12000000063 Hyatt Dam Inundation Report

• Contract/PO #: 12000000063
• Contractor Name: Farmers High Line Canal and Reservoir Company
• Contract Type: Grant
• Water District: 7
• County: Jefferson
• Loan Projects - Doc Type: Report

1.0 INTRODUCTION
Deere&Ault Consultants, Inc. (D&A)has prepared this Inundation Mapping Report at the request
of the Farmers' High Line Canal and Reservoir Company(FHL). This report documents the
procedure of modeling a clear-day dam breach of Hyatt Dam, and the development of the resulting
inundation maps downstream of the dam. The inundation maps will be used to update the existing
Emergency Action Plan (EAP) and to assist those involved with emergency preparedness planning
and response. The hydraulic models and inundation maps contained in this report were prepared
using the NAVD 88 vertical datum. The report and all associated models have been prepared in
accordance with the regulations and guidelines set forth by the Colorado Department of Natural
Resources, Office of the State Engineer(SEO).
1.1 Location and Background
Hyatt Lake is located near the western end of Arvada, Colorado in Section 7 of Township 3 South,
Range 69 West of the 6th Principal Meridian. Hyatt Lake Dam is currently classified as a Small
Significant Hazard Dam, per the Rules and Regulations for Dam Safety and Dam Construction of
the State of Colorado. It is an earthen compacted dam with a height of 24 feet and a normal storage
of approximately 760 acre-feet.
2.0 DAM BREACH ANALYSIS
2.1 Breach Parameter Estimation
Hyatt Dam was visually inspected on-site and with aerial photographs, and a ground survey was
conducted by D&A to determine the spillway crest elevation and the dimensions of the dam at the
maximum section.
Three empirical methods for predicting the average breach width and failure time were compared.
The methods, which are included in Appendix A, are the Froehlich (2008) equations, the Von Thun
and Gillette(1990) equations, and the USBR (1988) equations (collectively referred to as the
"empirical equations"),I The empirical equations predict the average breach width and failure time
as a function of depth of water, dam height, and volume of water stored. A comparison of the
breach parameters calculated by each of the empirical equations is shown below in Table 1.
Table 1. Hyatt Lake Dam Failure
Comparison of Dam Breach Parameters
Empirical Method Average Breach Time of
Width (ft) Failure(min)
Froehlich 79 46
Von Thun and Gillette 69 53
USBR 59 12
A fourth empirical method known as the MacDonald&Langridge-Monopolis/Washington State(2007)
method was not considered based on recommendations found in the Guidelines for Dam Breach Analysis.
HYATT DAM - 1 - June 21,2012
INUNDATION MAPPING REPORT