FLOOD04416

• Designation Number: 304
• County: Adams
• Community: Unincorporated Adams County
• Stream Name: Big Dry Creek, (ADCO), North area tributaries
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Big Dry Creek, ADCO, North Area Tributaries
• Date: 7/1/1989
• Designation Date: 1/1/1990
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

SECTION I
INTRODUCTION

A.

AUTHORIZATION
This study of the Big Dry Cn:ek (ADCO) North Area Tributaries Flood
Hazard Area Delineation (FHAD) was performed under contract with Wright
Water Engineers, Inc. (WWE) and the Urban Drainage & Flood Control
District (UDFCD) dated August 19, 1988 (Agreement No. 88-02.06). The
local sponsors were Adams County (ADCO) and the City of Thornton
(Thornton).

The notice to proceed was issued effective September 2, 1988. The
draft FHAD report was submitted on June 8, 1989. Comments were
received on June 2 I, 1989 and the final report was submitted on July
21, 1989.

B.

PURPOSE AND SCOPE
The purpose of the study was to evaluate the hydrological and hydraulic
aspects of storm drainage for the Big Dry Creek tributaries between
144th Avenue and l68th Avenue and to define the 100-year floodplain and
water surface profile. The scope of the work for this study is sum-
marized as follows:

1. Define the hydrologic. lopographic. and land use features of the
basin.
2. Define the floodplain and the floodway for the 100-year flood.
3. Prepare plan and profile drawings of the tributary drainageways
showing the 100-year 1l00dp1ain and the 10-year and 100-year flood
profiles based upon future hasin development and existing channel
conditions.

I-I

Floodplains are often altered hy road and hridge construction, develop-
ment within the floodplain, Ilood control improvements, or by natural
processes. Prior to utilizing the information contained in this report
for the purposes of planning or design. the user is advised to contact
the UDFCD or the Colorado Water Conservation Board (CWCB) to determine
if the information in this rep011 has been amended.

C.

DATA COLLECTION
During the course of the study, numerous amounts of data were made
available to WWE from the project sponsors as well as from interested
parties. The information included such data as copies of previous
studies, mapping of the study area, land use data, and various city and
county regulations. A complete list of information obtained and uti-
lized in the pe1formance of this FHAD is presented in the reference
section of this report.

Mapping for the project was provided hy the UDFCD through Delta Aerial
Surveys. Inc. at a scale of I inch = 100 feet and a contour interval of
2 feet. A survey of the existing culverts at road crossings in the
study area was conducted by Delta Aerial Surveys, Inc. under contract
with UDFCD.

Two studies were previously prepared and include a portion of this
study area: "Outfall Systems Planning Big Dry Creek (AD CO) and Tribu-
taries", August 1987, and "Flood Hazard Area Delineation Big Dry Creek
(ADCO)", November 1986. These two studies were for Big Dry Creek only.
No studies were previously prepared for the tributaries to Big Dry
Creek between 144th Avenue and 168th Avenue. A concurrent "Outfall
Systems Planning" study for this area was also prepared by WWE.

]-2