Res 168-92 11/3/1992RESOLUTION NO.
RESOLUTION TO APPROVE THE CRITERIA FOR STORM
WATER FACILITIES, REVISION B, IN THE CITY OF
WICHITA FALLS
WHEREAS, the City of Wichita Falls has previously adopted a
Criteria for Storm Water Facilities;
WHEREAS, the Council has examined the proposed Criteria for
Storm Water Facilities, Revision B, and desires to adopt same.
NOW, THEREFORE, BE IT RESOLVED BY THE CITY COUNCIL OF THE
CITY OF WICHITA FALLS, TEXAS, THAT:
The attached Criteria for Storm Water Facilities, Revision
B, are hereby adopted.
PASSED AND APPROVED THIS THE 3rd day o - ember, 1
M A
7401111111:
1ff
ATTEST:
CITY CLER
Revision B
CITY OF WICHITA FALLS
CRITERIA FOR STORM WATER FACILITIES
I. PURPOSE
1. 1 It is the purpose of this document to state the criteria to
be used in designing storm water facilities which are to be
constructed in the City of Wichita Falls, Texas. It is the
intent of this document to state acceptable criteria while
encouraging innovation and creativity on the part of the
technically qualified designer. Designers are encouraged to
coordinate their projects with the Engineering Division of
the City of Wichita Falls early in the design process.
1. 2 This document accepts the premise that preventive measures
addressing storm water are ultimately less expensive to the
tax payers than implementation of corrective measures. It
is recognized that the cost of storm water facilities
ultimately is borne, and is inevitably passed on, to the
user of the product via a higher cost of goods, housing, or
services.
1. 3 These criteria are intended to supplement the storm water
detention/retention ordinance fNe--43-68} as set forth in chapter 32
of the Municipal Code of Ordinances.
II. DESIGN-FLAWS STORM RUNOFF
2 . 1 It is recognized that urban hydrology is both an art and a
science. It is the intent of this document to use only a
level of precision suitable for the situation under
consideration. The level of precision shall be based on
sound engineering judgement by technically qualified
personnel.
2 . 2 Storm water flows from watersheds of less than 150 acres
will be developed using the "rational formula" Q = CIA
where:
Q = Peak rate of runoff in cubic feet per second
C = Coefficient of runoff (see Attachment 2)
I = Rain intensity in inches per hour (see Attachment 1)
Rainfall duration will be based on tc as defined below.
A = Basn-area Drainage area of watershed in acres (Drainage area of
development tract in acres,for detention)
Revision B
tc = Time of concentration in minutes equals the time required for a drop of water to
flow from the most remote point in the drainage area to the point of interest.
see Attachment 3)
2 . 3 For storm water flows from watersheds in excess of 150
acres, the engineering staff for the City of Wichita Falls
should be consulted for guidance in methodology to be used.
i74--Beterminat4en o reeiu4red st-eprage- eapaei'y
tBetent4enfRetentlen-fl -rra ,e- 1--843-r-may- e-t rmir -by
elthert
a}---Me el 4€le el-re 3 i--hydrograph4e-me*kec -a8—set—fol.-tail--4n
uHrban-Storm-Water-Management-Spee4al-Repent-Ne 7-49 3-7
Attaehment-37--3-t 4s--reeogrrized t -Y-- h -aa-set
erth-4n- ttetehment-3--i-s--ge a a-l-l-y--ea -ier Leo--appy-and
w4ii---norma-1.1.y----resu-1 t --4n-- 1c33cr--- ere.ge---volume
refit lrements-than-fa}-abeve-
III OPEN CHANNELS AND CULVERTS
z 75 3.1 All storm open channels and eenelu4ts culverts will be
designed to give a mean velocity, when flowing full, of not
less than 2 . 0 feet per second.
i-6 3.2 Open storm channels are acceptable and may be either paved
er-unpaved concrete lined or grass lined for erosion control. It should be
recognized that an--tmperved a grass lined channel has a much
larger easement requirement as--eert peeeel---to----he---paved
ehannei- than a concrete lined channel. Hnpaveel--cheer tei-s--skra-1+-3ee
grass--- 4ned--for---eorrt r1. An additional
consideration which should be born in mind by the designer
is the potential displeasing aesthetics involved in an
unpaved grass lined channel during periods of low flow.
