762ORDINANCE N0.
AN ORDINANCE FOR THE ADOPTION BY REFERENCE
OF A CODE FOR DRAINAGE DESIGN CRITERIA
AND DRAINAGE IMPROVEMENTS FOR THE CITY OF
WEST MEMPHIS, ARKANSAS
BE IT HEREBY ORDAINED BY THE CITY COUNCIL OF THE CITY OF
WEST MEMPHIS, ARKANSAS:
Section 1. There is hereby adopted by the City Council of
the City of West Memphis, Arkansas pursuant to Arkansas Statute,
~ 19-24.21, which allows adoption of Technical Codes by reference,
a Code for Drainage Design Criteria and Drainage Improvements
for the City of West Memphis, Arkansas, of which not less than
three (3) copies shall be filed in the office of the clerk of
the City of West Memphis, Arkansas, and same are adopted and
incorporated as fully as if set out at length herein and from
date on which this Ordinance shall take effect, the provisions
thereof shall be controlling within the City Limits of the City
of West Mem his Arkansas.
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Section 2. It shall be the duty of the City Engineer of
the City of West Memphis to see that this code is enforced.
Section 3. All ordinances or parts of ordinances in conflict
with this ordinance are repealed.
Section~L... Any person, firm or corporation who shall violate
any of the provisions of this Code or fail to comply substantially
therewith, or who shall violate or fail to comply substantially
with any order or regulation made thereunder, or who shall build
in violation of any detailed statement or specification or plans
submitted and approved thereunder, or any certificate or permit
issued thereunder, shall be guilty of a misdemeanor and upon
conviction thereof shall be fined not more than 25.00 for any
one specified offense or violation of this Code, or double that
sum for each repetition of such offense or violation. If a thing
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prohibited or rendered unlawful is in its nature con ous
in respect to time, the fine or penalty for allowing the
continuance thereof, in violation of this Code, shall not exceed
15.00 for each day that the same may be unlawfully continued.
~.y"""' Section 5. Emergency Clause. It being found and determined
by the City Council of the City of West Memphis, Arkansas, that
there is an immediate need for a Code for Drainage Design and
Improvements, an emergency is hereby declared to exist and this
ordinance shall_ be in full force and effect from and after its
passage and approval.
ADOPTED this lst day of February, 1973.
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MAYOR
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ATTEST
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CITY C LERK
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INTRODUCTION
The Pzcrpose and Intent n t7,, _ ~
i;r to insure tJeat ry.ll ~Ir~zina~e,f~lowin.7 a'rainage reguln.ttons
1:'PI.~t^hi:, roi11 he controllcrl f J in thr, Citr~ of We;Jt
^,,rfzce inter anR that awrc~~rcatetandavn~~~or~ dispo;,a1 cf
'ion of a1 I drainage str,~ctr~rPy wiZ1 hr Provi~'e lginaall fut:zr cc
~'~' ve~1 v~»~en t,
ntc ~.n, pot is i e:;, chart,;; rync~' ~^rocedures reco.
for 'use in the re »arcrf; rm. rnr+nd me in.ten~;vd
p on of all project:, in the CitJ end
sha11 r~,nora adoption anp1J to all a~'~plicahle sttunt,icn; includ-
i~z~ anJ construction or reconstruction n
zlteration to existing or additional o:rat~aert which re2uirPs
9e structreres.
TAJ3I.E OF CO.NTEr~,"lS
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SLCTI0IJ I - Design Criteria
SF,CTIOPJ II - 1;'ateria,Is and Specifications
SI~:CTION III - Improvement Requirements and Regulattona
SUCTION IV - Ilardrltips
CtJART I - Rainfall Inten~itr/ Dt~ratten Frequency
Ref a~t i onsh ip
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SUCTION I
DESIGN CRITERIA
A. TJze rntional method of calculating storm runoff sha11 be u..^.ed for
storm drainage improvements in I/cst Memphis. Runoff fs gtvrn in _~~~
feet er ^ • .o12t'~at tJt~' drainage ;;tructztre. This rrcthod is l,Za,~°~~ orL t,he.
rltrect rclationsl.tn hctu~cen ra.l~~~fa~1j a~-~14~,f rzrzd is atvcn ,~~t~e
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forma .a
q =CIA
Q =cubic feet per second of ncnoff for a given area.
C ~ a coefficient, related to the impervious area, representing the ratio
of ncnoff to rainfall.
I =the intensity of rainfall in finches per hour for a duration equal to
the time of concentration and for a stated frequency.
A a area to be drained in acre:;.
1, "C" the T-tmoff coefficient encompasses several factors including
the r~1 ope of the land, the d iatance of water f1 om ovcr the area,
and the imperviousness of the drainage area. This factor is
,medicated on the IarzcZ rise as established in the West Memphis
Corzprehensive Plan and tJze following coefficients sha11 be used
for the indicated land uses:
r
.rrldil,^,trial .................... • ~• 0
'Rcsiaential .................... 0.~0
1~.4c1 t i-Pani1 y excl~cding rkcplex .. O.GU
W1zen a drntnage area consists of a combination of the above
land uses, their runoff coefftcicnts sha11 be combined in
proportion to their relative arca~.
