Sanitary Sewer System GIS Asset Inventory and Hydraulic Modeling
Sanitary sewer issues such as collection and conveyance, capacity, management, operations, wet weather system impacts, maintenance, and expansion created a need for a holistic analysis providing clear and quantifiable solutions for the City of Indianola. It was decided in August 2013 that a hydraulic model of the City’s sanitary system was necessary to integrate rainfall impacts with existing sanitary sewer flows to provide Indianola with the information needed to make informed infrastructure decisions. In order to create this model, however, a comprehensive data collection effort for the entire City’s sanitary system was necessary.
This inventory, consisting predominantly of manhole inspections, involved not only collecting high-accuracy locations and depths on system assets but also collecting additional attributes, such as asset sizes, materials, and condition ratings. All of this data was collected in the field using mobile Geographic Information Systems (GIS) technology equipped with custom collection forms built to maximize efficiency and minimize user error. This field data was synced daily with a project GIS database designed both to accommodate the field data and the subsequent analysis outputs from the SewerGEMS modeling software.
HR Green set an ambitious schedule for the GIS development and asset inventory field work to avoid delays due to winter weather, allow sufficient time for conducting the hydraulic analysis, and to be as responsive as possible to the needs of the client. Existing GIS databases and mobile applications were leveraged to hasten development efforts, allowing field work to commence less than a week after the contract was approved. Despite delays due to weather, City support staff availability that only allowed for a single crew at any given time, and challenges locating assets that were in many cases buried, sealed shut, or tucked in overgrown or otherwise difficult settings, the City’s 1600+ manholes were inventoried in less than three months. This allowed hydraulic modeling to commence in December 2013. While an updated GIS for the City’s sanitary system was not the primary deliverable for this project, the asset inventory GIS should be a significant value-added resource that Indianola can use to aid in operations and in prioritizing system improvements going forward.