HomeMy WebLinkAbout1994-O-05 - Storm DrainageORDINANCE NO. 1994-5
AN ORDINANCE AMENDING THE CITY OF STEPHENVILLE DESIGN STANDARDS
(1989) WHICH WERE MADE A PART OF THE SUBDIVISION REGULATIONS
ADOPTED BY ORDINANCE NO. 1991-12 APPROVED BY THE CITY COUNCIL ON
JUNE 4, 1991, BY DELETING ARTICLE II, STORM DRAINAGE, AND REPLACING
SAME WITH A REVISED ARTICLE II, STORM DRAINAGE, LABELED EXHIBIT "A"
AND ATTACHED HERETO.
WHEREAS, the City Council approved a Drainage and Stormwater
Control Ordinance, Ordinance No. 1987-17, on August 4, 1987, and
Ordinance 1985-13, and
WHEREAS, the City Council subsequently adopted Sections III through
VIII of Ordinance No. 1987-17 as Article II, Storm Drainage, of the
City of Stephenville Design Standards made a part of the
subdivision Regulations adopted by the City Council by Ordinance
No. 1991-12 on June 4, 1991, and
WHEREAS, the City Council of the City of Stephenville wishes to
modify portions of said Article II, Storm Drainage,
NOW, THEREFORE, BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF
STEPHENVILLE, TEXAS:
That Ordinance No. 1985-13 and Ordinance No. 1987-17, Drainage and
Stormwater Control Ordinance, and Chapter II, Storm Drainage, of
the Subdivision Regulations adopted by Ordinance No. 1991-12 are
hereby repealed and replaced by the attached Exhibit "A".
This Ordinance shall become effective on the 3rd day of May,
1994.
INTRODUCED, PASSED and APPROVED on this the 3rd day of May,
1994.
Lavinia Lo rmann, Mayor
ATTEST:
��Cindy L taf ord,
II III City Se retary
n cu �6"
Reviewe by Donald E. Davis,
City Administrator
Approved at -to form and legality
Randy Thomas, City Attorney
ARTICLE II
STORM DRAINAGE
SECTION 2.1 Standard Provisions
Standard Provisions
All construction for storm drainage in the development or improvement of property within the City
of Stephenville shall conform to the following standards and requirements:
Storm sewer inlets shall be provided along paved streets at such intervals as are
necessary to limit the depth of flow as follows:
All Streets - Streets shall be designed to flow not more than curb deep during the 5 year
storm.
Residential Streets - Based on parkway slopes of 1/4 inch per foot behind the curb, the
100 year Design Frequency flows shall not exceed a depth of 2 1/z inches over the top of
curb, and the area behind the curbs must be graded in such a manner as to contain the
100 year flow within the right-of-way.
Collector Streets - Based on parkway slopes of 1/4 inch per foot behind the curb, the 100
year Design Frequency flow shall not exceed a depth of 21/2 inches over the top of curb,
and the area behind the curb shall be graded in such a manner as to contain the too
year flow within the right-of-way.
Arterials - Based on a transverse slope of 1/4 inch per foot on the pavement, the 100 year
Design Frequency flow shall not exceed a depth of 1 inch over the lowest curb and the
area behind the curb shall be graded so as to contain the 100 year flow within the street
right-of-way.
Alleys - The 100 year Design Frequency flow shall not exceed the capacity of the alley
right-of-way.
Positive Overflow - The approved drainage system shall provide for positive overflow at
all low points. The term 'positive overflow' means that when the inlets do not function
properly or when the design capacity of the conduit is exceeded, the excess flow can be
conveyed over land along a concrete paved course. Normally, this would mean along
a street or alley but may require the dedications of special drainage easements on private
property.
2. A closed storm sewer system shall be required to accommodate runoff exceeding the
street capacity, as provided above, up to and including the design capacity of a seventy-
two (72) inch concrete pipe. The following are recommended maximum design velocities:
Culverts 15 fps
Inlet Laterals 10 fps
Storm Sewers 12.5 fps
Discharge velocities cannot exceed the permitted velocity of the channel or conduit at the
outfall.
} 3. An open channel may be permitted to accommodate runoff exceeding the design
f capacity of a seventy-two (72) inch pipe, as provided below:
3438 2.1
EXHIBIT "A"
a. Channels draining an area with a'CA' factor (coefficient of runoff and drainage
area, as used hereinafter described 'rational formula") of less than 250 shall be
1 concrete lined to the design depth, plus six (6) inch freeboard except that a
closed system as provided above may be used. A twenty (20) foot wide access
easement shall be provided along at least one side parallel to the channel.
b. Channels draining an area with a'CA' factor of more than 250 but less than 500
shall be concrete lined to contain the runoff from a ten (10) year return frequency
storm with the balance of the required design frequency storm contained within
grassed slopes no steeper than three (3) horizontal to one (1) vertical and with
a minimum of one foot (1') freeboard.
