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.
Existing Conditions Model Development Process
The watershed study models are created using the information the City has and additional information we collect.
Information the City has includes storm sewer and storm access structure information, topographic information, the locations of our ponds and greenways, and land cover. Data we collect includes some survey data (where we need more information), monitoring data (rain depths and water levels), and anecdotal information from the public about where it has flooded in the past.
All the information is entered into the computer modeling software.
We use the monitoring information and anecdotal information to verify that the computer model is reflecting what actually occurs.
After the model is constructed and verified, we run the City’s “design” storms through the computer model. Design storms are discrete events that the stormwater industry uses to design stormwater infrastructure. They are referred to either as a frequency or a statistical chance. For example, you may have heard of the 100-year storm or the 1% chance event. They both mean the same thing. They are 6.66 inches over 24 hours.
Flood Solution Development Process
Potential solutions are created using the following steps.
- The computer models that were created for existing conditions are reviewed to see why flooding is occurring at specific locations.
- Public input is sought to “ground truth” the models existing conditions flood inundation areas to see if they reflect real life conditions.
- 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.
- Available information is reviewed to understand if something could impact construction (such as wetlands, utility conflicts, historical designations, etc.)
- The potential solutions are modified until the computer modeling shows the flooding targets are met, or reduced to the maximum extent practicable.
- 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.
- A cost estimate is developed for each of the potential solutions.
- Project solutions are then reviewed with residents and property owners to provide comment for potential refinement.
- 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.
- Modifications are made based on public comments where applicable, and then a Final Watershed Study report is approved by City Boards, Commissions and Committees.
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.
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.