What Causes Flooding?

Flooding is a natural and cyclical phenomenon - whereby during storms water overflows onto the land from adjacent waterbodies - that humans have adapted to for millennia. Within the last several hundred years, many have come to expect that large public expenditures in flood control infrastructure can eliminate floods, an assumption that is at odds with current drivers of increasing flood risk (Tarlock 2012). These include increased development, more intense rainfall, sea level rise, and aging and inadequate infrastructure that prioritized drainage, channelization, and the illusion of total control (Davenport et al. 2021; US NCA 2018; Tarlock 2012). Ongoing development - including more roads, parking lots, buildings, and intensively managed lawns across the state – have all increased the rate and volume of rain that runs off the landscape, significantly increasing downstream flood risk (Blum et al. 2020; Parr and Wang, 2014). Development in floodplains combined with draining wet meadows and wetlands, has further reduced the landscapes ability to absorb/store flood water and has further increased exposure to downstream floods and their economic consequences (Armal et al. 2020; Wohl 2021). 

In the past, our approach to flood control has been to build dams and levees to encourage and protect floodplain development. These historical infrastructures are now aging, and many of them were only designed to function reliably for 50-100 years without major reinvestment. The average age of Connecticut’s 67 large flood control dams is 64 years old (NID 2022, ArcGIS hub 2023). The average age of Connecticut’s 25 miles of large flood control levees is likewise 62 years old (NLD 2023), and some systems, like those in the Hartford Region, are currently under study for necessary maintenance. Our current approaches also rely heavily upon the National Flood Insurance Program to provide subsidized flood insurance for flood prone properties, a program that operates at a deficit, and appears to have also contributed to increasing risk (Cutter et al. 2018). Upgrading and maintaining large built infrastructures is costly and has significant greenhouse gas emissions, requiring a balanced and transparent discussion over the diverse costs and benefits of long-term flood management options. 

“Extreme” precipitation has increased in the Northeastern United States (Huang et al. 2021). Extreme events, defined as more than six inches of rainfall over 24 hours, may be six times more likely by 2100 than today (Jong et al. 2023), and will likely cause increases in flooding events (Ivancic and Shaw 2015). 

Connecticut’s coastal zone is a global sea level rise (SLR) hotspot (Sallenger et al. 2012), with observed SLR being over half a foot in the last half century, a rate expected to double by 2050 (CT DEEP, 2023). Rising sea levels and increasing tide heights will increase the flood risk associated with hurricanes and other coastal storms (Knutson et al.. 2021). 

What can be done?

Flood risk reduction comes down to adapting infrastructure and land use to increasing flood frequency and intensity along with mitigating human impacts on climate change.  While strategies must be place specific, here we provide starting point guidance on how different stakeholders in Connecticut’s land and infrastructure can contribute to reducing floods. 

What Can Municipalities Do?

• Flood resilience can be dramatically increased by municipalities through adopting model regulations and zoning more strictly regulating land use in flood prone areas, disconnecting impervious cover, and encouraging flood smart agriculture. 
• Connecticut Public Act 21-115 enabled municipalities to create new flood prevention, climate resilience, and erosion control boards which can support interjurisdictional and watershed based planning among other measures. 
• Engaging in comprehensive disaster planning and community preparedness measures through the Community Rating System can further reduce insurance rates for homeowners in your town beyond the cost savings provided by the National Flood Insurance Program. 
• Zoning used to create dedicated vegetated buffers with limited or no development around streams, rivers, and coastal zones can expand recreational amenities, habitat for wildlife, and zones for floodplain agriculture. 
• Creating flood resilient parkways, trails, and restored ecosystems can increase surrounding property values and the tax base. 
• Removing floodplain development through buyouts supported by FEMA’s Severe Repetitive Loss program,  can further improve municipal bottom lines by eliminating the cost of maintaining infrastructure in flood prone areas, and in some cases may be the only way to reliably manage long term risk. 
• Municipalities can also engage in watershed planning either alone or as part of watershed organizations supported by Connecticut DEEP’s watershed program. 
• Zoning and building codes can also be adapted to require new development to maintain or improve upon pre-development runoff behavior as has been done in other states (Harbor 1994; Dietz 2007). 
• Implementing/requiring Low Impact Development (LID) practices that reduce runoff & green stormwater infrastructure (GSI) practices, such as rain gardens, bioretention, pervious pavement, green roofs, etc., that encourage infiltration in new developments and as retrofits to improve infiltration capacity, reduce runoff, and help alleviate downstream burdens on undersized infrastructure. Practices can and should be designed to handle larger storms wherever possible.

