I-5 Ship Canal SW Facility Flow Analysis
Monitored vs Modeled Flow Comparison (Oct - Dec 2025)
2026-01-29
Overview
This analysis compares monitored (Manning equation) and modeled stormwater discharge flows at the I-5 Ship Canal SW Facility for both WSDOT and City of Seattle drainage systems. Rainfall data from rain gauge RG33 is included for context.
Analysis Period: October 1, 2025 - December 31, 2025
Key Findings
WSDOT (I-5)
| Metric | Monitored | MGSFlood Modeled | Difference |
|---|---|---|---|
| Total Volume | 13,551,805 gal | 15,594,928 gal | -2,043,123 gal (-13.1%) |
| Peak Flow Rate | 18.49 cfs | 22.2 cfs | -3.71 cfs (-16.7%) |
Monitored flow is lower than modeled by volume.
City of Seattle - U District (MGSFlood Modeled)
| Metric | Monitored | MGSFlood Modeled | Difference |
|---|---|---|---|
| Total Volume | 7,758,820 gal | 14,163,723 gal | -6,404,902 gal (-45.2%) |
| Peak Flow Rate | 7.15 cfs | 20.5 cfs | -13.35 cfs (-65.1%) |
Monitored flow is lower than modeled by volume.
City of Seattle - U District (MGSFlood Conveyance)
| Metric | Monitored | MGSFlood Conveyance | Difference |
|---|---|---|---|
| Total Volume | 7,758,820 gal | 14,156,927 gal | -6,398,107 gal (-45.2%) |
| Peak Flow Rate | 7.15 cfs | 19.6 cfs | -12.45 cfs (-63.5%) |
Monitored flow is lower than modeled by volume.
Rainfall Summary
| Metric | Value |
|---|---|
| Total Rainfall (RG33) | 17.11 inches |
| Analysis Period | October 01, 2025 to December 31, 2025 |
| Data Points | 26,404 (5-minute intervals) |
WSDOT (I-5): Monitored vs Modeled Flow
City of Seattle - U District: Monitored vs Modeled Flow
WSDOT (I-5) vs City of Seattle - U District Comparison
Monitored Flows
Modeled Flows
All Flows Overview
Generated: 2026-01-29 13:38:38.264353
Herrera Environmental
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