FLOOD09316

• County: Teller
• Community: Cripple Creek
• Stream Name: Pony Gulch, Poverty Gulch
• Basin: Arkansas
• Title: Drainage Master Plan
• Date: 4/1/1992
• Prepared For: Cripple Creek
• Prepared By: GMS
• Floodplain - Doc Type: Floodplain Report/Masterplan

1.

Replace existing struClllre no,19(dua140.inchslee] culverts)....ith a structure
capahle of conveying runoff from the lClO-year design storm event, 65l! CFS.
An 1]'5"x7'3" arch culvert complete with headwall, and wingwalls would
convey approximately 675 CFS when set at a headwater depth of
approximately!l.5'.

2,

Replace existing structure no. 18 (dual 36-inch CMP) with a structure capable
of conveying runoff from the loo-year design storm event, 679 CFS. An
11'5"x7'3" arch culver! with headwall and wingwalls would convey
approximately 675 CFS when set at a headwater depth of approximately 8.5'.

3,

The existing channel between existing structure numbers 19 and 18 is grass
lined, has a relative flat slope and has inadequate capacity to convey the
1()()-year design storm runoff of 679 CFS. This channel should be replaced
with a riprap lined channel similar to the typical channel section shown in
Figure 4 of Appendix A A channel with a bottom width of approximately 5
feet and a flow depth of approximately 4 feet would adequately convey the
design flow. Approximately 950 feet of this channel lining will be required.
Provisions should be made for access from the school buildings to the foothall
field and track on the opposite side oftbe channel.

4,

Existing structure numbers 11, 12, 13, 14 and 15 are all at road crossings of
Puny Gulch and are all severely undersized and incapable of conveying the
runuff from ll)()-year design storm event which varie, from 713 CFS to
767 CFS. For example, existing struClllre no. 11 (dual 36-inch CMPs with
approximately 5 feet of available headwater) has a total capacity of IJOCFS
while a design capacity of 767 CFS is required. Also, the existing channel
between these Slructures is very poorly developed and a pOlcntial hazarddut"
to near vertical side slopes. Severa! alternatives were reviewed for
replacemeotoftheexi,tingstructuresandchannclbetwccnstructurenumhcrs

VI-3

11 and 18. Land aequisition COMS and COSIS associatell with the large required
structure sizes at each street crossing made use of an open channel cost
prohihitive. Large structures are required at roall crossings of open channels
due to the pondingdepth required to force flow into the culvert. Once flow
is in a (,ulvert, pipe size can he reduced a~ there are no additional headlosses
assodated with entrance conditions. Hydraulic calculations indicate that a
72-inch RCP installed at a slope of approximately 3.5 percent between existing
structure nos. 18 and 11 which would adequately convey the l00-year design
flow. Approximately 1,400 lineal feet of 72-inch RCP would bc requirell. In
alldition, a means of intercepting the small overlot flows within basin PG-C
is necessary. Preliminary design indicates that construction of a shallow swale
over the new 72-inch RCP and installation of five strategically placed inleH
will adequately intercept these flows and convey them into the new 72-inch
outfall.

It is important to note that existing conllitioos result in significant flooding of
privatc property during a design runoff event. BStrectisgradedhigherthan
surrounding land, thus directing excess runoff nut of the road right-of-way
unto adjacent land.

5,

Improvements to the channel below existingstmcture no. 11 (Bennett Avenue
cro~slng) are not recommended at this time as that channel passes through
prest'ntly un.lIevelopell property anllthe potential for nooding lIamage is
minimal. k tha.t property develops, it will be the re~ponsibilily of the
developer tll eliminate any encrO<lchment of development upnn the !looll
plain as lIefinell in the SCS Flood Plain Management Study or develup the
channel as required to reducc the limits of the flood plain.

VI.4