How Can Homeowners Assess, Prepare for, and Reduce Their Flood Risk?

• Homeowners can learn about their flood exposure by looking up their current and future flood risk using the Federal Emergency Management Agency’s (FEMA) address look up tool, Flood Factor’s analysis of local flooding not represented on FEMA’s flood maps, and CT ECO’s coastal hazards viewer. 
• Individual properties can also restore coastal and streamside buffers to reduce their immediate flood risk, along with making structural improvements to existing buildings to increase their flood resilience. If these measures are inadequate, buyout programs can benefit repeat loss properties. 
• Sign up for flood alerts if you live in a flood prone area, have a go-bag and plan for pets and all family members, along with pre-established evacuation routes. 
• If moving from flood prone areas is not an option, purchasing flood insurance through the National Flood Insurance Program is a cost-effective near-term strategy for risk mitigation. NFIP insurance requires your municipality to meet FEMA’s requirements for basic flood awareness and preparedness.

The Role of Farmers and Forest Owners in Reducing Flood Risk

• Water sensitive forest management – including terracing and roadway design -  slows and retains surface runoff, preventing erosion across the landscape, improving soil water storage capacity, and groundwater recharge (Tomczyk et al. 2016).
• Water smart agricultural practices include flood resilient crops, restoring floodplains to serve as fish nursery habitat and marshland agriculture (like traditional systems of wetland hay, pasture, and wetland root crops). 
• Upslope farm conservation practices, like contour tillage and terracing can slow surface runoff and improve rates of infiltration, which can also increase drought resilience.

Federal, State, and Municipal Infrastructure Agencies

• Roads can be made more flood resilient by elevating bridges and increasing culvert sizes to handle increased peak flows, while also improving migratory fish passage (Neeson et al. 2018). 
• Roadways can also be re-designed using complete street principles to integrate improved runoff controls while making safe corridors for pedestrians and cyclists (US FHA 2018). 
• Larger scale green storm water infrastructure – like green roofs, rain water storage, multi-use parks, tree pits, bioswales, and systematic disconnections of impervious cover – can increase retention and infiltration of flood waters to address persistent urban flooding due to extreme precipitation, and can address river flooding as well (Junqueira et al. 2021). 
• Critical infrastructure, including power generation, waste water treatment, and emergency response facilities, can be updated through new design features and building materials using existing federal guidance to improve flood resilience.

Closing Thoughts

Flood resilience comes from improved and evolving flood management approaches. Ultimately our ability to protect ourselves from flooding will rely on continuously updating our understanding of future climate impacts and how landscapes respond to the management strategies outlined above. 

References

Blum, A. G., Ferraro, P. J., Archfield, S. A., & Ryberg, K. R. (2020). Causal effect of impervious cover on annual flood magnitude for the United States. Geophysical Research Letters, 47, e2019GL086480. https://doi.org/10.1029/2019GL086480

Breen, M. J., Kebede, A. S., & König, C. S. (2022). The Safe Development Paradox in Flood Risk Management: A Critical Review. Sustainability, 14(24), 16955. 

CLEAR Map viewer on coastal hazards

Costa, J. E. (1978). The dilemma of flood control in the United States. Environmental Management, 2, 313-322.

