FLOOD00668

• County: Arapahoe
• County: Douglas
• Community: Englewood, Littleton, Greenwood Village
• Stream Name: Big Dry Creek
• Title: Major Drainageway Master Plan
• Date: 6/1/1975
• Prepared For: Englewood, Littleton, Greenwood Village
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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

Drainage Channels," !.!.zQr_:lUlic Dcsi~li-',cri~)s _.No ~~" May 1%5. (Tablc 2,

Manning Roughness Coefficients). For the initial hydraulics calculations

for the channel under existing concli tions, the following "n" valucs

were used.

From
Source
County Line Road
E. Arapahoc Road
Orchard Road

To
County Line Road
E. Arapahoc Road
Orchard Road
S. Platte River

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

o.o~o
0.035
0, 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 being that for

the greater flood flows, the stream channel characteristics arc such

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

main channel is well defined with limj~:(,d vegetative gro1Yth providing

little flow resi stance. The second reason is that in the greater f1 00,L-;

tho depth of flow is greater and the channel surface influence diminishe,;,

Finally, the 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 \-Iere taken along the basin channel where changes

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

\-Ihere levees begin or end, and at hridges. Cross section data was

obtained by digitizing from mapping (scale:

I" = 100', th'O foot canton)'

-11.1-