Congress Authorizes Flood Risk Management Study for Southeast Michigan

This study is authorized in the 2022 Water Resources Development Act (WRDA) which allows the U.S. Army Corps of Engineers (USACE) to work on flood risk management in Southeast Michigan.

In WRDA 2022, Congress expanded USACE’s authority to study comprehensive flood risk management. This authority may help communities better manage flood risk in urban areas.

Non-Federal Sponsor

Following legislation passed in 1986, congress required USACE to partner with a non-Federal sponsor to develop feasibility studies. This legislation identified cost-sharing provisions as well as key roles and responsibilities for sponsors to play in project planning and design. The sponsor must contribute 50% of the study costs that exceed $100,000, and the sponsor plays a key role in defining the water resources problems, objectives, and study scope.

The non-Federal sponsor for this study is the Great Lakes Water Authority (GLWA). GLWA is the regional wastewater utility for southeast Michigan, providing wastewater services for nearly 30% of Michigan. GLWA has requested USACE to study comprehensive flood risk in southeast Michigan, to address flooding issues including:

• Flooding caused by heavy rainfall
• Fluctuating water levels in the Great Lakes and connecting waterways
• Impacts from climate change

About the Study

Southeast Michigan has experienced repeated, widespread flooding for decades and has received five federal disaster declarations due to flooding since 2000. Flooding in the region has resulted from more intense and frequent rainfall, storms, and fluctuating Great Lakes and connecting corridor water levels. This flooding causes damage to structures and infrastructure, impacts the local, regional, and national economy, and creates social hardship for Michiganders. The transportation system includes numerous below-grade highways, which require pumps to clear streets during rain events. During large storms, these highways can be closed for days at a time. Basement backups are increasingly common in portions of the region during large storms, where local or downstream surcharging leads to recurring household flooding.

According to the Federal Emergency Management Agency (FEMA), there have been more than 260,000 flooding-related Individual Assistance claims in the study area since 2004. 97% of the claims in Detroit occur outside FEMA’s Special Flood Hazard Area, highlighting a significant urban flooding issue in the region. FEMA has also reported more than 40,000 high flood-risk properties in the study area since 1978.

These high flood-risk properties have experienced either:

1. Individual Assistance (IA) Repetitive Loss, where a structure has had at least two IA FEMA inspections showing some level of flood water in the structure, including basements/crawlspaces, or
2. IA Severe Repetitive Loss, where a structure has had at least four IA FEMA inspections showing some level of flood water in the structure, including basements/crawlspaces, or
3. National Flood Insurance Program (NFIP) Repetitive Loss, where a FEMA NFIP-insured structure has had at least two paid flood losses of more than $1,000 each in any 10-year period since 1978, or
4. NFIP Severe Repetitive Loss, where
   1. Four or more $5,000+ claim payments were made, or
   2. Two or more claim payments were made cumulatively exceeding the structure’s value (before flood damage).

Explore FEMA’s Historical Flood Risk and Costs tool to better understand historical flood impact in your county.

In August 2014, the region experienced record-breaking rainfall—more than six inches in four hours—resulting in a federal disaster declaration. Another federal disaster declaration was issued after more than six inches of rain fell within 24 hours on June 26, 2021. After the June 2021 floods, the Great Lakes Water Authority worked with congressional representatives to authorize the study under the WRDA 2022 legislation. In 2024, USACE received an initial $500,000 to begin the study.

Our Shared Vision

To foster a shared vision for the Southeast Michigan Flood Risk Management Study, the USACE Detroit District and the Great Lakes Water Authority (GLWA) launched the study with a planning charrette that included local, regional, state, and federal government stakeholders in Detroit from Sept. 16-18, 2024. The group developed a preliminary shared vision, which will continue to evolve as more stakeholders are engaged. 

