Flooding Strategies

  • Use Bioretention to collect stormwater runoff
    • Bioretention is an adapted landscape feature that provides onsite storage and infiltration of collected stormwater runoff. Stormwater runoff is directed from surfaces to a shallow depression that allows runoff to pond prior to infiltration in an area that is planted with water-tolerant vegetation. As runoff accumulates, it will pond and slowly travel through a filter bed where it either infiltrates into the ground or is discharged via an underdrain. Small-scale bioretention areas are often referred to as rain gardens.
  • Use a blue roof to hold precipitation after a storm event and discharge it at a controlled rate
    • A blue roof is designed to hold up to eight inches of precipitation on its surface or in engineered trays. It is comparable to a vegetated roof without soil or vegetation. After a storm event, precipitation is stored on the roof and discharged at a controlled rate. Blue roofs greatly decrease the peak discharge of runoff and also allow water to evaporate into the air prior to being discharged. Precipitation discharge is controlled on a blue roof through a flow restriction device around a roof drain. The water can either be slowly released to a storm sewer system or to another green infrastructure practice such as a cistern or bioretention area.
  • Use permeable pavement to allow runoff to flow through and be temporarily stored prior to discharge
    • Permeable pavement includes both pavements and pavers with void space that allow runoff to flow through the pavement. Once runoff flows through the pavement, it is temporarily stored in an underground stone base prior to infiltrating into the ground or discharging from an underdrain. Permeable pavers are highly effective at removing heavy metals, oils, and grease in runoff. Permeable pavement also removes nutrients such as phosphorous and nitrogen. Soil and engineered media filter pollutants as the runoff infiltrates through the porous surface. The void spaces in permeable pavement surfaces and reservoir layers provide storage capacity for runoff. All permeable pavement systems reduce runoff peak volume.
  • Use underground storage systems to detain runoff in underground receptacles
    • Underground storage systems vary greatly in design. They detain runoff in underground receptacles that slowly release runoff. Often the underground receptacles are culverts, engineered stormwater detention vaults or perforated pipes. One of the benefits of underground storage is that it does not take up additional surface area and can be implemented beneath roadways, parking lots, or athletic fields. Underground storage systems are typically designed to store large volumes of runoff and therefore can have a significant impact in reducing flooding and peak discharges.
  • Use a stormwater tree trench to store and filter stormwater runoff
    • A stormwater tree trench is a row of trees that is connected by an underground infiltration structure. At the ground level, trees planted in a tree trench do not look different than any other planted tree. Underneath the sidewalk, the trees sit in a trench that is engineered with layers of gravel and soil that store and filter stormwater runoff. Stormwater tree trenches provide both water quality and runoff reduction benefits.
  • Use a retention pond to manage stormwater
    • A retention pond is one of the earliest prototypes of green infrastructure and is now considered a more traditional type of stormwater infrastructure because it has been integrated into gray infrastructure design. It is an engineered stormwater basin designed to store runoff and release it at a controlled rate while maintaining a level of ponded water. Pollutants and sediment loads are reduced as the runoff is retained in the basin. Retention ponds are a very common stormwater management practice and may be designed with sustainable elements to increase water quality and decrease peak discharges. Vegetated forebays may be added to increase sediment removal as well as provide habitat. Another enhancement to traditional stormwater retention ponds is the addition of an iron-enhanced sand filter bench that removes dissolved substances such as phosphorus from runoff.
  • Use extended detention wetlands to reduce flood risk and provide water quality and ecological benefits
    • Extended detention wetlands may be designed as a flood mitigation strategy that also provides water quality and ecological benefits. Extended detention wetlands can require large land areas, but come with significant flood storage benefits. Extended detention wetlands can be created, restored (from previously filled wetlands) or enhanced existing wetlands. Wetlands typically store floodwater during a storm and release it slowly, thereby reducing peak flows. An extended detention wetland allows water to remain in the wetland area for an extended period of time, which provides increased flood storage as well as water quality benefits. Extended detention wetlands are distinct from the preservation of existing wetlands, but the two practices often are considered together as part of a watershed-based strategy.