C. Channels draining an area with a 'CA' factor of more than 500 but less than
1,000 shall be constructed with a reinforced concrete pilot channel not less than
twelve feet (12') in width and having at least six inch (6') curbs, a four inch (W)
depressed invert and an appropriate edge protection as accepted by the City's
authorized representative. The remainder of the channel shall consist of earthen
side slopes with proper vegetative cover on slopes not steeper than 3 to 1.
d. Channels draining an area with a 'CA' factor over 1,000 shall be designed to
carry the capacity of a 100 year flood frequency storm. The specific design and
type of construction improvements for this drainage facility shall have specific
approval by the City's authorized representative after review of maintenance,
erosion, and site conditions.
e. All areas of an earth channel section shall be improved by the Developer with a
low maintenance vegetation as approved by the City's authorized representative
prior to planting. The selection of materials shall comply with the current ground
cover listing for North Central Texas furnished through the Texas Agricultural
Extension Service.
f. The setback for the building line shall be as follows:
1) A maintenance strip shall be provided with a twenty (20) foot width along
each side of the top of the channel unless approved otherwise by the
City's authorized representative and shown on the filed plat.
2) A drainage flume section, which provides for limited flow of stormwater,
shall be located within a drainage easement of sufficient width to permit
future maintenance accessibility.
g. A drainage feature which is to remain in its natural state of native growth may be
accepted by the City to remain as an unimproved facility so long as the water
conveyance capacity of the area is adequate to handle the future drainage
requirements.
h. In lieu of the improvements of a channel draining an area with a 'CA' factor in
excess of 500, the City Council may elect to accept the dedication of all land
within the 100 year floodway of the existing drainage channel as a permanent
drainage right-of-way.
I. The criteria for drainage improvements as herein -above set forth in Paragraphs
(a) through (a) of this section shall be applicable to publicly owned lands solely
fat the discretion of the City of Stephenville.
3438 2.2
j. Easements - Drainage and floodway easements shall be provided for all open
channels. Easements shall encompass all areas beneath a ground elevation
defined as being the highest elevation of the following:
1) One (1) foot above a design storm having a recurrence interval of one
hundred (100) years, calculated by the City's criteria.
2) The top of the high bank.
3) Maintenance access.
k. Ground Cover - Any ground cover or vegetation which is planted and is a part of
the improvement project will not be accepted by the City until the growth has
been established to the satisfaction of the City.
SECTION 2.2 Responsibility of Owner of Developer for Storm Drainage
The owner or developer of property to be developed shall be responsible for all storm
drainage flowing through or abutting such property. This responsibility includes the
drainage directed to that property by ultimate development as well as the drainage from
ultimate development that naturally flows through the property by reason of topography.
It is the intent of this Ordinance that provision be made for storm drainage in accordance
with Section 2.1 at such time as any property affected is proposed for development, use
or modification.
2. Where the improvement or construction of a storm drainage facility is required along a
property line common totwo or more owners, the owner hereafter proposing development
of his property shall be responsible for the required improvements at the time of
r ` development, including the dedication of all necessary right-of-way or easements, to
accommodate the improvements.
3. Where a property owner's proposed development uses only a portion of his property,
provision for storm drainage in accordance with Section 2.1 shall only be required in that
portion of the property proposed for immediate development, except as construction or
improvements of a drainage facility outside that designated portion of the property is
deemed essential to the development of that designated portion.
4. When a property owner proposes a development, the owner shall include provisions and
plans for control of siltation and downstream erosion. If siltation or downstream erosion
occurs, the owner will be responsible to remove siltation or make repairs to eroded areas
at his own expense until the owner has established ground cover or vegetation to a
condition of growth acceptable to the city.
5. The owner or owners shall dedicate to the City the required drainage easements.
Determination of the minimum easements required shall be made by the City's authorized
representative.
6. In the event that a property owner or developer desires to modify an existing pond or lake
or desires to impound storm water by excavation, filling or construction of a dam within
a property for retention or detention, thereby creating a lake, pond, lagoon or basin as
a part of the planned development of that property, the standard provisions for storm
drainage as established in Section 2.1 of this Ordinance shall be applicable and shall also
/ provide the following:
i
a. An engineering plan for such construction, accompanied by complete drainage
design information prepared by registered professional engineer, shall have been
approved by the City of Stephenville.
