Split-flow theory: Stormwater design to emulate natural landscapes

This article reviews the development and application of existing stormwater management theories with a focus on emulating natural on site hydrological processes and discusses the design intentions, merits, and weaknesses of each theory. A new stormwater management theory is then proposed using elements found in each of these existing theories. This new theory proposes to systematically split runoff into three volumes and evaporate, infiltrate and discharge; and manage these volumes in ways that emulate natural hydrological site processes, thereby creating stormwater management systems that are more ecologically based. The intent is to provide a stormwater management theory that can be used to emulate natural processes of evapotranspiration, infiltration, and runoff and, by extension, emulate pre-development stormwater rate, quality, frequency, duration, and volume. The article then discusses limitations of this theory, including lack of established methods, need for evaluation against existing methods, obstacles to implementation under current regulations, and suggested additional research.