HomeMy WebLinkAboutOrdinance 3228 ORDINANCE NO. 3228
AN ORDINANCE OF THE CITY OF NORTH RICHLAND HILLS, TEXAS,
AMENDING SECTIONS 102 -124, 102 -125, 102 -142, 102 -143, AND 102-
144 OF THE NORTH RICHLAND HILLS CODE OF ORDINANCES AND
CHANGING THE CRITERIA FOR ALLOWING DETENTION /RETENTION
PONDS; ESTABLISHING A PENALTY; AND PROVIDING FOR
PUBLICATION.
WHEREAS, staff has recommended amendment of the City's regulations concerning
the use of detention /retention ponds where development is unlikely to be
able to occur without such ponds; NOW, THEREFORE,
BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF NORTH RICHLAND
HILLS, TEXAS:
Section 1: THAT Sections 102 -124, 102 -125, 102 -142, 102 -143, AND 102 -144 of the
North Richland Hills Code of Ordinances are hereby amended by
changing the criteria for allowing detention /retention ponds which shall
read as follows:
"Sec. 102 -124. - When detention /retention ponds will be allowed.
Detention /retention ponds will only be allowed if the proposed development is
discharging into a developed downstream system that does not have the capacity to
handle the runoff as mandated in the city's drainage criteria. A developed downstream
system may include state department of transportation drainage facilities and /or existing
city subdivisions that have drainage improvements that were constructed after 1984.
Detention /retention ponds will be allowed to discharge to an undeveloped street or
property if one of the following criteria is met and the development is approved by City
Council as part of a Special Use Permit (SUP).
1. Future downstream drainage infrastructure is not required or cannot be
constructed at time of development due to lack of easements or right -of-
way, OR
2. The pond discharges directly into a studied recognized watercourse or 1%
Chance Floodplain, contributing less than 10% of the fully developed flow
into said watercourse, OR
3. Future downstream improvements fall outside of the City's jurisdictional
boundaries.
In all cases:
1. The pond shall be designed such that it can be abandoned if /when a
downstream system is constructed.
Ordinance No. 3228
Page 1 of 7
2. The pond discharge shall not create adverse flooding or erosion
conditions downstream and is in all cases subject to the approval of the
Public Works Department.
3. Discharge shall arrive on downstream properties in a similar manner as it
occurred under pre - developed conditions.
Sec. 102 -125. - Definitions.
The following words, terms and phrases, when used in this article, shall have the
meanings ascribed to them in this section, except where the context clearly indicates a
different meaning, subject to final interpretation by the public works department:
Concentrated flow means the flow of stormwater in a swale, ditch or channel, typically
occurring after an outlet point or along a recognized water course.
Design flood means the flood having a one percent chance of being equaled or
exceeded in any given year based upon fully developed watershed conditions. This is
commonly known as the 100 -year frequency flood, or base flood. Fully developed
conditions shall be based on the most current future land use assumption plan for the
city, or current zoning map, whichever produces the higher runoff coefficients for the
drainage area generating the design flood discharge.
Detention basin means a dry basin or depression constructed for the purpose of
temporarily storing stormwater runoff and discharging all of that runoff over time at a
rate of flow equal to or less than which would have occurred prior to installation of the
basin. This definition includes all structural components proposed for the basin (i.e.,
inlet structures, outlet structures, walls, fences, piping, headwalls, etc.)
Federal Emergency Management Agency (FEMA) means the federal agency which has
and does assist the Federal Insurance Administration administering the National Flood
Insurance Program.
Federal Insurance Administration (FIA) means the division of the federal government
which oversees the Flood Insurance Program with the help of FEMA.
Freeboard means the vertical distance between the design flood surface and the top of
an open channel, dam, levee, detention or retention basin. The freeboard allows for
wave run -up, wind tide, hydraulic jump, or other design conditions without overtopping
the structure.
Frequency means the reciprocal of the exceedance probability. For example, a 100 -
year frequency storm is one which has a one percent chance of being equaled or
exceeded in any year, and a five -year storm has a 20 percent chance of being equaled
or exceeded in any year.
