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Policy Statement 421 - Floodplain Management

Approved by the Energy, Environment, and Water Policy Committee on January 22, 2018
Approved by the Public Policy Committee on May 6, 2018
Adopted by the Board of Direction on July 13, 2018


The American Society of Civil Engineers (ASCE) recommends governments at all levels to adopt proactive floodplain management policies that:

  • Hold paramount the public's safety, health, and welfare.
  • Protect and restore natural floodplains in situations where the benefit is greater than the costs.
  • Enact and enforce land use policies, ordinances and building codes that consider life safety and account for increased risk due to development or major redevelopment of communities in floodplains.
  • Inform residents and community planners of the risk associated with development in both floodplains and the upstream areas.
  • Develop flood disaster mitigation and relief plans commensurate with residual risk.
  • Develop and exercise flood disaster preparedness and evacuation plans commensurate with residual risk.
  • Support creative partnering between all levels of government to adopt floodplain management policies. 
  • Fund the design and implementation of floodplain management policies and flood mitigation projects, both structural and non-structural.
  • Incorporate the concept of building disaster resistant communities consistent with sustainable development.
  • Encourage risk appropriate, multiple-uses of flood prone areas.
  • Pursue nonstructural flood mitigation facilities, including river restoration, and wetland restoration that include improvements in habitat, ecosystems, recreation and open space use.
  • Incorporate floodplains into comprehensive watershed management programs.


Development and associated infrastructure in flood prone areas has increased rapidly as people are attracted to historically fertile floodplains and coastal areas. Compounding the quantity of property at risk, there have also been increases in the magnitude and frequency of flooding as a result of changing precipitation patterns. Even though the benefits of preserving the natural floodplains as flood storage areas and wildlife habitat have been recognized, floodplains continue to be developed and new inhabitants are subjected to periodic flooding and related devastation. People living and working in flood prone areas often have developed a false sense of security. Once a flood occurs, residents and businesses often expect government to reduce or eliminate the risk of flooding through large capital projects. These populations need the protection of an efficient floodplain management program implemented before the flood occurs. By recognizing the likelihood of future flooding and the beneficial aspects of the natural floodplain, areas can be protected and communities can become disaster resistant.

Floodplain management includes the operation of an overall program of corrective and preventive measures for reducing flood damage, including, but not limited to, emergency preparedness plans, land use policies, buy-out of flood prone structures, and flood risk reduction systems. Methods for evaluating the benefits and costs of mixed systems allow for the consideration of both tangible and intangible benefits and costs and should allow formulation of programs, including both structural and nonstructural elements, which provide the greatest return on society's investment.

It has been repeatedly demonstrated that the cost of well-planned mitigation efforts is far less than the expense of repair to damaged property. According to the National Institute of Building Sciences "Natural Hazard Mitigation Saves: 2017 Interim Report" released in January 2018, every dollar spent on mitigation translates into an average savings of $6 for the American public.


Throughout the US, significant populations and property are currently at significant risk from flooding. Much of the development, and residents at risk, occurred prior to modern floodplain development approaches and regulations. Effective floodplain management works to both mitigate the existing risk and to prevent or minimize the creation of future risk.  This requires a balanced approach to:

  • AVOID future risk through land use controls that keep people out of and property from being built in harm's way through prohibitions and required protection levels; 
  • REDUCE existing risk through structural projects such as channel improvements, levees, detention and other flood control structures or projects;
  • MITIGATE individual property risk through programs such as elevation of existing structures and demolition, and rebuilding of compliant structures; and
  • RESTORE natural floodplains and riparian zones primarily through buyouts and restoration activities.

It is the responsibility of civil engineers to provide appropriate planning to reduce risk in order to save lives and property and to educate the public on existing risks.

ASCE Policy Statement 421
First Approved in 1994