  • Assess whether green infrastructure could be included as a control measure in Municipal Separate Storm Sewer Systems (MS4s)
    • Municipal Separate Storm Sewer Systems (MS4s) transport stormwater runoff that is often discharged into water bodies. Since 1999, even small MS4s within and outside urbanized areas have been required to obtain National Pollutant Discharge Elimination System permit coverage. Jurisdictions with MS4s can include green infrastructure as a control measure. USEPA published a factsheet that discusses how green infrastructure can be integrated into stormwater permits and provides examples of communities that have done so.
  • Consider offering incentives for green infrastructure to manage stormwater
    • Consider incentives such as fast-track permitting for projects that adhere to a stricter set of requirements (e.g., projects that manage 80% of runoff onsite or incorporate a green roof).
  • Consider regulatory changes at the federal or state level
    • Consider regulatory changes at the federal or state level to minimize variance regarding stormwater infrastructure guidance and regulations among communities.
  • Convene stakeholders from across the watershed to address barriers
    • Bringing together relevant agencies, organizations and individuals responsible for stormwater management decisions from across watersheds can help address barriers presented by different regulations, budget limitations and expectations for growth. Representatives of water management, environmental, land use planning, public works, and transportation departments (among others) are important to include because each of these agencies plays a role in stormwater management.
  • Coordinate across federal, state, local and tribal agencies
    • Engage the full suite of agencies and departments, particularly at the federal level, that affect or could be affected by solutions to address changing climate conditions in stormwater management. Consider involving, for example, FEMA, the Army Corps of Engineers, Departments of Transportation, Parks and Recreation and State Departments of Ecology or Natural Resources. Also encourage a "no wrong door policy" (i.e., that data and information are shared across web portals and resources are shared across agencies). Seven federal agencies have come together with nongovernmental organizations and private-sector entities to support the Green Infrastructure Collaborative, a network to help communities more easily implement green infrastructure.
  • Coordinate regional policies to minimize the impact on individual communities
    • While development may be deterred when individual communities change local standards independently, potentially negative impacts could be avoided if surrounding municipalities agree to adopt similar policies.
  • Develop a methodology and schedule for maintenance that includes details about who is responsible for maintenance and new protocols
    • Establish this protocol early in the project planning phase to avoid future confusion or mismanagement. For example, Washington, DC's Stormwater Management Guidebook (CWP, 2013), provides for a stormwater retention credit program for certification. To be eligible for certification, a best management practice must, among other criteria, provide a contract or agreement for ongoing maintenance and pass ongoing maintenance inspections.
  • Find ways that the state or county can provide incentives to Incorporate green infrastructure and Low Impact Development into existing plans
    • Find ways that the state or county can provide incentives for regions to develop watershed-scale plans.
  • Incorporate green infrastructure and Low Impact Development into existing plans
  • Look for opportunities to develop a regional or watershed-scale plan for stormwater management
    • This may be more cost effective than developing individual plans.
  • Provide individual homeowners and businesses with information about how to correctly maintain green infrastructure design elements
    • Some examples are rain gardens, vegetated swales, and other installations. This may also entail offering financial incentives in places where individual homeowners are responsible for installation and maintenance, to help individuals pay for the maintenance of this public good.
  • Request modifications to reporting requirements
    • Request modifications (e.g., MS4, others) so that schedules are complementary to efforts and the same/complimentary goals are being targeted for different projects. Also, seek schedule variances for some reporting requirements (e.g., MS4, others), as needed, within a given community.
  • Seek opportunities to incorporate climate change adaptation measures into existing plans
    • Examples may include comprehensive plans or watershed-scale plans. Determine the level of plan that may be the best scale at which to address climate change.
  • Use pilot projects

  • Build flood barriers to protect infrastructure
  • Build infrastructure needed for aquifer storage and recovery
    • Increasing the amount of groundwater storage available promotes recharge when surface water flows are in excess of demand, thus increasing climate resilience for seasonal or extended periods of drought, and taking advantage of seasonal variations in surface water runoff. Depending on whether natural or artificial aquifer recharge is employed, the required infrastructure may include percolation basins and injection wells.
  • Plan and establish alternative or on-site power supply
    • Water utilities are one of the major consumers of electricity in the United States. With future electricity demand forecasted to grow, localized energy shortages may occur. The development of "off-grid" sources can be a good hedging strategy for electricity shortfalls. Moreover, a redundant power supply can provide resiliency for situations in which natural disasters cause power outages. On-site sources can include solar, wind, inline microturbines and biogas (i.e., methane from wastewater treatment). New and back-up electrical equipment should be located above potential flood levels.
  • Relocate facilities to higher elevations

