Am I Missing Something in My Drainage Design?

Introduction With the advent of low-impact design (LID) or green infrastructure being coupled with traditional stormwater infrastructure becoming more widespread and desired in land development projects, drainage design has become increasingly complex. LID structures are designed to slow down and infiltrate stormwater in order to better mimic the natural hydrology of a site once it's developed and provide a level of treatment to improve water quality, versus a traditional approach involving a centralized location to simply store and control the release stormwater. There are multiple ways that a system like this could be modeled for design purposes either through the hydrology, a simplified hydraulic method, or a detailed physics based hydraulic method. Like most modeling efforts, there are pros and cons to each. Comparing Methods Many municipalities around the country have particular standards, and its often difficult to introduce new and innovative technology with different workflows. As more research becomes available and as computers have been able to handle more and more processes, the methodologies and standards used by cities are quickly becoming the 'old way of doing things'. In this presentation, we'll take a look at some of the common methods used for drainage design and how they compare (the good and the bad) to a fully dynamic solution with the latest EPASWMM5 engine. We'll also cover comparisons between modeled results using these different methods and how they compare to field monitored flow data. This will provide an in depth look into what aspects you could be missing in both traditional and green infrastructure stormwater design and how a more complete and robust analysis will provide a more accurate result. Intentional Focus Most low impact design structures have different soil layers with different characteristics which can impact how water moves through them. Specifically with regard to how much and how long it takes for water to leave the structure through underdrains, overflows, or through exfiltration. Many of these nuances aren't captured with a simplified modeling approach and their impact on each other is often ignored by modeling these structures in isolation. In this presentation I intend to highlight: -What goes on in the back end of H&H analysis tools -How these different approaches changes the output of the design -How these different methods compare with field monitored flow data Conclusion New technologies can take time for engineers and regulators to accept them regardless of whether they are the better approach. With this common mentality, there could be a lot missing from the designs leading to inefficient designs, over or under-sized structures, and problems down the road. The technology and development behind the EPASWMM5 engine has been decades in the making and with today's computing capabilities, we can and should be using more robust routines to develop green infrastructure and drainage design plans.