Widespread flooding in Southeast Michigan has led to significant economic burdens and social hardships. Urban, riverine, and coastal flooding in the region has increased risks to public safety and health, caused property damage, disrupted critical infrastructure, and led to economic losses for residents, businesses, industries, and local and state governments. The Southeast Michigan Flood Risk Management Study will investigate options to reduce risks to human life and lessen economic, industrial, and commercial flood damage in the study area over the period of analysis. Opportunities exist to improve community and infrastructure resilience, water quality and associated public health outcomes, public awareness of flood risk management and preparedness, and the overall quality of life in Southeast Michigan.

Scope, Schedule, and Budget

The key components of the study scope are investigating the pluvial (rainfall-driven) flooding analysis, a full array of alternatives and comprehensive benefit considerations, design maturity of alternatives, environmental and real estate analyses, and community outreach.

The study team received a policy exception to the schedule and funding requirements established by Section 1001 of the Water Resources Development Act of 2014 (3 years and $3M). The exception allows for exceeding the three-year timeline and $3 million study cost limit, given the scale and complexity of the project. A 4 year and $5M study budget were approved by the Assistant Secretary for the Army of Civil Works in May 2026, pending availability of future Federal funds. The study will produce a technical report and a bulk of the study time and funding will be allocated to the alternative evaluation and analysis phase. This phase will include developing 2D hydraulic and hydrologic modeling, creating various economic models, preliminary engineering and design of potential alternatives, and analyzing environmental and real estate considerations, as well as community considerations.

The Six-Step Planning Process

The USACE planning process is a structured approach to problem-solving. A six-step planning process is used iteratively, allowing steps to be repeated as needed for better problem understanding. Planning is performed by an interdisciplinary group of engineers, scientists, economists, and others. Stakeholder and public engagement play a major role, and public input in the decision-making process is valued.

Step 1: Identify Problems and Opportunities

Problems

1. During heavy precipitation events, local surcharging (e.g. sewer blockages, collapses, overloading of house leads, and sanitary lateral backups) or downstream surcharging (e.g. combined sewers and backwater from pump stations and combined sewer overflow outfalls) has led to recurring pluvial flooding. Pluvial flooding has caused significant economic damage and social hardship throughout the study area as described by the following:
   1. Damage to residential structures. Pluvial flooding has led to recurring flood damages to residential structures and associated contents.
   2. Impacts to commerce and industry. Pluvial flooding has impacted important sectors of the economy (e.g. automotive manufacturing) through direct (e.g. inundation) and indirect (e.g. decreased access, user delays, lost revenue) damages.
   3. Damage to infrastructure. Pluvial flooding in the study area has caused significant damage to infrastructure throughout the study area, including wastewater and water utilities, power, and pumping stations.
   4. Traffic user delays. Economic impacts of pluvial flooding and associated damage extend to user delays and associated costs from interstate and road closures.

2. Pluvial flood inundation or damage to structures and infrastructure increases life safety risk throughout the study area as described by the following:​
   1. Loss of life due to inundated occupied vehicles. Flooding-related injuries and fatalities in the study area have occurred due to the inundation of occupied vehicles.
   2. Elevated life safety risk to inundated structures. Elevated life safety risk is associated with direct inundation of structures within the study area and may put the population living in or utilizing said structures at risk of losing their life.
   3. Inundation of or damage to critical infrastructure and structures. Inundation of or damage to critical infrastructure within the study area, including infrastructure associated with emergency services, first responders, critical utilities (e.g. power, roads, combined sewer systems), can also result in increased life safety risk.
   4. Social Hardship. Inundation of and damage to residential structures and roadways reduces access to critical facilities and services and leads to isolated individuals and communities during and following flood events. This leads to increased life safety risk, including the potential for indirect life loss.

3. During periods of high Great Lakes water levels elevating riverine levels and/or during heavy precipitation events, rivers and streams within the study area overflow their banks, resulting in elevated flood risk for affected communities. Recurring riverine flooding has caused economic damage, social hardship, and isolation of communities throughout the study area as described by the following:
   1. Damage to residential and commercial structures. During periods of elevated Great Lakes water levels, riverine flooding causes damage to residential and commercial structures.

4. Recurring riverine flooding increases life safety risk throughout the study area as described by the following:
   1. Social Hardship. Inundation of and damage to residential structures and roadways reduces access to critical facilities and services and leads to isolated individuals and communities during and following flood events. This leads to increased life safety risk, including the potential for indirect life loss.

