DEEP: Coastal Hazards Primer - Flooding

Coastal Hazards Primer - Flooding
Coastal Hazards Primer
 Introduction   Precipitation
 Flooding    Tropical Storms and Hurricanes 
 Erosion   Winter Storms 

Flooding from severe storms or regular extended precipitation events is the foremost natural hazard facing Connecticut.8 When floods occur they are generally grouped into the following three categories:9

  • River Flooding: When water levels overtop river banks due to short-term intense events or longer term periods of precipitation.
  • Flash Flooding: A rapid rise of water along a stream or low lying urban area, usually within 6 hours of significant rainfall from a severe storm; these can also occur when dams or levees fail.
  • Coastal Flooding: Hurricanes, tropical storms, or tropical depressions can create situations that overwhelm low-lying coastal areas. Storm surge is the sea rising above its normal tidal level due to wind and pressure. Storm tide is the actual level of water from a storm event counting the tidal level and any additional surge.10

Any of these events can be quite severe, causing millions, and in some cases billions, of dollars in damages and significant loss of property and life.

A Brief History of Flooding In Connecticut
Connecticut has no distinct flood season; in fact major flooding can occur in almost any month of the year. However, NOAA has studied a number of past floods and noted three times of the year relevant to flood activity:11
  • Late winter/spring melt;
  • Late summer/early fall; and
  • Early winter

FEMA records show that since 1954 Connecticut has had eleven major declared disasters that resulted in severe flooding. Some of the most significant include:

The Flood of 1936: The "Great Connecticut River Flood" of March 1936 was the result of melting snow and moderately heavy rains over a 13-day period. Rainfall amounts of six to eight inches occurred affecting the Connecticut, Housatonic, and Thames Rivers. Each reached record flood heights, and the Connecticut River was estimated to be at a 500-year flood stage. All totaled, this caused an estimated $20 million (1936 dollars) in property damage.12
The Flood of 1955: On August 11-12, Hurricane Connie produced four to six inches of rain throughout Connecticut. One week later, on August 18-20, Hurricane Diane produced another 10 to 20 inches of rain. Severe flooding caused road/bridge washouts, loss of drinking water, and severe damage to utility and communication infrastructures. These events resulted in:
  • 91 persons dead and 12 others missing or presumed dead;
  • 86,000 persons unemployed;
  • More than 1,100 families homeless, another 2,300 required temporary shelter;
  • 20,000 families suffered flood damage;
  • At least $1.5 billion in estimated damage to property and businesses.13
The Flood of 1982: Three to 16 inches of rain fell over most of Connecticut from June 4 - 7, 1982, where flood frequencies between 200 and 500 year intervals were recorded in south-central Connecticut. Damages were estimated at more than $276 million (1982 dollars). Eleven deaths were recorded and over 15,000 homes and 400 commercial and industrial establishments were damaged. The flood also resulted in damages to state and local roads, bridges, dams, and utility infrastructure.14
The Floods of April 2007 (aka the 2007 April Nor’easter): Rain began on April 15, and by early morning April 16, floodwaters, downed trees, and power lines caused numerous state highway and local road closures. Flooding continued on the Connecticut River at Middletown through April 27. Some rivers recorded return frequencies of 20 – 50 years, according to USGS. A joint Federal/State Preliminary Damage Assessment (PDA) identified 2,406 single family residential units were damaged by flooding. Overall residential damages were estimated at $23.7 million and business damages at $7.4 million.
Flood Mapping
Flood maps are created by using mathematics, physics, engineering, and surveying to model storm and flood events. Accurate flood maps can provide important information for a wide variety of users. Lending institutions and federal authorities use them to identify structures that require flood insurance and to determine federal flood insurance rates. Private insurers, realtors, and citizens in turn, use them to determine flood risks. State and local governments use them for planning and zoning, preparation of floodplain ordinances, hazard mitigation plans, and emergency response plans. Coastal managers use them to identify "refugia" where coastal wetlands can retreat from rising seas or to assess threatened natural resources.

