Abstract

Calculating Impervious Surface as a Stormwater Service Measure
Track: Water, Wastewater, and Stormwater
Authors: Julia Cole

In April 2008, MSD implemented a revised structure for charging customer stormwater services. Fees were calculated based upon the quantity of impervious surface on the customer's property. Considerations included landuse type, multi-unit billing situations, estimations for buildings under construction, and allowances for environmentally friendly building practices. GIS was used to capture manmade surface features, intersect by parcels to subdivide, determine percentage of ownership and assign each to an appropriate owner. MSD was able to process approximately 1.6 million impervious features, create a versioned editing workflow for updating surfaces on a daily basis, summarize calculations and transfer information to the billing system. In addition, replication allowed for bi-annual data updates. GIS enabled the generation of individual property maps to allow verification by both customers and MSD staff. Our project demonstrates the power of GIS in responding to customer service with financial accountability.