33 The storm open channel er-eendtit; shall be designed far to
convey a 10-year reoccurring storm event wltheut-tire--ei*a i.e
er-esnelu4t--beeerti within the channel banks and a 100-year
storm within a designated flowage easement or right of way.
3.4 All culverts and bridges shall be designed so as not to increase the 10-year flood stage
upstream and to convey a 100-year storm without overflowing the street more than 12
inches above the roadway crown.
3.5 The storm facility shall be designed to prevent storm
water from entering any structure during a 100-year
recurring storm event.
III IV INLETS AND eeNBWIT STORM DRAINS
37i 4.1 Inlets on streets and eenelu4ts storm drains shall be designed
to meet the following conditions:
Revision B
a) The water depth in the public street shall not exceed
top of curb during a 10-year storm event, nor 12 inches above
top of curb during a 100-year storm event.
b) The minimum storm sewer pipe diameter shall be 12
inches.
c) New storm water conduits shall have required clearances
with potable water and sanitary sewer lines as set
forth in the applicable state regulations.
d) Minimum velocity with the pipe flowing full shall be 2.5 feet per second.
e) The hydraulic gradient line shall be computed and plotted for all sections of a
storm drain system flowing full or under pressure flow. The 10-year hydraulic
grade line shall not exceed 6 inches below the gutter flow line for all storm
drains and inlets.
V. DETENTION
5.1 Determination of storage capacity for watersheds under 150 acres will be calculate by
the Modified rational h dro ra hic method as set forth in "Urban Storm Waterer
Management Special Report No. 49" (see Attachment 4). Storm duration increments of
5 minutes shall be used to determine the critical capacity required for all sites larger
than 10 acres, 2 minutes increments for sites between 5 and 10 acres and 1 minute
increments for sites less than 5 acres.
5.2 For watersheds in excess of 150 acres, the engineering staff for the City of Wichita
Falls should be consulted for guidance in methodology to be used.
5.3 Each detention facility shall contain a spillway for the control of potential storm water
overflow. The spillway shall have adequate capacity to convey a 10-year storm from
the watershed serving that basin. Erosion protection will be required to protect the
spillway from the resulting velocities. A minimum freeboard of 6 inches is required in
the storage area above the spillway flowline.
5.4 A minimum 10 foot access easement shall be provided to all City maintained basins
5.5 A conveyance channel or conduit will be required from the detention facility and
spillway to a topographically identifiable receiving channel or public conduit
downstream. An easement will be required for any portion of this conveyance which
crosses private property.
5.6 Prior to the final acceptance of construction for any commercial detention facility, an
as-built certification will be required. This certification requires the signature of a
registered professional engineer, and shall state that the detention facility has been
constructed in conformance with the approved plan for that site. The Certificate of
Occupancy for each site will be withheld until its detention facility is approved.
Revision B
IV.: VI. CONSTRUCTION
471 6.1 Where the storm conduit crosses an existing or proposed
sidewalk, driveway or street, the trench shall be backfilled
with a suitable material compacted to 90% of modified
proctor density, or portland cement stabilized sand
containing no less than 1. 5 sacks per ton.
472 6.2 Manholes or inlets with rings and covers shall be
installed on enclosed storm sewer systems as follows:
a) At the end of each line.
b) At all changes in grade, size, or vertical and
horizontal alignment.
c) At distances no greater than 600 feet for sewers of 30
inches or less in diameter.
Vr VII SUBMITTALS
71 All drainage plans and calculations shall be prepared under the direct supervision of a
registered professional engineer, licensed by the State of Texas, and shall bear the
signature and seal of the submitting engineer.
7.2 A drainage plan shall include all pertinent information required by the City Engineer
and may include but is not limited to the following:
a) A topographic drainage area map delineating the tributary watershed.
b) An engineering hydrologic analysis of storm water runoff under existing site
conditions and under proposed developed conditions. Design calculations shall
include runoff coefficients, time of concentration, area, rainfall intensities and
flow rates.
c) The location of all existing drainage channels, subsurface drainage facilities,
drainage easements and other public and private utilities.
d) The on-site 100-year flood boundaries of any major drainage system.
e) An engineering hydraulic analysis for the control and conveyance of storm
water runoff under proposed developed conditions.
f) A master drainage plan shall be submitted for a parcel under active
consideration for development. Construction plans will only be required at the
time of final platting.
