In 2020, Broomfield engaged Smith Environmental and Engineering (SMITH) to develop a reservoir management plan that outlined an approach to the maintenance of Plaster Reservoir. The impetus for the project was the odor complaints that Parks and Open Space & Trails had received in the past from residents who live around the reservoir.

The management plan consisted of three phases: Data Gathering, Public Engagement and Development of Recommendations. The Data Gathering phase consisted of field measurements of flood storage capacity, an assessment of ecosystem health through the observation of vegetation and wildlife as well as the review of water quality data, and the observation of existing passive recreation opportunities. The Public Engagement phase included a public open house, and two presentations to the Open Space and Trails Advisory Committee (OSTAC) for their review and input.

Finally, the Development of Recommendations phase was divided into four improvement type categories: flood capacity, ecological, water quality, and passive recreation recommendations. These recommendations were divided into three phases. Phase 1 issues were deemed high priority and were planned to be addressed beginning in 2021, Phase 2 issues could be completed when staff and budget allowed, and Phase 3 issues were noted to be implemented only after reservoir dredging, if this was deemed necessary. Recommendations are summarized in the table below:

After completion of the Plaster Reservoir Management Plan, SMITH, the management plan consultant, was subsequently asked to provide a scope of work to begin to address Recommendation FC2 for Broomfield to better understand the scale of excavation being recommended (and associated costs) and to better understand some of the externalities that would be associated with the construction. This scope of work included:

• Detailed topographic survey and recalculation of the existing flood storage capacity,

• Alternatives analysis evaluating the possibilities for construction access,

• Preliminary excavation plan to meet live storage capacity requirements,

• Opinion of probable construction cost,

• The 100-year inundation areas pre- and post-excavation,

• Visual inspection of outlet structure and report by a structural engineer, and

• A hydraulic analysis of existing and proposed conditions.

Broomfield conducted an internal review of the above listed items and determined that moving forward with excavation of the reservoir at this time was not in the best interest of the community for the following reasons:

• Without additional modeling, benefits of increased flood storage capacity are unclear,

• Based on the current hydraulic/hydrologic model, no surrounding structures would be inundated in the current condition, so no benefit to structures immediately surrounding the reservoir would be achieved,

• Disruption to surrounding residents for excavation activities would be significant, with an estimated 1,200 to 1,400 truck trips during construction,

• Excavation was estimated to cost between $1.2 and $1.5 million, and

• Ecological disruption would be significant, and would require extensive restoration, likely over several years to re-establish pre-construction conditions.

Broomfield has requested instead that the Mile High Flood District (MHFD) add the Quail Creek and Plaster Reservoir Floodplain and Open Space Areas to their Five-year Master Drainage Plan (MDP) Studies list to develop appropriate maintenance activities and schedules as well as re-evaluate tributary area and floodplain extents. This approach allows for greater collaboration, coordination, and potential cost-sharing with communities located downstream. The strategy also brings the project into the overall MHFD master planning efforts.

Broomfield staff has determined that with no dredging planned in the foreseeable future, all other recommendations may be evaluated for programming into Parks and Open Space & Trails maintenance activities, subject to available budgets. The City and County of Broomfield has developed a draft operations plan for Plaster Reservoir that will be presented to OSTAC on October 28, 2021 for their review and comment.