Olsson Associates

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Storm drainage master plans yield big benefits for communities

Tuesday, October 14, 2014

Deb Ohlinger, PE, CFM, Water Resources

Every five years, the City and County of Denver is required, by ordinance, to update its storm drainage master plan. To meet an October 2014 deadline, Olsson was chosen to be part of a collaborative team of four engineering firms to complete this enormous task. The selected firms have on-call services contracts with Denver, and each firm managed projects in different sections of the city. Olsson worked primarily in the northeastern sections of Denver and in the south-central area. The master plan update took 18 months and 6,000 hours to complete. In September, the Denver City Council unanimously approved the plan.

Storm drainage plans are most effective with regular updates. Over time, storm drainage needs and conditions change in a community. These changes include:

  • Development of new residential and commercial areas with resulting alterations in stormwater flow rates and patterns
  • Availability of updated studies
  • Upgrades to systems or new storm drains

Denver’s updated master plan is a guiding document for making effective, prioritized decisions. It also includes some new features such as the identification of potential inundation areas. The plan not only helps Denver use their tax dollars more efficiently, but it also helps residents and developers make better flood mitigation and planning decisions.

Tasks included:

  • Researching the improvements, construction projects, and designs for construction that have occurred since the last master plan update and incorporating this data into a Geographical Information System (GIS) database.
  • Incorporating Urban Drainage and Flood Control District (UDFCD) studies and recommendations into the master plan.
  • Performing FLO-2D studies to better understand stormwater flows in key areas of Denver for mitigation and planning purposes. For example, Olsson performed a FLO-2D analysis of stormwater flow around the Washington Park area to identify the flow patterns and potential inundation areas.
  • Meeting with City Council members to discuss the master plan and storm drainage issues in their districts. Lisa Zoeller of Zoeller Consulting, LLC, was part of Olsson’s team to provide public outreach services for the overall project and coordinated with all of the consultants.

Denver’s updated master plan offers new benefits for city departments, developers, and residents. For example, if the city’s bridge program is working at a location where a UDFCD study recommends enlarging a bridge or culvert, the master plan will reflect the UDFCD recommendation. The program can also combine the bridge and drainage upgrade into one project. In the past, this work might have been done as two separate, more costly projects.

Potential inundation areas are also identified visually in the master plan basin maps so that city council members, residents, and developers can easily identify potential problem areas. The maps and technical data available in the master plan appendices are highly valuable for developers as they work with the city’s planning department. These supporting documents could save developers the expense of hiring an engineer for this initial analysis.

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