East Isthmus and Yahara River Watershed Study
The existing conditions computer modeling is in the verification and calibration phase. Once results are ready, the second Public Information Meeting will be scheduled.
The City of Madison will complete a watershed study in the East Isthmus and Yahara watershed (as shown below). The watershed study will identify causes of existing flooding and then look at potential solutions to try to reduce flooding. The study will use computer models to assist with the evaluations.The City of Madison has hired a consultant, Tetra Tech, Inc to complete the first half of the study where the existing conditions are modeled.
For more information please see the Flash Flooding Story Map.
*Note: Please view the story map using Firefox or Google Chrome browsers. Story maps are not viewable with Internet Explorer.
The East Isthmus & Yahara study area drains primarily to the Yahara River and parts on the far east and west sides of the watershed drain directly to Lake Monona. The study extends west past the isthmus Yahara River watershed because the surface water is connected to an area that drains directly to Lake Monona and it’s important to study both together. The study extends to the east where a part of the watershed drains to Lake Monona because the City anticipates upcoming construction projects in this area, and therefore would like to have the stormwater system studied.
Still have questions? Get some answers here from our additional information page on the Watershed Studies.
The study is beginning Spring 2020 and is expected to take over 12 months. During this time, the City will look at watersheds as a whole to understand the interaction of flash flooding and the increased risk of flooding due to high lake levels. The East Isthmus and Yahara River watershed study will be done in two phases where a consultant will first develop an existing conditions model and analyze the impact of the Yahara River elevations on localized flash flooding. Following the completion of that work, the City will set up a separate contract for the solutions phase of the study.
There are a number of points of contact during this project where the public is encouraged to give feedback as part of public information meetings and public hearings. Dates and times are indicated below:
Public Information Meetings
Public Information Meeting No. 1 was held virtually Aug. 26, 2020.
Aug. 26, 2020 Public Information Meeting No. 1 PowerPoint Presentation
Aug. 26, 2020 Public Information Meeting No. 1 Recording
Following the presentation, participants had an opportunity to break out into smaller “focus groups” to discuss neighborhood-specific flooding issues. If you are unsure which neighborhood you live in, you can search your address in the top left corner of the neighborhood look-up map. The non-interactive map showing the focus groups is shown below:
If you don’t have access to a computer or smart phone, set up an appointment to use computers to view the presentation at a City of Madison Library, or at the UW Memorial Library. You can also register online and receive a phone number to dial into the meeting from any phone. Additionally, you can set up a time to view the recorded presentation on a library computer once the presentation is posted (a few days following the meeting).
If anyone has experienced flooding, and is willing to share with the City, please report it on the City's Report Flooding Portal. Even if a homeowner reported flooding to 2-1-1, FEMA, or a City official, the City needs standardized information to create stormwater models that show existing flooding conditions. The flood data helps the City prioritize different flood projects and future watershed studies.
The key to good reporting is including specific details and visuals.
If it is possible to do so safely, collect the following information when it is flooding:
- Date of the flooding
- Total time flooding occurred
- The time the flood water reached its highest point
- Photos of flooded areas when they are the most flooded
- Videos showing how the water is moving into and out of the flooded area
Once the flood waters have receded, and it is safe to do so, look for clues of the flood waters extent and depth. Clues include:
- Debris lines outside (twigs, leaves, dirt are left behind in a line on the lawn, sidewalk, mailbox post, shrub etc)
- Border of disturbed vegetation—if half the vegetation has been bent or is stuck to the ground in the direction of the flow, you can see the reach of the flood water
Document these clues and measure any depths where debris lines are above the ground. Pictures with descriptions are very helpful. For example:
If you were unable to capture any photos, descriptions are also helpful:
- Flood water reached the base of the first step on the front walk of our house at X address.
- Flood water was 12” deep at the mailbox in front of X address.
The City of Madison has 22 watersheds. Watersheds are an area of land that drain to the same location (the outlet).
There is a stormwater drainage system in all watersheds. This system is what conveys the stormwater to the outlet of the watershed. The City of Madison's stormwater drainage system includes approximately:
- 570 linear miles of stormwater pipes
- 42,800 stormwater inlets and access structures
- 250 stormwater ponds
- many miles of open greenways, channels and ditches
- many stormwater infiltration areas.
The City's system dates back to the 1880s. Very few, if any, standards were available in the 1880s. As the City developed, so did the guidance for design and construction. Today, we have comprehensive City, State, and Federal regulations to guide design and construction. The area of the City you live in used the regulations in place at the time it was developed. You can view the StoryMap to see what the regulations were for your neighborhood.
The extreme storm events in 2018 shed light on the deficiencies of the City’s stormwater drainage system. Many areas of the City experienced devastating flooding. This prompted the City to begin a comprehensive watershed study program in 2019. The intent of the program is to study each of the City’s watersheds one-by-one. The studies will help us to understand the causes of flooding. The studies will also provide recommended solutions to reduce the risk of flooding.
The watershed studies result in a list of proposed mitigation measures. Once constructed, the measures will reduce the risk of flooding to specific areas of the City. These mitigation measures are generally very costly. Due to limited stormwater management funding, all the mitigation measures cannot be implemented at one time.
The average Stormwater Utility Capital Budget each year is approximately $12 million. Within that, an average of about $2.4 million is used for flood mitigation. As of late 2021, recommended flood mitigation measures for the first five watershed studies were identified. The total cost from the first five studies is approximately $125 million. We expect the remaining 17 watershed studies will have similar flood mitigation project needs. Implementation of these flood mitigation measures will take many decades.
The Stormwater Utility funds the stormwater management for the City. This includes the construction, operation, and maintenance of the entire stormwater drainage system. The Stormwater Utility rates are set each year consistent with Wisconsin Statute. § 66.0821(4) and as described in Madison General Ordinance section 37.05 . These rates are under the purview of the public service commission. The rates are required to be deemed “reasonable” to comply with state statute. During the annual budgeting process, the City tries to balance the stormwater needs with the stormwater rate charged to its customers. These needs include:
- Implementation of flood mitigation measures
- Replacement, extension, and upgrades of existing the existing stormwater system
- Mandated water quality needs and requirements
When possible, the City attempts to get grant funding to partially fund the flood mitigation measures. Grant funding makes up a small part of the funding needed for stormwater management.
The City has created a draft prioritization process. This process creates a proposed order to construct the flood mitigation measures. This process accounts for many factors including:
- Impact on emergency services,
- Location of vulnerable populations,
- If the project also improves stormwater quality,
- Whether other projects are occurring nearby, and
- If outside funding is available.
Flash Flooding Resilience Story Map *Note: Please view the story map using Firefox or Google Chrome browsers. Story maps are not viewable with Internet Explorer.
- Lake Level Flooding Story Map *Note: Please view the story map using Firefox or Google Chrome browsers. Story maps are not viewable with Internet Explorer.
- Watershed Studies 2019 Audio Presentation.
- Frequently Asked Questions about the Watershed Studies
- City of Madison Flood Website
- Engineering Waterways Newsletter 2020 Issue
- Flood Prevention Flyer and website
- Dane County's Yahara River Sediment Removal Project
- Dane County's Flood Facts and Initiatives
- Download the Engineering's Podcast: Everyday Engineering on iTunes and Google Play.