FLOOD10420

• County: Adams
• County: Broomfield
• County: Weld
• Community: Broomfield, Westminster and Thornton
• Stream Name: Lower Big Dry Creek
• Title: Lower Big Dry Creek Hydrology Study
• Date: 6/1/2005
• Prepared For: Big Dry Creek Watershed Association
• Prepared By: Wright Water Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Lower Big Dry Creek Hydrologic Study

however, that wastewater-related baseflow conditions are not expected to significantly
increase due to the planned implementation of wastewater reuse programs in the
watershed. Actual conditions will depend on how augmentation plans are administered
and the degree to which the wastewater reuse programs are implemented. Irrigation
return flows in both the upper and lower watershed also contribute to baseflows. The
extent to which non-wastewater related baseflows associated with urbanization will be
offset by potential reductions in wastewater discharges was not quantified in this study.

10. Although land management practices in the lower watershed do not typically cause
erosive storm flows and flooding, they do increase the susceptibility of banks to erosion
in some locations where the ground is denuded or trampled. Similarly, any type of
constriction to the creek's flow path such as bridges or culverts have the potential to
contribute to flooding and erosion.

Recommendations to Improve and Address Drainage Problems in the Lower
Watershed

1. The Big Dry Creek Northern Area Tributaries Outfall Systems Plan Update planned to
begin in 2005 under the direction of the Urban Drainage and Flood Control District and
sponsored by Adams County, Broomfield, Thornton and Westminster is an important
component in !laying a framework for managing stormwater flows in one of the key
developing areas in the watershed. Given that the entities sponsoring the update are also
participating in the Big Dry Creek Watershed Association, there are significant
opportunities to recognize the existing downstream flooding and erosion concerns and
recommend stormwater management strategies to help minimize impacts of future
development in this area. The Big Dry Creek Watershed Association must ensure that the
findings of this hydrologic study are considered in the alternatives evaluated in the outfall
systems plan update.

2. Downstream landowners within or in the: vicinity of the 100-year floodplain along Big
Dry Creek should take appropriate steps to plan for and protect themselves from flooding.
For properties in the floodplain (i.e., all of the properties visited in this study), flooding

971-179.092
June 2005

Wright Water Engineers, Inc.

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