5- --Be gn-eaietiletlens-shell- rbitti. -erg--w-i-th--a-1-1--storm-weter
eeneentrat en--area,--ra+n€aii-+ntensit es-and-€iew-ra€es-
5-2--The-tlra-irrase--ea-1-etrl-c ixr-etr9rn t -shell--i- e-l-ttee--a--eenteur
map-de+4neat+net-the-appropriate-dra4nage-area7
Revision B
5-3--The-hpdraule-sr de-44 e-s e44- m,--a--1-C--year-sterm
event-
5-4--Bea gn--eaietr+at arre--s3 171 - --stticmArt v a--suff a ent
nature-to-defne-any-required-detentien-veiume-
5 75 7 . 3 All required detention facilities shall include an
easement dedicated to the City. Such easement shall provide
for:
a) owner maintenance for detention facilities serving
all other than single family residential land use.
b) owner maintenance for multi-purpose detention
facilities serving single family residential land
use.
c) City maintenance for sole purpose detention
facilities serving single family residential land
use.Such detention facilities shall include
provisions for adequate access by City forces and
shall be designed to minimize maintenance
requirements.
576-7.4 Commercial development requiring detention shall include a
site grading and drainage plan showing all storm water
facilities.
57 --A-master-dreAnage-plan-shall-be-subm tted-fer-a-pareel-under
aet4ve--ecxrs= ion--fer--de ei-opttetrt.---{?o 1.Mmn i t-plans
w411-enly-be-requ red-at-the-tme-ef-f nal-plait ng-
Q
y an n
W x E W
41 1 CC a Q
XrM Y- JfaitU .NA o G.
lOWza_OJI-W
I-4JW a
000Ia_ i
1-11- I 0 zZZVW
Ua0 <2000000000m0 . m 1O•p
r-0 . m r W IA o n Al o 0
0 3 Q E)j
i ,,... o xmssC r o 8
m :.unact.•:leiii::•hun:: :1----I-----: . C ."'A1:I .r.GI'.li
e°=EAR-':Eijia:i!I:.I:I:---xe;111::..1::19.
MWIYp NYII'1•NNIIN:IIIHI-AM.IYIIIIII1I1I,A III NI:I:YN•'
MM NYNWYN MM.II. N W I.-,- IIM.I.=MII-ul11YY ANNY I. .I
NNNNMNI. mlN1111 IumunwNl ii r.YA.w MA•AUlluII11II,sI 4 nWINY-
MMMMMM . NIIINIII M MIS IMMI.M M..muiinii.IIIMII 0
MNM
IMM.INII MIN
uINII
rAMMWAIMMIAM.. saNl.....1annum N
NN..mam IIII NI.I.NN INN W.M.N. M.IMMW I. a r.INNIIIYI.I.NN
MM YI..MaaUNYMIMNII M A /=1•1MJINW1111•Y1111YM
MM MIIMNM4/M Ma..IMII.MIIMa..aa a MUM.I...a rAM.M'AN M.ANIN.NI1114MIIIraMMMMMMI.III.IIWMM111In11N III. A MM MINIM AIYNMYIIIH WA 0
