📋 Case Study

Mountainous Ski Resort Stormwater Retrofit in Aspen, CO

Preventing erosion and sediment delivery to Roaring Fork River (Class I trout stream) under high-intensity snowmelt pulses and freeze-thaw cycles

🏗️ Project Overview

Upgrading 1970s-era concrete channels on 32° slopes serving base village and parking lots

🎯 Challenge

Preventing erosion and sediment delivery to Roaring Fork River (Class I trout stream) under high-intensity snowmelt pulses and freeze-thaw cycles

🔧 Design Approach

Rock-lined stepped chutes with energy dissipators, bioswales with cold-tolerant vegetation (Carex spp.), and sediment basins with vortex separators

📐 Design Diagram

AI-generated project design illustration

📐 Key Calculations

Chute Velocity Limit

V_max = √(2gΔh)

Result: 21.3 ft/s

Kept below threshold for incipient motion of D₉₀ rock

Sediment Basin Detention Time

t_d = V / Q_peak

Result: 4.8 min

Ensures >90% removal of particles >75 μm

Freeze-Thaw Cycle Resistance

N_f = (σ_t / σ_f)^m

Result: 1,280 cycles

Exceeds Aspen’s 500-cycle design life requirement

📊 Results

Zero sediment exceedances in 3 years of monitoring; 100% compliance with Colorado Water Quality Control Commission’s Class I standards; slope stabilization certified by USFS

💡 Lessons Learned

•Rock chute joints require elastomeric sealants rated to −40°F
•Bioswale plants must survive 120+ days of snow cover
•Vortex separators require quarterly vacuum cleaning to maintain efficiency

✅ Key Takeaways

1Rock chute joints require elastomeric sealants rated to −40°F
2Bioswale plants must survive 120+ days of snow cover
3Vortex separators require quarterly vacuum cleaning to maintain efficiency