The Utilities Committee met 06/24/2025. They spent nearly 50 minutes receiving an update on the Northland-Bellaire Flood Study and asking questions about it. Although the final report and recommendations will not be available until probably the end of the year, there were a couple initial findings that were discussed. One finding was that even if huge stormwater ponds had been placed at locations upstream of where the worst flooding happening during the July 2024 flooding events, a significant decrease in flooding would not have occurred. The second was that it was possible that in some circumstances the water conveyance system was being under-utilized because there were not enough inlets to allow water to flow as quickly as it needed to into the sewer system, this could potentially be improved by changing the style of inlets that were installed in the area.
I’ve prepared a transcript of the discussion for download:
The committee last received an update on the study in March of this year, and they will continue to receive quarterly reports until the study is completed which is expected to be near the end of this year.
Deputy Director of Public Works Pete Neuberger provided an overview of tasks that had already been completed and reported on during the 03/25/2025 Utilities Committee meeting. Those included:
Kickoff meeting held December 11, 2024
Reviewed location and description of July 2024 and historic flooding reports with DPW – The July 2024 rainfall events produced around 150-160 unique reported flooding incidents, more than half of which were within the Northland-Bellaire drainage areas.
Updated the previously developed system models to reflect current industry standard rainfall distributions and depths – Initial studies had been performed in both the Northland and Bellaire areas, but industry standards have changed since those reports were created so the data tables in the reports were updated to the newest industry standards.
Merged previously developed Northland model and Bellaire model into one combined model incorporating both watersheds – Brown and Caldwell (the company performing the current study) had performed the Northland study many years ago. A different company had performed the Bellaire study. Brown and Caldwell had to familiarize themselves with the other study and bring both the studies into compatibility in order to combine them.
Performed field site visits to verify previously modeled existing conditions, including flow paths – This was a way to test the accuracy of the model by looking at what was happening in real life and verifying that the model components reflected what seemed to be happening in reality.
He then reviewed tasks that had been completed since the Utilities Committee had been last updated. Those included:
Reviewed and updated model based on existing/surveyed storm sewer information from Town of Grand Chute – A portion of the Northland drainage area is in the Town of Grand Chute which had some good information about their sewer system to share with Appleton that was then able to be incorporated into the model.
Performed subwatershed-level inlet capacity calculations – They reviewed inlets that exist in backyards and streets that allow water to flow into the sewer system. This was important because sometimes the amount of water the sewer system conveys is limited not by the capacity of the main sewer pipes but rather by the inlets not allowing enough water to enter quickly enough into the sewer system. Knowledge of this could allow them to identify locations where flow might be improved by installing higher capacity inlets.
Ran sensitivity analyses for two different antecedent moisture conditions – This had not been done in previous studies. They ran the model with a normal level of moisture in the soil and they also ran it with higher moisture in the soil (as had been the case during the July 2024 flooding events). They found that when the moisture level in the soil was high it increased the amount of runoff that happened, to the point that if the soil was already saturated it not much more absorbent than concrete.
Ran sensitivity analyses for concept-level scenarios using 10-year and 100-year storm events to narrow down potential locations and types of practices for more detailed evaluation – Deputy Director Neuberger noted that a 10-year even and a 100-year event are not events that only happen every 10 or 100 years. Rather they are events that have a 10% change or a 1% chance of happening every year. There are other factors that come into play including the duration of a rainfall event.
Began alternatives evaluations using sensitivity analysis findings – One of the things they particularly wanted to look at was whether increase flood storage could decreased the worst flooding that had been experienced in July of 2024. Per Deputy Director Neuberger, “There just simply wasn’t enough storage that we could feasibly provide upstream and get and get significant reductions. So, what that told us was we could still look at storage as part of a part of a system of improvements, but […] improved conveyance would also have to be part of that.”
Conducted an initial utility conflicts evaluation of the Central Northland Watershed Area for potential storm sewer improvements – This was essentially identifying how changes to the sewer system in the Northland watershed would impact adjoining parts of the system. It was also aimed at identifying ancillary costs associated with potentially having to relocate any existing utilities.