FEMA Flood Maps
FEMA's National Flood Insurance Program (NFIP) conducts a Flood Insurance Study (FIS) for each town. The FIS contains information regarding flooding history, engineering methods used to create mapping products, and flood profiles for certain waterbodies. One of the primary products of an FIS is a Flood Insurance Rate Map (FIRM). FIRMs show the extent of flooding from a hypothetical 100-year storm event. By definition a 100-year storm has a 1-percent probability of being equaled or exceeded in any given year. (This is not the same as saying that it’s a storm that will only happen once every hundred years.) FIRMS are divided into the following zones:

  • A - Areas subject to inundation by the 1-percent-annual-chance flood event generally determined using approximate methodologies. Detailed analyses are not performed for such areas so no depths or base flood elevations* are shown.
  • AE - The base floodplain where base flood elevations are provided.
  • V - Coastal areas with a 1% or greater chance of flooding and an additional hazard associated with storm waves. No base flood elevations are shown.
  • VE - Coastal areas with a 1% or greater chance of flooding and an additional hazard associated with storm waves. Base flood elevations derived from detailed analyses are shown at selected intervals within these zones.

*Base Flood Elevations (BFEs) are the computed elevation to which floodwater is anticipated to rise during the base flood.

Areas subject to coastal storm surges may also be shown as Special Flood Hazard Areas (SFHAs.) The SFHA is where the NFIP's floodplain management regulations must be enforced and the mandatory purchase of flood insurance applies.

FIRMs for coastal Connecticut municipalities were originally produced between 1973 and 1990. Although FIRMs provide very useful baseline information for flood risks, they do have limitations (e.g., they do not account for erosion or potential sea level rise) and may not be appropriate as the only way to assess flood risk. The Massachusetts Storm Smart Coasts site has a useful guide to understanding the limitations of FIRMs.

A recent FEMA initiative called the Map Modernization Program (MapMod) sought to update FIRMs by converting them from hardcopy to digital products.  FEMA has developed technical bulletins that specify map revision guidelines for these "digital FIRMS" (DFIRMS).  However, while they increase the usability and availability of the data, they still exhibit many of the same limitations of their predecessors.

MapMod is now being expanded through a new program called RiskMAP. RiskMAP builds on the MapMod efforts to "deliver quality data that increases public awareness and leads to action that reduces risk to life and property."15 To do this, FEMA and State and Local stakeholders are collaborating to achieve the following goals:

  • Flood Hazard Data: Address gaps in flood hazard data to form a solid foundation for risk assessment, floodplain management, and actuarial soundness of the National Flood Insurance Program (NFIP).
  • Public Awareness/Outreach: Ensure that increases in the awareness and understanding of risk result in reduction of current and future vulnerability.
  • Hazard Mitigation Planning: Lead and support communities to engage in risk-based mitigation planning resulting in sustainable actions that reduce or eliminate risks to life and property from natural hazards.
  • Enhanced Digital Platform: Provide an enhanced digital platform that improves management of RiskMap, stewards information, and improve communication and sharing of data and products to all levels of government and the public.
    • Alignment and Synergies: Align Risk Analysis programs and develop synergies to enhance decision-making capabilities.16

FEMA provides an excellent summary on flood map products as well as a handy FAQ list. Additionally, the FEMA Map Service Center lets you locate digital flood mapping data, view online Flood Maps, and create a personal "FIRMette" – a user-defined section of an official FIRM capable of being printed on a standard home or office printer.

The 1994 US Army Corps of Engineers "Connecticut Hurricane Evacuation Study: Technical Data Report" uses the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model to estimate flooding from storm surge. Here, storm surges from hypothetical hurricanes were modeled using the storm track, the direction of travel, forward speed, and intensity. The NOAA National Hurricane Center selected the ranges of values based on the region's historical hurricane activity and an assessment of probable future storms.