~~, "I" the intensity rate is determined fro. tJze time of cor:centra-
t i on and tJze des ig,z rainfall fry°rlraenc?/. The time of concentra-
t ion is the t irre of f1 ocv from flee nrcatcst d istancc the uxcter
u,i11 travel frog: the most remote point in the drainage aria to
the inlet of the drainage structure. T1zo rainfall frerp~ency
is the frequency in yrars in which a rainfall measured in inches
per hour is~expected to occur. .Tice• following sha11 be u;,e.d for
storm drninage design in Wcst 1'.~mnJcis:
Drainage areas less than 100 acres ..... 5 year' storm frequency
30 minutes, rraximun:
time of concentration
Drainage areas greater than 100 acres .. 10 year storm frequency
4Jr minutes, maximum
time of concentration
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Using t}ze above criteria the intensity sha11 be determined from
Chart I. 13y scaling the time of concentration, which is equal
to rainfall duration, a1 ong the: bottom of the chart and mooing
up to the design storm frequency, the intensity "I" may be
read by moving horiaontally to the left. ,
I7. For rainfall rrcnoff that may be cha~zncled in the streets, c~i'•h;Q,,~eninga
arul inlcG:, slcall be adcgrcatcly spaced along .;trcets to intercept such
rztrtoff generated bJ the design storm. To prevent large quantities of .
ux~tcr from by parsing the inlets, the flow should be retained within a
10-foot rcaxinrian spread from the curb but' in no case sha11 the depth of
The following formula
flow at the curb be greater than six inc}:es (6 ).
may be used to determine t}ce area of curb and inlet openings required to
handle a speoific amozent of inter:
q = CA~-~Z,~Tt-' X Factor for clogging (Use 2/~)
where,
Q =quantity of runoff reaching the inlet in.cubie
feet per second.
. ,,,:,?; C =orifice coefficient (0.6 for openings with square
'' °-' edges and 0. d f yr rounded edges).
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A =net area in square feet. -1 •., -~.i~,~
h =allouxzble head on tlcc inlet irz feet.
.~ztch in..Ieia ^ha11 normally be Located at ^trect intersections in such
a u~x.~c ao to prcucnt the storm uxtter from cn.tcrinn the intersection or
pede:'tri!cn crossings; }cou~;vcr, in all canc.; G}cc inlet design and spacing
sha11 he ~:uhject to the approval of the City I.ngineer.
C. ht rent crorcrc:~ sha11 not be flattened, or razrped from one ^ic3c of the
street to the of}zcr for the pur,~ose of cartsing water to flow fran aze
side cif t}c~' street to the other.
D. .'~7,~? c1.r'ceirccgc s~/^tem sha11 have manho.}e:~ at intervals of 300 to ,r00
feet and nt evcr'y chanr~c in 1 inc or grade so t.lcat the storm servers wi11
be st,rctight bctwcrn rcanholes to facil itate cleaning.
I~;. ,era ~~cn.cr'a.l, rainfall rctnoff that cannot be }candled in the streets
s7ca1.T Lr, put into piped or 1 fined channel: , except as otherwise indicated
fist t}c~r: c rcgrtl.n.t i ons.
r'. t,vrr7 seu~~r pipe, culucrt and open cha.nncl drainage facilities sha11
be designed tcsinrr Manning~s Formula for capacity calculations. 1'hte
formula is as follows:
Q C ~ Z... ~~~~ 2/.3 ,~/2
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q =capacity in cubic feet per second .
A =cross-sectional area square feet '
N = coefficient of rour~hness
R = hydraiel tc radiics in feet er oot
S = longittcdinal slope in feet P ,f
Unless otherwise directed by the City L3'egtneer the following vq~ea sha11
be used for the coefJ'icient of roughness (n):
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Cnncrrte Pipe ........,••••••••••• 0.01.3
0.01 ~~'
COnCrCtA, lined channels ..••••••'• n•O`~
Cnrrcegated metal Pipe (coated) ...
o. 0.30
Dutch, non-vegetated earth • • • • • • • 0 0,35
a t bank ....... •
Ditch, weeds on e r h
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:L _ .,... SECTION II
1-~TF.RIAT•S AND SPLCII'ICATIOIJS
A11 matcrtal^, corzstrrtction and.Ililt~edaP~licablenarticles~and. sPCt,fons
drainaCe :7/:;tcm. ..^.3ra11 cnnfor~n wa
~ ".~ tnndarci Socc i f i crzt i on:, or
of thr ilr';~irn^as Statc Ili~tu~,rn/ Gnm.v:is.,ion s ~~i.t, L'rr ineer.
