During the Watershed Study process, City staff hears from residents through in person meetings, focus group meetings, public comment periods and other means. We welcome as much engagement and feedback as possible to support the studies, to allow questions and concerns to be heard, and to help inform potential solutions in the City. City Engineering staff have put together the following information that responds to the most frequently asked questions.

Watershed Study Basics

Definition of a Watershed

A watershed is a land area that drains rainfall runoff (or stormwater) to a single outlet, or “discharge point.” The discharge point can be a lake, river, ditch, or storm sewer pipe discharge or outfall. The City of Madison is divided into 22 major watersheds.

Definition of a Watershed Study

A watershed study is an analysis of a watershed. Individual studies might focus on water pollution, aquatic life, flooding, or other issues impacting that watershed. The City watershed studies focus on chronic flooding, which we investigate by using computer models that are created to estimate rainfall/runoff and routing of stormwater. The study will analyze where and why flooding occurs and then evaluate possible solutions.

Watershed Study Duration

Each study takes a minimum of 18-24 months to complete. Some studies are more complex and will take longer based on the level of detail needed and the public input process.  Engineering plans to systematically complete a study for all 22 watersheds in the City. This process started in 2019 and will take approximately 5-10 years to complete.

Flood Solution Development Process

Potential solutions are created using the following steps.

  1. The computer models that were created for existing conditions are reviewed to see why flooding is occurring at specific locations.
  2. Public input is sought to “ground truth” the models existing conditions flood inundation areas to see if they reflect real life conditions.
  3. Potential solutions that could reduce flooding are developed and are entered into the computer model.  The watershed model is then run again to determine the positive or negative impacts of the change/s on flooding extents.
  4. Available information is reviewed to understand if something could impact construction (such as wetlands, utility conflicts, historical designations, etc.)
  5. The potential solutions are modified until the computer modeling shows the flooding targets are met, or reduced to the maximum extent practicable.
  6. The solutions are reviewed with other City Engineering staff, and other City agencies (such as Parks Division, Planning Division and Emergency Services) to understand how the solutions would impact them.
  7. A cost estimate is developed for each of the potential solutions.
  8. Project solutions are then reviewed with residents and property owners to provide comment for potential refinement.
  9. Once modified, a Draft Final Watershed Study report is posted online and residents have 30 days to provide additional feedback—see “Public Comment Period” section below.
  10. Modifications are made based on public comments where applicable, and then a Final Watershed Study report is approved by City Boards, Commissions and Committees. 

Implementation of Flood Projects

Drainage systems are often interconnected and complex. Altering one area of the system may inadvertently change another area. A solution isn’t viable if it simply moves a flooding problem to another area where it would cause others to be negatively impacted. Holistic solutions for the major flooding issues identified in each study will be proposed and will then be prioritized for potential future implementation depending on funding availability and the yearly capital budgeting process. Some solutions that have been identified are very expensive or have other challenges that may need to be addressed prior to or as part of implementation. These challenges include need for alternate funding sources, land requirements, permitting complexities, other regulatory issues, and public involvement and /or support. 

As the watershed studies are completed, there will be many more projects identified that will need to be prioritized.  Once all the watershed studies are completed, the number of projects identified will exceed the ability of the Stormwater Utility to fund.  Once prioritized it could take decades before the projects are constructed. Some project solutions identified in the reports may never be constructed for a variety of reasons, or additional alternatives may be developed instead.

The studies should be considered a feasibility level of report that identifies potential solutions that are viable but more refinement and design would be required prior to any implementation.  The studies can also be used to determine if no viable solution exists that fully meets our flood reduction goals.  This allows property owners and policy makers can make decisions based on that information.

Project Considerations

Each fiscal year Engineering evaluates projects to include in the capital budget. As part of that evaluation, staff considers such things as:

  • Flood reduction abilities
  • Racial Equity and Social Justice
  • Ability to improve emergency service access
  • Cost/available funding sources, including external funding such as grants
  • Water quality benefits
  • Co-benefits to other City infrastructure such as streets and utilities
  • Timing of the specific project (some projects require downstream solution built first else they will not work or may even be detrimental to the goal of flood reduction)
  • Project support
  • Tree loss, wetlands and other environmental aspects
  • Local, state and federal regulations (Landmarks, DNR, FEMA, etc.)