Ordinance No. 3228
Page 2 of 7
Hydraulics means concerned with the determination of the maximum stage or elevation
reached by the waters of a flood at a given location. A flood is said to have occurred
when the maximum stage or elevation results in an overflow upon lands that are
traditionally useable by man and not normally covered by water.
Hydrology means concerned with the magnitude and frequency of the flood flow. The
magnitude of the flood flow is the statement of the quantity of water that results from a
given storm, whereas, the frequency is the statement of the average return or
occurrence of a flood event.
Inflow hydrograph means hydrographs used to determine the stormwater flow volume
into a detention basin or retention basin. A hydrograph describes the variation in flow
rate over a fixed period of time.
Landscaping plan means a plan that identifies how the detention basin or retention
basin will be landscaped. This plan will need to include the types of plants, trees,
shrubs, grass, decorative fencing, etc., that will be used and will need to be approved by
the city.
Normal pool elevation means the level at which a retention basin was designed to be
prior to a rainfall /runoff event. In a retention basin, this elevation will be the water
surface of the conservation pool.
Open channel means a channel, branch, creek, or stream in which water flows with a
free surface.
Pond means a still body of water located on the surface of the earth.
Rational formula means a means of relating runoff from an area and the intensity of the
storm rainfall as defined in the Public Works Design Manual.
Retention basin means a pond which has been designed to have both a conservation
pool for holding water indefinitely, and a flood storage pool for storing stormwater runoff
on a temporary basis, for the purpose of reducing the peak discharge from the basin.
This definition includes all structural components proposed for the basin (i.e., inlet
structures, outlet structures, walls, retaining walls, fences, piping, headwalls, aeration
systems, etc.).
Surface water means water on the surface of the ground, the source of which is so
temporary or limited that it cannot maintain for any considerable time a stream or body
of water having well- defined and established existence. Surface water is derived from
falling rains and melting snows, and continues to be such until it reaches some well -
defined channel in which it concentrates and flows with other waters, whether derived
from the surface or springs, and then it becomes the running water of a stream and
ceases to be surface water.
Ordinance No. 3228
Page 3 of 7
Swale means a shallow waterway. Swales are required above underground storm
drains with capacity, along with the storm drain, to carry a 100 -year frequency storm.
The city's Public Works Design Manual requires that such swales shall be concrete
lined.
Time of concentration means the estimated time in minutes required for runoff to flow
from the most remote section of the drainage area to the point at which the flow rate is
to be determined.
Watercourse means a stream of water of such well- defined existence as to make its
flow valuable to the owners of the land along its course. A "recognized" watercourse is
further defined as a channel, creek, or underground storm drain which has at least a
ten -year conveyance of capacity without flooding adjacent property.
Watershed means the area contributing storm runoff to a stream, pond, or drainage
system.
Sec. 102 -142. - Runoff calculations.
Detention /retention facilities shall be designed based on a 100 -year frequency storm
runoff for the upstream drainage watershed area.
1. Rational method. The "rational method" can be used to calculate the
runoff rate and volume for drainage areas less than 250 acres. The
formula for this method is Q = CIA.
Hydrograph method. The "hydrograph method" will be used to calculate the
runoff rate and volume for drainage areas equal to or greater than 250 acres.
The HEC -HMS method developed by the Hydrologic Engineering Center (HEC)
of the U.S. Army Corps of Engineers shall be used. Use of other hydrograph
methods must be approved by the public works department prior to beginning
design.
Sec. 102 -143. - Flood routing methods.
The flood routing computer program to be used shall be either HEC -2 or HEC -RAS from
the U.S. Army Corps of Engineers. Use of other computer program routing methods
must be approved by the public works department prior to beginning design.
Sec. 102 -144. - Parameters.
a) Inlet. The inlet structure shall allow for the upstream 100 -year runoff to be
discharged to the pond in a manner which minimizes erosion.
