HomeMy WebLinkAboutResolution 1993-009
RESOLUTION NO. 93-09
WHEREAS, the City Council finds that in order to protect the health, safety and general
welfare of the City it is desirable to amend the "Public Works/Utilities Manual" of the City which was
adopted by Resolution 89-17; and
WHEREAS, the Section to be amended is Section 1-05.
NOW THEREFORE, BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY OF NORTH
RICHLAND HILLS, TEXAS, that:
1.
Section 1-05 of the "Public Works/Utilities Design Manual" is hereby repealed.
2.
Exhibit" A", attached hereto, and made a part hereof, shall replace the Section 1-05 repealed
by this Resolution.
3.
Exhibit "A" (the new Section 1-05) shall be in full force and effect from and after this date of
passage and approval of this Resolution.
PASSED AND APPROVED this 22nd day of February, 1993.
c ~l ~(1}~
Tommy Brow, ayor
ATTEST:
Rex
EXHIBIT "A"
SECTION 1-05
STORM DRAINAGE IMPROVEMENTS
A. GENERAL
The criteria herein provided shall govern the design of storm drainage improvements
within the City of North Richland Hills. Improvements shall include streets, alleys,
storm sewers, channels, culverts, bridges, swales, and any other facility through
which storm water flows. All drainage improvements shall be constructed in
accordance with City specifications and be in dedicated -R-9W right-of-wav (ROW)
or drainage easement. or floodwa',. casement. The Developer shall provide all the
necessary easement and ROW required for drainage structures, including storm
sewers and open channels with access ramps. Easement width for storm sewer
pipe shall be not less than fifteen (15') feet, and easement width for open channels
shall be at least forty (40') feet wider than the top of the channel with twenty (20')
feet on each side to serve as access ways for maintenance purposes.
The Developer shall be required to install at his own expense all storm sewers and
drainage structures. This policy is applicable to all reauired drainage facilities
including the channel imcrovements on the main channels and tributaries of
Mackey, Calloway, Wall<or Walkers Branch, Little Bear and Mesquite Branch Creeks,
but excepting the main channel of Big Fossil Creek. The Developer shall be
responsible for excavation and full concrete channel liner improvements based on
the fully urbanized one hundred (100) year frequency discharge for the channel.
unless otherwise approved by the City Council.
B. BASIS OF DESIGN
1. Rational Method: The method of calculation for storm runoff for drainage
areas less than seven hundred fifty (750) acres will be the Rational Method.
The method is expressed by the following equation:
O=CIA
o = storm discharge at the design point in cubic feet per second.
C = runoff coefficient representing the ratio of peak runoff to the rainfall.
I = average rainfall intensity for the time of concentration at the design
point in inches per hour. (see Figure 3)
A = area contributing runoff to the point of design in acres.
2. Unit Hvdroarach Method: Peak discharges for drainage areas exceeding
seven hundred fifty (750) acres shall be determined by using the unit
hydrograph method. The unit hydrograph for this method shall be developed
by using the criteria as outlined in "Flood-Hydrograph Analysis and
Computation", U.S. Army Corps of Engineers, Engineering and Design
Manuals, EM 110-2-1405, Washington D.C. dated August 31,1959.
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Typically a unit period of fifteen (15) minutes should be used for the
determination of the unit hydrograph.
In lieu of this procedure, there are several public domain micro-computer
programs available which will provide satisfactory results. If the Developer
elects to use a computer program, he should obtain prior approval from the
Director of Public Works or his designated representative.
3. Runoff Coefficient: Storm drainage improvements shall be designed based
on the drainage areas being fully developed. The zoning as shown on the
current City Zoning maps or the City's Master Land Use Plan, whichever is
more restrictive, shall determine the particular coefficient value selected.
The table below indicates the runoff coefficients for the different land uses.
