed and bank erosion (Goldman and others, 1986), 2) do not address post-development increases in runoff flow rates, and 3) do not mitigate for the decline in benthic macroinvertebrate communities in the receiving waters (Dunne and Leopold, 1978). Horner and others (2006) suggest that structural MPs are not as effective in protecting aquatic communities as a continuous riparian buffer of native vegetation is.
Alternative methods of urban flood control include land-use zoning and planning tools such as: flood-proofing structures within the floodplain; prohibiting or restricting development of homes and other infrastructure in areas prone to flooding (such as FEMA certified 100-year floodplains and/or areas adjacent to streams); and reducing impervious surfaces throughout the watershed. Other alternative methods to reduce urban flooding include: flooding groundwater recharge areas within the watershed thereby reducing peak storm volumes; and utilizing low impact development throughout the watershed.
Management Practices
- Refer to MM 5.1A - Stream Channel Modification, Channelization/Channel Modification for more information on relevant management practices relating to channelizing streams for urban flood control purposes.
- Refer to MM 5.2B - Stream Channel Modification, Flow and Temperature for more information on relevant management practices relating to modeling and managing flow and temperature in urban streams and flood control channels.
- Limit and reduce the amount of impervious areas throughout the watershed. Refer to MM 3.1C – Planning and Design, Impervious Surfaces for relevant management practices.
- Conserve and protect areas such as floodplains for groundwater recharge. Refer to MM 1G - Groundwater Protection for related management practices. Seasonal inundation of floodplains can provide essential habitat for plants and animals, including those dependent on periodic floods. Use conjunctive management and/or restrict development of impervious surfaces and other urban infrastructure in areas prone to flooding.
- Promote the conservation, enhancement, and protection of adequately sized natural buffer areas surrounding streams and rivers. Refer to MM 6, Wetlands, Riparian Areas, and Vegetated Treatment Systems for more information on relevant management practices.
- Utilize natural soil processes and phytoremediation to attenuate pollutants commonly found in polluted runoff from urban areas e.g. sediment (turbidity), nutrients, oil & grease, and metals. Refer to MM 6C - Vegetated Treatment Systems for more information on relevant management practices.
- Utilize diffuse low impact development technologies throughout the watershed in order to reduce peak discharge rates. Refer to MM 5.2C – Hydromodification, Low Impact Development.
Programs
- Department of Water Resources (DWR) FloodSAFE has five main goals, 1) to increase flood protection, 2) to improve preparedness and response to flooding, 3) to support a growing economy, 4) to enhance ecosystems, and 5) to promote sustainability. This program is funded by Propositions 1E and 84.
- Federal Emergency Management Agency (FEMA) is part of the U.S. Department of Homeland Security (DHS). The primary mission of FEMA is to reduce the loss of life and property and protect the Nation from all hazards, including natural disasters, acts of terrorism, and other man-made disasters, by leading and supporting the Nation in a risk-based, comprehensive emergency management system of preparedness, protection, response, recovery, and mitigation. FEMA certifies maps designating 100- and 200-year floodplains.
- US Army Corps of Engineers (USACE), Water Resources is overseen by the Directorate of Civil Works. Funds for the Civil Works program come from the annual Energy and Water Development Appropriation, not the Defense budget, many projects also receive cost-sharing funds supplied directly by non-Federal sponsors for specific projects. Activities that are funded include projects relating to improving and maintaining navigable waterways, flood damage reduction, hydroelectric power generation, shore protection and recreation.
Information Resources
- Fresno Metropolitan Flood Control District provides flood control and urban storm water services in a 400-square mile watershed located between the Kings and San Joaquin Rivers. The District is home to 700,000 people and includes both urban and agricultural land uses. Governed by a seven-member board, the District provides: Flood control, Urban drainage, Groundwater Resource Management, and Recreation Opportunities and Open Space.
- Sacramento Area Flood Control Agency (SAFCA) was formed in 1989 to address the Sacramento area’s vulnerability to catastrophic flooding. This vulnerability was exposed during the record flood of 1986 when Folsom Dam exceeded its normal flood control storage capacity and several area levees nearly collapsed under the strain of the storm. In response, the City of Sacramento, the County of Sacramento, the County of Sutter, the American River Flood Control District, and Reclamation District 1000 created SAFCA through a Joint Exercise of Powers Agreement to provide the Sacramento region with increased flood protection along the American and Sacramento Rivers.
- BASMAA, Best Management Practices (BMP) for Routine Flood Control Maintenance Activities, is a desk reference that describes and illustrates appropriate flood control BMPs.
- UC Berkeley, Water Resources Center Archives, California Water Districts and Associations.
Urban Stream Restoration and Buffers
- Stormwater Manager’s Resource Center provides resources for those involved in local storm water management. These resources include several resources pertaining to aquatic buffers and restoration practices.
- Urban Creeks Council of California works to protect and restore waterways in urban areas through shoreline stabilization, the establishment and protection of buffers and riparian zones, and educational programs for the general public.
- A.L. Riley, Urban Stream Restoration: A Video Tour of Ecological Restoration Techniques, is a documentary tour of six urban stream restoration sites. It provides background information on funding, community involvement, and the history and principles of restoration. The demonstration includes examples of stream restoration in very urbanized areas, re-creating stream shapes and meanders, creek daylighting, soil bioengineering, and ecological flood control projects.
- California Department of Water Resources, Planning and Local Assistance, Urban Stream Restoration Program provides funding for projects to assist communities in reducing damages from streambank and watershed instability and floods while restoring the environmental and aesthetic values of streams. The Web site offers an overview of past projects funded by the program as well as guidelines for project proposals.
- Federal Interagency Stream Restoration Working Group, Stream Corridor Restoration provides background information on stream corridors, the development of stream corridor restoration plans, and details on restoration practices.
- USDA NRCS, Buffer Strips: Common Sense Conservation provides background information on the benefits of buffers, technical guidance, and examples of successful buffer implementation.
- USDA NRCS, Watershed Technology Electronic Catalog is a source of technical guidance on a variety of restoration techniques and management practices, to provide direction for watershed managers and restoration practitioners. The site is focused on providing images and conceptual diagrams.
- USEPA, Model Ordinance for Coastal Buffers can serve as a guide for municipalities looking to establish stream buffers to protect coastal resources.
References:
Dunne, T and L.B. Leopold. 1978. Water in Environmental Planning. San Francisco W.H. Freeman and Company
Goldman S.J., K. Jackson, and T.A. Bursztynsky. 1986. Erosion and Sediment Control Handbook. McGraw Hill. San Francisco.
Horner, R.R. 2006. Investigation of the Feasibility and Benefits of Low-Impact Site Design Practices (LID) for the San Diego Region. Available at: http://www.projectcleanwater.org/pdf/permit/case-study_lid.pdf