ORD NO 11-2012 CITY OF VAN BUREN, ARKANSAS
ORDINANCE NO. 2012
BE IT ENACTED BY THE CITY COUNCIL, FOR THE CITY OF VAN BUREN,
ARKANSAS, AN ORDINANCE TO BE ENTITLED.
AN ORDINANCE AMENDING ORDINANCE NO. 40-
1980 TO MODIFY THE MINIMUM DRAINAGE
STANDARDS FOR THE CITY OF VAN BUREN,
ARKANSAS.
WHEREAS, the City of Van Buren, Arkansas, adopted an Ordinance to implement
minimum drainage standards in 1980 identified as Ordinance No. 40 -1980; and
WHEREAS, the purpose of the Ordinance was to protect the public as it applied to all stonn
drainage facilities, whether an enclosed structure, pipe, open channel, ditch, or
stream; and
WHEREAS, there is now a need to update these standards in order to address maintenance
issues and to account for new methods in hydrologic design; and
WHEREAS, notice of a Public Hearing was duly published, and a Public Hearing was
conducted by the Van Buren Planning Commission to consider these proposed
modifications; and
WHEREAS, the proposed procedures herein were recommended by amajority vote of the
entire Planning Commission.
NOW, THEREFORE, BE IT ORDAINED BY THE CITY COUNCIL OF THE
CITY OF VAN BUREN, ARKANSAS, THAT:
SECTION 1. The modifications to the minimum drainage standards set forth in attachment
"A" hereto are adopted and incorporated.
SECTION 2. These standards are the Storm Drainage Standards that are referred to in
Ordinance No. 7 -2003 (Subdivision Regulations) as amended.
SECTION 3. Should any portion of this ordinance be Unconstitutional or invalid and so
declared by a court of competent jurisdiction, then the remainder of this
ordinance shall not be affected by such partial invalidity.
SECTION 4. Any ordinances or parts of ordinances in conflict herewith are repealed.
IN WITNESS WHEREOF, the City of Van Buren, Arkansas, by its City Council, did
pass, approve, and adopt, by a vote of for and 0 against, the foregoing Ordinance at
its Regular Meeting held on the 16th day o f July, 2012.
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Roaer D. Fr nian
Mayor
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ATTESTED: `C;\;,I' A PRO ED AS TO FORM:
47t/thi—C, etOrt:;.—; "L
Barbie Curtis c. Candice A. Settle
City Clerk/Treasurer City Attorney
Attachment "A"
MINIMUM DRAINAGE STANDARDS
FOR THE
CITY OF VAN BUREN, ARKANSAS
MAY 1980
ORDINANCE NO. 40-1980
CITY OF VAN BUREN
MINIMUM STORM DRAINAGE STANDARDS
1 . SCOPE
1. a. Shall apply to all storm drainage facility, whether an
enclosed structure, pipe, open channel, ditch or stream.
1. b. These minimum Storm Drainage Standards are those
referred to in Ordinance No. 8 1963 7-2003 as amended,
(Sub-Division Regulations) Section IV, IMPROVEMENTS, c.
Storm Drainage.
2. GENERAL DESIGN REQUIREMENTS AND DESIGN SUBMITTALS
2. 1 . A. All designs, plans and specifications submitted to
the Planning Commission for approval shall be
prepared by a registered professional engineer,
licensed in the state of Arkansas.
B. Plan Requirements
Plans shall be submitted on 24" by 36" sheets.
The plans shall include:
-Locations of the project with respect to well-known
roads, streets, subdivision or survey lines on a key
Map of the entire project.
-Plans and profiles for each storm sewer line shall
be provided which show location, size, flow line
elevations, gradients, materials and any soil boring
information. Plan profiles submitted shall have a
vertical scale of not less than one inch equal to five
feet.
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-All easements, storm sewers (enclosed or open
Channel), utilities and facilities, both existing and
Proposed shall be shown.
-Elevations submitted shall use USGS Datum
NAVD 1988. Location and elevation of all
benchmarks shall be indicated
-The critical section and typical cross sections shall
be shown.
-Details of drainage structures shall be provided.
C. DRAINAGE AREA MAP
An area map showing topography shall be furnished with the drainage
basin and subareas outlined. Area map shall be of 1": 100' scale and
shall have two (2) foot contour interval when required.