Ordinance No. 3228
Page 4 of 7
b) Outlet. The outlet structure for detention basin /retention basin shall be
constructed to minimize erosion and allow for the 2 -, 5 -, 25 -, 50- and 100 -year
storm runoff to be discharged in a controlled manner. An outlet control structure
will be installed on detention /retention basins to achieve the design discharge
equal to or less than the runoff rate which existed from the watershed prior to this
proposed development. On the outlet structure for retention basins, an
emergency outlet valve and pipe shall be installed. The valve and pipe shall be at
least eight inches in diameter and meet all city requirements for water system
pipe and valves. Installation of the emergency outlet valve and pipe shall allow
the retention basin to be drained to within a maximum of one foot of its design
bottom. In addition:
i. Outlet structures shall be located at least 50' from a property line and shall
be designed to minimize potential erosion.
ii. Discharge rates shall not increase for the 2 -, 5 -, 25 -, 50- and 100 -year
storms.
iii. Outlet velocity: No significant increase (maximum 5 %) is allowed in
concentrated flow velocities for the 2 -, 5 -, 25 -, 50- and 100 -year storms.
Post - development concentrated flow velocities cannot be increased by
more than 5% above pre - development velocities. If existing concentrated
flow velocities exceed six (6) feet per second, no additional increase in
velocities will be allowed.
iv. Flood heights (depth of flow) shall not increase across downstream
properties.
c) Storage. The detention /retention storage basin shall be designed to store that
volume required to reduce the discharge rate out of the basin to not more than
the runoff rate which existed from the watershed prior to this proposed
development which includes the basin. The detention /retention storage volume,
excluding conservation pool, shall drain out completely within 24 hours of the end
of a rainfall event.
d) Freeboard. A minimum freeboard of one foot shall be required. This will be the
difference in elevation between the 100 -year storm design water surface
elevation, plus increased elevation created by wave action, wind time or
hydraulic jump, anywhere on the detention /retention basin or decorative pond,
and the lowest point on the surrounding embankment within the drainage
easement.
e) Side slopes. The embankment side slopes for the different basins or ponds will
be as noted below. The top of the side slope shall be a maximum of 12 inches
above the surrounding ground. The embankment of the basin shall not "act" as a
levee. The 100 -year event shall not be higher than the surrounding ground.
(1) Detention basin. Slopes shall be five to one or milder.
Ordinance No. 3228
Page 5 of 7
(2) Retention basin. Slopes shall be four to one below normal pool depth and
five to one above.
f) Overbank. The overbank of the retention basin (and all detention basins) shall be
block sodded with a public works department- approved native grass. The grass
must be relatively established prior to final approval of the construction by the
city.
g) Depth.
(1) Retention basin. The minimum depth of the retention basin shall be four
feet from the normal pool elevation to the bottom between the toe of
slopes. The maximum depth of a retention basin shall be no greater than
ten feet.
(2) Detention basin. The maximum depth of the detention storage in a parking
lot can be designed is eight inches. For all other detention storage basins,
the maximum depth shall not exceed ten feet.
h) Velocity. The average velocity of flow through the detention or retention basin
shall be no greater than five feet per second.
i) Erosion control. Erosion control upstream and downstream of the basins shall be
considered in the design. Erosion control systems shall be installed where
necessary as determined by the public works department.
j) Aeration. All retention basins will require aeration systems to be installed. The
aeration system will be designed to keep the standing water from stagnating. All
electrical service and maintenance costs for an aeration system shall be the
owner /developer or homeowners association responsibility to pay. The aeration
system will need to be approved by the public works department with the
approval of the basin. The owner /developer's engineer will provide appropriate
design calculations and /or shop drawings showing that the aeration system is
"sized" adequately for the pond. The aeration system will need to have a
screening /filter device to minimize pump blockage.
k) Water supply. Provisions shall be made to keep the water surface elevation in a
retention basin at the normal pool elevation. This will require the developer to
submit plans and specifications for installation of a water well. Another alternative
is a separate irrigation service connection to the city's water system to provide
the water supply to recharge the basin or pond as needed. The cost of the water
used to recharge the basin shall be the owner /developer or homeowners
association responsibility to pay. Recharge design shall comply with all state and
federal requirements.
Ordinance No. 3228
Page 6 of 7
1) Type of detention. The city will consider different types of detention facilities.