Surge heights at a given location depend, in part, on its distance from the storm's center. Since an exact storm track is difficult to predict, emergency planning demands predictions for an entire section of coast.  SLOSH maps therefore depict a maximum envelope of water (MEOW) by taking the maximum surge height from multiple storm simulations that vary only by storm track. These maps are available in Appendix A of the Connecticut Hurricane Evacuation Study.

In 2004, DEP repackaged some of the storm surge flood maps produced in the USACE's 1994 Connecticut Hurricane Evacuation Study. Estimated SLOSH flood extents were overlaid on newer basemaps. These are available by request from the Flood Management Program of DEEP Inland Water Resources Division (IWRD).

Flood Damage Estimation
Flood maps can be used to develop important secondary data. For example, planners and decision-makers often want estimates of the damage to buildings and public infrastructure, and emergency managers want to assess the viability of evacuation routes.

The 1983 Connecticut Coastal Flood Vulnerability Assessment estimated the number of structures (insured and uninsured) for coastal municipalities. The motivation was to see how the development boom since 1955 had increased vulnerability to flood damages. At the time, the authors concluded that adequate laws were in place, but enforcement was often lacking. However, it is presently unclear if those conclusions remain valid.

More recently, FEMA produced HAZUS-MH (Hazards United States Multi-Hazard) software to estimate damages from possible storms and floods. In 2004, DEP and the Northeast States Emergency Consortium (NESEC) used HAZUS-MH to estimate the damages of a hurricane similar to the "Long Island Express" of 1938. The complete results are in the Connecticut Natural Hazards Mitigation Plan, but it was estimated a similar storm would cause on the order of $36 billion in damages and create 23 million tons of debris.

Flood Management
According to the National Flood Insurance Program (NFIP) most homeowner's insurance does not cover flood damage. Thus, it is critical to develop effective flood management techniques. Generally, managing coastal flood hazards can be achieved by:
  • Flood Mitigation: reducing the frequency or intensity of flooding;
  • Flood Damage Mitigation: reducing the vulnerability of human activity and the built environment to flooding;
  • No Adverse Impacts: taking measures to identify potential impacts of present or future development in a floodplain and implement action to mitigate them before they occur

Early U.S. flood responses used flood mitigation as the primary method of reducing flood hazards. Since the 1960's, people have realized that flood damage mitigation is at least as important as flood mitigation. More recently, due to rising flood losses and continued development in flood-prone areas, the concept of implementing better land use planning and higher building standards have begun to emerge. In Connecticut, the Department of Energy and Environmental Protection’s Inland Water Resources Division oversees Flood Management and Hazard Mitigation efforts.

Reducing the frequency or intensity of flooding requires preventing floodwaters from reaching flood zones. "Soft" and "hard" measures can be used. Hard measures include groins, jetties, bulkheads, revetments, seawalls, tide gates, and pumping facilities (used in conjunction with walls or dikes). Soft measures include beach nourishment, wetland restoration, and dune management projects.

Fighting the forces of nature can be expensive, harmful to the coastal environment, and likely to fail over the long-run in three primary ways. First, hard structures can deflect wave and wind energy onto adjacent sections of shoreline, exerting additional or new erosion forces. Second, hard protection can increase flood hazards by starving or redirecting sediment.  (Coastal bluffs and escarpments are natural sources of sediment for beaches and dunes. Beaches and dunes, in turn, provide flood protection by absorbing wave energy and providing higher elevations for floods to reach before they affect human-built structures.)  Lastly, as sea level rises, hard structures can impede the natural migration of tidal wetlands and marshes, reducing their viability as protective measures.

Since many flood and erosion control projects are constructed water-ward of the high tide line, the state of Connecticut, through the Office of Long Island Sound Programs (OLISP), has significant power to decide where and how these projects are constructed. The Connecticut General Statutes, Section 22a-92(b)(2)(F) and Section 22a-92(b)(2)(J) state:

"Structural solutions are permissible when necessary and unavoidable for the protection of infrastructural facilities, water-dependent uses, or existing inhabited structures, and where there is no feasible, less environmentally damaging alternative and where all reasonable mitigation measures and techniques have been provided to minimize adverse environmental impacts."