Objectives

1. Reduce damages and associated economic and social impacts to residential structures/communities resulting from the individual and/or combined effects of riverine and pluvial flooding:
   1. Inundation of and damage to residential structures.
   2. Inundation of and damage to infrastructure for which residential communities rely (e.g., roads, water and wastewater utilities, power and pumping stations).

2. Reduce direct and indirect economic damages to industries and commerce resulting from the individual and/or combined effects of riverine and pluvial flooding:
   1. Direct impacts through inundation of and damage to commercial and industrial facilities.
   2. Indirect economic impacts through road closures and user delays.

3. Reduce direct and indirect life safety risks resulting from the individual and/or combined effects of riverine and pluvial flooding:
   1. Inundation of occupied structures and vehicles.
   2. Individual and community isolation due to inundated or damaged transportation infrastructure resulting in loss of emergency services and/or access to critical facilities.
   3. Damage to critical infrastructure and loss of associated services.

Opportunities/Considerations

• Resiliency. Increase community and infrastructure resiliency, the sustained ability to adapt and recover from significant flooding events, in the study area over the 50-year period of analysis.
• Transportation. Reduce flooding-related impacts to transportation infrastructure in the study area over the 50-year period of analysis.
• Quality of Life. Improve quality of life for individuals living within the study area impacted by flood inundation and associated damages.
• Water Quality. Improve water quality and associated public health outcomes in the study area.
• Public Education. Increase public awareness of flood risk management and preparedness for flood events through community education.

Step 2: Inventorying and Forecasting Conditions

Existing Conditions

The conceptual model below represents the flood risk conditions across southeast Michigan. Key flood risk drivers in the region include increasingly frequent and extreme precipitation, urbanization, and extreme water levels. These drivers are exacerbated by the primary and secondary stressors described below, which lead to the flood related impacts endured by southeast Michiganders such as street and highway closures, floodwaters backing up into basements, and combined sewage overflowing into the Detroit and Rouge Rivers. These impacts can then be measured by a number of performance metrics including structural damages, life safety and public health risk, commerce and industry losses, and other metrics.

Future Without (Federal) Project (FWOP) Conditions

To evaluate alternatives (potential solutions), the study team will develop the “Future Without (Federal) Project” (FWOP) scenario, or a forecasted future scenario without a USACE/Federal project to mitigate flood risk in the region. This FWOP scenario is based on existing conditions trends and variability in the study area to forecast reasonably foreseeable conditions in the absence of Federal action.

FWOP Economics:

Currently, the economics team is assessing how future flooding could financially affect homes, businesses, and infrastructure across southeast Michigan. In a large urban area like Metro-Detroit, this means estimating damages to residential, commercial, industrial, and public assets such as roads, utilities, and transit systems. In addition to physical damage, costs that families, businesses, and local governments may face during and after a flood event may also be evaluated, to determine the cost of emergency response, debris removal, and emergency cleanup.

To ensure accurate results, the team collects detailed information on structure characteristics across the study area. Instead of relying on market-based real estate values, which can reflect factors unrelated to building construction, we follow established Federal guidelines to estimate the cost to repair or rebuild each structure in its current condition. This approach ensures that our damage estimates reflect true structural value based on building type, materials, age, and wear.

The outcome of this analysis is an estimate of the expected annual flood damages the region could face in the future if no new flood risk management measures are implemented—known as the “Future Without Project” condition. This baseline is essential for comparing alternatives and understanding the economic benefits of potential flood-risk-reduction solutions. By defining the cost of taking no action, the study can better identify solutions that provide meaningful protection for Michiganders.

FWOP Hydrology & Hydraulic Engineering:

The hydrology and hydraulic engineering (H&H) team is evaluating how sewer system and overland flooding may affect the region in the future without new flood-risk-reduction measures. This analysis forms the technical foundation for assessing potential solutions. Current efforts focus on understanding rainfall, runoff, and sewer system performance across the region.

