Watershed & Hydraulic Modeling

JR Engineering prepared a comprehensive Stormwater Master Plan for the Town of Vail, Colorado. The project evaluated the hydrologic and hydraulic performance of the Town’s existing stormwater system across approximately 45 square miles (28,800 acres) of watershed. The study included the five primary tributary basins—Mill Creek, Spraddle Creek, Middle Creek, Red Sandstone Creek, and Buffehr Creek—and evaluated the network of storm sewers, culverts, open channels, and roadway crossings that convey runoff toward Gore Creek. JR Engineering compiled and evaluated Town GIS data, a digital elevation model, previous drainage studies and construction documents, FEMA flood information, and historical flooding information. Field verification and coordination with Town staff were used to confirm existing infrastructure and drainage conditions and identify data gaps.

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Hydrologic & Hydraulic Modeling

A watershed-wide hydrologic and hydraulic model was developed using EPA SWMM, with PCSWMM used to support model development, spatial data management, and analysis. The resulting model included 554 sub-basins with runoff routed through the Town’s existing drainage network. Design storms ranging from the 2-year through 100-year recurrence intervals were evaluated to identify potential conveyance limitations and areas of concern. A significant technical challenge was developing representative hydrology for Vail’s high-elevation mountain environment, where runoff is influenced by both rainfall and seasonal snowmelt. The hydrologic analysis evaluated precipitation, diurnal peak snowmelt runoff, and precipitation concurrent with rain-on-snow conditions, accounting for the reduced infiltration associated with snow-covered areas at higher elevations. The analysis determined that the highest total runoff conditions were driven by combined rainfall and snowmelt rather than either process independently.

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Model verification and refinement were another important component of the project. Available USGS gage data from Middle Creek, Red Sandstone Creek, and Gore Creek were evaluated through statistical flood-frequency analysis, using HEC-SSP, and runoff-response comparisons. Observed precipitation and streamflow records were used to evaluate how the watershed responds to rainfall events, and modeled results were compared with observed and published flood-flow estimates. The modeling process was further complicated by the mountainous terrain, limited available survey information, and an existing stormwater system developed through numerous projects over several decades. These challenges required integration of GIS data, historical drainage reports, field observations, hydrologic analysis, and engineering judgment to establish representative drainage patterns and infrastructure characteristics. The hydraulic analysis then evaluated flow rates, flow depths, and conveyance performance throughout the modeled system, identifying locations where capacity, velocity, aging infrastructure, sediment accumulation, or maintenance could affect long-term system performance.

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Capital Improvements & Implementation

The technical analysis was ultimately translated into a practical, multi-objective implementation plan for the Town. Seventeen site-specific improvement projects were identified and prioritized based on factors including public safety, critical infrastructure, frequency and potential consequences of drainage problems, water-quality and environmental impacts, multi-objective benefits, and project feasibility. The Plan also established recommendations for routine inspection and maintenance, stormwater design criteria, water-quality improvements, and future technical studies, including potential hydraulic modeling and additional hazard assessments. A key success of the project was integrating watershed-scale hydrologic and hydraulic modeling with field observations and Town staff knowledge to develop recommendations that are both technically sound and implementable. The completed Plan provided the Town with a long-term framework for managing its stormwater infrastructure, prioritizing capital improvements, maintaining existing conveyance capacity, addressing water-quality concerns, and improving long-term stormwater drainage system performance.