RUNOFF COEFFICIENT "C"
Single Family Zoning Districts 0.55
Duplex Zoning Districts 0.60
Townhome and Garden Home Districts 0.65
Multi-family Districts 0.75
Commercial Districts 0.90
Industrial Districts 0.85
School, Church, and Institutional Districts 0.65
Parks and Agricultural District 0.30
4. Time of Concentration: The time of concentration shall be defined as the
time required for a drop of water to flow from the upper limits of a drainage
area to the point of concentration. Times of concentration shall be
calculated for all inlets, pipe junctions, and other critical design points in the
proposed storm sewer systems. The following minimum inlet times of
concentration may be used in place of calculated times. When calculating
inlet times, consider overland flow channelized at such time as the distance
traveled exceeds one hundred (100') feet.
TABLE V-2
Minimum Inlet Time of Concentration
Tvee of Area
Minimum of Inlet Time
Business and Commercial
Industrial
Multi-family
Residential
Parks and Open Spaces
10 Minutes
10 Minutes
10 Minutes
1 5 Minutes
20 Minutes
5. Rainfall Intensitv-Duration-Freauencv: The rainfall intensity-duration-
frequency compiled in Technical Paper No. 40 by the U.S. Weather Bureau,
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Department of Commerce shall be utilized in computing rainfall intensity.
(See Figure 3)
6. Desiqn Storm Frequency (see Fiqure 2): Storm frequency to be used in
design shall be as shown in the following table:
TABLE V-3
Desiqn Storm Frequency
Tyee of Facility
Minimum Desiqn Frequency
Storm Sewers
Streets
Culverts, Bridges, Channels,
Underpasses, and Creeks
5 Years
5 Years
100 Years
A storm sewer shall be designed to pick up flow from the street when the
runoff from a five (5) year frequency storm exceeds the capacity of the
street to its top of curb, or the spread of water on a collector street does not
leave one (1) traffic lane dry, or the spread of water on a arterial street does
not leave two (2) traffic lanes dry, whichever is more restrictive. The
combined capacity of the street and ROWand/or drainage easements and
the storm sewer pipe shall be adequate to safely convey the runoff from a
one hundred (100) year frequency storm.
7. Flow in Streets: Street capacity shall be determined by utilizing Manning's
equation (see Figure 4).
Q = 1.486 AR2/3 S 1/2
o
n
Q = discharge in cubic feet per second
n = Manning's roughness coefficient, use 0.016 for pavement and gutters
A = cross-sectional area of flow in square feet
R = hydraulic radius in feet
So = street or gutter slope in feet per foot
For parabolic crown streets, the cross slope shall be represented by the
following formula:
w
2"
c
y
4CX2
Y=7
3
All discharge of runoff from street to an open channel shall be in a flume or
through an inlet with adjoining pipe and headwall.
8. Storm Drain Inlets: The capacity of a depressed curb inlet on grade will be
based on the following equation:
=
[ H, _1 HJ [H,)'" - (H,)5I'l
discharge into inlet per foot of inlet opening in c.t.s./ft.
q,
0.7
q, =
H, =
H2 =
Yo =
a + Yo
a = gutter depression in feet
depth of flow in approach gutter in feet
The capacity of low point or drop inlets will be determined based on the
broadcrested weir formula:
q, = 3.0 (H, )3/2
9. Storm Sewer Svstems: Storm sewers shall be designed using the continuity
equation and Manning's equation.
Q = A V and
Q = 1.486 AR213 Sf'/2
1'1
Q = discharge in cubic feet per second
A = cross-sectional flow area normal to pipe in square feet
V = mean velocity of flow in feet per second
1'1 = Manning's roughness coefficient
R = hydraulic radius in feet
Sf = friction slope in feet per foot
The coefficient of roughness to be used in design shall be as shown below:
Pice Material
Reinforced Concrete Pipe 0.012
Corrugated Metal Pipe
Annular, unpaved with bituminous coating 0.024
Annular, 25% paved with bituminous coating 0.021
Annualr, 100% paved with bituminous coating 0.013
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Helical, unpaved with bituminous coating 0.014 - 0.26 *
Helical, 100% paved with bituminous coating 0.013
* To be determined by diameter and size of corrugations.