I,
b. The owner or developer shall have agreed to retain under private ownership the
lake, pond, lagoon, or basin constructed, and to assume full responsibility for the
protection of the general public from any health or safety hazards related to the
lake, pond, or lagoon constructed.
C. The owner or developer shall have agreed to assume full responsibility for the
maintenance of the lake, pond, lagoon, or basin constructed.
d. The obligation herein shall run with the land and shall be a continuing obligation
of the owner or owners of such land.
e. All Federal, State, and County laws pertaining to impoundment of surface water
are complied with including the design, construction and safety of the
impounding structure. Any existing structure, which is included in a project
development area, shall be improved to comply with the applicable Federal,
State, County and City safety requirements for structures. The design flows shall
be based upon the urbanized drainage flows which can result from a 100 year
flood. All improvements shall be made to the dam structure at the expense of the
developer, prior to acceptance of the adjacent street, utilities and drainage
improvements as provided for under the Subdivision Ordinance.
f. On any existing structure, the owner will furnish a study by a professional
engineer to the City for approval prior to any proposed alteration. Compensatory
storage shall be provided in some manner such that equal or comparable flood
I 1 retention capacity is maintained.
7. The maintenance of private drainage facilities shall be provided by the property owner or
assigned agent. The City shall be kept advised of the responsible agent.
8. All existing water seepage springs or flowing water shall be connected into an
underground storm sewer system where such a system is available.
9. The developer shall provide detailed off -site drainage plans for the proper transition to
natural ground or stream elevations. Criteria for on -site development shall apply to off -site
improvements as required by the City's authorized representative.
SECTION 2.3 Engineering Design
Each storm drainage facility, including street capacities, shall be designed to convey the
runoff which results from a certain prescribed design storm.
Drainage design requirements for open and closed systems shall provide protection for
property during a storm having a 100 year recurrence interval with this projected flow
carried in the streets and closed drainage systems in accordance with the following:
3438 2.4
Drainage Facility
Closed storm sewer systems
Closed storm sewer systems at street
low point or sag
Culverts and bridges
Channels - Concrete Lined (CA<250)
Concrete Lined
(CA>250<500)
Concrete Pilot Channel
(CA> 500 < 1000)
Earthen Channels
(CA> 1000)
Design Recurrence Interval
5 yr. w/emergency 100-yr. overflow
25 yr. w/emergency 100-yr. overflow
25 yr. (structure or adjacent real
property must not be damaged by
100-yr. storm)
25 yr. w/emergency 100-yr. overflow
10 yr. w/100-yr. overflow contained
within grassed slopes
100 year
100 year
2. Computation of stormwater runoff for drainage areas less than 150 acres shall be by the
'Rational Method', which is based on the principle that the maximum rate of runoff from
a given drainage area for an assumed rainfall intensity occurs when all parts of the area
are contributing to the flow at the point of discharge. The formula for calculation of runoff
by the 'Rational Method' is:
Q = CIA, where
Q = The maximum rate of discharge, expressed in cubic feet per second.
= Rainfall intensity in inches per hour from the applicable curves of Plate 1.
Time of concentration or duration of rainfall for use in Plate 1 shall be
calculated by velocity data shown in Table 2.1.
C = A runoff coefficient which varies with the topography, soil, soil cover, land
use and moisture content of the soil at the time the runoff producing rainfall
occurs. This runoff coefficient shall be based on the ultimate use of the
land as recommended by the Master Plan for the City of Stephenville and
shall be selected from Table 2.2 herein on the basis of the use shown on
land use and zoning map of the Comprehensive Zoning Ordinance for the
City of Stephenville. If an area has had a change of zoning to give the area
land use for which the 'C' in Table 2.2 is higher than use shown on land
use and zoning maps, the higher 'Ca factor shall be used.
A = The drainage area, expressed in acres, contributing to the runoff at the point
in question. Calculation of the drainage area shall be made from a contour
map of one (1) foot intervals of which a copy shall be submitted with the
engineering plans for approval. On large drainage areas or areas with steep
slopes and 'rf approved by the City's authorized representative, maps with
a contour interval of greater than one (1') foot may be used for drainage
area computations.
34M 2.5
For drainage areas over 150 acres but less than 1000 acres, either the
Rational Method or the Unit Hydrograph Flood Determination Method may
be used.
For drainage areas in excess of 1000 acres, the use of a Unit Hydrograph
Flow Determination shall be made. The use of a unit Hydrograph
calculation will be based upon standard and accepted engineering
principles normally used in the profession subject to the approval of the
City's authorized representative. The Soil Conservation Service Technical
Release Number 55 is an acceptable method.
