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C-102 · Agencies, primes, and property owners

Stormwater design and modeling

Water quality treatment, detention, and flow control, sized in WWHM and written up in the report the reviewer asks for. We can design a complicated system. On most sites we would rather find the simplest one that passes.

Stormwater requirements stack up fast: treatment, flow control, detention volume, and the analysis that proves all of it to a reviewer. We work to Oregon DEQ and Washington Ecology requirements and to the local manual that governs the site, Clean Water Services in Washington County for example, and we look for the layout that satisfies the jurisdiction at the lowest cost to build.

What you get

  • Hydrologic and hydraulic modeling

    Continuous simulation in WWHM, with the spreadsheet sizing behind it, so every facility dimension traces back to a documented input.

  • Water quality treatment

    Biofiltration units such as Filterra, modular wetland systems, filter cartridge vaults, and the simpler options when the site allows them.

  • Detention

    Vaults, ponds, oversized pipe, or arched pipe, chosen to fit the site and the budget.

  • Flow control structures

    Orifice and weir structures, sized by iterating the model until the release rates pass.

  • Flow duration analysis

    Where the jurisdiction requires it, the run that shows the developed site meets the standard.

  • Erosion and sediment control plans

    With the stormwater report, for the permit or land use submittal.

  • Small sites

    Onsite stormwater for an ADU, an addition, or a new parking area, to the county's onsite requirements.

Projects

  • Detached accessory dwelling unit, Washington County, 2026. Site plan and onsite stormwater to the county's requirements, prepared alongside the architect's set and submitted for plan review.
  • Office addition, Washington County, 2018. New parking, water quality treatment, and flow control, with service provider letters obtained from Clean Water Services and the water district.
  • Multifamily development, Tacoma, 2018. Stormwater reports and plans for a boundary line adjustment and the development review application.
  • Low impact design road project, City of Portland, 2017. Paving and erosion control plans.

Standards

Oregon DEQ, the Washington Department of Ecology, Clean Water Services, and the city or county stormwater manual that governs the site.