  • Design new coastal drainage system
  • Develop adaptive stormwater management practices (e.g., remove impervious surfaces, replace undersized culverts)
  • Plug drainage canals

  • Conduct extreme precipitation events analyses
    • An increase in the magnitude or frequency of extreme events can severely challenge water utility systems that were not designed to withstand intense events. Extreme event analyses or modeling can help develop a better understanding of the risks and consequences associated with these types of events.
  • Develop models to understand potential water quality changes
  • Model and monitor groundwater conditions
    • Understanding and modeling groundwater conditions will inform aquifer management and projected water quantity and quality changes. Monitoring data for aquifer water level, changes in chemistry and detection of saltwater intrusion can be incorporated into models to predict future supply. Climate change may lead to diminished groundwater recharge in some areas because of reduced precipitation and decreased runoff.
  • Model and reduce inflow/infiltration in the sewer system
    • More extreme storm events will increase the amount of wet weather infiltration and inflow into sanitary and combined sewers. Sewer models can estimate the impact of those increased wet weather flows on wastewater collection systems and treatment plant capacity and operations. Potential system modifications to reduce those impacts include infiltration reduction measures, additional collection system capacity, offline storage or additional peak wet weather treatment capacity.

  • Acquire and manage ecosystems
    • Intact natural ecosystems have many benefits for utilities: reducing sediment and nutrient inputs into source water bodies, regulating runoff and streamflow, buffering against flooding and reducing storm surge impacts and inundation on the coasts (e.g., mangroves, saltwater marshes, wetlands). Utilities can also work with regional floodplain managers and appropriate stakeholders to explore non-structural flood management techniques in the watershed. Protecting, acquiring and managing ecosystems in buffer zones along rivers, lakes, reservoirs, and coasts can be cost-effective measures for flood control and water quality management.
  • Implement green infrastructure on site and in municipalities
  • Implement watershed management
    • Watershed management includes a range of policy and technical measures. These generally focus on preserving or restoring vegetated land cover in a watershed and managing stormwater runoff. These changes help mimic natural watershed hydrology, increasing groundwater recharge, reducing runoff and improving the quality of runoff.
  • Integrate flood management and modeling into land use planning
    • It is critical that future water utility infrastructure is planned and built in consideration of future flood risks. Infrastructure can be built in areas that do not have a high risk of future flooding. Alternately, appropriate flood management plans can be implemented that involve 'soft' adaptation measures such as conserving natural ecosystems or 'hard' measures such as dikes and flood walls.
  • Study response of nearby wetlands to storm surge events
    • Coastal wetlands act as buffers to storm surges. Protecting and understanding the ability of existing wetlands to provide protection for coastal infrastructure in the future is important considering projected sea-level rise and possible changes in storm severity.

  • Monitor current weather conditions
    • A better understanding of weather conditions provides a utility with the ability to recognize possible changes in climate change and then identify the subsequent need to alter current operations to ensure resilient supply and services. Observations of precipitation, temperature and storm events are particularly important for improving models of projected water quality and quantity.
  • Monitor flood events and drivers
    • Understanding and modeling the conditions that result in flooding is an important part of projecting how climate change may drive change in future flood occurrences. Monitoring data for sea level, precipitation, temperature, and runoff can be incorporated into flood models to improve predictions. Current flood magnitude and frequency of storm events represent a baseline for considering potential future flood conditions.

