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Boulder Creek Restoration Master Plan

Boulder Creek Restoration Master Plan

OVERVIEW

The Boulder Creek Restoration Master Plan was initiated as a result of the September 2013 flood event. The City of Boulder joined regional partners, including the Urban Drainage & Flood Control District (UDFCD), Boulder County, and the City of Longmont on the development of the Boulder Creek Restoration Master Plan. This study was also partially funded through the Colorado Water Conservation Board (CWCB) grant program. The purpose of the master plan is to develop guidance in planning ongoing and long-term watershed recovery efforts.

This project encompasses nearly 24-miles along Boulder Creek pdf, extending from the confluence with Fourmile Creek, located within Boulder Canyon upstream of the City of Boulder, downstream to the confluence with St. Vrain Creek in the City of Longmont. The master plan area crosses through the City of Boulder and also includes city-owned open space lands, outside of the city limits.

The focus of this master plan is to provide a planning tool for stream and ecological restoration along Boulder Creek. As such, this master plan does not comprehensively evaluate Boulder Creek through the city limits given that Boulder Creek through this reach resembles more of an urban stream corridor.  Instead, the plan addresses specific areas of concern identified by the city staff and other interested parties who participated in the planning processes. Similarly, the plan does not reevaluate the current 100-year floodplain limits regulated by FEMA, although it is likely that the implementation of some proposed projects would improve flood conveyance and the regulatory floodplain limits.

Icon Engineering was retained by the project team to develop and evaluate alternatives for Boulder Creek and prepare the master plan, which identifies and prioritizes feasible drainage, flood management and restoration opportunities. The acceptance of this plan at the February 29, 2016 City Council meeting, will help guide future projects within the planning area and be a tool to help identify projects for future funding through the Capital Improvement Program (CIP), grants, UDFCD funding requests and other funding opportunities.

BACKGROUND

The Boulder Creek watershed is approximately 440 square miles. It extends west of the City of Boulder to the Continental Divide with elevations exceeding 13,000 feet.  Boulder Creek generally flows east, and then northeast across the city. There are 14 other major drainageways tributary to Boulder Creek.

Boulder Creek has experienced several major flooding events, with the earliest reports dating back to the 1840’s. The flood of record is reported to have occurred in 1894, where nearly 3 days of rainfall washed out bridges and resulted in major damage to homes and businesses.  In 2013, between Sept. 9 and Sept. 15, a large rainfall event resulted in widespread flooding along the Colorado Front Range. Boulder Creek experienced peak flows ranging from approximately 5,000 cubic feet per second (cfs) in downtown Boulder, to over 9,000 cfs downstream of US Highway 287, equating to a 25- to 50-year flood event. Although emergency flood repairs were completed, portions of Boulder Creek outside of the city limits would benefit from post-flood ecological restoration, highlighting the need for a restoration master plan. Planning for floods within the City of Boulder and Boulder County dates back to the early 1900’s. In 1910, Fredrick Law Olmsted, Jr. recommended against allowing development to encroach upon the creek channel. Since then, Boulder Creek has been the focus of numerous flood studies and master plans. 

In 2012, the City of Boulder completed a floodplain mapping study update for Boulder Creek from the area west of 61st Street, upstream to the mouth of Boulder Canyon, west of Boulder city limits. The study area encompassed a reach length of five and a half miles. The new floodplain mapping was adopted by City Council on Sept. 18, 2012. For more information about the floodplain mapping study, visit the mapping project website: Boulder Creek Floodplain Mapping Update

SUMMARY

Icon Engineering was retained by the project team to develop and evaluate alternatives for Boulder Creek and prepare the master plan, which identifies and prioritizes feasible drainage, flood management and restoration opportunities.

The plan provides general guidance for stream and ecological restoration among other multiple objectives including:

• Identification of immediate project needs;
• Provide general guidance for stream restoration;
• Identify ecological needs and benefits;
• Identify floodplain management strategies;
• Identify transportation improvements at Boulder Creek stream crossings;
• Identify concurrent recreation and open space access planning;
• Identify an improvement prioritization plan; and
• Develop cost estimates for financial planning.

The Boulder Creek Restoration Master Plan divides the Boulder Creek corridor into 10 different reaches, with reaches 5, 6, and 7 containing lands managed by City of Boulder Open Space and Mountain Parks and reaches 8 and 9 running through the City of Boulder. The master plan recommendations for these reaches are summarized below:

Reach 5 – From U.S. 287 to approximately 4,200 ft. upstream of 95th Street
Master plan improvements on city managed land for this reach include stream and floodplain restoration from 95th Street upstream to the White Rocks Trail bridge. Eventual replacement of the bridge at 95th Street is also recommended. 

Reach 6 – From approximately 4,200 ft. upstream between 95th and 75th streets
Master plan improvements for this reach include modifying Leggett Ditch for aquatic species passage and improving the 75th Street crossing to a 220 ft. span bridge. The roadway crossing at 75th Street should be evaluated at a future time to determine whether the structure can be removed based on the transportation needs in the area.

Reach 7 – From 75th Street to Valmont Road.
Projects within Reach 7 include the installation of gravel pond spillways, protection of the City of Boulder’s sanitary sewer trunk line, improved roadway crossings, stream restoration, and modification of existing diversion structures. Seven gravel pit spillways are proposed to protect Walden Ponds near the downstream limit of Reach 7. Several gravel pond spillways are proposed within the Walden Ponds Wildlife Habitat area and along private ponds within Reach 7. Stream stabilization and bank protection is proposed to provide additional protection from erosion and degradation in the vicinity of the City of Boulder’s central sanitary interceptor. Stream restoration from Valmont Road to 61st Street is proposed to restore ecological functions and provide additional protection for Boulder’s sanitary inceptor. These locations will be protected using grade control structures and bank stabilization. Master plan improvements through this reach also include modifying two irrigation ditch diversion structures to accommodate aquatic species passage.

Reach 8 – From Valmont Road to 30th Street.
Master plan improvements within Reach 8 are comprised of stream restoration, improving the railroad crossing conveyance capacity, access to Boulder Community Health and management of accumulated sediment. Stream restoration is proposed from the downstream limit of Reach 8 at Valmont Road through Foothills Parkway. No improvements are proposed for the 55th Street crossing as the existing bridge structure conveys the 100-year discharge. The BNSF railroad is a significant obstacle for Boulder Creek; the crossing is proposed to be increased to a 180 ft. span bridge to better convey flood flows and accommodate geomorphic channel conditions.

Reach 9 – From 30th Street to City of Boulder Limits
Master plan improvements within Reach 9 include mitigating flood hazards, improving access near Boulder Creek, modifying irrigation diversions and sediment maintenance. Downstream of 28th Street, along Cordry Court, realignment of the Boulder Creek Trail is proposed to increase conveyance and mitigate the high hazard conditions near residences. In accordance with city objectives, property acquisition along this reach should be considered as a means to eliminate high hazard designation and improve overall public safety. Near the CU campus, two new pedestrian bridges are proposed to improve access to the North of Boulder Creek campus. These bridges, or walkways, will provide emergency access to areas otherwise susceptible to isolation during flood events. To mitigate flood hazards along the Boulder Slough, an overflow diversion structure is proposed at 14th Street. 

NEXT STEPS

The Boulder Creek Restoration Master Plan will help guide creek restoration and flood mitigation projects within the master plan area.  It will be a long-term planning tool to help identify projects for future funding through the CIP, grants, UDFCD funding requests and other funding opportunities.

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