Andy Reese reports that he has been repeatedly reminded of the black box nature of urban stormwater hydrologic design, and the often minimal level of understanding of many designers. The article points out some of the methodologies that can be used to obtain any number of “correct” answers.
“Volume-based criteria can only be rightly developed by understanding the long-term flux of water volume; and the only way to accurately do this is through well-constructed continuous simulation modeling that accounts for drying processes between storms,” writes Andy Reese.
“We are now facing another sea change in thinking that is reaching’pandemic’ proportions. Recent discussion by stormwater opinion leaders is now pointing to a convergence on what we will call volume-based hydrology (VBH) and movement away from the peak-flow-based version,” writes Andy Reese.
“Having both tools accessible from the same website provides drainage modellers with a choice, depending on the modelling objectives and the capabilities of the user,” states Ted van der Gulik.
These sessions deal with computer modelling and the lessons that Jim Dumont has learned over the years. They are intended to provide a foundation of knowledge to those professionals just starting in the field and as a review for more experienced practitioners.
The report emphasizes that progressive jurisdictions are developing water balance approaches to rainwater/stormwater management for urban development to mitigate the geomorphic and biotic impacts that result from current practice. Such approaches utilize best management practices to infiltrate or evaporate water and minimize increases in runoff volume.
“Have you ever felt that justifying your detention design to a reviewing agency was a game of numbers? Do you have ways of making that marginal design look like a winner? Most engineers do,” wrote Glenn E. Brooks in the September 2007 issue of Stormwater magazine.
“There is a need for a new approach to hydrologic design. A key message is that a rainfall-based approach does not work effectively. This is why I advocate a runoff-based approach. Duration of discharge is important because it links directly to stream health”, stated Jim Dumont.
“Founded on British Columbia case study experience, the Guidebook formalized a science-based understanding to set performance targets for reducing rainwater runoff volumes and rates,” reports Kim Stephens.