State Street Reconstruction | Madison, WI

GIS technique helps solve sewer system challenges

Todd Halvorson, GISP | with 0 Comments

GIS technique helps solve sewer system challenges

Client Challenge
The City of Newport, located along the Mississippi River southeast of St. Paul, Minnesota, has aging sewer infrastructure constructed in bedrock. At various intervals, the water table rises and the City faces significant inflow and infiltration (I/I) in the sewer system, despite having completed significant sewer improvement projects. 
Televising the City’s sewer mains exposed numerous failing or leaking water laterals, which appeared to be the source of the I/I problems. The City needed to notify property owners of these poor lateral conditions, but was challenged with how to quickly identify which residents were affected.
GIS Solution
The solution the City implemented utilizes GIS (geographic information systems) spatial technology in a three-step approach.
1.  Accurately identify City sewer laterals on a sewer map
Accurately map the City sewer laterals, and then identify the failed laterals. This required a sanitary sewer system mapped in a GIS database. Manholes require an ID that matches those used in the Televising reports.  Sewer mains will have a GIS length attribute that can be leveraged to help map tap locations. 

2.  Apply ownership attributes to each sewer tap 
Televising report data comes in a database format. We then set up a process to use the sewer main length in the GIS layer and the recorded distances in the TV database as basis to plot lateral locations automatically. This can occur once the two databases are set up properly to “talk” or link with each other. 

3.  Extract the failed laterals by a condition code applied by the inspector

The third step involves acquiring the parcel layer with ownership attributes which we will bring into our GIS sewer map.  Because GIS understands distance and proximity we can apply the attributes of the nearest parcel owner to the nearest sewer main tap.   Finally, we can select the taps based on their poor condition as scored in the TV database and create mailing list from the ownership attributes. 
Basic GIS Principals Used

 Spatial Overlay
Data can be extracted  and applied to other data layers by having  similar geography. This is used in the  ownership attributes being applied to the  sewer taps.

Graphic courtesy of National Geographic

 Linear Referencing: Data can be  “referenced” or “plotted” along a mapped  line if the data has measurement units. The  GIS sewer main in mapped in feet and the  taps are measured at distances along the  main in the TV database.

Example of report by MSA’s GIS staff.

Our GIS team works with other disciplines throughout MSA to develop databases for a wide variety of applications. We help communities compile and maintain data on sewer and water systems, trees and other city assets, citywide or recreational mapping, and much more. For more information on GIS solutions for your community, contact Todd Halvorson.

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