A Methodology for Using Rainwater Harvesting as a Stormwater Management BMP

Abstract

Rainwater harvesting is a dynamic stormwater management tool that can be used to address multiple objectives and provide several stormwater, water and energy conservation and financial benefits. However, it is currently underutilized as a stormwater BMP. In many cases, rainwater harvesting systems are designed in isolation, instead of being incorporated as an integral component of a site's stormwater design. One major reason for this is that there is not a consistent means to account for the water quantity and quality benefits provided by rainwater harvesting. As a result, local plan reviewers and design consultants do not have a "common language" when it comes to compliance calculations and design features. This paper presents a rainwater harvesting specification developed to account for the water quantity and quality standards in Virginia's new stormwater program. The specification provides design guidance and a spreadsheet to model various system and demand scenarios to assess system performance. These tools provide designers with a unified method to size rainwater harvesting systems to meet stormwater management requirements and plan reviewers with a consistent set of guidelines with which to assess compliance. The objective of the spreadsheet is to put rainwater harvesting on a level playing field with other stormwater BMPs so that its use can become more widespread. By creating a common statewide specification, the multiple benefits of rainwater harvesting can become realized on a broader scale.