D. DESIGN CALCULATIONS
Storm drainage calculations shall be provided which support the
drainage system shown on plan submittal. Calculations summarized in
a form similar to Figure 1 and 2.
2.2 DESIGN FLOWS
A storm sewer system shall be designed to contain all run-off from a
10 year. 24-hour storm except in the following cases:
A. Arterial street drainage shall be designed such that curb flows are
not to inundate the center two lanes of roadway with a 50-year
storm. This shall include back water from storm sewers.
B.
en on the final plat
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is
2.3 FLOW TOWARDS STREETS
Any concentration of surface flow in excess of 6 c.f.s. shall be
intercepted before crossing the curb (or curb line) and carried by enclosed
storm sewers. No storm water concentration will be allowed to empty into
the street except as stated above.
2.4 METHODS OF CONVEYING WATER
A. All flows within the R/W of non-estate streets not carried in the
gutter and side lot flows to drainage channels at the rear of lots
shall be in storm sewers.
B. Storm flows in areas not listed in 2.4.A. may be carried in open
channels as defined in Section 5.
C. Natural drainage channels (not relocated or channelized) may be
used in new developments providing the channel will carry the
storm runoff used in the design storm without erosion problems
and sufficient land for a one foot (1') freeboard is included in a
drainage easement.
2.5 SYSTEM DISCHARGE
A. All storm sewer systems shall be adequate to contain the design
storm runoff to the discharge point at the down-stream property
line. The point of storm water discharge from the developed
property shall be the same as the pre-development discharge
point. All reasonable effort should be taken to insure that storm
water discharge volume and velocity would be limited to the pre-
development discharge conditions.
B. If detention ponds are used to meet the requirements of Section
2.5 A. then the following standards apply to the detention pond:
1 . Side slopes shall not exceed 4h: lv.
2. Pond must completely dewater between storm events.
3. Sediment accumulation shall be removed at the end of the
subdivision warrantee period.
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4. Discharge pipe shall have an inlet control structure to limit
discharge during smaller storm events.
2.6 EASEMENTS
All storm sewers shall be located in street right-of-way or in an
easement dedicated to public use:
A. Enclosed drainage structures require a minimum easement
width of 15' or the width of the drainage structure plus 10',
whichever is greater.
B. Open channel easements shall be required to contain the
entire channel design width including freeboard with the
minimum width being 15'.
3.HYDROLOGY
3.1 HYDROLOGIC DESIGN METHOD
The Rational Method shall may be used to determine storm water
runoff characteristics for storm sewer design when tributary drainage
area is 200 acres or less.
200 acres, Oother methods such as the SCS Method, hydrographs,
or computer models shall may be used as approved. The Rational
Method uses the basic formula Q = CiA for estimating runoff from
rainfall, where:
Q = Rate of runoff in cubic feet per second
i = Average rainfall intensity in inches per hour for the design storm
} having duration equal to the time of concentration for the critical
upstream drainage area.
C = Run off coefficient, which is the fraction of the rainfall which
Becomes runoff.
A = Tributary drainage area in acres
3.2 RAINFALL AND INTENSITY
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The duration — intensity relationships are shown by the curves in
Figure 3; and shall be used for all storm sewer design.
A. The time of concentration equals the overland flow time plus
The time for the water to flow down the pipe or channel to the
point in question. The overland flow time, Tt, may be figured from
the following equation*:
Tt = L
0.5
K Y
Where: Tt — overland flow time, seconds;
L = overland flow distance, feet;
K = conveyance factor which depends
On ground cover;
Y = ground slope, percent
K Ground Cover
0.25 Forest With Heavy Ground Litter and Meadow
0.47 Fallow or Minimum Tillage Cultivations
0.71 Short Grass Pasture and Lawns
1.00 Nearly Bare Ground
fi 1 .52 Grassed Waterway
2.00 Paved Area (Sheet Flow) and Shallow Gutter Flow
*Adapted from Fig. 1-3 pp 3-2 of SCS TR-55, U.S. Dept. of Agriculture
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B. Where a section of the storm sewer system is being designed in
the middle or lower portion of a drainage basin, the designer shall
design the system based on the future development of the upland
tributary area.