MI MMM)IVA WMM MINI1A11NINI MI I W N. IMM.M M•MrAMM M rAMM M.AMM/A 1101011•1111111111111/All-A
MMIMIIYNlNWI1 I WWII IIIIIIIIWap1l
MM•M I MIMIIM MM•MMI.MIWI•1•11,11Y11•AMH
1••••••=1•Miumuunnannommsi 111a1M111MIMEMfMI..MU M • ••••rAM /. MAMWIINIIIt11N11WAl1MH
Mmuumuu 11 n MIIIWINNE411111Y111
MMMMMM IMI1uIYIntu MM IIi 11141141'941114114
MMMMMM 11W11MYYW IMMIIM I unay.I1r1 A MM••MMIMNn IAn,11nM n
1 IINIMMM11HN11 IIHIIMIHNIMMIIHMIMIIIUII M1 1 IIIMIMIIM000A /VA/I I A WIWII.NIMYIIII 1 -
1IIII/NNNINNIIWIMIMIIYIIM 1111 H11111MINA Ansvmmousammewmananutnsi
IA MONAMMINlllnllllallllllll:1111111 111111 IIIIMNIIIIIIIIIIIIU;1,111/AN1V.IIII I, •MMIa IEVAININININIII 1
U 1111,m1111111111mu1a1a1uumaun 111IOUM111uuu111144au•/IIIFIMI INarAa 111i1pJ innuNmium y
img mimmU IN IInInI11111111mu11111N111IIIlsnuma111mi M/I rAII tmeranow N r onnunu auoNW Q
miumimm muu mmluummmillim umminummia lumuna oriewa N mummumN1m1u11u 0 N D
NU amNUmmumnimuommuuuululu mmenulull au ammorANNNr.at uu uummi: - o
MMIXIWIWIIII111111UIIWWIIIIIIII11I11 1111111111111111 I1UUIIII11111 MMI1L11OMA IIKI III O%ENII MIUNIIIMIMINI x
MINIUMIN1111111nlu1uu1111M1nnlnu1HIUMIUMINIWIIp'Alu/211WAMIAII IIKUNI r4 111M111UIUUUm1111lI
MEM m IIMMU M111111111u111W111U1111111MUUMBIIWAIIIMIID i1IIII aIIIIIII/AIIIII•VtlI IU INNI IWNI_g
r E`:e=!is- --= a I"zi=s. _€ =---- ___=___&`
gam:=e c.—e_
Le:Lasicaii erg=_=s. 47 --.
I==-c--=mac=z:s= ._==. - 6 _ ter-0
aEifEi6=,:1___r_,^I 1`*•:-.F.,
E[_s___i!!E__e.
I
EL"= .s_____=-.. = =_ ...e. 3."f Q'
L: C L1 L:CI .
CNN LII' 2r gIj===,• ri._-_ Sq1 CNN O - M '
n i:-AWS .1E's EtA
4IL:.. M EEEE-,
y .
aa:o
nee .=.i.sins=-= '+4?en ark- rE«LEc =aEErs= effa_=a'i0 p mr=N.-.iA - er _ . sirs to===-_----"E:: g=f2.
w»
R
s - ?e__:
i
7 °e=5
ms:
c
E-
o__ ::=.
EESE EE ." EE-:: s-=2rsE?AFFlir rte i F4-:=.7.=.0_
r D
r .. :•.
Cin.%1'•'Y" ':- •..L
CCCC C -.--
c
NN :
1"':iiiw
Narz
4.4.7........,.. EES~E «.x::i o F
OG 11 pmara I-u:-m• -•----- .II;...r .rNNY rAI.::YN...AM r.......=.......,....... ' .„ 4
NI INM IC..
N. .
M. Al••••A1.•N....NI N NN y
NN- NMM.
1.®IMWTMINII III:=11i...•.. •'A :.A.a M.rAIMI.
pIIV.