Storm sewer pipes shall be designed so that the mean velocity of flow is
equal to or greater than 2.5 feet per second and equal to or less than 15
feet per second. All corrugated metal pipe shall have an exterior bituminous
or polymer coating. Internal paving shall be used at the discretion of the
Director of Public Works or his designee.
The appropriate hydraulic grade line shall be plotted for all storm drainage
design. The elevation of the hydraulic grade line shall in no case be closer to
the gutter flow line than 1.5 feet.
Points of entry into the main storm drain shall be provided at least every five
hundred (500') feet.
10. ODen Channels: When the runoff exceeds the capacity of a seventy-two
(72") inch diameter concrete pipe or equivalent cross sectional pipe area
(i.e., 2-51 inch diameter concrete pipe), the discharge shall be carried in an
open channel. Open channels shall be designed to carry the one hundred
(100) year frequency storm runoff from a fully urbanized watershed with one
(1') foot of freeboard. in a fully concrete lined ditch. All ODen channels will
be fullv concrete lined exceDt for the main channels of Callowav Branch.
Little Bear Creek. Mackev Creek. MesQuite Branch. and Walkers Branch
which mav be earthen channels as defined herein. All open channels shall
have a minimum bottom width of eight (8') feet.
a. Full Concrete LininQ (see FiQure 1 ): All open ditches in all
subdivisions that are used to carry surface runoff across from more
than two (2) lots shall be fully concrete lined, except as otherwise
determined by the City Counoil. stated above. Lining of drainage
ditch floors is to be a minimum of 8 feet wide and minimum of six
(6") inch thick, 3,000 psi compressive strength concrete. Walls are
to be lined with five (5") inch thick concrete, sloped no steeper than
one (1') foot vertically to (1 .5') feet horizontally. All concrete slabs
are to be reinforced with a minimum of #4 steel reinforcing bars
placed at eighteen (18") inches or less on center each way, and
provided with minimum two (2") inch diameter weep holes with
approved filter media placed at intervals no greater than twenty-five
(25') foot centers. One (1 ') foot wide concrete wings shall be
provided at the top of each concrete side slope and four (4") inch
diameter, PVC plastic sleeves formed in the wings for constructing
fences along the top of the channel on each side. Vertical concrete
retaining wall sections shall be designed with adequate footing and
reinforcing steel to support all anticipated soil and water pressure
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loads acting on each side of the structure. In addition, retaining walls
shall be designed to support at least a "high surcharge" load unless
otherwise approved by the Director of Public Works.
The height of concrete channel liner shall be at least one (1') foot
above the fully urbanized one hundred (100) year water surface
profile. Such profile shall be determined by backwater calculations
using the HEC-2 computer program or other approved modeling
methods which take into account backwater effects from
downstream bridges, culverts, and other obstructions. Additional
lining height may be required in areas of supercritical flow or super-
elevation.
In cases where the top of channel liner must be constructed above
natural ground level as required to fully contain the one hundred (100)
year flow, and where construction of levees or berms are permitted,
provision shall be made for draining the local runoff which ponds
behind the levees after the water surface in the channel recedes.
Finished floor elevations may be established at least 1.5 feet above
the peak one hundred (100) year water surface which ponds behind
the levees, if approved by the Director of Public Works.
If levees are not approved by the Public Works Department, then
compacted earthen fill shall be placed along side the channel within
the entire flood plain area as required to concrete line the channel to a
height of one (1') foot above the fully urbanized one hundred (100)
year water surface elevation. Side slopes of the channel banks
behind the concrete channel liner shall be no steeper than five (5')
foot horizontal to one (1') foot vertical within the drainage channel
easement, or for a distance of twenty (20') feet behind the top of
channel whichever is greater. Side slopes beyond the twenty (20')
foot minimum shall be no steeper than three (3') foot horizontal to
one (1') foot vertical unless concrete lined or covered with approved
soil erosion protection materials. Fencing shall be placed along the
top of the concrete channel liner unless a sanitary sewer main or
water line is located within an easement along the channel bank, in
which case the fence shall be located on the easement line to permit
Public Works unrestricted access to the utility line.