CT Changing Climate: https://portal.ct.gov/-/media/DEEP/education/kellogg/CT-Changing-Climate-Booklet.pdf 

CT SLAMM results on sea level rise impacts on coastal marshes and roadways: https://maps.cteco.uconn.edu/projects/slamm/results/ 

CT Mirror. 2023. Ag losses from climate extremes https://ctmirror.org/2023/07/17/ct-flooding-storm-farming-crops-destroyed/ 

Davenport, F. V., Burke, M., & Diffenbaugh, N. S. (2021). Contribution of historical precipitation change to US flood damages. Proceedings of the National Academy of Sciences, 118(4), e2017524118.

Dietz, M. E. (2007). Low impact development practices: A review of current research and recommendations for future directions. Water, air, and soil pollution, 186, 351-363.

EPA Climate Change in the Northeast (precipitation and sea level rise): https://climatechange.chicago.gov/climate-impacts/climate-impacts-northeast#Precipitation%20and%20sea%20level 

First Street foundation. 2023. Flood Facto Results for Connecticut. https://riskfactor.com/state/connecticut/9_fsid/flood 

Harbor, J. M. (1994). A practical method for estimating the impact of land-use change on surface runoff, groundwater recharge and wetland hydrology. Journal of the American Planning Association, 60(1), 95-108.

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Ivancic, T. J., & Shaw, S. B. (2015). Examining why trends in very heavy precipitation should not be mistaken for trends in very high river discharge. Climatic Change, 133, 681-693.

Junqueira, J. R., Serrao-Neumann, S., & White, I. (2022). Using green infrastructure as a social equity approach to reduce flood risks and address climate change impacts: A comparison of performance between cities and towns. Cities, 131, 104051.

Jong, B. T., Delworth, T. L., Cooke, W. F., Tseng, K. C., & Murakami, H. (2023). Increases in extreme precipitation over the Northeast United States using high-resolution climate model simulations. npj Climate and Atmospheric Science, 6(1), 18.

Knutson, T. R., Chung, M. V., Vecchi, G., Sun, J., Hsieh, T. L., & Smith, A. J. (2021). Climate change is probably increasing the intensity of tropical cyclones. Critical Issues in Climate Change Science, Science Brief Review. https://doi. org/10.5281/zenodo, 4570334(4).

National Climate Assessment 2018: Northeast: https://nca2018.globalchange.gov/chapter/18/ 

National Oceanographic and Atmospheric Administration. Climate Change in Northeast Shelf Ecosystem: https://www.fisheries.noaa.gov/new-england-mid-atlantic/climate/climate-change-northeast-us-shelf-ecosystem 

National Weather Service information on Flooding in CT: https://www.weather.gov/safety/flood-states-ct

Neeson, T. M., Moody, A. T., O'Hanley, J. R., Diebel, M., Doran, P. J., Ferris, M. C., ... & McIntyre, P. B. (2018). Aging infrastructure creates opportunities for cost‐efficient restoration of aquatic ecosystem connectivity. Ecological Applications, 28(6), 1494-1502.

Parr, D., & Wang, G. (2014). Hydrological changes in the US Northeast using the Connecticut River Basin as a case study: Part 1. Modeling and analysis of the past. Global and Planetary Change, 122, 208-222.

Sallenger Jr, A. H., Doran, K. S., & Howd, P. A. (2012). Hotspot of accelerated sea-level rise on the Atlantic coast of North America. Nature Climate Change, 2(12), 884-888.

Tarlock, A. D. (2012). United States flood control policy: The incomplete transition from the illusion of total protection to risk management. Duke Envtl. L. & Pol'y F., 23, 151.

Tomczyk, A. M., White, P. C., & Ewertowski, M. W. (2016). Effects of extreme natural events on the provision of ecosystem services in a mountain environment: The importance of trail design in delivering system resilience and ecosystem service co-benefits. Journal of environmental management, 166, 156-167.

US Army Corps of Engineers. 2023. Current CT Flood Risk projects. https://www.nae.usace.army.mil/Missions/Civil-Works/Flood-Risk-Management/Connecticut/ 

US Geological Survey Factsheet on flooding: https://pubs.usgs.gov/fs/fs07603/

Wohl, E. (2021). Legacy effects of loss of beavers in the continental United States. Environmental Research Letters, 16(2), 025010.