Computation of runoff shall be based on a fully developed drainage area or
watershed in accordance with the land use projected in the current
comprehensive land use plan for the City of Stephenville. The developer
and/or builder shall develop site development plans so that the rate of runoff
created by the development of their property does not exceed the rate of
runoff resulting from an R-1 zoning unless the Developer, through an
engineering analysis, can demonstrate to the City's authorized
representative that the proposed runoff has no adverse effect either on the
receiving stream or downstream real property.
Table 2.1
Average Velocity for Use in Determining Time of Concentration
Description of 0% to 3% V. 4% to 7% V. 8% to 11 % V. Over 12% V.
Water Course in f.p.s. in f.p.s. in f.p.s. in f.p.s.
f Surface drainage 5 9 13 15
Channels Determine V. by Manning's Formula
Storm sewers Determine V. by Manning's Formula
Average velocities of Table 2.1 are to be used for calculating the time of
concentration or 'Rainfall Duration' as set forth on Plate 1 unless the
designer shows calculation of velocities for streets and/or storm sewers.
3. The Rational Method will be used for drainage areas less than 150 acres and may be
used for areas between 150 and 1,000 acres. As the Rational Method is used and
detention is required, the volume of water supplied by the design storm may be
calculated by converting the runoff rate, during a specific duration, to volume. The inflow
volume should be determined for a period of at least twice the time of concentration for
the site.
3438 2.6
Table 2.2
Values of 'C' for Use in 'Rational Method' Formula Q = Cl
Value of 'C' (Runoff Coefficient -
Slope Land Use From Master Plan Rational Method)
Flat 0% to 1 % Park areas, No developable land
0.20
Park and school land tract
0.30
Single family residential
0.45
Duplex
0.50
Multiple family
0.55
Local business
0.65
Central business
0.80
Commercial
0.80
Industrial
0.75
Moderate
Park areas - No developable land
0.30
1 % to 34/2%
Park and school land tract
0.40
Single family residential
0.50
Duplex
0.55
Multiple family
0.60
Local business
0.70
Central business
0.85
Commercial
0.85
Industrial
0.80
Steep
Park areas - No developable land
0.35
3.5% and
Park and school land tract
0.45
over
Single family residential
0.65
Duplex
0.70
Multiple family
0.75
Local business
0.80
Central business
0.85
Commercial
0.85
Industrial
0.85
Retention and detention are two generalized types of storm runoff storage used
to control the rate of runoff. All detention ponds should be designed to empty
within a 24 hour period.
Using the average velocities from this table, the designer shall calculate the time
of concentration by the following formula unless more data is shown on the plans
for calculating time of concentration.
'Inlet Time' = 5 minutes for property zoned for multiple family, local business,
central business, commercial or industrial; 10 minutes for property zoned for
parks, schools, single family residential and duplex.
T = 'Inlet Time' + D Where:
V x 60
t�
3438
2.7
T = Time of concentration in minutes for use in Plate 3
D = Distance in feet from point of concentration to upper end of drainage area
under consideration.
V = Velocity in feet per second from this table or velocity calculated by designer
for streets and/or storm sewers.
The existing soils are such that erosive conditions are created at certain
velocities. The following velocities are considered to be maximum acceptable
design conditions:
Earth (with no concrete protection) 0 to 5 feet per second
Shale 6 to 10 feet per second
Rock 10 feet per second
4. The minimum curb inlet size shall be eight (8) feet in length with a minimum
capacity of 8 cfs.
5. The construction of all improvements shall be in accordance with the standards
set forth in the City's rainfall intensity chart in years (Plate 1), the Inlet Capacity
for Low Point Inlets (Plate 2), the Drainage Capacity for Road Sections (Plate 3),
and the Typical Sections of Drainage Channels (Plate 4) are hereby adopted as
a part of this Ordinance.
6. Complete engineering plans for storm drainage facilities shall be prepared by a
professional engineer, registered in the State of Texas, and experienced in civil
r engineering work. The total cost for such engineering plans and specifications
1 1 shall be borne by the owner or the developer and shall be furnished to the City's
( 1 authorized representative for review and approval.
7. In any development, alternation or improvement of property, the owner may be
required to provide at his expense a preliminary drainage study for the total area
to be ultimately developed. This study shall be submitted to the City's authorized
representative as a part of the submitted data for consideration of Preliminary Plat
or Site Plan approval.
