FLOOD09312

• Designation Number: 370
• County: Crowley
• Community: Ordway
• Stream Name: Local Drainage
• Basin: Arkansas
• Title: Floodplain Study and Master Drainage Plan - Ordway, Colorado
• Date: 6/1/1987
• Designation Date: 7/1/1994
• Floodplain - Doc Type: Floodplain Report/Masterplan

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27

Bas i c des i gn cri teri a contai ned in the draft Town of Ordway "Street and
Stonn Drainage Criteria Manual" were followed when designing street and
drainage facilities for the alternative evaluation process. All local facili-
ties were des i gned to flow full. Roughness values for the hydraul i c cal cul a-
tions ranged from .025 for natural stream bedding to .045 in areas where
natural channels were deemed to be overgrown.
The following design criteria were followed in the analysis of existing
and proposed systems:

1. Minimum roughness values.

a. Concrete pipe, channel linings and culverts, .013.
b. Corrugated metal pipe (CMP), .024.

c. Corrugated metal pipe, lined, .013.

d. Natural stream beds, .035.

e. t~aintained grasslined channels, .030.

f. Street secti ons, .015.

2. Design velocities for grasslined channels were limited to five feet per
second, with maximum side slopes of four horizontal to one vertical.

3. Minimum freeboard depth of one foot for all improved channels and ponds.

Basis of Damage Assessment
In order to assess to level of flood protection economically justifiable,
calculations of the dollar loss associated with the 10- and 100-year flood
events were carried out. To do this, several assumptions were made to facili-
tate the calculations. The major assumptions were:

1. Loss of wages = Total hours lost x $6.50/hour.

2. Loss of workdays: 10-year event, 3 days
100-year event, 5 days

3. Loss of business was assumed equal to loss of wages.

4. Average single family house and content value:

a. With basement = $60,000
b. Without basement = $46,000