FLOOD05658

• County: Weld
• Basin: South Platte
• Title: Project Notebook for I-25 Corridor Master Drainage Plan South Weld County: Volume 1 of 2
• Date: 12/6/1999
• Prepared For: Weld County Public Works
• Prepared By: Anderson Consulting Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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INPUT PARAMETERS

The user needs to input the following catchment parameters to generate a unit and stonn hydrograph:
A. Input Parameters
The following catchment parameters are needed for the program to generate a unit and storm
hydro graph.
1. Area - Catchment area in square miles
2. Catchment Length - The length in miles from the downstream design point of the
catchment or sub-catchment along the main drainageway to the high point on its
respective catchment or sub-catchment. When a catchment is subdivided into a series of
sub-catchments, the sub-catchment length used shall include the distance required for
runoff to reach the major channel from the farthest point in the sub-catchment.
3. Centroid Distance - Distance in miles from the design point of the catchment or sub-
catchment along the main drainageway to its respective catchment or sub-catchment
cemroid.
4. Percent Impervious - The fraction of the catchment surface which is impervious in
percent.
5. Catchment Slope - The length weighted average slope of the catchment in feet per foot.
See instructions in the USDCM to determine the weighted slope.
6. As an option for small urbanized areas, (e.g. less than 90 acres), you may enter time of
concentration in minutes. Procedure for estimating time of concentration is given in the
USDCM, VoL 1. By specifYing the time of concentration, hydrograph peaks will be
computed and displayed using both the CUHP methad and the Rational Formula. This
option will be aercised only if the I-hour rainfall option is used for Card B2' .
7. Pervious retention - Maximum depression storage on pervious surfaces in inches.
8. Impervious retention - Maximum depression storage on impervious surfaces in inches.
9. Irrfiltration rate -Initial infiltration rate for pervious surfaces in the catchment in inches
per hour. If this entry is used by itself; it will be used as a constant infiltration rate

. Cud B2 is cquiwleIIt to !iDe 2 of the <:;uHPF1PC input file.

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