3.3 RUNOFF COEFFICIENT
In selecting a runoff coefficient, the ultimate development of the
drainage area must be considered. The following values should be
used as a guide in selecting the runoff coefficient:
Description of Area Runoff Coefficients
Residential
Single-family 0.30 to 0.50
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Multi-Units, detached 0.40 to 0.60
Multi-Units, attached 0.60 to 0.75
Residential (suburban)
1 acre or more 0.25 to 0.40
Apartment 0.50 to 0.70
Industrial
Light 0.50 to 0.80
Heavy 0.60 to 0.90
Parks, Cemeteries 0.10 to 0.25
Playgrounds 0.20 to 0.35
Railroad Yard 0.20 to 0.35
Unimproved 0.10 to 0.30
In some cases it may be necessary to develop a composite runoff
coefficient, in which case the following value should be used:
Character of Surface Runoff Coefficients
Pavement
Asphalt and Concrete 0.70 to 0.95
Brick 0.70 to 0.85
Roofs 0.75 to 0.95
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Lawns, sandy soil
Flat, 2 percent 0.05 to 0.10
Average, 2 to 7 percent 0.10 to 0.15
Steep, above 7 percent 0.15 to 0.20
Lawns, heavy soil
Flat, 2 percent 0.13 to 0.17
Average, 2 to 7 percent 0.18 to .022
Steep, above 7 percent 0.25 to 0.35
4.PIPES AND CULVERTS - GENERAL REQUIREMENTS AND DESIGN CRITERIA
4.1 Culvert Hydraulics
Culvert flow may be limited by conditions existing at either the inlet or
or the outlet of the pipe, when inlet control governs the cross
sectional area of the barrel, the shape of the inlet and the amount of
{
ponding (head-water) at the inlet are primary design considerations.
outlet control is dependent upon the depth of water in the outlet
channel (tailwater), the slope of the barrel, type of culvert material
and length of the barrel. The basis for all hydraulic design
calculations will be Manning's Formula and the Continuity Equation:
V = 1.486 R 0.67 S0.50
N
Q=AV
Where V = mean velocity of flow in feet per second (fps)
N = Manning's coefficient of roughness
R = hydraulic radius (ft.)
S = slope (ft./ft.)
Q = discharge (cfs)
A = area of flow (sq. ft.)
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A. Coefficients of Roughness
The coefficients of roughness to be used for culverts of the various
kinds of pipe are as follows:
Portland Cement Concrete n = 0.012-0.013
Corrugated Metal n = 0.024
Corrugated Metal with Paved
Invert (25% paved) n = 0.021
Smooth Flow Corrugated Metal n = 0.013
Asbestos Cement n = 0.013
B. Inlet Control
The size of a culvert operating with inlet control is determined by
the size and shape of the inlet and the depth of ponding allowable
(headwater) as shown in Figure 4.
Factors not affecting inlet control design are the barrel roughness,
slope and length and the depth of tailwater.
The headwater (HW) depth for a culvert of a given diameter or
height (D) for a given discharge can be determined by obtaining
the HW/D value from Figure 6 to Figure 9. The elevation of
adjacent facilities (i.e., buildings, etc.) must be examined to avoid
flooding.
C. Outlet Control
A culvert will operate under outlet control when the depth of
tailwater, the length, slope or roughness of the barrel act as the
control on the quantity of water able to pass through a given
culvert as shown in Figure 5. The energy head required for a
culvert to operate under outlet control is comprised of velocity
} head (Hv), entrance loss (He), and friction loss (Hf). This energy
head (H) is obtained from Figure 10 to figure 13 and entrance loss
coefficients from Table 1.
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The headwater depth (HW) at the culvert entrance is calculated by
the following formula:
HW = h + ho — LSo
Where:
H = energy head
L = length of culvert (ft.)
So = slope of barrel (ft. per ft.)
Ho = dc+D or TW, whichever is greater
2
Dc = critical depth of flow in barrel. Critical depth may be
Determined by using Figure 14 through 16
D = height of pipe or box
TW = tailwater depth
The maximum desirable headwater depth for culverts operating
under the outlet control shall be the same as described in Section
4.1 .B.