  • Adopt insurance mechanisms and other financial instruments
    • Adequate insurance can insulate utilities from financial losses due to extreme weather events, helping to maintain financial sustainability of utility operations.
  • Conduct climate change impacts and adaptation training
    • An important step in developing an adaptation program is educating staff on climate change. Staff should have a basic understanding of the projected range of changes in temperature and precipitation, the increase in the frequency and magnitude of extreme weather events for their region and how these changes may affect the utility's assets and operations. Preparedness from this training can improve utility management under current climate conditions as well.
  • Develop coastal restoration plans
    • Coastal restoration plans may protect water utility infrastructure from damaging storm surge by increasing the protective habitat of coastal ecosystems such as mangroves and wetlands. Restoration plans should consider the impacts of sea-level rise and development on future ecosystem distribution. Successful strategies may also consider rolling easements and other measures identified by USEPA's Climate Ready Estuaries program.
  • Develop emergency response plans
    • Emergency response plans (ERPs) outline activities and procedures for utilities to follow in case of an incident, from preparation to recovery. Some of the extreme events considered in ERPs may change in their frequency or magnitude due to changes in climate, which may require making changes to these plans to capture a wider range of possible events.
  • Develop energy management plans for key facilities
    • Energy management plans identify the most critical systems in a facility, provide backup power sources for those systems and evaluate options to reduce power consumption by upgrading to more efficient equipment. Utilities may develop plans to produce energy, reduce use and work toward net-zero goals.
  • Establish mutual aid agreements with neighboring utilities
    • Beyond the establishment of water trading in times of water shortages or service disruptions, these agreements involve the sharing of personnel and resources in times of emergency (e.g., natural disasters).
  • Identify and protect vulnerable facilities
    • Operational measures to isolate and protect the most vulnerable systems or assets at a utility should be considered. For example, critical pump stations would include those serving a large population and those located in a flood zone. The protection of these assets would then be prioritized based on the likelihood of flood damage and the consequence of service disruption.
  • Integrate climate-related risks into capital improvement plans
  • Participate in community planning and regional collaborations
    • Effective adaptation planning requires the cooperation and involvement of the community. Water utilities will benefit by engaging in climate change planning efforts with local and regional governments, electric utilities and other local organizations.

  • Incorporate consideration of climate change impacts into planning for new infrastructure (e.g., homes, businesses)

  • Adopt more stringent policies
    • Adopt more stringent policies such as stormwater fees and requirements for developers to manage water onsite to the maximum extent feasible. Similarly, requiring developers to make decisions informed by future climate, and local governments to incorporate climate change into decision-making processes.
  • Build awareness and knowledge via climate change and stormwater management curriculum
    • On-the-job training and continuing education opportunities, which can help to increase the climate literacy of existing staff and ensure the timely application of research designed to address decision-maker needs. Also, use educational projects in schools or at community centers as opportunities to disseminate climate change information to the public.
  • Collaborate with community groups
    • Collaboration through activities such as tree planting or installing rain gardens can be an effective adaptation measure. In all work with individuals and community groups, be sensitive to hot button topics that may distract from the purpose of the conversation and the issues that the work intends to address. For example, if climate change is a highly political issue, it may be useful to steer the conversation towards observed and projected changes for specific endpoints of concern (e.g., changes in 25-year storm event or the intensity of brief downpours) or green infrastructure's co-benefits to a community's livability and economic vitality. Focusing on issues of vulnerability and future weather changes can help to move discussions forward and avoid some of the potential barriers that arise when using the term "climate change."
  • Create opportunities for staff to exchange experiences and ideas for programs
    • Some examples are interdepartmental meetings, workshops, webinars, online forums. Ensure that senior management is on-board and that the administrative and fiscal mechanisms of the city enable interdepartmental collaboration.
  • Developers can demonstrate attractive, cost-effective, marketable solutions
    • If the market offers innovative stormwater solutions or climate resilient developments that are attractive and effective, the public will more likely favor these best available options. A developer-driven solution may be most effective in an area that is rapidly changing. For instance, the recently developed Celebrate Senior Center in Fredericksburg, Virginia, is using 65 bioretention areas and 15 water quality swales to treat 43 acres of manicured landscape. Stafford County anticipates that this project will demonstrate that green infrastructure solutions can offer amenities that increase the value of the landscape while managing stormwater onsite.
  • Engage in existing peer-to-peer networks
  • Showcase green infrastructure climate adaptation projects
  • Take advantage of existing resources that promote information sharing
    • USEPA, as well as NOAA and other federal agencies, provide tools, guides, and case studies of green infrastructure projects conducted with a large number of communities across the country.