In practice, the permitting and enforcement activities of the Connecticut Coastal Management Program are consistent with the Connecticut Coastal Management Act's statutory statement concerning the construction and repair of erosion control structures.

Reducing the vulnerability of people and property can be achieved by creating and enforcing regulations and ordinances related to human activities and land use in flood-prone areas. The primary vehicle for this is the National Flood Insurance Program (NFIP) a federal program through FEMA that offers flood insurance to communities based on how they agree to adopt measures that meet or exceed FEMA requirements to reduce flood risk.

Central to the NFIP is the Community Rating System (CRS) which derives how discounts are calculated. In general, discounts are applied based on how a community rates over 18 different activities in the following categories:

  • public information
  • mapping and regulations
  • flood damage reduction
  • flood preparedness

While the NFIP provides significant assistance or flood damage mitigation, municipal enforcement of floodplain regulations and ordinances isn't perfect and in many cases even the minimum standards do not provide enough protection against present and future coastal hazards. Therefore, the NFIP alone may not be sufficient for effective floodplain management.

The Connecticut Flood and Erosion Control Board (FECB) program provides assistance to municipalities that have an active FECB for preventing potential hazards due to flooding, stream bank erosion, or beach erosion.  In addition, the FECBs may repair unsafe municipal dams or undertake non-structural measures that mitigate flood damages.

FECB funding is provided to towns and cities that apply for assistance on a non-competitive basis.  A budget is provided by the legislature bi-annually, and Connecticut General Statutes Section 25-71 establishes the level of state participation in a project.  FECB monies are not available to private dam owners or private property owners.  However, tax districts are considered municipalities for the purpose of FECB funding if the district is established in accordance with Connecticut General Statutes Section 7-339a.

When a municipality does not have an existing Flood and Erosion Control Board, an ordinance can be promulgated to adopt Connecticut General Statues Sections 25-84 through 25-94 to establish one.  If a municipality decides to form a FECB, please contact CT DEEP staff for guidance.

The Association of State Flood Plain Managers (ASFPM) has created a concept called No Adverse Impact (NAI) that guides their recommendations for state and local floodplain ordinances.  NAI floodplain management takes place when the actions of one property owner are not allowed to adversely affect the rights of others. Because it is a local initiative, it removes the stigma that floodplain management is imposed by the federal government. With the flexibility to adopt locally tailored management plans (which would be recognized by FEMA as the acceptable management approach) the community gains control of its land use decision-making process and is supported in adopting innovative approaches.

ASFPM created a Coastal NAI handbook specifically for coastal state and local planners to create floodplain management plans and policies that go well beyond the NFIP standards of floodplain management. 

The Connecticut Department of Emergency Services and Public Protection (formerly DEMHS) Emergency Management Division leads flood response and recovery efforts. In the event of a disaster declaration, DESPP initiates the State of Connecticut Natural Disaster Plan. This explains how DESPP coordinates disaster response through the State Emergency Operations Center (EOC) and defines the roles and responsibilities of various state and local municipalities, utility companies, and relief organizations.

In addition, the Department of Energy and Environmental Protection has developed a FEMA-approved Disaster Debris Management Plan to help guide recovery and clean-up efforts as part of a disaster response. The plan:

  • establishes the framework for management of debris generated by a natural disaster, with the goal of prompt and efficient recovery that is cost effective, eligible for FEMA reimbursement, and protective of the environment;
  • describes the State contracts (both debris removal and monitoring) that are in place;
  • outlines the planning and operation functions for Temporary Debris Storage and Reduction Sites and the phases of clean-up. It also includes a number of appendices that provide references to waste management resources.
In Summary
What can you do when it comes to the threat of flooding in Connecticut?
Content Last Updated August 9, 2019