E ..11.......1 N-tWIY.,l1NIl 1-VAVAINN.NII
MMMMMM= NNNYNNUNII MMNInan.sa'. IY'Au..M/•.NY'A A
a111I111 IIXIYIM•IIY.Io Il1
C
MI NMMNIINN IINII-.IYI'•.Me.AI..IAe.'I rN Y
NMNMM NM1IMINIIII•IMIwu.10....0 n•••••N•• ,'.Mf1WN... .N A'11II1ypIIIUI MN11YY1
M IM_MIMI NU1.u.n IIMINYNYM.NIM.VJM.N aa.'I '1.. YW1111 M.un.N 0
1.NMNINwNI1NI1NN.NwMwIW A...NI...'A NM a.rAMaaa M NM reellINWIININI0ell O
MMMMM MMMIIMN YIIMIMIHIIMIMNINIMANIM/II VA "A M Aaa•••• M MM14YH11111N•WY111•NN
MMMMMIMYIW.WNNIIYIIIIHIIIN 1/1/1111
It'AIM.=-iii a.aM.aY t.MNMINIIIU aMU.a11 le Ipj II.YIMllt,w11We
Mt11Y1M11Y11 YYMI/MMIIII'AIIMI: III'//N•I/IIIMIWIINIY MWIIUApMMHIMt1M1I J
MMMMMM MY1 MMMIAUIM,AIII•AII.I.II MIA MMILII•IIMWYINIIIMI
JIIMMMMMMMIIIIYIMI .m.Ium MM1:MIMr IMMII M••MIIIM1,Il MNIMIIIIIMIMIYHY 1
IµypgryryMlMMM1MIM1 Aww"VAMI
MN11I1I'/
I/•1/A M11MMI MMIIWIommu HMI
MMMMMMmNMI IMIIIIIIHIIaNOA/IHAIIIIVAII1 AHEM M110111411111144111414114 LL
Y miume mueuHMYuNMII III1A IIIIuAUIIIUiuIi MMM M.MMI IIIIIINYMm1 M Z
w•Cr"N..-•r...-"--N.. 4-
E".i.EEE""4N.•1, M yW"_N~'._~'
M
v5 E"•°w,....
N•
N M___
NNm":1N .' :: a
NN==N1 UIININN.
MNI
arm, ---I..:.1`.:
A -
W
NI... MMMM MMM_M_WIIMIIMIlar Y
Mw.w--i in:i1.
1N
iM 111•
ilw•:r-i.wM IIYIINIII.WINNON
MN.ININN•.NI.•
I1.-
y11•
N.
1Y.
IN•
IN. 11=11 AIM..
M.:
1:1 A..Y.-M.sN.N:A •
N.
u .jrI1= iN
MYIIIIYNH.11111111MM1HteMel NIANNN.M.I rM MM Ma
NIHNIIWIM.IWIWMY
IINY
MNMM M 1IYI INII..
II.Ynuramtn''A
IIN.'
AM ....s.aaa.a..IM
NI..N...Naa.M..NN M
MN
I'.'
INMIYNINYYM•.
I...1.NMMMMMIIIMIIII.N.MIMIIIMINIt'YNtIpAY/N..I . IM NNN.MI..NM. M 4NNMIYINUMIM1IIY
MMNM=.
m I IHMVMIIIUIIIWI/M..IYY Ma•••M '
NMNIN..,MMN IIN.
M.NN NN_NM I.IwnmMnw.mNi...••o
M..MNIIIIYN In AMNnan..I/A.....I.MY.....rm....M..MI......fM INN.uu,unu N`•
MMMMMM tlWtI1NWII'Awww M. MM=IIIWWINI.IaNNINNI1 H)
MI 1 mei/A/NewisM.M•....M....l. IIMI.I.IIIIINIII IW W11111111I1NM W
MM MIM p5
1 11 1111 WI) IMMIIMEMhhhh.& MMIIIIIU1111W IIN11NY11Mp11NYI11Ill'
111111'
AI1.NaallarM I1NM.II M MWIIIIIIIIIIHIYIIMII f•
MMMMMMII M IMP =NIP M Wr I MWM M1M1NN IININIII1 INIINYIIMIII M
MMMMMM 1 111W 1111N/MIMIIIA IW. MM MiI111Y11I1.,..I111M1 Z
MM N IYI IIIYIAYYItl/1111'1 1/I INIINIIININI IMIMW -
MMMMMMII gin AIMntq•/MUarJlIIMV norm MM MWIIIIIIIIIIMYIIN M
MMM WHIN=A luU
11uI
411411111114114111111141141111111111
u
MIIINIINIMNMM n
I 0uuauvI1% IuMg uu N NN IMtIM 1_IEu•M rluM I 1lHPAOMMf11lHluU11. uu nnIMUMN1M11 I
mN1%NI /Ujuuu z111Iuuuu • . MMIN1uu
u
1HIp1IUu emo WInuuuu uu •• EMS111 11111uM1
oYtl
p
nnllnmalll III1IlIAIIIIINNNNIIIIIa111111It11/IIIIIIINI MMMMMM N HIIIININItlNNlmll