Project Construction

The projects shown in the watershed study reports are concepts. To construct a project, it must move from the concept stage to the design stage. The design stage cannot begin until a project is programmed into the City’s 5-year Capital Improvement Program (CIP).

Programming a project is a complex process and involves many factors. Factors include:

  1. What is the estimated project cost and is it possible to program it into the Stormwater Utility CIP given other needs and demands of the Utility?
  2. Are other projects happening in the same area? For example, is the street being reconstructed where an opportunity exists to partner with other agencies or utilities that may be otherwise impacted?
  3. Is there alternate funding available, such as grants?

The 5-year CIP is updated every year. For example, in 2020, the CIP for 2021-2026 is developed. In 2021, the CIP for 2022-2027 is updated. Because new information comes up every year, the order the projects are programmed can and will change. 

The City has 22 watersheds. Currently, Engineering has the solutions for the first five watersheds. As more watershed studies are completed, more projects will be identified.  Newly identified projects may take priority over previously programmed projects. Projects that have started design and permitting or have sunk costs will be taken into consideration so efforts are not wasted. However construction may be delayed if other priorities arise.

It is expected that it will take decades to implement the projects shown in the watershed study reports. It is also expected that the projects will not be implemented exactly as proposed in the watershed study report since the studies are to be considered a high level feasibility report. There are two main reasons for this:

  1. Watershed models will be updated as the watershed develops or redevelops and stormwater projects are constructed and
  2. Additional, more detailed, information is obtained during the design phase.  This more detailed information typically modifies project concepts. Additional information collected during design typically includes topographic survey, geotechnical information, full utility information, wetland delineations, tree surveys, changing regulatory requirements, etc.

When being programmed for design each project will have its own separate public meetings and input process as it goes through design and permitting which may alter original concepts.

Watershed Study Model Updates

The computer models constructed for the watershed studies will be updated periodically.  Generally, the update will occur when a major stormwater infrastructure project is in design and the computer model is being used to inform the storm sewer design for of the project.  At this time, all stormwater infrastructure improvements (local sewers and regional solutions) will be updated in the computer models.

City-Funded Solutions on Private Property

The Stormwater Utility is the primary source of funding for stormwater projects.  City ordinances prohibits the use of stormwater utility funds on private property improvements if the solution does not also benefit the public stormwater management system. 

For example the Stormwater Utility could not fund elevating a private structure or closing a private low opening if that was the only property benefitting from the improvement.

Purchasing Houses, Buildings or Structures

The 1% Chance Storm Risk mapping was developed using a specific set of assumptions for purposes of the watershed studies. If a building or structure is shown to be in an area of inundation, it does not mean the structure will flood; it means the structure has a chance of flooding under certain conditions and more detail (such as survey elevations) may be necessary to determine the true risk.

There is a potential the City could purchase structures that have a history of flood damage or that may be necessary to implement a larger flood mitigation project. Purchase of private property would occur on a case-by-case basis. It would depend upon many things including, but not limited to:

  • The willingness of the property owner to sell the property and the willingness of the City to purchase the property
  • If a reasonable public solution can be built to reduce flood risk instead of purchase of the property
  • If adjacent properties also need to be purchased to make an impact to the larger regional flood solution
  • The current rules and regulations concerning purchase of private property
  • If the cost-benefit analysis indicates this is a viable option
  • Funding availability

Projects on Other City Property

Public property is managed by a variety of City agencies.  Only some of the property in the City of Madison was dedicated solely for stormwater purposes.  Coordination with other City agencies is required if the City of Madison Stormwater Utility wants to do a project on public land was not dedicated for solely stormwater purposes. For example, Olin Park is owned by City of Madison Parks.  If the City of Madison Stormwater Utility wanted to do a project in Olin Park, the Stormwater Utility would need to request permission and support from City of Madison Parks Commission in addition to approval from the Board of Public Works and the Common Council.

Most projects will have to be reviewed to determine if there are other issues that need to be taken into consideration and get approval by the appropriate Boards, Commissions or Committees that are charged with the oversite of the property, in the hypothetical case of Olin Park, the Board of Parks Commissioners approval would be sought.  In addition, there may also be other concerns such as landmark or historical status and archeological impacts that would require Landmark Commission and State Historical Society approval as well. In other site there may be groundwater or well head protection zones or even landfill or contaminated soil concerns that need to be reviewed and permits or approvals granted. Other properties may have specific deed restrictions limiting the use of the lands. So just because the City owns property does not mean that it can be used in ways it was not originally intended.

