Collection System Strategies for Urban Streamway Vulnerabilities

Thunderstorms and severe weather are nothing new to residents of the Midwest. Yet the storm that inundated the Kansas City metropolitan area on October 4, 1998, was no ordinary storm. In a matter of hours, the storm unleashed more than 15 inches of rainfall resulting in widespread flooding, loss of life, and damage to millions of dollars worth of public infrastructure and private property.Johnson County Wastewater (JCW), a major wastewater utility serving the southwest side of the metropolitan area suffered significant collection system damage at several stream crossing sites. JCW's initial recovery from the storm and 2.2-million proactive repair and realignment program since should interest other wastewater utilities.During the cleanup after the '98 storm, it became apparent that the issue of stream conflicts was more insidious than previously realized. Subsequent JCW staff surveys in primary watersheds identified 104 other sites – including 36 locations prioritized as medium- to high-risk – for their vulnerability to ordinary and wet weather stream flows. Many problems, such as exposed manholes and below-grade crossings, could be traced to increased stream flows caused by development in the watershed - beyond those anticipated by the initial design. With further development expected, JCW faced the task of developing a comprehensive plan of improvements to address the newly recognized threat of sanitary sewer stream conflicts.Highlights of the approach employed by JCW included:Field surveys over winter months by “Stream Teams” of utility staff identified and ranked site vulnerability as low-, medium- or high-risk.A needs assessment by utility engineering staff determined priority and method of procurement: utility maintenance crews versus outside contractors/consultants.The use of softer, “Bioengineered” solutions would supplement the traditional hard armor approach of concrete and “rip-rap” to stream bank stabilization.The study of the stream mechanics and “geomorphology” would guide the proper location of sewer crossings. Native plantings and other soil reinforcements would be utilized where possible to lessen the impact on the stream and limit the potential for damage to the utility due to changes in the stream.A Design-Build project delivery method was developed and implemented to realize schedule savings and cooperative innovation. A two- to six-month schedule reduction was demonstrated in a pilot group of five project sites. Additional designbuild projects are planned.The combination of on-site field audits, sediment profiling, study of pre- and postdevelopment stream morphology, USGS map resources, and the County's geographic information system resources have resulted in an effective approach to a problem shared by other wastewater utilities. Review of the wastewater utility's program provides the insight of situational lessons that would benefit many collection system managers.