Older urban sewer systems are not sealed, dedicated route networks leading to sewage treatment plants.  Rather, to save money when they were built decades ago, in some places they shared pipes with storm water drainage systems that lead to creeks, rivers and bays.  As a result, when stormwater inundates the system, it carries with it some of the sewage directly into waterways. Many cities have been working to separate the two systems, but it’s a huge job.  Are there solutions other than “big digs?”

Earlier this year, INFORMS, the Institute for Operations Research and the Management Sciences gave its Edelman Award for analytic excellence to the city of Louisville and its partner, Tetra Tech, an engineering firm, for innovative analytic approaches to the problem.  They used a mix of techniques:

• • fluid dynamics models for flow patterns
  • predictive modeling for predicting when and where overflows would occur
  • mixed integer programming to make efficient use of distributed storage capacity

By diverting sewage temporarily to local storage facilities during heavy rains, the system could wait out the storm water flooding and return the sewage to the network when it could again be channeled exclusively to the treatment plant.