Charting a course for pipe re-build
In 2002, Houston completed a Water Infrastructure Replacement Prioritization (WIRP) plan for repairing small-diameter water lines. By using geographic information systems (GIS) and infrastructure asset management systems, the city identified the most critical water line replacement projects that are needed to begin tackling $180 million worth of improvements citywide.
Before WIRP, the Houston Public Works Department decided which neighborhood water lines needed replacing case by case. As a result, infrastructure maintenance groups and water quality groups often competed for different repair projects, each claiming theirs was the highest priority. Additionally, city planners wanted to expand the capacity of small-diameter water lines to accommodate growth. Residents and city council members sometimes questioned why some water lines were repaired before others, but the department did not have a systematic method to prioritize projects.
The department developed criteria for determining which waterlines were substandard and, therefore, needed replacement first. Substandard waterlines were less than six inches in diameter; were made of asbestos cement, cast iron or galvanized metal; and were more than 40 years old. Those waterlines were given a high replacement priority because they provided inadequate fire protection, poor water quality, low water pressure, and they had a high probability of failure.
Houston identified 456 miles of waterlines that were critical to replace and estimated that repairs would cost $180 million. However, the city could not afford to replace $180 million in waterlines in one year or even in the next five or 10 years. The city hired a consultant to help develop a detailed list of additional criteria to prioritize which waterlines to replace first.
Using work orders and asset inventories as guides, the consultant and city leaders created 18 weighted factors — such as water quality, customer complaints and age — to determine replacement priority. Then, using a GIS map of greater Houston, the team created a grid in which each square represented approximately one-half square mile. Once the composite values of the factors were totaled for each map grid, the grids were ranked to determine their relative priority. The 50 grids with the highest rankings were then considered for the city’s five-year capital improvement program (CIP), with the projects in the highest-ranked grids recommended for funding in the first year.
At least one specific replacement project was recommended for each high-priority grid on the chart. After the WIRP CIP prioritization analysis was complete, Houston had reduced the $180 million price tag for all improvements to a five-year plan to invest $59 million on 31 waterline replacement projects that were most needed.
As a result of the WIRP CIP plan, the Public Works Department is better able to respond to requests to complete repairs and to answer questions about how priorities are determined. In 2002, the city began its replacement program with 194,255 feet of water lines, all of which are under construction now. Last year, the city chose to replace 278,175 feet of water lines, all of which are being designed now and will be constructed next year. This year, Houston selected to repair 516,630 feet of water lines, which currently are in the design phase.
Jun Chang, chief engineer for the Houston Department of Public Works & Engineering, and Brian Long and John Hewitt, senior GIS analyst and manager of Water Resources, respectively, for Houston-based Lockwood, Andrews & Newnam.