September 11-13, 2013 Arvada Flood Event Reconstruction and Documentation Prepared for: Prepared by: City of Arvada Public Works Department Water & Earth Technologies, Inc. Engineering Division 1225 Red Cedar Circle, Suite A 8101 Ralston Rd. Fort Collins, CO 80524 Arvada, CO 80002 Final Report March 2014 September 11-13, 2013 Flood Event Reconstruction and Documentation March 2014 City of Arvada Table of Contents 1. Executive Summary ...................................................................................................................1 2. Introduction and Background ....................................................................................................3 2.1. Hydrologic Setting .............................................................................................................3 2.2. Flood Vulnerability and Flood History in Arvada .............................................................5 3. The Rainfall Event of September 11th – September 13th, 2013 .................................................6 3.1. September 9 through September 13 Precipitation Data for Arvada ...................................7 3.2. Stage/Discharge Data for Arvada .....................................................................................13 4. The Flood Event of September 11th – September 13th, 2013 ...................................................15 4.1. Van Bibber Creek .............................................................................................................15 4.2. The Croke Canal ...............................................................................................................18 4.3. Ralston Creek ...................................................................................................................23 4.4. Leyden Creek ...................................................................................................................34 5. Summary ..................................................................................................................................52 6. Recommendations ....................................................................................................................53 7. References ................................................................................................................................54 Table of Tables Table 1. Design Rainfall Depth Ranges from the Hydrology Report. ......................................... 12 Table 2. One-hour and 6-hour Incremental Rainfall Totals. ........................................................ 12 Table 3. Design Reservoir Inflow and Outflow for Design Frequency. ...................................... 13 Table 4. Historic Annual Peak Flows on Van Bibber Creek. ...................................................... 19 Table 5. Historic Annual Peak Flows on Ralston Creek. ............................................................ 26 Table 6. Reconstructed Ralston and Arvada/Blunn Reservoir Conditions During Flood ........... 29 Table 7. Historic Annual Peak Flows on Leyden Creek. ............................................................. 36 Table 8. Reconstructed Leyden Reservoir Conditions During Flood .......................................... 42 Table of Figures Figure 1. Location Map. ................................................................................................................. 4 Figure 2. Precipitation Monitoring Stations for Leyden, Ralston and Van Bibber Creeks ........... 8 Figure 3. Cumulative Precipitation at Gages on Leyden, Ralston and Van Bibber Creeks .......... 9 Figure 4. Precipitation Data Comparison. .................................................................................... 11 Figure 5. The Van Bibber Creek Watershed. ............................................................................... 16 Figure 6. Precipitation and Discharge Data for Van Bibber Creek. ............................................ 17 Figure 7. Entrance to Siphon Conveying Van Bibber Creek beneath the Croke Canal. ............. 18 Figure 8. Ralston Creek Pedestrian Bridge at West Woods ........................................................ 21 Figure 9. Ralston Creek Breach into the Croke Canal at West Woods. ...................................... 22 Figure 10. Moon Gulch Breach into Croke Canal. ...................................................................... 23 Figure 11. Ralston Creek Below Arvada/Blunn Reservoir. ......................................................... 24 Figure 12. Precipitation and Discharge Data for Ralston Creek. ................................................. 25 Figure 13. Outflow from Ralston Reservoir. Denver Water. ...................................................... 27 Figure 14. Ralston Creek at the Inflow Channel for Arvada/Blunn Reservoir. ........................... 28 Figure 15. Release from the Arvada/Blunn Reservoir Service Spillway. .................................... 30 Figure 16. Ward Road at Ralston Creek Peak Stage During the Flood. ...................................... 31 i Water & Earth Technologies, Inc. September 11-13, 2013 Flood Event Reconstruction and Documentation March 2014 City of Arvada Figure 17. Ward Road at Ralston Creek After the Flood, Showing Low Capacity ..................... 32 Figure 18. Ralston Creek at Carr St. PT Installation: Intake below Drop ................................... 33 Figure 19. Ralston Creek near Memorial Park ............................................................................ 34 Figure 20. Precipitation and Discharge Data for Leyden Creek. The Leyden Confluence Discharges are Calculated with a Provisional (Based upon the Peak Flow Estimate Survey Conducted after the September Flood Event). .................................................. 35 Figure 21. The Upper Leyden Creek Watershed. ........................................................................ 37 Figure 22. Leyden Road at Leyden Creek High Water Marks. ................................................... 38 Figure 23. Quaker St. at Leyden Creek. ....................................................................................... 39 Figure 24. Leyden Creek Breach of the Church Ditch Upstream of Leyden Reservoir. ............. 40 Figure 25. The Lower Leyden Creek Watershed. ........................................................................ 41 Figure 26. Aerial View of Leyden Reservoir, Leyden Creek at Indiana St. and Croke Canal During Flood. ................................................................................................................ 43 Figure 27. Overtopping of Indiana St. (Looking Northeast). ...................................................... 44 Figure 28. Water Main Damage at Indiana St. (Looking South East). ........................................ 45 Figure 29 Cameo Estates Flooding. .............................................................................................. 46 Figure 30 Cameo Estates Flooding. .............................................................................................. 46 Figure 31 Cameo Estates Flooding. .............................................................................................. 47 Figure 32 Cameo Estates Flooding. .............................................................................................. 47 Figure 33. Location Map of Croke Canal Break Area. ................................................................ 48 Figure 34. Location of Averted Breach of the Croke Canal Embankment. ................................. 49 Figure 35. Flooding Into The Croke Canal Below Indiana St. (Background) and the Location of the Controlled Release From The Croke Canal (Foreground). .................. 50 Figure 36. Conveyance for Leyden Creek Beneath the Croke Canal (After Repairs) ................. 50 Figure 37. Leyden Creek at Its Mouth. ........................................................................................ 51 List of Acronyms AAC Arvada Area Command Acre-ft Volume Equal to One Foot of Depth over One Acre AFPD Arvada Fire Protection District ALERT Automated Local Evaluation in Real Tine cfs Cubic Feet per Second; discharge measurement CoCoRaHS Community Collaborative Rain, Hail and Snow Network CRS Community Rating System (through FEMA) EDM Electronic Data Mapping (UDFCD Service) EOC Emergency Operations Center FEMA Federal Emergency Management Agency FHAD Flood Hazard Area Delineation FRICO Farmer’s Reservoir and Irrigation Company HIG Hazardous Information Group NFIP National Flood Insurance Program (through FEMA) NWIS USGS National Water Information System NWS National Weather Service UDFCD Urban Drainage and Flood Control District USGS United States Geological Survey ii Water & Earth Technologies, Inc. September 11-13, 2013 Flood Event Reconstruction and Documentation March 2014 City of Arvada 1. Executive Summary Record-breaking rains from September 9th to 13th, 2013 caused serious flooding in Arvada, Colorado. Unlike a typical summer thunderstorm and flash flood, the September 11th – 13th, 2013 Arvada Flood Event was the result of widespread long-duration rainfall. The heaviest rain fell on the headwaters of Leyden Creek, a tributary to Ralston Creek. Rainfall totals for gages located in the Leyden Creek watershed exceeded design rainfall totals for the 100-year precipitation event. In addition, storm runoff was routed into Leyden Creek from adjacent drainage basins, including Coal Canyon basin to the north (at Blue Mountain Drive, in the headwaters