Milwaukie reviews stormwater system plan update after modeling, data and permit changes

Milwaukie city staff and the project consultant told the City Council at an Aug. 19 work session that the stormwater system plan update is behind schedule after the team encountered missing and incompatible data while updating hydraulic models.

The plan update matters because it will guide capital projects, operations and permit compliance for drainage that discharges to Johnson Creek, Kellogg Creek and the Willamette River. Peter Passarelli, a city staff member, said the team has resumed modeling after data work and cautioned that additional surveying and data collection will be needed before the plan is finalized.

Passarelli said, “this plan, we're actually a little bit behind schedule, in terms of getting getting the work done.” He and consultant Scott Durham described two causes: newer model versions require more consistent elevation and structure data, and extending the model to smaller pipe diameters exposed gaps in the city GIS. Durham, vice president with Marsh Consulting, said the team initially tried to reuse older models and then rebuilt them when incompatibilities prevented reliable results.

The consultants said small elevation errors for…