City agencies work together on projects when possible however not all City property is available for stormwater and flood management.

Projects on Madison Metropolitan School District Property or County or State lands

The Madison Metropolitan School District is a completely separate entity from the City of Madison.  If the City of Madison Stormwater Utility wants to do a project on Madison Metropolitan School District property, the City works with the School District like it would work with any other private property owner. They City does not have the right to condemn lands owned by the school district, county, state or federal governments.

Projects in Parks that used to be Landfills

Some closed landfills have added some park amenities.  For example, Mineral Point Park allows walking and snowshoeing. Other landfills have dog parks.  These park and landfill spaces need to be mostly left “as-is” and cannot be reconstructed into stormwater projects areas.  The Wisconsin Department of Natural Resources (WDNR) regulates these areas for safe public use and if it’s a capped site there are WDNR permitting requirements or rules that would be necessary if any modification is done to the surface of the capped landfill.  

Public Involvement and Outreach

Public Information Meeting (PIM) process, frequency

Watershed Studies typically have at least three Public Information Meetings (PIMs).

  1. The first PIM introduces the study – what is studied and what the schedule is.
  2. The second PIM shows the existing conditions inundation mapping (inundation mapping shows how deep a water is and indicates areas of flooding concern) and asks the attendees if the maps show what they saw when it flooded.
  3. The third PIM shows the proposed solutions to reduce flooding and again asks attendees if they have concerns and is used to get input on the proposals.

Some watersheds may have a fourth PIM; this happens if all the questions asked during the third PIM or during the comment period could not be answered. See more information on the “Public Comment Period” below.

Some watersheds in the City are only undergoing the first phase of a study – determining where and why flooding occurs.  For these studies, proposed solutions are not developed.  These studies also do not have public engagement.  The final report will be posted on the City’s Watershed Study website.  The flood mapping will also be shared.

Focus Groups

A focus group is made of a group of property owners, residents or interested parties that are within an area that has known flooding (either historically reported or flooding areas indicated in computer modeling).  A specific study could have several such focus group areas. The focus group areas and focus group meetings are where the City hopes to get additional information and feedback from those living, working or owning property in the area that have specific knowledge or feedback that can help inform the computer modeling process. 

Most watershed studies will have two rounds of focus group meetings.

The first round will be to talk to the specific residents or property owners in the focus group areas to find out what they observed for flooding.

The second round of meetings will be to show those same focus groups the maps that were created from the computer models and ask if the maps match what has been observed during rain and flooding events.

Public Comment Period

Once the computer modeling and flood solutions are complete and the final draft report is created, the City hosts a public comment period, which would normally last a minimum of 30 days.  Interested parties are notified of this on the website, email blasts or via social media postings.  During that time, the draft final report is posted on the project’s webpage and the public is invited to review the draft final report and provide comments, questions, and feedback.

After the public comment period is over, City staff review the comments, questions, and feedback.  Responses are created and posted to the website.  Depending upon the level of interest, the responses may be provided quickly or they may take some time to develop. That feedback and responses will then be posted again and provided within the reports as supplemental information.

If the feedback is generally positive the watershed study will move forward to the approval process. If there are concerns that the City feels they need to address further, an additional Public Information Meeting may be required, along with an updated or amended report before it is approved.

Watershed Study Approval Process

Once a study is in a final draft format and has completed the public comment period, it will be determined by the City if that study should be finalized and approved. Approval of a watershed study includes approval by the Board of Public Works and potentially approval by the Board of Park Commissioners or other interested or impacted City Boards Commissions and Committees. These meetings are open to the public so interested parties can attend and provide public comment.

Flooding Information

Street Flooding in the City of Madison

Street Flooding is common. In most cities, streets (including curb and gutter) are part of the stormwater drainage system and are used to convey stormwater runoff. When it rains, water typically flows from adjacent lands to streets, then into storm pipes beneath the street, or into ditches, greenways, creeks, rivers, ponds or receiving waters. When the pipe or drainage system is full, the street itself could hold water until the storm system drains enough to allow the street itself to drain. Allowing streets to temporarily flood keeps water from damaging buildings and other infrastructure as long as the water is generally confined to the street itself.