4.2. Computation Format
Figure 2 is to be used to present culvert design calculations. Design
methods utilizing computers may be used with prior approval.
The procedures to follow in determining culvert size are:
1. List all design data.
2. Select a trail culvert size
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3. Determine the headwater depth for the trial size
a. Headwater for inlet control
b. Headwater for outlet control
c. Compare headwaters and use higher value
4. Compare this headwater with the allowable limit
a. If headwater is within allowable limit, proceed to
Step 5.
b. If headwater is above the allowable limit, repeat
Steps 2 through 4 until allowable limits are reached
5. Compute outlet velocity to determine need for channel protection.
4.3. Culvert Types and Sizes
The permissible types of culverts
embankments are reinforced concrete box, round pipe and pipe arch.
All Corrugated metal pipe placed within street right of ways shall be
asphalt coated. The minimum size of pipe for all culverts shall be 15
inches (15") or the equivalent sized pipe arch. Box culverts may be
constructed in sizes equal to or larger than 4' x 3' (span vs. height).
3-.
4.4. Velocity
All storm drainage pipes and culverts shall be designed to maintain a
Minimum velocity of 2.0 feet per second and a maximum velocity of
15 feet per second when flowing full.
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3':
4.5 Velocity Head
Large quantities or masses of water flowing at a high rate of speed
contain a large amount of kinetic energy which is defined a velocity
head, V2 : Any change in cross section, restrictions in pipes or inlets
2g
shall be considered energy losses and shall be taken into
consideration in the design of the system.
4.6. Structural Considerations
The minimum allowable fill or cover for structures (RCP, CMP,
concrete culverts) under roadways shall be one foot or a minimum
clearance of six inches from top of structures to the bottom of
pavement base, except for a special box culvert designed to carry
traffic on the top slab. Structural protection, such as special bedding,
shall be provided where adequate cover cannot be attained.
Maximum fill shall be determined on the basis of structural strength of
pipe and design loads. Outside of street right-of-ways, a minimum
cover of twelve (12) inches is considered desirable for purpose of
growth of vegetation and protection against unusual loading.
5. OPEN CHANNELS - GEN. REQUIREMENTS AND DESIGN CRITERIA
5.1 Open Channels
Shall be designed using the Manning Formula and "n" values shown.
CHANNEL LINING ---"n"---
Grass 0.03-0.05
Concrete 0.013-0.015
Riprap 0.017-0.03
All open channels shall have a minimum of one foot (1') of freeboard.
P
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5.2. Open Channels (Unpaved)
Unpaved channels may be used where the velocities of a 10-year
storm runoff are not greater than 3 ft/second. The sides shall have a
slope ratio not steeper than 3:1 . All unpaved channels shall be
seeded, plugged, or sodded immediately after their construction and
adequate measures taken to prevent erosion.
5.3. Open Channels (Paved)
Where velocities are greater than 3 feet per second, the channel
section shall be paved with concrete. The paved ditch may have
either vertical sides " or sloped sidewalls
with a maximum slope of 1 to 1. Ditches with vertical sides greater
than 30" in height shall have guardrails installed (2007 Arkansas Fire
Prevention Code (Building Codes.' Section 1013.1 ) The minimum flat
bottom width shall be three (3) feet.
5.4. Open Channels Erosion Protection
Special protection such as headwalls, riprap, or concrete lining will be
required in places such as bends, junctions, and inlets and outlets for
storm sewers where erosion is likely.
6. CURB INLETS - GENERAL REQUIREMENTS AND DESIGN CRITERIA
6.1 . Curb Inlets
Curb inlets will be required at low points of streets and at all other
location where water is removed from street gutters.
6.2. Areas of Potential High Pedestrian Volume
Inlets may be required near intersections to keep cross walks free of
storm water.
6.3. Arterial Streets
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Curb inlets shall be located on arterial streets so that the center two
lanes are free from water during runoff from a 50-year storm.
6.4. Minor and Collector Streets
Curb inlets shall be located on streets so that depth of runoff from a
10-year storm shall not exceed the top of standard 6" curbs. Curb
inlet capacity shall be determined as shown in Figure 17.
6.5. Swales
6.5.1 No swales shall be permitted across through streets.
6.5.2 All swales on "non-through" streets shall be of concrete
construction.
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