CU Denver team maps Wheat Ridge impervious surfaces, recommends more study and a tiered stormwater fee

A University of Colorado Denver student team presented the results of a semester‑long stormwater mapping and policy study and recommended that Wheat Ridge commission a fuller hydrological analysis before adopting any fee. The students mapped impervious area on more than 1,400 commercial parcels and 1,079 multifamily parcels, analyzed elevation and natural drainage basins and reviewed stormwater fee approaches used by other cities.

"Impervious surface refers to ground cover that does not allow water to penetrate easily into the ground," presenter Lauren Parkinson said. The team used high‑resolution USDA aerial imagery, automated remote sensing methods, OpenStreetMap features and manual edits to produce an impervious‑surface map the students reported is roughly 84% reliable given shadowing, recent construction and other classification limits.

The students identified roughly 58 miles of storm sewer pipe inside Wheat Ridge, noted that the city’s elevation varies by about 300 feet from highest to lowest points and mapped natural drainage basins feeding Clear Creek and the South Platte watershed. They emphasized that parcels with high impervious area concentrate runoff in lower‑lying basins and are more likely to stress pipe capacity.

The team reviewed fee structures used elsewhere and recommended options for Wheat Ridge. Examples cited included San Antonio (impervious square feet by property type), Englewood (flat fee split across property owners based on annual needs), Colorado Springs (flat residential fee with per‑acre nonresidential assessments), and Wheaton, Illinois (a hybrid tiered system that multiplies a per‑square‑foot rate by an impervious‑percentage tier). The students recommended that, if Wheat Ridge chooses a stormwater fee, a tiered design based on percent imperviousness could be more equitable.

Students also recommended two next steps: a citywide impervious‑surface analysis (rather than the current focus on commercial and multifamily parcels) and an in‑depth hydrological study to identify bottlenecks between natural and built stormwater systems. The team noted that the city could consider incentives or rebates (for example, credits for installing bioswales or other on‑site detention) as part of a fee design.

Councilors praised the maps and asked technical questions about bioswales, detention ponds, and how parking‑minimum policy changes might affect impervious area. Director Maria D'Andrea and staff said the city will incorporate the students' technical reports into the city’s ongoing rate‑setting and design work and that staff expect formal written reports from the students in the next two weeks.

Ending: The student team left council with three immediate recommendations: (1) complete a full citywide impervious analysis, (2) commission a targeted hydrological study to identify pipe and basin bottlenecks, and (3) pursue a tiered fee model with credit options if the city opts for a stormwater assessment.