There are many reasons why some areas flood. The following are just a few:

  • Some areas are low and water can easily pond on them or there is no overflow that allows water to drain. These areas are considered enclosed depressions.
  • Some areas have storm systems that cannot handle all the stormwater that flows into them if the storm sewer is at capacity.
  • Some houses were built below the curb elevation, or in a manner such that the home accepts water rather than shedding it to the right of way.

When an area of a City is developed, it is built using the guidance from that time period. Over time and as new and better engineering tools have become available, the City has changed its guidance and design standards to help reduce flooding. Many of the older storm sewers do not meet current sizing targets. As the streets in these areas are reconstructed, the storm sewers will be replaced with appropriate sized storm sewer, where possible. 

Storm sewers are typically designed for “normal” rainfall events. In Madison storm sewers are generally designed to the 10% chance event also known as the 10-year storm event.  When very heavy rains falls, even adequately designed sewers can be overwhelmed and flooding can occur. We see this a lot in fast flash flooding events.

Flash Flooding

Flash flooding occurs when more rain falls than the storm system can handle. Our storm sewers are designed for “normal” rain events, so in very heavy rains, the system can be overwhelmed.

Flash flooding can also occur when heavy rains or warm temperatures rapidly melt large volumes of snow; the rain combines with snow melt to act like much larger rain events, especially when the ground is still frozen or the inlets or storm drains are frozen or blocked.

The Watershed Study Flood Risk Map shows areas in the City identified as having a 1% annual chance of flash flooding.  These maps do not account for spring runoff events where the system may be impeded by frozen ground or blocked storm sewers.

Storm Infrastructure Basics

Approach to Storm Sewer Design is not a One-Size-Fits-All

Designing storm sewers to prevent all flooding would be cost-prohibitive and not feasible. The City’s current design target for newly constructed storm sewer is to fully convey stormwater in the storm sewer from rain events that have a 10% chance of occurring in any one year (10% Annual Exceedance Probability). This is the “10-year storm event” and in Madison is equivalent to about 4 inches of rain over a 24- hour period.  Not all storm sewer can be designed to meet this criteria, especially as part of reconstructions in older areas of the City that have been developed with lower/limited design standards.

During the August 2018 storm event, some parts of Madison received 12 to 15 inches of rain in a 12-hour period. This amount of rain is three to four times more rain than the system is designed for. Storm sewers that can carry this much water can be too big to physically fit within and under the road in many instances.

In new construction, the City’s design approach is to construct overflow pathways to direct the larger events safely to public-owned land or water bodies. In fully developed areas there is not always an option to provide an alternate overflow path so storm sewer must be sized to try to accommodate areas that cannot drain before flooding properties.

Purpose of a Stormwater Pond

Stormwater ponds typically have two jobs: they provide temporary storage for stormwater and they remove sediment and phosphorous from stormwater before it drains to our lakes and rivers. By storing the water in a designated pond it will slow it down enough to allow sediment to drop to the bottom where it can be removed by routine dredging. Some sediment is too fine to settle out and will stay suspended in the water but most large particles will settle out.

Please visit the City’s Stormwater Ponds webpage for more information. 

Removing Sediment from a Pond Does Not Help Reduce Flooding

Ponds with standing water in them are referred to as retention ponds. Generally speaking, the pond’s ability to hold water is referred to as “storage” is located in the part of the pond above the permanent water level. The permeant water level is set by the elevation of the pipe or structure that drains the pond.  Digging a pond deeper or dredging out the sediment generally only removes the sediment below the permanent water level. If the permanent water level does not change, the pond cannot store more water because the areas where the sediment was removed will just have standing water in its place since the normal water level remains the same.

Pond storage can only be changed by either adding taller walls to the storage area to allow it to hold more water or by lowering the permanent water level, which is usually done by modifying the outgoing pipe or discharge or outlet structure elevation.

Purpose of a Greenway

The purpose of a greenway is to convey, and if possible, treat stormwater.  At times, greenways can have ancillary uses such as walking trails, bike paths, habitat for native species, etc.  Because the main purpose is to convey stormwater, the stormwater utility manages them with that main purpose in mind. 

Greenways that are heavily wooded or heavily eroded cause issues with the management of stormwater. Greenways that have a dense canopy or invasive trees sometimes have issues getting healthy understory vegetation established that holds the soil in place. This can lead to a cycle of erosion and undercutting by erosion and can actually damage trees that are in the greenway.  Downed trees or debris can cause blockages that impede water while heavily eroded channels usually move sediment that can be deposited elsewhere in the system or find its way to our lakes. This sediment deposition in the lakes can cause water quality issues in addition to increased phosphorus loading and algae blooms. 