Underground detention and parking lot detention are two examples of alternative
detention facilities that may be allowed.
(1) Underground detention. Will need to include one or more access points for
maintenance, and be designed to minimize maintenance.
(2) Parking lot detention. Will need to be designed in the "extra" parking
spaces. No detention will be allowed in the required parking spaces. As
stated previously, the maximum depth for parking lot detention shall be
eight inches."
Section 2: Violation of this ordinance shall be punishable by a fine of up to Five
hundred dollars ($500.00). Each separate violation shall be punishable
hereunder and each day each such violation shall be allowed to exist or
continue shall constitute a separate violation punishable hereunder.
Section 3: The City Secretary is hereby authorized and directed to cause the
publication of the descriptive caption and penalty clauses of this ordinance
as an alternative method of publication provided by law.
AND IT IS SO ORDAINED.
PASSED AND APPROVED on this the 10th day of December, 2012.
CITY ORTH LAND HILLS
\\ �oa�mmmmiuu��� i
04 RtC H ` �NO��' %,� By:
o tl ti�� scar Tre 'no, Mayor
ATTEST.
Patricia Huts46
ary
APP TO FORM AND LEGALITY:
George A. Staples, City ttorney
APPROVED AS TO CONTENT:
ike urtis, E., Managing Director
Ordinance No. 3228
Page 7 of 7
INVOICE
Star - Telegram Customer ID: CIT13
808 Tbrockmorton St. Invoice Number: 324595451
FORT WORTH, TX 76102
(817) 390 -7761 Invoice Date 3/1/2013
Federal Tax ID 26- 2674582 Terms: Net due in 21 days
Due Date: 3/31/2013
Bill To:
CITY OF NORTH RICHLAND HILLS /SE PO Number:
PO BOX 820609 Order Number: 32459545
NORTH RICHLAND HILLS, TX 76182- Sales Rep: 073
Description: CITY OF NORTH RI
Attn:: STACEY _ SON Publication Dates: 2/28/2013 - 3/1/2013
APPROVED AS TO FORM:
/s/ Wayne K. Olson, City Attorney.
C CITY ORDINANCEIN0. HILLS
3228 ' HILLS 13580 1 31 31 LINE $6.14 $380.72
Sa ($346.08)
Mi f Legal Noti ces $10.00
An ordinance of the City of North
Richland Hills Texas, amending
Sections 102 - 1 125,102 -142,
102 -143, and 102 -144 of the North
Richland Hills Code of Ordinances Net Amount $44.64
and changing the criteria for al-
lowing detention /retention ponds;
establishing a penalty; and pro-
viding for publication.
Violation of this ordinance shall be
punishable by a fine of up to Five
hundred dollars ($500.00). Each
separate violation shall be pun-
ishable hereunder and each day each
such violation shall be allowed to
exist or continue shall constitute = --N RISTY LYNNE HOLLAND
a separate violation punishable hereunder. ry Public, State of Texas
Passed and Approved on this 10th Commission Expires
day of December, 2012 July 31, 2016
/s /Oscar Trevino
T Oscar Trevino - Mayor
c ATTEST:
/s /Patricia Hutson
Patricia Hutson - City Secretary
B APPROVED AS TO FORM AND for said County and State, this day personally appeared Deborah Baylor Norwood, Bid and Legal Coordinator for
LEGALITY:
tt /s /George Staples a Star- Telegram, Inc. at Fort Worth, in Tarrant County, Texas; and who, after being duly swom, did depose and say
e George Staples - City Attorney 'ertisement was publish in the above named paper on the listed dates: BIDS & LEGAL DEPT. STAR TELEGRAM
(817) 215 -2323 (�
Signed `\
SUBSCRIBED AND SWORN TO BEFORE ME, THIS Monday, Mar 13.
Notary Public
Thank You For Your Payment
---------------------------------------------
Remit To : Star - Telegram Customer ID: CIT13
P.O. BOX 901051 Customer Name: CITY OF NORTH RICHLAN
FORT WORTH, TX 76101 -2051 Invoice Number: 324595451
Invoice Amount: $44.64
PO Number:
Amount Enclosed: $