FLOOD00770

• Designation Number: 45
• County: Adams
• County: Arapahoe
• County: Douglas
• Community: Denver Metro Region
• Stream Name: Big Dry Creek
• Title: Major Drainageway Master Plan Big Dry Creek, Volume I
• Date: 6/1/1975
• Designation Date: 7/1/1975
• Floodplain - Doc Type: Floodplain Report/Masterplan

Values for Manning's "n" were taken from t!lC "Design of Hoadside

Drainage Channels," !.!.zQr.:lUlic Desi~li-'.cri~)s _.No ~~.' May 1%5. (Table 2,

Manning Roughness Coefficients). For the initial hydraulics calculations

for the channel under existing conch tions, the following "n" values

were used.

From
Source
County Line Road
E. Arapahoe Road
Orchard Road

To
County Line Road
E. Arapahoe Road
Orchard Road
S. Platte ]1.iver

~Jja_~~_!2B_~~._~~~_'.

o.o~o
0.035
O. cns
0.030

The above values of "n" are composite values and therefore, no

attempt was made to vary "n" with water profile stage or cbannel con-

fi.guration. The single values of "n" are justified in this initi.al

study for a combination of hydrauliC reasons, the first bcing that for

the greater flood flows, the stream channel characteristics are such

that overbank flows appear to be a minor part of the floodway. The

maJn channel is well defined with l.imj~:(,d vegetative gro1Yth providing

little flow resi stance. The second reason is that in the greater f1 ooeL-;

tho depth of flow is greater and the channcl surface influence diminishe'i.

Finally, thc width of the flood plain from the inspection of the topo-

graphic maps indicates a rather steep channel indicative of a single

value roughness coefficient.

Cross sections \Vere taken along the basin channel where changes

occurred in slope, cross sectional area, channel roughness, locations

\Vhere levecs begin or end, and at hridges. Cross section data was

obtained by digitizing from mapping (scale:

I" = 100'. th'O foot contour

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