b. Partial Concrete Liner (see Figure 1 ): If the one hundred (100) year
fully channel-contained water surface is above the natural ground line
and levees are not approved or flood plain fill is not feasible, the
concrete channel liner shall be extended to the natural ground line
along each side of the channel. In no case shall the concrete lined
capacity provided be less than that required to convey the twenty-
five (25) year frequency discharge. Floodvo'ay Drainaae easements
shall be provided along the sides of the concrete lined channel
sufficient to encompass all areas beneath the water surface elevation
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resulting from a fully urbanized one hundred (100) year discharge,
plus such additional width easements as may be required to provide
ingress and egress to allow maintenance and to protect adjacent
property against erosion, caving-in of over-banks, etc., as determined
and required by the Public Works Department. The Developer shall be
responsible for furnishing complete cross-sections, grading plans,
HEC-2 computer runs and all other documentation requested by the
Public Works Department which is required to justify less than full
section concrete channel lining and to establish the limits of the one
hundred (100) year overflow flood plain lines. Water surface profile
calculations shall be based on backwater effects created by an
existing bridge, culvert or other obstruction regardless of future
downstream proposed improvements.
c. Earthen Channels (see Fiaure 1 ): Earthen channels may only be
constructed after specific apßroval of the City Counoil. on the main
channels of Callowav Branch. Little Bear Creek. Mackev Creek.
Mesauite Branch and Walker's Branch. Approval of clans may be
given bv the Director of Public Works only if the following stipulations
are met:
1. The velocity of flow will not exceed eight (8') feet per second.
k That reinforced concrete liner or other accroved material is
used to crotect outside sloces in channel curves.
~ That sufficient enerav dissacation is desianed and constructed
at all locations where concrete lining meets earthen sloces and
bottoms.
4. That sufficient easements are dedicated to provide protection
of adjacent properties or facilities.
5. That floodway easements are dedicated to encompass the
area below the elevation of the water surface profile of a fully
urbanized one hundred (100) year frequency storm, plus one
foot of freeboard and any additional area necessary to provide
access for maintenance, but not less than sixty (60') feet in
width.
6. That arrangements have been made for perpetual maintenance
of the channel by the adjacent property owners or the channel
has been dedicated and accepted for City Park purposes.
7. That, in the judgement of the Director of Public Works, the
appropriate use of the neighboring property or the health and
safety of persons affected will not be substantially injured.
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Earthen channels, when approved, shall be constructed with a
trapezoidal shape and a minimum bottom width of twelve (12')
feet and side slopes not steeper than throo (2') four (4') feet
horizontal to one (1') foot vertical (4 Q to 1 preferred). A
reinforced concrete pilot channel not less than twelve (12')
feet in width or, as determined by the Director of Public
Works, shall be constructed. The side slopes shall be smooth,
free of rocks, and contain a minimum of six (6") inches of top
soil. Gobi blocks, rock rubble riprap, or other such similar
materials, shall be placed a minimum of four (4') feet along
both sides of the pilot channel to a depth of at least two (2')
feet. Size and gradation of such material shall be determined
based on peak discharge velocity requirements. The pilot
channel shall be constructed as approved by the Public Works
Department. The easement width for earthen channel shall
extend at least twenty (20') feet beyond the top of each
channel bank and shall not be cross-fenced. The tOD of bank
areas shall remain ODen for maintenance Durcoses.
After proposed earthen side slopes are cut, slopes shall be
covered by grass according to the City's specifications but no
less than one 2-inch hiah sDrino Der half SQuare inch of sloDe
and bottom. The grass shall be planted to twenty (20') feet
outside the top of banks.
The water surface profile (hydraulic grade line) for the one hundred
(100) year frequency storm shall be shown. Maximum permissible
mean velocities for the one hundred (100) year frequency discharge
shall be eight (8) feet per second in partially concrete lined channels
and in fully concrete lined channels, the maximum permissible mean
velocities for one hundred (100) year frequency discharge shall be
fifteen (15) feet per second.
Special consideration should be given to outlet structures on channels
where concrete lining meets earthen banks. '/¡/hon volooitios O>(Qood
oight (8') foot por sooond.