Funding Process

Non-Assessable Flood Mitigation Project Funding

Flood mitigation projects are not generally assessable to residents. However there are some instances where if a project is driven by a development, some portion of the flood mitigation projects would be assessed in accordance with the Stormwater Assessment Policy if they are required as a condition of the new development.   

The City has funding set aside through the Stormwater Utility for non-assessable flood mitigation projects that serve a public good. Some stormwater projects may be incorporated into planned street reconstruction projects, which would include assessments to property owners, however storm sewer improvements are not assessable.  The only exception is private lateral connections to connect to serve specific properties.

Watershed Studies and Flood Reduction Project Funding

Funding for the watershed studies comes from the Operating Budget and is part of the overall City Budget that gets adopted every year.

Funding for the public work construction projects comes from the City’s yearly Capital Improvement Program (CIP) Budget, specifically the Stormwater Utility portion of the CIP.

The Stormwater Utility for operating and capital budgets is funded by stormwater utility fees, which property owners see on their monthly municipal services bills. These fees pay for many things including funding staffing and wages, operations, repairs and maintenance of the existing stormwater infrastructure, construction of new infrastructure for flood mitigation, water quality practices and land management, debt service, Yahara WINS, and more.  The average residential monthly charge in 2022 is $11.31.

Green Infrastructure/Water Quality/Ecological Information

Green Infrastructure and the Watershed Studies

Green Infrastructure (GI) is smaller infrastructure that filters and absorbs stormwater where it falls. GI uses plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters. Madison is committed to installing GI.  However, as part of the watershed studies GI has been reviewed and it is generally not considered to be a significant tool for flood management.  GI does many things well but conveying or reducing the peak flows in a 1% chance storm event are not one of its core strengths, even when implemented on a large scale.  You may have read of cities on the east and west coasts using GI, however that is generally to address the problem of combined (storm and sanitary share a pipe) sewer overflows to the waters of the state (rivers, lakes, stream…). The City of Madison has separate storm and sanitary sewers, so GI is not needed for that application.

As part of the watershed studies a GI analysis was conducted for one of the watersheds in the City. The purpose of the analysis was to specifically understand how much green infrastructure would be needed to meet flood reduction targets. The numbers generated by that analysis indicate that GI is not a cost effective measure to manage the 1% chance or 100 year event flooding.  As noted above however, GI has other environmental, economic and social benefits.  Again this analysis only reviewed GI’s impacts on flood control.

Runoff is stormwater that does not soak (infiltrate) into the ground. Stormwater that lands on hard or impervious surfaces such as roofs, driveways, streets all becomes runoff. This runoff ends up in our stormwater system if it doesn’t flow over a pervious surface and soak into the ground. The runoff from hard surfaces that flows directly into our stormwater system without infiltrating into a pervious surface is considered “directly connected impervious area.” For example, a roof downspout drains onto a driveway that then goes to the street is considered directly connected impervious area.  The study found that all of the directly connected impervious area in the watershed needs to be treated with green infrastructure to meet the flood targets. 

The estimated cost to construct all that green infrastructure is twice as much as the estimated cost for constructing traditional stormwater management. For purposes of the watershed studies, traditional stormwater management include items such as installing larger pipes or creating bigger ponds. Additionally, GI is extremely maintenance intensive and more prone to failure in places where it snows—sand and salt applied to streets and parking lots can clog pervious pavements, seal soils that are intended to infiltrate, and freeze thaw cycles can cause failure of pervious pavement.

The study concludes that even though green infrastructure could be used to meet the flood study targets, it is cost-prohibitive to only use green infrastructure for flood reduction.

The City will be using green infrastructure where feasible.  But, it will not be the only part of the solution.

Green infrastructure also continues to be implemented citywide through other City initiatives.

Water Quality and the Watershed Studies

Water quality – aka – pollution reduction – was not included in the watershed studies. This is because these particular watershed studies focus on flooding. The analysis for flooding is typically for large storm events. The analysis for water quality is typically for small storm events which results in the “first flush” effect of concentrated pollutants entering the stormwater system with the initial part of the rainfall. The water quality analysis also typically uses different computer modeling software.