  • Implement policies and procedures for post-flood and/or post-fire repairs
    • Post-disaster policies should minimize service disruption due to damaged infrastructure. These contingency plans should be incorporated into other planning efforts and updated regularly to remain consistent with any changes in utility services or assets.
  • Implement saltwater intrusion barriers and aquifer recharge
  • Improve pumps for backflow prevention
  • Increase capacity for wastewater and stormwater collection and treatment
    • Precipitation variability will increase in many areas. Even in areas where precipitation and runoff may decrease on average, the distribution of rainfall patterns (i.e., intensity and duration) can change in ways that impact water infrastructure. In particular, more extreme storms may overwhelm combined wastewater and stormwater systems.
  • Increase treatment capabilities
    • Existing water treatment systems may be inadequate to process water of significantly reduced quality. Significant improvement to existing treatment processes or implementation of additional treatment technologies may be necessary to ensure that quality of water supply (or effluent) continues to meet standards as climate change impacts source or receiving water quality.

  • Address the likely need to facilitate a change in thinking to enable action in the face of uncertainties that have not been traditionally considered in decision making but now should be
    • There will likely never be a tool to predict storm events with precision. Communities will need to develop new ways of thinking and planning, such as analyzing decisions by their robustness over a range of potential changes, employing risk management techniques, using principles that maximize minimum losses or minimize maximum losses and other approaches for decision making under uncertainty.
  • Assemble existing data sets with information such as historic land use, planned development, topography, and location of floodplains
    • They are often sufficient to support a near-term conversation about how stormwater management may need to change to accommodate changes in climate. Land use has a tremendous effect on climate change impacts on stormwater management; managers can incorporate land use change maps into planning discussions. USEPA's Integrated Climate and Land Use Scenarios (ICLUS) project can serve as a resource. Consider updates to data management practices to facilitate use of the best and most recent data.
  • Communicate the overlap of "short-term" infrastructure lifetimes with longer-term climate changes
  • Consider how current design standards are formulated a starting point to the discussion
    • Rather than starting a conversation with a discussion of climate change projections, understand the current design standard for stormwater management. Then, engage decision makers to seek agreement on a threshold (e.g., the community will prepare for X storm) that is informed by historical data and reflects the risk tolerance of the community (e.g., what level of damage or disruption the community can tolerate at different costs). This also entails understanding the current design standard and whether performance can be enhanced for projects in the region.
  • Demonstrate the use of dynamical downscaling on research projects at the site scale
    • Decision makers can use local resources for climate change data from researchers at organizations within the area, such as universities, state meteorological agencies and other organizations that may be involved in downscaling of climate change scenarios.
  • Develop a "wish-list" of data that should be collected to improve understanding of climate changes
    • Stormwater managers and geographic information system (GIS) staff can begin to collect this needed local data (e.g., establish and maintain more local weather gauges and monitoring stations). Partners in the community or neighboring jurisdictions may also be interested in pooling resources to develop or improve data sets.
  • Develop regional scenarios
    • These scenarios (complete with uncertainty bounds) can be used by communities across a region, minimizing the need for individual communities to spend limited resources to determine which climate model results are appropriate to their planning needs (see SFWMD, 2011 for example of regional climate and sea level rise scenarios produced for south Florida counties and municipalities by the South Florida Water Management District).
  • Expand staff expertise in GIS or other data management processes
    • Via training, new hires or sharing of staff across the county or a group of municipalities.
  • Mine existing data sources to ensure that decisions are based on the best available data
    • Local decision makers are often working with old data. Simply updating storm standards to match current precipitation patterns can result in a marked improvement. Accurate historical climate information can help serve as a bridge to discussions regarding future climate projections (which are less certain and may be less readily received by skeptical planners and decision makers).
  • Routinely re-evaluate the accuracy of land use maps
    • Re-evaluating the accuracy of land use maps, especially in areas experiencing rapid development, can ensure the best available data about the extent and location of impervious surfaces is used.
  • Seek partnerships that can contribute to the field of knowledge
    • For example, the U.S. Army Corps of Engineers has been helping communities better understand hydrologic modeling (U.S. ACE, 2015) and Federal Emergency Management Agency (FEMA) helps with preparedness planning for extreme events (FEMA, 2015). Communities can work with universities to make sure that research is applicable to local needs. Such partnerships can be fruitful when there are several crucial players working with the data to identify solutions (check local university websites for potential resources and partnering opportunities).
  • Use land use build-out models to understand the maximum allowable use
  • Use land use build-out models to understand the maximum likely development in a region
  • Use resources to show historical and future trend lines
    • To understand future climate changes, techniques that use historical data, such as analogue events or other sensitivity and threshold information in the historical record, can be used as illustrations (e.g., see the Intergovernmental Panel on Climate Change report, Climate Change 2001: Working Group II: Impacts, Adaptation, and Vulnerability, Section 3.5. The U.S. Environmental Protection Agency's National Stormwater Calculator and Storm Water Management Model Climate Adjustment Tool provide regional downscaled climate projections. The USEPA also offers the Global Change Explorer, a web application for visualizing and downloading climate model output.
  • Use scenarios to develop a set of possible futures, rather than seeking consensus on a particular projection
    • In addressing future precipitation changes in stormwater management, decision makers may need assistance determining which climate change scenarios to evaluate, where to get appropriate climate data and assessing whether the climate projections coincide with locally driven concerns.