One reinforced concrete access ramp shall be provided at all
intersections of #te everv ODen channel with a public street. Access
ramps shall be a minimum of twelve (12') feet wide with a maximum
slope of sixteen (16%) percent.
11 . Bridaes and Culverts: All bridges and culverts shall be designed in
accordance with the current edition of the "Hydraulic Manual" prepared by
the Texas Department of HighwQ'{s and Publio Transportation, Bridge
Division. The fully urbanized one hundred (100) year frequency storm
hydraulic grade line shall be plotted. All culverts shall have headwalls and
wingwalls upstream and downstream. All culverts shall pass the fully
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urbanized one hundred (100) year frequency storm runoff without allowing
runoff to pass over the road. All bridges shall have channel bottom and
slopes concrete lined. The low point on the bridge structure shall be at least
one (1') foot above the fully urbanized one hundred (100) year frequency
storm water surface.
12. Lot Grading: Lot grading shall be conducted in a manner which will not
allow runoff to cross more than two (2) lots (including the lot on which the
drainage originates). If this is not possible, then a drainage easement must
be provided and any necessary facilities shall be constructed and installed by
the Developer.
Finished floor elevations shall be set a minimum of one (1') foot above the
top of curb at the centerline of the lot or one and one-half (1.5') feet above
the one hundred (100) year frequency storm water surface elevation,
whichever is higher.
13. Off-Site Drainaae: In respect to offsite drainage, the following provisions
shall apply:
a. The Developer shall be responsible for all runoff from fully developed
property upstream of his proposed development. Runoff coefficients
utilized to design drainage systems for the properties involved shall
use the current zoning and/or the future use of the property as shown
in the Future Land Use Plan, whichever is the most intensive use.
b. Effect of the development's drainage design on downstream
properties and adjacent properties shall be given proper consideration.
Water concentrated in streets, pipes, drains, culverts, and channels
will be moved to a recognized watercourse without damage to
intervening structures or undue spreading across intervening land.
A "recognized watercourse" shall herein be defined as either an open
channel with hydraulic characteristics which provide capacity for at
least a ten (10) year frequency storm after ultimate development of
its watershed, or an underground storm drain with capacity for at
least a five (5) year frequency storm plus overland relief sufficient to
safely discharge up to a combined ten (10) year frequency flow
(based on ultimate watershed development) without damage to
adjacent property. Such ten (10) year capacity shall extend at least
one hundred (100') feet downstream from the point of discharge or
from the Developer's property line, whichever is the greater distance.
Typical examples of such "recognized watercourses" are the main
channels of Mackey, Calloway Branch, Walkers Branch, Big Fossil,
Little Bear, and Mesquite Branch Creeks, or those tributary creeks,
streams, channels, or underground storm drains which meet the
hydraulic capacity requirements of a "recognized watercourse". The
Developer is responsible for constructing all offsite channelization or
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underground storm drain with overland relief required to discharge
concentrated stormwater from the low end of his development to the
recognized watercourse, and also to obtain all the necessary
easements from intervening land owners. Calculations will be
required to show that connecting offsite drainage ways are capable of
handling any increase in runoff due to development, concentration, or
diversion for at least the ten (10) year storm frequency.
Any drainage or fI008'11a'l easements necessary due to the
Developer's alteration of existing concentrated discharge locations
(i.e., existing creeks,channels, or storm sewers) shall be acquired by
the Developer at no cost to the City.
c. Where the preliminary drainage study by the Developer indicates that
additional runoff from the developing property shall overload
downstream drainage facilities and result in hazardous conditions, the
City may withhold approval of the development until appropriate
provisions have been made. These provisions shall include any
drainage studies or plans necessary to indicate the offsite drainage
problem will be corrected by offsite drainage construction.
d. When required, the Developer will furnish to the City, a "hold
harmless agreement" and a "release of liability" indemnifying the City
of North Richland Hills from any liabilities due to damages caused to
the downstream property owner by the discharge of storm drainage
water from the said development.
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