12-053 SOW

• Applicant: Highland Ditch Company
• Grant Type: Non-Reimbursable
• Fiscal Year ‎(i.e. 2008)‎: 2012
• Project Name: Inundation Mapping for Highland Ditch Company
• Contract/PO #: OE PEA 12000000053
• Grants - Doc Type: Scope of Work

January 4, 2012
Project: Inundation Mapping for Highland Ditch Company
Vendor: The Highland Ditch Company, P.O. Box 649, Mead, Colorado 80542-0649
Phone [phone], Fax [phone],
c/o Jill Batty, Company Manager, Email [e-mail]

Consultant: Deere & Ault Consultants, Inc., 600 S. Airport Road, Building A, Suite 205, Longmont, CO 80503
Phone: [phone] , Fax: [phone]
c/o Mark A. Severin, P.E., Project Manager, [e-mail],
SCOPE OF WORK
This is a study to perform dam breach modeling of six dams in the Highland Ditch Company’s (Company)
system in accordance with the latest Breach Guidelines published by the Colorado Dam Safety Branch. The
level of analysis shall be “Simple” as described in Table 1 of the Guidelines for both the breach modeling and
flood inundation mapping. Flood routing models and inundation mapping shall be based on the USGS 10-
meter Digital Elevation Model (DEM) or best available topographic mapping. Field measurements of
bridges/culverts at critical sections shall be incorporated into the model as necessary.
The limits of the dam breach flood mapping shall extend from each reservoir downstream to where the
breach flood impacts are no longer significant. The inundation mapping downstream from Foothills
Reservoir is expected to extend from the dam down to the St. Vrain River and to the South Platte River with
the emphasis on the reach between the reservoir and I-25.
The Highland #2 Reservoir has two dams (North Dam and South Dam) requiring inundation mapping
downstream from each. The inundation mapping downstream from the North Dam is expected to extend
from the reservoir down to the Little Thompson River and to the South Platte River. Much of this inundation
mapping follows the same flow path as the recently prepared inundation mapping for Ish Reservoir. This
scope assumes that the base map, survey information, and hydraulic model used for the Ish Reservoir study
will be made available to assist in preparation of inundation mapping for the Highland #2 North Dam. Failure
of the South Dam at Highland #2 Reservoir would result in overland flow from the reservoir through the east
side of Longmont and into the St. Vrain River. The inundation mapping is expected to extend downstream to
I-25. The City of Longmont has proposed a regional detention pond to the north of Highway 66 that will be
represented in the modeling and the inundation mapping of the failure of the South Dam.
Failure of the dam at Highland #1 Reservoir would flow to the east across I-25 and into New Thomas
Reservoir. The surcharge storage volume in New Thomas Reservoir is expected to contain the majority of the
flow resulting from a clear day failure of Highland #1. The inundation mapping is expected to extend from
Highland #1 down to New Thomas Reservoir. A blue line will be shown on the mapping illustrating the flow
path from the New Thomas Reservoir spillway down to the South Platte River.
Failure of the dam at Highland #3 Reservoir would generally flow south toward the St. Vrain River located
approximately 2 miles away. The inundation mapping is expected to extend downstream to I¬25.