The City does have a separate program and model for water quality, as described in its Wisconsin Pollution Discharge Elimination System (WPDES) Municipal Separate Storm Sewer (MS4) Permit. Many of the proposed watershed study solutions do include water quality components as part of the design.

Ecological Impacts of Solutions

During the design phase of each solution, engineers work with landscape architects, and vegetation specialists to incorporate native vegetation that will aid the stormwater infrastructure to serve its purpose.

Deep roots of native vegetation help hold soil in place and help water infiltrate. Additionally, native vegetation is essential food for insects which are the base for our local food web.

Also, during the design phase, engineers work with Wisconsin Department of Natural Resources (WDNR) staff to comply with all natural resources rules and permitting.

Ecological Restoration in Stormwater Ponds and Greenways

The City of Madison is actively working to restore its stormwater ponds and greenways.  See the Ecological Restoration In Stormwater Ponds and Greenways StoryMap for more information.

Other Information

Difference between a Park and a Greenway

One way that land is categorized is by its intended use.  The intended use is what the land was originally supposed to be used for when the City obtained it.  They City typically is dedicated land as a requirement of development and the platting process.  In other instances land is sometimes gifted, purchased or even condemned by the City for a specific use. There are other instances where lands also have deed restrictions on them that dictate the intended use.

For instance, a park could be used for only a park, or, it could be used for both a park and a stormwater practice depending on the way in which it was acquired by the City.   Blackhawk Park in the Blackhawk Neighborhood on the far west side of Madison is an example where the lands were intended to be only used as a park and were dedicated that way as part of the subdivision process.  But, right next to it is Blackhawk Pond.  Blackhawk Pond is intended to only be used as a stormwater pond.  Because Blackhawk Park and Blackhawk Pond were designed at the same time, it can be hard to understand they are categorized differently. There are many locations across the City where parks and stormwater management properties abut each other to allow for larger areas of open space so parsing out the different uses and ownerships is not always easy unless you have more information.

A stormwater practice, like a greenway could be used for only stormwater conveyance, or, it could also have park-like uses, like walking trails.  For example, Sauk Creek Greenway’s intended use is for stormwater conveyance.  But, the current maintenance path for the sanitary sewer along the greenway is used for a walking trail.  Just like the Blackhawk Park and Blackhawk Pond example, it can be hard to tell the difference.

So, how would you know?  Currently the best clue is to find out which agency in the City owns it.  The City’s Park and Open Space Plan has an inventory of the public park lands and is a good place to start.  Public land in the park inventory are typically considered parkland, and, may occasionally have greenways or other stormwater treatment facilities within them. Properties owned by the City of Madison Engineering are almost exclusively considered ponds or greenways and meant for stormwater management.

Groundwater versus Stormwater

Groundwater is the water that is found underground.  It is found in the cracks and spaces in soil, sand, and rock.  Some groundwater comes from infiltration.  When it rains, some of the rainwater soaks into the ground, or infiltrates.  The portion of the water that does not soak in, but runs off, is stormwater.

Groundwater issues are related, but not directly linked, to surface and stormwater. They do interact, but the degree to which they interact is different for different locations and situations.

Groundwater's Role in the Watershed Studies

Groundwater is acknowledged in the watershed studies, but is not included in the evaluation. For example, when talking to residents that flooded in August 2018, many reported they had water in their basement.  The water came up through the foundation, not from overflowing from a door or window.  This means the water is from groundwater and not from flooding. 

Groundwater evaluation is a different type of study. Groundwater typically covers a much larger area than a watershed study area. Groundwater modeling uses different modeling software and different information.

In a separate effort, the City is working with area agencies to understand groundwater impacts and planning accordingly.
Groundwater Recharge through Infiltration

Infiltration (water soaking into the ground) is one component of the water cycle that recharges groundwater in certain areas. Some of the proposed solutions include an infiltration component. The infiltration from these solutions may or may not affect groundwater levels.  It should be noted that creating large amounts of infiltration in areas that have not had infiltration in decades and were not designed for it can have unintended consequences and infiltrated water can end up in adjacent basements.

Watershed Study Impact on Your Flooded Basement

This effort may or may not help your flooded basement. It depends. The watershed studies are designed to quantify flooding risks throughout the City due to stormwater runoff from large storms. They will not include a detailed look at specific site grading or home / building design issues, groundwater conditions, groundwater-surface water interactions, or flooding that could occur due to a series of continuous, low-level storm events. Basement flooding at any given property may or may not be due to surface water runoff, and therefore may or may not be solved by the solutions laid out in this study.

