FLOOD05435

• County: Elbert
• Community: Elizabeth
• Stream Name: Running Creek
• Basin: South Platte
• Title: Floodplain Information Report
• Date: 7/1/1979
• Prepared For: Elizabeth
• Prepared By: WRC Engineering, Inc.
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

Drainage channels should be de~igned for the 100-year frequency flood
event wherever rights-of-way and existing development will allow. Reducing
the design flood frequency results in only a amall consrructioncos t.aVlngSrOr
the channels. A 2;-year frequency flood design may be used ror more restric-
ted areas where channel overflow onto adjacent land does not present a serious
flood hazard or potential for lo.sof life. Aneasemcnt is required for this
option on both .ides of the channel to contain channel overflow. during . 100-
year frequency flood.

B. o.:.sil\nStormFreQuencies-The gcnerallyaceepteddeaign frequency
for urban areas i. the lOO-yearevent. Iti.desirabletoprevent1l18jor
propertydallWlge and loss of life during a lOO-year flood OcCurance. This event
is aha connonly used for floodphin regulati.on and for flood hazard analy.is
in the Federal Flood Insurance program.

The design frequency for dr<linage structures and channel improvements
ln the Town of Elizabeth should consider local applicable conditions. Some
of the more important local conditions that should be considered include:

C. Hydraulic nesiKn Standards -

1. The streets in the Town of Elizabeth are generally gravel surfaced
and the street profiles provide minimal clearance for drainage
structur"..

(1) Open Channels

2. The depth. of flooding from a 100-year event are .hallow and the
relative magnitude of floods ia .mall.

Side Slope.:
flow Depth:
Bottom Width:
Slope:

3. The damage to street. due to overtopping has been minimal in the
past and occaaional regrading of the streets ia considered accep-
table.

4. The low street profile. do not provide <I significant damming effect
onfloodflo.....

Velocity:

S. Existinc de~elopment, rizht-of-...ay constraints, and street profilc.
limit the level of design impr<.>ve_nt. which Can be economically
implemented.

The follo...ing mlnlmum design standards are
recommended.

A. flat as po.sible, 3:1 minimum.
3.5 feet maximum.
4 to 6 timea the flo... depth.
Elizabeth topography is generally steep. Drop strucrures
may be required to reduce slopes and prevent erosion of
channels. Channet slopes in the range of 0.5% to 1.0% are
desirable.
The maximum velocity should not exceed 4.0 feet per second
for unlined channels during the loo-year event.

(2) Culverts - Tb" follo...ing standards ate recommended.

Bused c"lcarcful conaiderationof the items above, it lsrecommended that
the 25~year frequency event be used for desigo of drainage structures in the
residential arCllS of rhe Town of Elicabeth. Drainagestructuresinbusine..
and commercial areas should be designed to convey the 50~ye.r flood. However,
the effects of the 100-year event must alao be analyzed to as.ure that exces-
sive or undesirable property damage is avoided. The difference in flood flo...
between the design flood and the 100-year flood ...ill be allowed to overtop the

Type:

rnlet60utlet
Treat"""nt:

streee.

Slope.:
Minimum Allow-
sbleSiz...:

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Culverts may be or an acceptable shape and materiai suitable
tothe.ite.pplication. However, thepropo..edscr\lcture
shall be approved by thc.designated representative of the
town.
Flared end aectiona or headwalls with wingwalis are desir-
ablc to minimizc entrance and frLction 10'$e8 .nd to blend
intostopes. Erosion protection may be required at pipe
outlets where velocities are high.
Culvert slope. shall be at least 2.0~ tel redute sedimentation.
No culvert shall be installed with an equivalent area leos
than 18 inch diameter round pipe.

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