FLOOD01374

• Designation Number: 521
• County: Weld
• Community: Erie, Firestone, Dacono
• Stream Name: Tri-town drainageway, Godding Hollow Basin
• Title: South Weld I-25 Corridor Master Drainage Plan
• Date: 9/8/1999
• Prepared For: Weld County
• Prepared By: Anderson Consulting Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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4,3 Hydrologic Modeling Parameters

The hydrologic modeling of the Godding Hollow and Tri-Town Basins involved the
determination of several hydrologic parameters associated with each subbasin. These parameters'
are summarized in the following paragraphs. Table 4.1 presents hydrologic modeling parameters
developed for the existing condition analyses.

4.3.1 Subbasin Delineation and Basin Characteristics

The Godding Hollow and Tri- Town Basins were subdivided into smaller subbasins ranging
in size from approximately 14 acres to nearly 950 acres, The delineation of subbasins was based
on several considerations including the location of drainage facilities, road crossings, and potential
flooding problems, The location of major drainage facilities and the desire to obtain peak
discharge data at several design points resulted in the wide range of drainage areas noted above,
The subbasin delineation for the Godding Hollow and Tri-Town Basins is presented on
Sheet 2. The U,S.G,S. topographic mapping with a lO-foot contour interval, was used to
determine the subbasin characteristics and significant hydrologic parameters. These data included
subbasin area, length (distance from the downstream design point along the flow path to the high
point of the basin), distance to the basin centroid, and basin slope.

4.3.2 Land Use

The majority of the existing land use in the Godding Hollow and Tri-Town Basins is
agricultural. The Godding Hollow Basin is primarily undeveloped agricultural land with the
exception of lands along the 1-25 corridor. Within a half mile of 1-25, there are numerous
commercial and light industrial developments. In the upper Tri- Town Basin, the urbanized areas
ofDacono, Frederick, and Firestone consist primarily of medium density residential housing. The
remaining area of the Tri- Town Basin consists of agricultural lands with pockets of very low to
medium density residential.
For existing conditions, the imperviousness of each subbasin was estimated from aerial
photography provided by Weld County and verified during field investigations, This photography
displays only existing developments through the fall of 1998, Information regarding developments
approved for construction as of March 1, 1999 was obtained from the local jurisdictions of Erie,

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4.3

September 8, /999