Since 2018: Stormwater Ordinance
The City of Madison Engineering Division is focusing on a number of projects to show what the City and Engineering has done ‘Since 2018’ when a flood devastated our community. In this blog post, we spoke with City of Madison Engineering Division Principal Engineer Janet Schmidt and Assistant City Engineer Greg Fries about the changes the City has made to its Stormwater Ordinance, which is a set of rules that anyone who wants to build in the City needs to follow. From a stormwater perspective, these rules makes sure anyone who wants to build in the City of Madison limits does so in a way that either improves or helps the stormwater system by moving water responsibility through the area while protecting any property near the construction.
What was the problem (or need for updates) with the stormwater ordinance for the City?
"After the extreme storm of August 2018, and the 100 year events in experienced by the Westside in 2016 and 2017, it was pretty clear it was time for an ordinance update. After reviewing the research on increasing storm intensity and depth done by University of Wisconsin Madison Engineering Professor Daniel Wright, it was clear several parts of the ordinance were not up to the task of managing stormwater in a responsible manner going forward."
What happened in 2018? View the City’s story map.
What did we do to fix it?
"The City of Madison Engineering Division staff reviewed the existing the existing ordinance and updated several parts allowing the City to better manage stormwater runoff from new and redevelopment sites. This included:
- Removal of “grandfathering” which had previously allowed large lots to develop under the standards that were in place at the time of platting (which could have been decades ago).
- Increasing the required detention for new developments to include management of the 200-year event on the standard Atlas 14 - NOAA intensity duration curves.
- Requiring both detention and volume control from redevelopment sites (at the time we were the only municipality in Wisconsin to require this that does not have a combined sewer system).
- Requiring new developments take into account unintended detention that is occurring on the site already and add new detention requirements on top of existing detention amounts."
Why was there a problem/why did we fix it?
"The problem exists/ed as a result of the manner that engineers have reviewed and modeled stormwater runoff historically. Generally speaking, hydrology and runoff is a pretty young field, modern modeling methods really began in the late 60’s and no standards for treatment really began to be implemented until the 1980’s. Modeling and treatment methods and the way stormwater is thought about continue to evolve and to move away from the idea of stationarity and embrace a “moving target” for design storms."
How much was the project?
"This project had no “cost” to the tax payers except the (significant) amount of time spent going to meetings and reaching out to stakeholders to gain acceptance."
How long did it take us to fix it?
"The outreach for this ordinance change took two years."
How much of an impact does this project have from a bigger picture perspective? Why is this important?
"Updating codes to reflect changes in rainfall patterns by adopting a larger recurrence interval storm (200 vs 100) is a first step toward adopting a “live” rainfall distribution that uses data a recent as the previous year to generate storm events via statistical methods. The storm events we are using now “stop” in 2010 and the data prior to 2014 “stopped” in 1966. WICCI now has a website that uses “current” data and changing to referencing that standard would be the next step toward a better design standard."