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Boulder Slough

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The Boulder Slough is an irrigation channel that has historically carried flood overflows from Boulder Creek, downstream of Broadway. The Slough trends east‐northeast terminating at its confluence with Goose Creek east of Foothills Parkway. The Boulder Slough Mapping Study defines new flood zones for this area. 

FEMA formally accepted the mapping study on Nov. 2, 2018.

For more information about your property, flood zone definitions and frequently asked questions, please open the Boulder Slough Interactive Map by clicking the image below.

This is a link to the Boulder Slough Floodplain Mapping Study - Interactive Story Map.












Boulder Slough Mapping Study Project Background

Floodplain mapping studies provide the basis for flood management by identifying the areas subject to flooding. This information is essential for determining areas where human safety is threatened and property damage is likely. Floodplain maps must be updated periodically to reflect changes in the floodplain resulting from land development, flood mitigation improvements and new study technologies.

In 2013, the City completed a floodplain study for Boulder Creek to reflect the numerous changes authorized by City floodplain permits and update hydraulic models based on better, more detailed topographic information. The Boulder Creek floodplain study did not initially include the flow path for the Boulder Slough, but the upstream reach of the Boulder Slough was added to the Boulder Creek Study during the FEMA adoption process. 

The Lower Boulder Slough study includes hydraulic models and flood hazard mapping for the 100-year flood event and conveyance zone for the reach of Boulder Slough from approximately 300-feet downstream of 30 th Street to where the Slough confluences with Goose Creek, east of Foothills Parkway. Modeling and mapping of this reach, as well as split flow paths, utilizes 2013 Lidar-based topographic data.

City Council accepted the mapping study on Sept. 5, 2017 at which time the mapping became effective for permitting purposes by the City of Boulder. FEMA formally accepted the mapping study on Nov. 2, 2018 for insurance purposes.

Upper Boulder Slough Information

The Upper Boulder Slough Study includes the area from the Boulder Creek floodplain, approximately 100-feet downstream of 18th Street to approximately 300-feet downstream of 30th Street.  The Upper Boulder Slough Study was completed in 2015.