3438 2.8
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NOTE:
CHANNELS DRAINING AREAS EXCEEDING CA FACTOR OF 1,000 SHALL BE
DESIGNED TO CARRY
THE CAPACITY
OF A 100 YEAR FREQUENCY STORM, THE SPECIFIC DESIGN
AND TYPE OF
CONSTRUCTION
IMPROVEMENTS SHALL HAVE SPECIFIC APPROVAL BY THE
DIRECTOR OF PUBLI(
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TYPICAL
DRAINAGE
CHANNEL
SECTIONS
PLATE 4
nn mvcsnnem aemce jor rumtc Tunas
RESOLUTION
AMENDING AUTHORIZED REPRESENTATIVES
WHEREAS, City of Stephenville
("Participant") is a political subdivision of the State of Texas and is empowered to delegate to a public funds
investment pool the authority to invest funds, to act as custodian of investments purchased with local
investment funds; and,
WHEREAS, the Treasurer of the State of Texas, acting by and through the Texas Treasury
Safekeeping Trust Company ("Trust Company"), has created "TexPool", a public funds investment pool, to
effectuate the goals of providing investments at the highest possible yield and maintaining complete safety of
the funds of the Participant; and,
WHEREAS, the Participant hereby requests the following changes regarding the individuals
authorized to act on behalf of the Participant.
NOW THEREFORE, be it resolved as follows:
A. That City of Stephenville
has entered into a Participation Agreement and has established an account in its name with the
Trust Company's Local Government Investment Pool, "TexPool", for the purpose of
transmitting local funds for investment by the Trust Company in TexPool;
B. That the individuals, whose signatures appear on page 2 of this Resolution, are
officers, employees, or authorized representatives of the Participant and are each hereby
authorized to transmit funds to the Trust Company for investment in TexPool and are each
further authorized to withdraw funds from time to time, to issue letters of instruction, and to
take all other actions deemed necessary or appropriate for the investment of local funds:
(over)
ORDINANCE NO. 1994-6
SPEED ZONE ORDINANCE
AN ORDINANCE ALTERING THE PRIMA FACIE SPEED LIMITS ESTABLISHED FOR
VEHICLES UNDER THE PROVISIONS OF SECTION 167 AND 169 OF ARTICLE
XIX, R.C.S. 6701d, UNIFORM ACT REGULATING TRAFFIC ON HIGHWAYS, UPON
THE BASIS OF AN ENGINEERING AND TRAFFIC INVESTIGATION UPON CERTAIN
STREETS AND HIGHWAYS, OR PARTS THEREOF, WITHIN THE CORPORATE LIMITS
OF THE CITY OF STEPHENVILLE AS SET OUT IN THE ORDINANCE: AND
PROVIDING A PENALTY OF A FINE NOT TO EXCEED $200.00 FOR VIOLATION
OF THIS ORDINANCE.
WHEREAS, Section 167 and 169 of Article XIX, R.C.S. 6701d, Uniform
Act Regulating Traffic on Highways, provides that whenever the
governing body of the City shall determine upon the basis of an
engineering and traffic investigation that any prima facie speed
therein set forth is greater or less than is reasonable or safe
under the conditions found to exist at any intersection or other
place or upon any part of a street or highway, with the City taking
into consideration the width and condition of the pavement and
other circumstances on such portion of said street or highway, as
well as the usual traffic thereon, said governing body may
determine and declare a reasonable and safe prima facie speed limit
thereat or thereon by the passage of an ordinance, which shall be
r effective when appropriate signs giving notice thereof are erected
at such intersection or other place or part of the street or
highway, now therefore,
BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF STEPHENVILLE,
TEXAS:
Section 1. Upon the basis of an engineering and traffic
investigation heretofore made as authorized by the provisions of
Section 167 and 169 of Article XIX, R.C.S. 6701d, Uniform Act
Regulating Traffic on Highways, the following prima facie speed
limits hereafter indicated for vehicles are hereby determined and
declared to be reasonable and safe; and such speed limits are
hereby fixed at the rate of speed indicated for vehicles traveling
upon the named streets and highways, or parts thereof, described as
follows:
From Station 147+07, northeast 0.570 miles to Station
177+18.6, zoned at 45 MPH.
From Station 177+18.6, northeast 0.638 miles to Station
210+85, zoned at 55 MPH.
Section 2. Any person violating any of the provisions of this
ordinance shall be deemed guilty of a misdemeanor and upon
conviction thereof shall be fined in any sum not more than two
hundred dollars ($200.00).
This ordinance supersedes all previous ordinances pertaining to the
above -referenced highway.
PASSED and APPROVED this 5th day of May, 1994.
APPROVED:
Lavinia Lohimann, Mayor
ATTEST:
I
Cindy Staffo ,
City S cretary
Reviewed by Donald B. Davis,
City Administrator
Approved —a to form and legality
Randy Thomas, City Attorney