Difference between Watershed Study and FEMA Floodplain Map

FEMA Flood Insurance Rate Maps (FIRMs) show areas subject to flooding from primary flooding sources, typically major rivers and their tributaries. Flooding within an urban watershed may be caused by local issues, which would not be included in a FEMA floodplain analysis. Local issues are things such as undersized storm sewer pipes, not enough inlets, ponding at intersections, etc. For instance, a FEMA floodplain map will show what areas are at risk when the Yahara River, Starkweather Creek, Lake Mendota or Monona floods, but not what areas are at risk when a large rainfall floods a specific roadway or property or when the storm sewer system capacity is exceeded.

Flood Insurance, Especially outside FEMA Floodplain

Having flood insurance is a decision each property owner makes for their situation. FEMA Floodplain Maps show flooding from rivers and lakes and can be used to determine what flood zone a property is located.

Much of the flooding that occurs in parts of Madison is because of the local surface drainage and the storm sewer system, not the rivers and lakes. Many homes flood because excess stormwater cannot drain into a storm drainage system fast enough to prevent localized flooding. Also, many homes are in high groundwater areas where seasonal basement flooding can occur without rain.

Homeowners can purchase flood insurance through the National Flood Insurance Program even if they are not in a FEMA floodplain.

Private flood insurance may cover sump pump failures and sanitary backups. To learn more, visit the National Flood Insurance Website, and the City’s Understanding Flood Insurance webpage or contact your insurance agent to determine what your options are.

New Development/Re-Development Flood Prevention

The City of Madison recently revised its stormwater ordinance.  The ordinance describes the local rules and regulations for stormwater management in the City. 

The ordinance allows the City to set low building openings in areas where flooding is a risk for new development and re-development.  The low building opening is the lowest opening on a structure where flood water could overflow and enter the structure.  Where available, the information for the low building opening is taken from the watershed study computer model results which can help determine the appropriate elevation. However individual owners need to make decisions and do their own analysis on how to protect their buildings based on their specific levels of risk.

Setting this low building opening above the estimated flood elevation helps prevent new structures from flooding in the future.  One item to note is that the elevations are generally set based on the 1% chance event.  Therefore, if that structure experiences an event larger than that, it could still be at risk of flooding. 

The stormwater ordinance also has requirements for reducing flows and volumes from development.  This helps reduce the risk of flooding for properties downstream of the development.

For more information see the Stormwater Ordinance webpage and Development Standard for Stormwater webpage.

Lake Level Information and Questions

The Dane County Land & Water Resources Department maintains lake levels in Lakes Mendota, Monona, Waubesa, and Kegonsa. Target lake levels were set by the Wisconsin Department of Natural Resources in 1979. Information on Madison lake levels can be found at Dane County's Flood Facts and Initiatives webpage.

Climate Change Impact

Recent studies indicate the Midwest is experiencing more rainfall in general.  Additionally, the studies show the Midwest is experiencing more 3”+ storm events in the last 20 years. The City has acknowledged this vulnerability and frequently reviews its design standards and Stormwater Ordinance to address the more extreme storm events, as was done in 2020. The current design standards can be found on the Development Standards for Stormwater webpage or in Chapter 37 of the Madison General Ordinance.  While there are many goals for the watershed studies, the primary goal is no flooding of private structures during the current Atlas 14, 1% chance event (not including groundwater issues).  This goal cannot be met in all cases for multiple reasons discussed throughout this webpage.

The watershed studies include storm events that are larger than typical flood study events.  This was done to understand the impact of larger storms on the stormwater drainage system. Additionally, where possible, the solutions were increased in size to pass the larger storms.  For example, the goal is to size pipes that go under the road between greenways to pass the 1% chance event without water flowing over the road.  If there was room under the road and no other design constraints, the greenway crossing could be made bigger for the 0.2% chance event.

Stay Connected 

There are so many resources! Resources include City Engineering’s Flooding Website, Report Flooding form, Facebook page, and podcast. Many of these locations include a link to sign up for City flooding updates. If you have any other questions, please contact Hannah Mohelnitzky, City Engineering Public Information Officer, hmohelnitzky@cityofmadison.com or 608-669-3560.

 

Printable Watershed FAQ