DWR_2731616

• Document Date: 12/1/2014
• Document Type - Dam Safety: Report
• Division: 1
• Dam ID: 040229
• Dam ID: 040230
• Dam ID: 040904
• Dam ID: 040905
• Dam ID: 040906
• Subject: SEPT. 2013 LITTLE THOMPSON RIVER FLOODING & BIG ELK MEADOWS DAM FAILURES
• DWR Send/Recipient: DAM SAFETY BRANCH-COLORADO DIVISION OF WATER RESOURCES

11.1
No- Breach Model Results ....................................................................................
.............................28
11.2
Dam Breach Model Results ..................................................................................
.............................31
11.3
Flood Volumes .....................................................................................................
.............................34
11.4
Incremental Impacts Analysis ..............................................................................
.............................35
12
DISCUSSION OF OBSERVED DAMAGES and POTENTIAL CAUSES
............................ .............................38
12.1
Observed Damage ...............................................................................................
.............................38
12.2
Modeling Limitations ...........................................................................................
.............................40
12.3
Possible Causes of Events not Captured in the Modeling ...................................
.............................42
13
COMPARISON WITH PAST LITTLE THOMPSON RIVER FLOODS ...............................
.............................42
14
CONCLUSIONS ..........................................................................................................
.............................46
15
ACKNOWLEDGEMENTS ............................................................................................
.............................47
16
REFERENCES .............................................................................................................
.............................48
LIST OF FIGURES
Figure 1— Map of Study Area of September 8 -18, 2013 flooding on the Little Thompson River
Figure 2 — Map of total rainfall from September 8 -18, 2013 Storm
Figure 3 — Map of overall drainage basin included in this study.
Figure 4 —A Pre -Flood Aerial Image Map showing the Big Elk Meadows Association dams.
Figure 5 - Photo taken at 6:47 a.m. Sept. 12th, 2013 at the location of the CR 47 Culverts
Figure 6 —An aerial photo of Crow Lane No. 1 dam in Pinewood Springs, CO
Figure 7 —A Post -flood aerial photo of the Big Elk Meadows dams
Figure 8 — Gage- Adjusted Radar Rainfall analysis results for the Little Thompson River study area
Figure 9 - Sunset Dam breach looking across and downstream from left abutment.
Figure 10 - Rainbow Dam breach section viewed from left abutment.
Figure 11- Willow Dam breach looking downstream from within the reservoir on left abutment.
Figure 12 - Mirror Dam breach looking downstream from the left abutment.
Figure 13 — Panorama of the Meadow Lake Dam breach looking downstream
Figure 14 - Typical high water mark debris line on a slope adjacent to the dam.
Figure 15 - Example of bent grass line from overtopping flow.
Figure 16 - Map showing locations of peak flows estimated using indirect methods.
Figure 17 - Map of basin delineation for rainfall -runoff modeling
Figure 18 - Map of Big Elk Meadows Dams subbasin delineation for rainfall -runoff modeling.
Figure 19 — Temporal distribution of the gage- adjusted radar rainfall
Figure 20— No Breach Model Hydrographs at Calibration Sections
Figure 21— No Breach model outflow hydrographs for contributing basins
Figure 22 — Breach model outflow hydrographs at Big Elk Meadows dams
Figure 23 — Breach model outflow hydrographs at calibration sections.
Figure 24 — Peak flow stage analysis at below Meadow Lake dam calibration section.
Report of the September 2013 Little Thompson River Flooding COLORADO
and Big Elk Meadows Dam Failures, June 2014 (Revised, Dec 2014) Division of Water Resources
iv -: - .
DAM SAFETY BRANCH