DWR_2726118

• Document Date: 1/23/2015
• Document Type - Dam Safety: Report
• Division: 2
• Dam ID: 100469
• Subject: UPPER EMERALD VALLEY RANCH DAM - FINAL DAM FAILURE FORENSIC INVESTIGATION REPORT
• DWR Send/Recipient: JOHN HUNYADI, BILL McCORMICK - DSB

 Page 9 Upper and Lower Emerald Valley Dam Failure Report
January 23, 2015

 They reported that the abutments had washed
away during the flooding and that a distinct
rise in the creek had been observed at the
bridge shortly after Noon on 12 SEP 2013.
 They also reported that prior to rise in creek,
there was significant debris built up against
the bridge and the City was actively in the
process of trying to remove the debris with a
tracked “mini-excavator”.

7.0 Analysis
The DSB approached this investigation using standard means and methods established and
used by the Dam Safety Community for the study of similar events. The investigation followed
the “Dam Failure Investigation Guideline” by the Association of State Dam Safety Officials
(ASDSO) dated December 8, 2011. The U.S. Bureau of Reclamation (USBR) Hydraulic
Investigations and Laboratory Services Group was also consulted for recommendations on how
to conduct field investigations and interviews.

A combination of methods and software were used to conduct the investigation and analysis of
the Emerald Valley dam failures. The storm runoff and dam failure model was primarily
developed using the United States Army Corps of Engineers (USACE) Hydrologic Engineering
Center-Hydrologic Modeling System (HEC-HMS) software, version 3.5. Calibration with cross
section surveys to estimate peak flows was facilitated by the Bentley Systems, Inc.,
FlowMaster software, version 8i. Surficial soil information was obtained from the Natural
Resources Conservation Service (NRCS) Geospatial Data Gateway. ESRI ArcMap 10.0 was used
for processing Geographic Information System (GIS) mapping and spatial information. The
Colorado Dam Safety Branch guidance documents; Guidelines for Dam Breach Analysis (2010),
Guidelines for Hazard Classification (2010), and Hydrologic Basin Response Parameter
Estimation Guidelines, (2008), were also used as references for the analyses.
The following analysis was performed as part of this dam failure forensic study.

7.1 Rainfall Analysis
Applied Weather Associates, Inc. provided the SEO DSB with quality-controlled
spatial and temporal rain data of the September 2013 storm produced using their
SPAS program. The full SPAS rain data is included in Appendix C. The data set in
Appendix C is presented in UTC time reference, however, the data in HEC-HMS
were adjusted UTC-6hrs to appropriately represent Mountain Daylight Time.

7.1.1 Spatial Data
Figure 10 & 11 shows rain totals for A) Subbasin above Emerald Valley
Dams and B) Entire Basin Above Highway 115 (includes EV Dam Subbasin).
These figures indicate that the largest rainfalls occurred north and east of
the Little Fountain Creek Basin, which is around the East Slopes of
Cheyenne Mountain/Fort Carson area. It is worth noting that large rain
amounts occurred as high as 10,000 ft, in contrast to the often cited rule
that snowmelt driven runoff dominates at elevations above 7,500 ft in
Colorado’s Front Range.

SPAS tabular data Rain Totals:
Drainage Above Emerald Valley Only: 11.56 in
Entire Little Fountain Creek Drainage above Highway 115: 11.58 in