APWA Reporter Magazine Article Tackles Stormwater Prioritization, GIS, and PCSWMMPosted on Wednesday, March 31st, 2021 by Canyon Mallory
In Stormwater, tagged in
Affinis project engineer, John Spell, PE recently wrote an article for APWA’s Reporter magazine. It discusses a Kansas municipality’s stormwater study, which analyzed a historic portion of town. We interviewed John about the article, asking him about the project and his background with GIS and PCSWMM.
Can you tell us about the catalyst for the project?
A 600-acre site was facing failing infrastructure. The system ranged in age from 50-100 years. It had been built piecemeal over the decades. The public works director wanted our help in developing an easy-to-use plan that told them what needed to be replaced and at what level of urgency.
Why did you select this project for the article?
The project was such an interesting study. The client wanted the system rated based on condition and capacity. At the time, they rated their system, using good, fair, poor, or failed. While this is easy to look at in a singular pipe method, when we converted to a numerical rating system, we were able to overlap both condition and capacity and decide how impactful any singular pipe would be.
Composite Pipe Scoring
Why did you choose improvement prioritization as a topic?
Based on client feedback from prior projects, a single pipe replacement program is not easy to implement. For example, if three pipes are in a row, the first might be hydraulicly good, the second could be too small (results in bypass flow down the street), and the third could be hydraulicly good. When you upgrade the middle pipe to handle all the flow coming to it, the last pipe might then become too small to take the additional flow. Condition-wise, if the last pipe is in bad condition, but hydraulicly good, then that is a great time to upsize it, to allow the additional capacity from the improved second pipe.
Cluster Composite Scoring
As you can see, in a system of hundreds of pipe segments in dozens of branches, the client needs a way to simplify the data. We found a way to group sets of pipes that could logically be replaced at the same time by implementing a rating system that shows priority areas. This solution was effective for our client and would be beneficial to other municipalities.
What are some key takeaways from this project?
We received feedback from the client after the project was completed, and it was interesting to see how they used the report. Instead of picking the worst 10 clusters and getting started:
- They were able to do roadway improvements and target the adjacent cluster using our preliminary sizing and cost for quick estimates.
- They had a slope failure that damaged a retaining wall. They used our cluster map to identify the recommended improvements for that hydraulically connected system.
How have GIS and PCSWMM changed the way you work?
Modeling is not a perfect fit for every project. The time it takes to set up a model and get valuable answers can be too extensive for very small, simple projects. For those efforts, a spreadsheet or calculator exercise is the industry standard. However, if there is ponding in a street or flooding of a structure, the rules change. If there is water over the outlet of your last pipe segment, it gets complicated quickly. If you have pipes so flat that the water backs up in the system, then a model like this is invaluable.
When we do Preliminary Engineering Studies (PES) in Johnson County, one of the difficult requirements is to show flow depth in the street in a very large storm event, as well as whether it ponds high enough to get into a garage or basement window. PCSWMM has carved out a niche in the workflow. I take physical survey data between homes and along roadways and then, can tailor the output to show exactly what the county is asking.