Ilirljtuxzy Con:;tn~ction" °neavliallCLelcoatedeatCPerJt~eteaforementioned
A11 cornc(7ated mctal p ,
spec iftcations•
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SL'CTIOIV ,III
IIPROV~.l'11'.NT RI'QUIIiE'1'~-NTS AND 1tF'Glll~ATIONS
A. The CttJ wi11 stronrrl~ discourage the pln.tting of property for construc-
t ion purposes that is in a natural flood plain or other area that is :;rcbject
to flooding. Iri no case will t]re CitJ be 1 fable for damagrs clrce to flood-
ing.
Ir. The Ian~lourcer, rlr,velopcr and/or subdivirirr :~ha11 tcpon devc~rrent
on his property install at hi: r:rnense witlcin his pro;ertJ o.11 dm.~za.ge
facilities nrcr,ssnr?/ to handle the storm wo:fer or'iginat.ing witTrin hi.^, ,•
deve.lonr.:erct and icp-streaTM, which can be contained in si.rty (la~~'incle ?Z
diameter storm. seur,r's anri paved drainage ditches up to one hran.drerl (100)
sgrrarc fret, cross-^ect.ional area artd provide for all r_ecessar~ facil it.ies,
inclrcding trndergr'orend pipe, inlets, catchbarins or paves open ditches
for t):c arlcgrcate disposal of surface uatcr. Ile shall also provide other
improvements necessar?/ to mairctaire and natural drainage u~zJ including
required casements far Iarner rrainage cana.is, ,futicre scu~ers and outfalls.
In the case of a one 1 of single fa,^ri1 y res ident ia1 level opmcnt bJ an
or:,vicer, only the prol~er easerrent.s will be rerpcired.
For natural drainage wa?!s rvhicla require a ditch cross-section in excess
of one Ivcndred (100 sgrcare feet arr.d for natural drainage ua?/s that have
a different orv.cr on tlrr, opno^itc hank, the Iandor<vccr, devclorn~rr and/or
subdivider shrc.ll have the choice of two options before building:
1. Ile mn.J Pave the ditch t.o the 7'crncircd section a; per the City
l:'ngireeer+s Spec ificattons and provirie an. easement onlli wide
ernou~h to contain the paved ditch, or;
2. Ile mar/ leave tl:e ditch in its natural state and provide suffi-
cient eascr:ent for the ditch to meander and cave-in rvtthout
eruiangering improvements placed on. the property. If the ditch
a1 ignnrent is cTrangerl, sufficient easement must be provided for
both old arcd new channels.
C. F.a.srments sha.il be a minir:um of f iftecn feet from the top of brrrclc an
each side and wren widening is deemed neccs:;a.ry br/ the CitJ .Cngineer, thr.
ea^em~rrrL s1rn.11 be from the proposed top of ban T:. These easenrrnts si:a11 be
kept clear of all permanent structv.res such as buildings, fences and shrubs,
trees nr other plantings that rrcaJ interfere with tlce maintenance of the
ditches. All .^>rech ca:~enrents s1aa11 he indica~l.'ed on the official plat and
rlrerl a;a recorded in the Office of Circuit CLer1: and Ex-Officio Record r, r.
D. ~In no instance s]ra11 an~r natural dra.inrrge uXC;/ whether on private or
I~rcLlis property be disturbed or intcrruptecl without the express written
consrnt of tlcc City 1s5agincer. AnJ improverrercts such as widening, cleepcn-
irag, rcl.occcting, clearing, protecting or otlee.rwise improving ;rtream beds
rind otter, r uxztercourses within the Ci tJ ~Tta11 be done on1 i1 as approved b?/
the City L'ngineer.
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,SSCTION .TY
HIi.fZD,~IIPS
lsftcere tlae City Council finds that extraordinary hardships maJ result .
from strict coma3iance with the^e regulations, it r,:aJ rxiry th~eyula-
t ions so that, suhstant ia3 ju„t i cr; may be dome mid the Pub3 tc interest
secr~red; Provided that s:~ch rxzriat i on wi13 not have the effect of
rtu3.lifr/inC the intent and Puroo^r, of these or other re7tclations of the
City of West 1~fertnhis. In granting variances and modifications, the City
Courc i3 mark rer~ri i re such conditions as wi31, in t is judgment, substan-
t ia31 ~ secure the objectives of the standards or regte i cements so varied
or modified.
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. ~ . Kirpich Equation. :The Kirpich •equa'tion will be used "to define the ,
:f ~ '~ iii~le[ time. fora minor. dr:iiiiabe syste-n, i.e., subdivtston,' strectti, eEc.
. ~ where, Ti = the inlet time, minutes
~~L ~= the horizontal projection of the channel length's most
distant point 'to the design point, feet
S =the slope between the two points ~ •
'The above•equation is for natural basins with well-defined
channels, for overla:~d flow on bare earth, and~for mowed grass roadside
channels. The following modifications are made for other surfaces:
Surface Multiply Ti by
overland flow
• . grassed surface 2.0
concrete or asphalt surfaces U.4
concrete channels r ~ 0.2
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