FLOOD02825

• Designation Number: 150
• County: Adams
• Community: Thornton
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Direct Flow Area 0054 - Including Major Drainageway Planning DFA 0054 Phase A Report 11/79
• Date: 10/1/1979
• Designation Date: 1/1/1980
• Floodplain - Doc Type: Floodplain Report/Masterplan

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I.
MAJOR DRAINAGEWAY PLANNING
DIRECT FLOW AREA 0054

Introduction

North of Denver, in Adams County and the City of Thornton, lies a small un-named
drainageway which flows directly into the South Platte River, identified by the Denver
Regional Council of Governments as Direct Flow Area 0054. Historically, the land within
this drainage basin has been used for agricultural purposes and drainage was not a concern
for the local residents and farmers. In a relatively short period of time, mostly within the
last decade, however, the City of Thornton has experienced rapid growth and the trend is
toward fully developed conditions in the uplands of the drainage basin within a few years.
The increased residential development has caused an increase in the drainage flows from
the upland areas which has been the cause of numerous problems in the lower areas of the
basin still involved in agricultural activities.

As a result of the conflicts which have been growing over the increased runoff in
Direct Flow Area 0054, the City of Thornton and Adams County together with the Urban
Drainage and Flood Control District have contracted with Merrick and Company,
Consulting Engineers, to compile information, evaluate, study and to recommend design
solutions to the drainage problems on the creek which are in the best interest of the
involved parties and agencies. The results of the study are to be published in three
volumes:

I. Flood Hazard Area Delineation - Direct Flow Area 0054
IL Major Drainageway Planning - Phase "A" Direct Flow Area 0054
IlL Major Drainageway Planning - Phase "B", Direct Flow Area 0054

This report is the culmination of the development of alternative flood control plans
and concludes the Phase "A" portion of the Study. The necessary field work, compilation
of data, the development and consistent evaluation of feasible alternative flood control
plans has been completed and the results are presented herein. The contents hereof are
for the use of the Urban Drainage and Flood Control District and associated local
governments in their urban planning endeavors. Upon reviewing the study findings and
recommendations, the District and local governments will select an alternative plan for
implementation which most satisfies local interests, The selected plan will then be
further developed in the Phase "B" portion of this study.

Summary of the Recommended Plan

Floods as minor as the 2-year event in magnitude have occurred as recently as May
of 1979, causing damage to roadways, embankments, utilities, crop and pasture lands, and
creating various other problems associated with soil erosion and sediment deposition.
Implementation of the consultant's recommended plan in the lower portions of the
drainage basin, Reaches 1 and 2, would prevent the damage caused by the relatively minor
but frequent floods that occur almost annually and would also greatly reduce the impact
of the major flood events. In Reach 4, north of 112th Avenue, a detention facility coupled
with storm sewer and channel improvements designed to handle the 10-year event are
recommended. The recommended plan in Reach 3 takes advantage of existing right-of-
way with the enlargement of an existing detention pond and spillway improvements to
another pond coupled with an interconnecting lined channel. In selecting the recom-
mended plan, the overall continuity of the plan was a major consideration. Figure I-I
provides a geographical reference for the locations of the various recommended improve-
ments.

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