One key effort is the collection system analysis. The team is developing GLWA’s existing hydraulic SWMM model that represents the region’s sewer system. Currently the H&H team is improving the model’s computational efficiency, allowing long and complex simulations to run more quickly and reliably. This model helps estimate how the system behaves during rainfall/flooding events and identifies where capacity limitations may contribute to surface flooding.

Another ongoing effort is the hydrologic analysis using gauge-adjusted radar rainfall. Instead of assuming uniform rainfall across the entire region, the team is performing a “cloudburst sensitivity analysis” to understand how highly localized or uneven rainfall patterns may influence flooding. This provides a more realistic picture of how intense rainfall or cloudburst-type events can overwhelm parts of the system—even when total rainfall is similar to past events.

A topographic analysis is also underway to identify where water will flow and pond on the surface when the sewer system becomes overloaded. By identifying areas prone to overland flooding during major storms and where those areas intersect with critical infrastructure and assets, the team can better understand how surface flooding impacts streets, neighborhoods, and low-lying terrain.

To strengthen these assessments, we have partnered with the University of Wisconsin on an infrastructure resiliency analysis to evaluate flooding under future conditions. Their team is developing gridded rainfall projections that reflect potential changes in rainfall intensity, frequency, and distribution. These future rainfall scenarios will be run through the SWMM model to compare how both historic and projected storms may affect flooding patterns over time.

Flooding Focus Areas. Historic FEMA data show that the highest concentration of verified individual assistance flood claims of four Federal disaster flooding events occurred in the combined sewer service area. Hydrologic and hydraulic modeling confirmed these findings and showed that the combined sewer service area faces the highest flood risk. Additionally, the combined sewer service area has the most comprehensive data and existing tools available to better understand and evaluate flood risks from heavy rainfall (pluvial flooding) and the sewer collection system. For these reasons, the combined sewer service area was selected as the flood focus areas we will continue to evaluate in this study.

Step 3: Formulating Alternative Plans

The study team, in collaboration with local government, stakeholders, and the public, will identify an array of alternatives, or potential solutions, for managing flood risk in the region. The array of alternatives identified in the study thus far focus on storage, conveyance, and source removal.  

Storage: Increasing storage capacity at Combined Sewer Overflow (CSO) facilities provides more volume to temporarily hold excess stormwater and wastewater during heavy rain events. This helps prevent overflows and reduces the risk of flooding by storing flow within the sewer system or treating and discharging flow if necessary.

Conveyance: The goal to increase conveyance would be to move larger volumes of water through the sewer system by reducing hydraulic constraints, providing additional capacity during larger storm events. This may include building new sewers and pump stations or increasing the size of existing facilities.

Source Removal: Source removal reduces flooding by keeping rainwater out of the sewer and drainage system in the first place. This can include sewer separation, where combined sewer systems are replaced with separated sanitary and storm sewers. Additionally, this may include features such as rain gardens, permeable surfaces, and other improvements that capture or absorb stormwater where it falls. This can reduce sewer backups, street flooding, and the risk of overflows during major storms.

Step 4: Evaluating Alternative Plans

The Study team will quantitively and qualitatively compare each alternative to the “without project” scenario to understand the benefits of each alternative. 

Specifically, the economics team is looking at a range of factors to understand how each alternative could benefit the community. This includes reducing flood damage, minimizing transportation impacts, and improving quality of life. The economics team is estimating how much flood damage could be avoided compared with a future without improvements, as well as considering delays and extra travel caused by flooded roads and detours. The evaluation also considers broader community benefits, such as environmental quality, recreation, health, and community connections, recognizing that some of these benefits are more difficult to measure but are still important.

Step 5: Comparing Alternative Plans

Comparing alternative plans will reveal the plan expected to produce the greatest net benefits (benefits – costs) from among the alternatives considered.

Step 6: Selecting a Plan

A recommended plan will be identified based on the results of steps 4 and 5. That plan will be described in the technical report that outlines next steps for implementing environmental infrastructure projects under Section 219 of the Water Resources Development Act of 1992.