TABLE 5. RUNOFF COEFFICIENTS FOR RATIONAL FORMULA
Type of Drainage Area Runoff Coefficient
Business:
Downtown areas 0.70-0.95
Neighborhood areas 0.50-0.70
Residential:
Single-family areas 0.30-0.50
Multi-units, detached 0.40-0.60
Multi-units, attached 0.60-0.75
Suburban 0.25-0.40
Apartment dwelling areas 0.50-0.70
Industrial:
Light areas 0.50-0.80
Heavy areas 0.60-0.90
Parks, cemeteries 0.10-0.25
Playgrounds 0.20-0.40
Railroad yard areas 0.20-0.40
Unimproved areas 0.10-0.30
Sand or sandy loam soil, 0-3% 0.15-0.20
Sand or sandy loam soil, 3-5% 0.20-0.25
Black or loesslal soil, 0-3% 0.18-0.25
Black or loesslal soil, 3-5% 0.25-0.30
Black or loesslal soil, >5% 0.70-0.80
Deep sand area 0.05-0.15
Steep grassed slopes 0.70
Lawns:
Sandy soil, flat 2% 0.05-0.10
Sandy soil, average 2-7% 0.10-0.15
Sandy soil, steep, 7% 0.15-0.20
Heavy soil, flat 2% 0.13-0.17
Heavy soil, average 2-7% 0.18-0.22
Heavy soil, steep, 7%0.25-0.35
Streets:
Asphaltic 0.70-0.95
Concrete 0.80-0-95
Brick 0.70-0.85
Drives and walks 0.75-0.85
Roofs 0.75-0.95
from ASCE, 1960
BRIDGE DIVISION HYDRAULIC MANUAL 12-85
2 - 15
ATTACHMENT 2
1 2 3 5 I 2 3 5 10 20
50 50
IIMI%IH___
30 1111011111.1111111111111f 3 30
I-- 3
0C
1l1M1!41W 1 0
0 20 v = ,.E„ 1N Q 20
z ii 1111/10 c,: G, v d 10
J.wiii 0.4=
MM v A
w
0 i
CITY OF WICHITA FALLS
DEPARTMENT OF PUBLIC WORKS
OCT 2Z 1882
EXAMPLE OF DETENTION
AND
RELEASE RATE REQUIREMENTS f
OF z.
CITY OF WICHITA FALLS ORDINANCE
NO. 41-88 "DETENTION ORDINANCE"
DESIGN PARAMETERS
PROPOSED
UNDEVELOPED CONDITION p T
30 Ac Single Family Residential Subdivision. 0 Ac.
tc Undeveloped = 39 min. (per figure 5) n P
C Undeveloped = 0.25 (per table 5)k``\
Iwo Undeveloped = 5.5 in/Hr (per plate 1A)
Q1oo(Undeveloped) = (.25)(5.5 in/hr)(30 Ac) = 41.3 cfs
DEVELOPED CONDITION
tc (Developed) = 20 min. (per figure 5)
Storm Duration Intensity C Factor Peak Flow
minutes)inches/hour) cfs)
20 7.7 40 92
25 7.0 40 84
30 6.3 40 76
35 5.8 40 70
STORAGE CAPACITY REQUIRED:
MODIFIED RATIONAL METHOD)
100 92 CFS
80
84
Cn
76
70
U 60
40 —/ 41_CFS(ALLOWABLE DISCHARGE)i
20
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
TIME (MIN.)
DURATION STORAGE READ.
min) Cu Ft )
20 20MIN X 60 SEC/MIN (92 Cu Ft/SEC — 41 Cu Ft/SEC) = 61,200
25 25MIN X 60 SEC/MIN (84 Cu Ft/SEC — 41 Cu Ft/SEC) = 64,500 -40--
30 30MIN X 60 SEC/MIN (76 Cu Ft/SEC — 41 Cu Ft/SEC) = 63,000
35 35MIN X 60 SEC/MIN (70 Cu Ft/SEC — 41 Cu Ft/SEC) = 60,900
DESIGN FOR 84,500 Cu Ft STORAGE CAPACITY
41.3 cfs RELEASE RATE
DEEM'
I ATTACHMENT 4