There was some discussion about whether the rain events of July 2024 were 100-year flood events. That was challenging to answer because the two official rain gauges were at the Outagamie County International Airport and at the city’s operations building on Glendale Avenue. Per Deputy Director Neuberger, “The July 5 storm event was a very concentrated event, and the worst part of that event did not fall on those two rain gauge areas.” However, some private rainfall gauge data pointed to either a 25-year even or a 100-year event.
Deputy Director Neuberger was asked about how frequently 25-year rainfall events happened in Appleton. Off the top of his head, he could think of events occurring in 2024, 2018, 2013, 2010, 2003, and 2001. He went on to say, “[B]roadly speaking, these were not city-wide events. These were, these were specific areas of the city. For example, the 2003 event, it’s almost like this extreme cell found Calumet Street and it tracked west to east across Calumet Street, and it produced some pretty significant flooding within that Calumet Street area. But in that same storm event, people on the north side of the city just saw normal rainfall, nothing unusual about it.”
Deputy Director Neuberger then reviewed the ongoing tasks that were currently being worked on. Those included:
Analysis toward developing a prioritized list of potential inlet capacity improvements based on the subwatershed-level capacity calculations and other system information – One direction they could go would be to find areas that could benefit strictly by increasing inlet capacity and not increasing sewer size or doing anything else. Another direction they could go would be looking at a combination of inlet capacity improvement, sewer conveyance capacity improvements, and potentially increases in water storage. They had not yet determined recommendations and were still analyzing things.
Evaluating potential flood reduction benefits from increased stormwater detention within Memorial Park amongst other locations under multiple combinations of storage and conveyance scenarios – Memorial Park has one big storm water pond on the south end of the park. The rest of the areas in the park are not designed for flood storage although there may be some accidental flood storage that happens. So they are honing in on Memorial Park and trying to see if there are options there. They have begun to talk to the Parks and Recreation Department about expanding the existing stormwater pond so that it would add value both to the stormwater storage and conveyance system and provide recreational benefits to the park.
Deputy Director Neuberger then reviewed future tasks. Those included:
Continue to identify storage and conveyance improvement alternatives within the watersheds – Deputy Director Neuberger told the committee that there were not a lot of areas in the Northland flood plain that were not built out, paved, and developed. So Memorial Park stood out as one of the only areas with large open space. There was, however, also the option to start looking at creating some underground storage areas such as that which was under the parking lot at Appleton East High School. Those were, however, significantly more expensive than surface flood storage. Additionally, it might be beneficial to increase sewer pipe size/capacity because it would allow water to flow more quickly; however, they also wanted to be careful that they did not increase flooding at the bottom end of any newly expanded pipes.
Continue to refine potential improvements, check and adjust for potential significant utility conflicts.
Develop WinSLAMM water quality models to identify potential stormwater pollution reduction measures that could be incorporated into the alternatives under consideration – Any time they do a water quantity project, they look to improve water quality at the same time.
Group most highly ranked individual alternative components into three combined alternatives and present to Utilities Committee with recommendations for approval – Per Deputy Director Neuberger, “[W]e don’t yet know what these might look like. Broadly speaking, what we’re trying to do is take all these various individual components that seem to be potentially cost effective, boil them into groups of potential projects so that it’s digestible information, focusing on the ones that we think are going to have the best bang for the buck, and then present those to the utilities committee for with—what could be a recommendation, and then hopefully for an indication from the committee on what’s viewed favorably.”
Develop design refinements for selected combined alternative to facilitate resolution of utility conflicts in preparation of future design phases.
Prepare a technical memorandum documenting the procedures, recommended improvements, and conclusions for all tasks under this project – He expected this would be ready by the end of the year.
Department of Public Works Director Laura Jungwirth mentioned to the committee that during the budgeting process the Public Works Department was seeking funds to be allocated toward flood reduction. It was too soon to know exactly what those would go toward, but they did want to do some projects in 2026 aimed at that.
View full meeting details and video here: https://cityofappleton.legistar.com/MeetingDetail.aspx?ID=1314145&GUID=825F0F84-67D8-4C8A-BDB1-B4ED97054D10
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