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Sewer System Mapping

Londonderry is a fast growing southern New Hampshire town with a significantly expanding infrastructure. The town hired Wright-Pierce to develop a comprehensive Geographic Information System (GIS) that will interface with other town departments and optimize infrastructure management. 

The town’s sewer department had been using multiple sets of record drawings to manage the growing sewer system. To centralize data, and make it comprehensive, Wright-Pierce created a multi-layered GIS of the sewer system by utilizing high resolution color ortho-photos, planimetrics of land features, and record drawings.  Areas of the sewer system that were not recorded in the drawings were surveyed.

Coincident features from the record drawings and high-resolution aerial orthophotography provided an excellent base for digitizing the sewer system features. Attributes from the record drawings such as diameter, material, and invert elevations were included in the GIS data. Additional attribute fields were added to the GIS layers to help town staff identify the original source of the feature. If the feature was created based on a record drawing it indicated the name and date of the record drawing. Another attribute field indicated whether the sewer feature was visible in the aerial photography. These fields help town staff verify the accuracy of the GIS features.

Forty five miles of pipe and over 900 manholes were digitized. Several attributes associated with these features were added to the GIS for future analysis.

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Project Highlights

Background
To ensure optimal infrastructure management, the Town retained Wright-Pierce to develop a sewer system GIS that would interface with other town departments.

Challenges
Incomplete record drawings were the only existing format for sewer system management.

Solutions
A total of 45 miles of pipe and over 900 manholes were digitized. Several attributes associated with these features were added to the GIS for future analysis.

  • A GIS with multiple layers was created utilizing high resolution color ortho-photos, planimetrics of land features, and record drawings.
  • Coincident features from the record drawings and high-resolution aerial orthophotography provided an excellent base for digitizing the sewer system features.
  • Attribute fields denoted source of each feature.