The City of Portland has billed stormwater management charges for commercial and multi-family properties using impervious area (IA) as the basis for the charge since the 1970s. In order to determine the IA of a property in those days, staff pasted squares on a property map; each square represented 5,000 square feet and the city based charges on how many squares fit on the map. Staff has also used rulers to draw and measure on paper maps, and walked properties with a measuring wheel.

With advancements in mapping software, Environmental Services can now electronically measure and store IA data. ARC GIS allows the bureau to measure property more accurately and more efficiently than ever before. With our mapping software, we can now accurately measure, view, and store data using aerial photos.

As a result of the increased accuracy and efficiency of our mapping software, the bureau started an impervious area re-measurement project to systematically review IA measurements citywide.

Correcting stormwater billing errors through re-measuring makes billings more equitable for all customers. Correcting impervious area adds revenue to our budget and helps keep annual rate increases lower, which benefits all our ratepayers.