  • Build swales and rain gardens
    • Water temperature benefits include getting water underground and maintains aquifers. Other benefits can include keeping stormwater runoff out of waterways.
  • Control groundwater withdrawal
    • Water temperature benefits include maintaining groundwater sources that supply base flow to streams. Other benefits can include creating habitat and hydrological connectivity and restoring natural hydrology.
  • Control soil erosion in the watershed
    • Water temperature benefits include keeping sediment from clogging streambeds and interfering with groundwater exchange and keeping heat-trapping particles out of waterways. Other benefits can include returning to natural sediment transport and geomorphology and raising water quality.
  • Control stormwater runoff
    • Water temperature benefits include reducing high peak flows that contribute to erosion and channel changes. Other benefits can include restoring natural hydrology, returning to natural sediment transport and geomorphology, reestablishing natural disturbance and raising water quality.
  • Control stream bank erosion
    • Water temperature benefits include keeping stream channels from getting wider and shallower and warming more easily. Other benefits can include maintaining natural sediment transport and geomorphology and raising water quality.
  • Create deep pools or artificial logjams
    • Water temperature benefits include providing shade or deep water that limits direct heating from sunlight. Other benefits can include constructing biotic refugia or habitat and building biological communities.
  • Plant forest and floodplain habitat
    • Water temperature benefits include shading watershed lands, surface waters, and streambeds; reducing runoff; and promoting groundwater infiltration. Other benefits can include: creating habitat and hydrologic connectivity; rebuilding native vegetation and corridor networks; and raising water quality.
  • Plant trees
    • Water temperature benefits include shading the ground and keeping water temperature cooler. Other benefits can include controlling stormwater runoff and promoting infiltration.
  • Promote stormwater infiltration
    • Water temperature benefits include getting water into aquifers and away from exposure to the sun, and recharging groundwater that supplies baseflow that regulates stream temperature. Other benefits can include restoring natural hydrology, returning to natural sediment transport and geomorphology and reestablishing natural disturbance.
  • Remove unneeded channelization
    • Water temperature benefits include restoring natural groundwater exchange and connection to floodplains which promotes floodwater infiltration into aquifers. Other benefits can include restoring natural hydrology, returning to natural sediment transport and geomorphology and reestablishing natural disturbance.
  • Removing unneeded dams and impoundments
    • Water temperature benefits include keeping impounded waters from heating up. Other benefits can include restoring natural hydrology, returning to natural sediment transport and geomorphology and reestablishing natural disturbance.

  • Redefine river flood hazard zones to match the projected expansion of flooding frequency and extent

Source Documents

These strategies are adapted from existing U.S. Environmental Protection Agency, Centers for Disease Control and Prevention and other federal resources. Please view these strategies in the context provided by the primary source document: