HomeMy WebLinkAboutO-2021-3831 amending Chapter 94 "Floods" of the CoLP Code of Ordinances and Chapter 5 of the PICM ORDINANCE NO. 2021-3 831
AN ORDINANCE AMENDING CHAPTER 94 "FLOODS" OF THE CODE OF
ORDINANCES BY ADDING NEW DEFINITIONS AND INCORPORATING UPDATED
REGULATIONS RELATED TO FLOOD HAZARDS; PROVIDING A REPEALING
CLAUSE; CONTAINING A SEVERABILITY CLAUSE; FINDING COMPLIANCE WITH
THE OPEN MEETINGS LAW; PROVIDING THAT ANY PERSON VIOLATING THE
TERMS OF THIS ORDINANCE SHALL BE DEEMED GUILTY OF A MISDEMEANOR
AND UPON CONVICTION SHALL BE FINED IN A SUM NOT TO EXCEED TWO
THOUSAND DOLLARS; PROVIDING FOR THE PUBLICATION OF THE CAPTION
HEREOF; AND PROVIDING AN EFFECTIVE DATE HEREOF.
BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF LA PORTE, TEXAS:
Section 1: That Chapter 94, "Floods", of the La Porte, Texas, Code of Ordinances is hereby
amended in its entirety and shall hereinafter read as follows:
"Chapter 94- FLOODS
ARTICLE I. - IN GENERAL
Secs. 94-1-94-30. - Reserved.
ARTICLE II. - FLOOD HAZARD REDUCTION
DIVISION 1. - GENERALLY
Sec. 94-31. - Definitions.
Unless specifically defined below, words or phrases used in this chapter shall be interpreted to
give them the meaning they have in common usage and to give this ordinance its most reasonable
application.
Alluvial fan flooding means flooding occurring on the surface of an alluvial fan or similar landform
which originates at the apex and is characterized by high-velocity flows; active processes of
erosion, sediment transport, and deposition; and unpredictable flow paths.
Apex means a point on an alluvial fan or similar landform below which the flow path of the major
stream that formed the fan becomes unpredictable and alluvial fan flooding can occur.
Appurtenant structure means a structure which is on the same parcel of property as the principal
structure to be insured and the use of which is incidental to the use of the principal structure.
Area of moderate flood hazard is the land between the limits of the base flood and the 0.2-percent
annual-chance (or 500-year) flood. They are shown on flood maps as zones labeled with the letters
B or X (shaded).
Area of future conditions flood hazard means the land area that would be inundated by the one
percent annual chance (100-year) flood based on future conditions hydrology.
Area of shallow flooding means a designated AO, AH, AR/AO, AR/AH, or VO zone on a
community's flood insurance rate map (FIRM) with a one percent or greater annual chance of
flooding to an average depth of one to three feet where a clearly defined channel does not exist,
where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding
is characterized by ponding or sheet flow.
Area of special flood hazard is the land in the floodplain within a community subject to a one
percent or greater chance of flooding in any given year. The area may be designated as zone A on
the flood hazard boundary map (FHBM). After detailed rate making has been completed in
preparation for publication of the FIRM, zone A usually is refined into zones A, AO, AH, A1-30, AE,
A99, AR, AR/A1-30, AR/AE, AR/AO, AR/AH, AR/A, VO, V1-30, VE or V.
Base flood means the flood having a one percent chance of being equaled or exceeded in any
given year.
Basement means any area of the building having its floor subgrade (below ground level) on all
sides.
Breakaway wall means a wall that is not part of the structural support of the building and is
intended through its design and construction to collapse under specific lateral loading forces,
without causing damage to the elevated portion of the building or supporting foundation system.
Coastal AE zone means the area subject to inundation by the one-percent annual-chance flood
event that is also within the area of limited to moderate wave action as shown on the community's
FIRM.
Critical feature means an integral and readily identifiable part of a flood protection system, without
which the flood protection provided by the entire system would be compromised.
Development means any manmade change to improved and unimproved real estate, including but
not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation or
drilling operations or storage of equipment or materials.
Elevated building means, for insurance purposes, a non-basement building, which has its lowest
elevated floor, raised above ground level by foundation walls, shear walls, posts, piers, pilings, or
columns.
Existing construction means for the purposes of determining rates, structures for which the "start
of construction" commenced before the effective date of the FIRM or before January 1, 1975, for
FIRMs effective before that date. "Existing construction" may also be referred to as "existing
structures."
Existing manufactured home park or subdivision means a manufactured home park or subdivision
for which the construction of facilities for servicing the lots on which the manufactured homes are
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to be affixed (including, at a minimum, the installation of utilities, the construction of streets, and
either final site grading or the pouring of concrete pads) is completed before the effective date of
the floodplain management regulations adopted by a community.
Five-hundred(500) year floodplain elevation means the elevation of surface water resulting from a
flood that has a 0.2-percent chance of equaling or exceeding that level in any given year. The 500-
year floodplain elevation is shown on the flood insurance rate map for zones B and X (shaded).
Expansion to an existing manufactured home park or subdivision means the preparation of
additional sites by the construction of facilities for servicing the lots on which the manufactured
homes are to be affixed (including the installation of utilities, the construction of streets, and either
final site grading or the pouring of concrete pads).
Flood or flooding means a general and temporary condition of partial or complete inundation of
normally dry land areas from:
(1) The overflow of inland or tidal waters.
(2) The unusual and rapid accumulation or runoff of surface waters from any source.
Flood elevation study means an examination, evaluation and determination of flood hazards and, if
appropriate, corresponding water surface elevations, or an examination, evaluation and
determination of mudslide (i.e., mudflow) and/or flood-related erosion hazards.
Flood insurance rate map (FIRM) means an official map of a community, on which the Federal
Emergency Management Agency has delineated both the special flood hazard areas and the risk
premium zones applicable to the community.
Flood insurance study (FIS). See "flood elevation study."
Floodplain or flood-prone area means any land area susceptible to being inundated by water from
any source (see definition of"flooding").
Floodplain management means the operation of an overall program of corrective and preventive
measures for reducing flood damage, including but not limited to emergency preparedness plans,
flood control works and floodplain management regulations.
Floodplain management regulations means zoning ordinances, subdivision regulations, building
codes, health regulations, special purpose ordinances (such as a floodplain ordinance, grading
ordinance and erosion control ordinance) and other applications of police power. The term
describes such state or local regulations, in any combination thereof, which provide standards for
the purpose of flood damage prevention and reduction.
Flood protection system means those physical structural works for which funds have been
authorized, appropriated, and expended and which have been constructed specifically to modify
flooding in order to reduce the extent of the area within a community subject to a "special flood
hazard" and the extent of the depths of associated flooding. Such a system typically includes
hurricane tidal barriers, dams, reservoirs, levees or dikes. These specialized flood modifying works
are those constructed in conformance with sound engineering standards.
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Floodproofing means any combination of structural and nonstructural additions, changes, or
adjustments to structures which reduce or eliminate flood damage to real estate or improved real
property, water and sanitary facilities, structures and their contents.
Floodway. See "regulatory floodway."
Functionally dependent use means a use, which cannot perform its intended purpose unless it is
located or carried out in close proximity to water. The term includes only docking facilities, port
facilities that are necessary for the loading and unloading of cargo or passengers, and ship
building and ship repair facilities, but does not include long-term storage or related manufacturing
facilities.
Highest adjacent grade means the highest natural elevation of the ground surface prior to
construction next to the proposed walls of a structure.
Historic structure means any structure that is:
(1) Listed individually in the National Register of Historic Places (a listing maintained by the
Department of Interior) or preliminarily determined by the Secretary of the Interior as meeting the
requirements for individual listing on the National Register;
(2) Certified or preliminarily determined by the Secretary of the Interior as contributing to the
historical significance of a registered historic district or a district preliminarily determined by the
Secretary to qualify as a registered historic district;
(3) Individually listed on a state inventory of historic places in states with historic preservation
programs which have been approved by the Secretary of the Interior; or
(4) Individually listed on a local inventory or historic places in communities with historic
preservation programs that have been certified either:
a. By an approved state program as determined by the Secretary of the Interior or;
b. Directly by the Secretary of the Interior in states without approved programs.
Levee means a manmade structure, usually an earthen embankment, designed and constructed in
accordance with sound engineering practices to contain, control, or divert the flow of water so as
to provide protection from temporary flooding.
Levee system means a flood protection system which consists of a levee, or levees, and
associated structures, such as closure and drainage devices, which are constructed and operated
in accordance with sound engineering practices.
Lowest floor means the lowest floor of the lowest enclosed area (including basement). An
unfinished or flood resistant enclosure, usable solely for parking or vehicles, building access or
storage in an area other than a basement area is not considered a building's lowest floor; provided
that such enclosure is not built so as to render the structure in violation of the applicable non-
elevation design requirement of Section 60.3 of the National Flood Insurance Program regulations.
Manufactured home means a structure transportable in one or more sections, which is built on a
permanent chassis and is designed for use with or without a permanent foundation when
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connected to the required utilities. The term "manufactured home" does not include a "recreational
vehicle".
Manufactured home park or subdivision means a parcel (or contiguous parcels) of land divided
into two or more manufactured home lots for rent or sale.
Mean sea level means, for purposes of the National Flood Insurance Program, the National
Geodetic Vertical Datum (NGVD) of 1929 or other datum, to which base flood elevations shown on
a community's flood insurance rate map are referenced.
Moderate flood hazard area. See "area of moderate flood hazard."
New construction means, for the purpose of determining insurance rates, structures for which the
"start of construction" commenced on or after the effective date of an initial FIRM or after
December 31, 1974, whichever is later, and includes any subsequent improvements to such
structures. For floodplain management purposes, "new construction" means structures for which
the "start of construction" commenced on or after the effective date of a floodplain management
regulation adopted by a community and includes any subsequent improvements to such
structures.
New manufactured home park or subdivision means a manufactured home park or subdivision for
which the construction of facilities for servicing the lots on which the manufactured homes are to
be affixed (including at a minimum, the installation of utilities, the construction of streets, and
either final site grading or the pouring of concrete pads) is completed on or after the effective date
of floodplain management regulations adopted by a community.
Primary frontal dune means a continuous or nearly continuous mound or ridge of sand with
relatively steep seaward and landward slopes immediately landward and adjacent to the beach
and subject to erosion and overtopping from high tides and waves during major coastal storms.
The inland limit of the primary frontal dune occurs at the point where there is a distinct change
from a relatively steep slope to a relatively mild slope.
Recreational vehicle means a vehicle which is (i) built on a single chassis; (ii) 400 square feet or
less when measured at the largest horizontal projections; (iii) designed to be self-propelled or
permanently towable by a light duty truck; and (iv) designed primarily not for use as a permanent
dwelling but as temporary living quarters for recreational, camping, travel, or seasonal use.
Regulatory floodway means the channel of a river or other watercourse and the adjacent land
areas that must be reserved in order to discharge the base flood without cumulatively increasing
the water surface elevation more than a designated height.
Riverine means relating to, formed by, or resembling a river (including tributaries), stream, brook,
etc.
Sand dunes mean naturally occurring accumulations of sand in ridges or mounds landward of the
beach.
Special flood hazard area."See "area of special flood hazard."
Start of construction (For other than new construction or substantial improvements under the
Coastal Barrier Resources Act (Pub. L. 97-348)), includes substantial improvement and means the
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date the building permit was issued, provided the actual start of construction, repair,
reconstruction, rehabilitation, addition placement, or other improvement was within 180 days of the
permit date. The actual start means either the first placement of permanent construction of a
structure on a site, such as the pouring of slab or footings, the installation of piles, the construction
of columns, or any work beyond the stage of excavation; or the placement of a manufactured
home on a foundation. Permanent construction does not include land preparation, such as
clearing, grading and filling; nor does it include the installation of streets and/or walkways; nor
does it include excavation for basement, footings, piers or foundations or the erection of temporary
forms; nor does it include the installation on the property of accessory buildings, such as garages
or sheds not occupied as dwelling units or not part of the main structure. For a substantial
improvement, the actual start of construction means the first alteration of any wall, ceiling, floor, or
other structural part of a building, whether or not that alteration affects the external dimensions of
the building.
Structure means, for floodplain management purposes, a walled and roofed building, including a
gas or liquid storage tank, that is principally above ground, as well as a manufactured home.
Substantial damage means damage of any origin sustained by a structure whereby the cost of
restoring the structure to its before damaged condition would equal or exceed 50 percent of the
market value of the structure before the damage occurred.
Substantial improvement means any reconstruction, rehabilitation, addition, or other improvement
of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure
before "start of construction" of the improvement. This term includes structures which have
incurred "substantial damage", regardless of the actual repair work performed. The term does not,
however, include either: (1) Any project for improvement of a structure to correct existing violations
of state or local health, sanitary, or safety code specifications which have been identified by the
local code enforcement official and which are the minimum necessary to assure safe living
conditions or (2) any alteration of a "historic structure", provided that the alteration will not
preclude the structure's continued designation as a "historic structure."
Variance means a grant of relief by a community from the terms of a floodplain management
regulation. (For full requirements see Section 60.6 of the National Flood Insurance Program
regulations.)
Violation means the failure of a structure or other development to be fully compliant with the
community's floodplain management regulations. A structure or other development without the
elevation certificate, other certifications, or other evidence of compliance required in Section
60.3(b)(5), (c)(4), (c)(10), (d)(3), (e)(2), (e)(4), or (e)(5) is presumed to be in violation until such
time as that documentation is provided.
Water surface elevation means the height, in relation to the National Geodetic Vertical Datum
(NGVD) of 1929 (or other datum, where specified), of floods of various magnitudes and
frequencies in the floodplains of coastal or riverine areas.
Sec. 94-32. - Statutory authorization.
The Legislature of the State of Texas has in Article 8280-13 V.T.C.S. delegated the
responsibility of local governmental units to adopt regulations designed to minimize flood losses.
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Sec. 94-33. - Findings of fact.
(1) The flood hazard areas of La Porte, Texas are subject to periodic inundation, which
results in loss of life and property, health and safety hazards, disruption of commerce and
governmental services, and extraordinary public expenditures for flood protection and
relief, all of which adversely affect the public health, safety and general welfare.
(2) These flood losses are created by the cumulative effect of obstructions in floodplains
which cause an increase in flood heights and velocities, and by the occupancy of flood
hazard areas by uses vulnerable to floods and hazardous to other lands because they are
inadequately elevated, floodproofed or otherwise protected from flood damage.
Sec. 94-34. - Statement of purpose.
It is the purpose of this article to promote the public health, safety and general welfare and
to minimize public and private losses due to flood conditions in specific areas by provisions
designed to:
(1) Protect human life and health;
(2) Minimize expenditure of public money for costly flood control projects;
(3) Minimize the need for rescue and relief efforts associated with flooding and
generally undertaken at the expense of the general public;
(4) Minimize prolonged business interruptions;
(5) Minimize damage to public facilities and utilities such as water and gas mains,
electric, telephone and sewer lines, streets and bridges located in floodplains;
(6) Help maintain a stable tax base by providing for the sound use and
development of flood-prone areas in such a manner as to minimize future flood
blight areas; and
(7) Insure that potential buyers are notified that property is in a flood area.
Sec. 94-35. - Lands to which this article applies.
The article shall apply to all areas of special flood hazard and moderate flood hazard within
the jurisdiction of City of La Porte, Texas.
Sec. 94-36. - Compliance.
No structure or land shall hereafter be located, altered, or have its use changed without full
compliance with the terms of this article and other applicable regulations.
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Sec. 94-37. - Interpretation.
In the interpretation and application of this article, all provisions shall be; (1) considered as
minimum requirements; (2) liberally construed in favor of the governing body; and (3) deemed
neither to limit nor repeal any other powers granted under state statutes.
Sec. 94-38. - Basis for establishing the areas of special flood hazard and moderate flood
hazard.
The areas of special flood hazard and moderate flood hazard identified by the Federal
Emergency Management Agency in the current scientific and engineering report entitled, "The
Flood Insurance Study (FIS) for City of La Porte, Texas" dated June 18, 2007, with accompanying
flood insurance rate maps and/or flood boundary-floodway maps (FIRM and/or FBFM) dated June
18, 2007, and any revisions thereto are hereby adopted by reference and declared to be a part of
this article. A true and correct copy of said study and maps is on file in the office of the City
Engineer of the City of La Porte.
Sec. 94-39. - Methods of reducing flood losses.
In order to accomplish its purposes, this article uses the following methods:
(1) Restrict or prohibit uses that are dangerous to health, safety or property in times
of flood, or cause excessive increases in flood heights or velocities;
(2) Require that uses vulnerable to floods, including facilities which serve such
uses, be protected against flood damage at the time of initial construction;
(3) Control the alteration of natural floodplains, stream channels, and natural
protective barriers, which are involved in the accommodation of flood waters;
(4) Control filling, grading, dredging and other development which may increase
flood damage;
(5) Prevent or regulate the construction of flood barriers which will unnaturally
divert flood waters or which may increase flood hazards to other lands.
Sec. 94-40. -Abrogation and greater restrictions.
This article is not intended to repeal, abrogate, or impair any existing easements,
covenants, or deed restrictions. However, where this article and another ordinance, easement,
covenant, or deed restriction conflict or overlap, whichever imposes the more stringent restrictions
shall prevail.
Sec. 94-41. -Warning and disclaimer of liability.
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The degree of flood protection required by this article is considered reasonable for
regulatory purposes and is based on scientific and engineering considerations. On rare occasions
greater floods can and will occur and flood heights may be increased by manmade or natural
causes. This article does not imply that land outside the areas of special flood hazards or uses
permitted within such areas will be free from flooding or flood damages. This article shall not
create liability on the part of the community or any official or employee thereof for any flood
damages that result from reliance on this article or any administrative decision lawfully made
hereunder.
DIVISION 2. - ADMINISTRATION
Sec. 94-61. - Designation of the floodplain administrator.
The city engineer or his/her designated appointee is hereby appointed the floodplain
administrator to administer and implement the provisions of this ordinance and other appropriate
sections of 44 CFR (Emergency Management and Assistance - National Flood Insurance Program
Regulations) pertaining to floodplain management.
Sec. 94-62. - Duties and responsibilities of the floodplain administrator.
Duties and responsibilities of the floodplain administrator shall include, but not be limited
to, the following:
(1) Maintain and hold open for public inspection all records pertaining to the
provisions of this article.
(2) Review permit application to determine whether to ensure that the proposed
building site project, including the placement of manufactured homes, will be
reasonably safe from flooding.
(3) Review, approve or deny all applications for development permits required by
adoption of this article.
(4) Review permits for proposed development to assure that all necessary permits
have been obtained from those federal, state or local governmental agencies
(including Section 404 of the Federal Water Pollution Control Act Amendments of
1972, 33 U.S.C. 1334) from which prior approval is required.
(5) Where interpretation is needed as to the exact location of the boundaries of the
areas of special flood hazards (for example, where there appears to be a conflict
between a mapped boundary and actual field conditions) the floodplain
administrator shall make the necessary interpretation.
(6) Notify, in riverine situations, adjacent communities and the state coordinating
agency which is Texas Commission on Environmental Quality, prior to any
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alteration or relocation of a watercourse, and submit evidence of such notification
to the Federal Emergency Management Agency.
(7) Assure that the flood carrying capacity within the altered or relocated portion of
any watercourse is maintained.
(8) When base flood elevation data has not been provided in accordance
with section 94-38, the floodplain administrator shall obtain, review and reasonably
utilize any base flood elevation data and floodway data available from a federal,
state or other source, in order to administer the provisions of division 3.
(9) When a regulatory floodway has not been designated, the floodplain
administrator must require that no new construction, substantial improvements, or
other development (including fill) shall be permitted within zones A1-30 and AE on
the community's FIRM, unless it is demonstrated that the cumulative effect of the
proposed development, when combined with all other existing and anticipated
development, will not increase the water surface elevation of the base flood more
than one foot at any point within the community.
(10) Under the provisions of 44 CFR Chapter 1, Section 65.12, of the National
Flood Insurance Program regulations, a community may approve certain
development in zones A1-30, AE, AH, on the community's FIRM which increases
the water surface elevation of the base flood by more than one foot, provided that
the community first completes all of the provisions required by Section 65.12.
Sec. 94-63. - Establishment of development permit.
A floodplain development permit shall be required to ensure conformance with the
provisions of this article.
Sec. 94-64. - Permit procedures.
(1) Application for a floodplain development permit shall be presented to the floodplain
administrator on forms furnished by him/her and may include, but not be limited to, plans in
duplicate drawn to scale showing the location, dimensions, and elevation of proposed
landscape alterations, existing and proposed structures, including the placement of
manufactured homes, and the location of the foregoing in relation to areas of special flood
hazard or moderate flood hazard. Additionally, the following information is required:
(a) Elevation (in relation to mean sea level), of the lowest floor (including basement) of all
new and substantially improved structures;
(b) Elevation in relation to mean sea level to which any nonresidential structure shall be
floodproofed;
(c) A certificate from a registered professional engineer or architect that the nonresidential
floodproofed structure shall meet the floodproofing criteria of section 94-87(2);
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(d) Description of the extent to which any watercourse or natural drainage will be altered or
relocated as a result of proposed development;
(e) Maintain a record of all such information in accordance with_section 94-62(1);
(2) Approval or denial of a floodplain development permit by the floodplain administrator
shall be based on all of the provisions of this ordinance and the following relevant factors:
(a) The danger to life and property due to flooding or erosion damage;
(b) The susceptibility of the proposed facility and its contents to flood damage and
the effect of such damage on the individual owner;
(c) The danger that materials may be swept onto other lands to the injury of others;
(d) The compatibility of the proposed use with existing and anticipated
development;
(e) The safety of access to the property in times of flood for ordinary and
emergency vehicles;
(f) The costs of providing governmental services during and after flood conditions
including maintenance and repair of streets and bridges, and public utilities and
facilities such as sewer, gas, electrical and water systems;
(g) The expected heights, velocity, duration, rate of rise and sediment transport of
the floodwaters and the effects of wave action, if applicable, expected at the site;
(h) The necessity to the facility of a waterfront location, where applicable;
(i) The availability of alternative locations, not subject to flooding or erosion
damage, for the proposed use.
Sec. 94-65. -Variance procedures.
(1) The appeal board, as established by the community, shall hear and render judgment on
requests for variances from the requirements of this article.
(2) The appeal board shall hear and render judgment on an appeal only when it is alleged
there is an error in any requirement, decision, or determination made by the floodplain
administrator in the enforcement or administration of this article.
(3) Any person or persons aggrieved by the decision of the appeal board may appeal such
decision in the courts of competent jurisdiction.
(4) The floodplain administrator shall maintain a record of all actions involving an appeal
and shall report variances to the Federal Emergency Management Agency upon request.
(5) Variances may be issued for the reconstruction, rehabilitation or restoration of
structures listed on the National Register of Historic Places or the state inventory of historic
places, without regard to the procedures set forth in the remainder of this article.
(6) Variances may be issued for new construction and substantial improvements to be
erected on a lot of one-half acre or less in size contiguous to and surrounded by lots with
existing structures constructed below the base flood level, providing the relevant factors
in section 94-64(2) have been fully considered. As the lot size increases beyond the one-
half half acre, the technical justification required for issuing the variance increases.
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(7) Upon consideration of the factors noted above and the intent of this article, the appeal
board may attach such conditions to the granting of variances as it deems necessary to
further the purpose and objectives of this article (section 94-34).
(8) Variances shall not be issued within any designated floodway if any increase in flood
levels during the base flood discharge would result.
(9) Variances may be issued for the repair or rehabilitation of historic structures upon a
determination that the proposed repair or rehabilitation will not preclude the structure's
continued designation as a historic structure and the variance is the minimum necessary to
preserve the historic character and design of the structure.
(10) Prerequisites for granting variances:
(a) Variances shall only be issued upon a determination that the variance is the
minimum necessary, considering the flood hazard, to afford relief.
(b) Variances shall only be issued upon: (i) showing a good and sufficient cause;
(ii) a determination that failure to grant the variance would result in exceptional
hardship to the applicant, and (iii) a determination that the granting of a variance
will not result in increased flood heights, additional threats to public safety,
extraordinary public expense, create nuisances, cause fraud on or victimization of
the public, or conflict with existing local laws or ordinances.
(c) Any application to which a variance is granted shall be given written notice that
the structure will be permitted to be built with the lowest floor elevation below the
base flood elevation, and that the cost of flood insurance will be commensurate
with the increased risk resulting from the reduced lowest floor elevation.
(11) Variances may be issued by a community for new construction and substantial
improvements and for other development necessary for the conduct of a functionally
dependent use provided that (i) the criteria outlined in section 94-65(1)—(9) are met, and
(ii) the structure or other development is protected by methods that minimize flood
damages during the base flood and create no additional threats to public safety.
Secs. 94-66-94-85. - Reserved.
DIVISION 3. - STANDARDS
Sec. 94-86. -General standards.
In all areas of special flood hazards and moderate flood hazards the following provisions
are required for all new construction and substantial improvements:
(1) All new construction or substantial improvements shall be designed (or modified) and
adequately anchored to prevent flotation, collapse or lateral movement of the structure
resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy;
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(2) All new construction or substantial improvements shall be constructed by methods and
practices that minimize flood damage;
(3) All new construction or substantial improvements shall be constructed with materials
resistant to flood damage;
(4) All new construction or substantial improvements shall be constructed with electrical,
heating, ventilation, plumbing, and air conditioning equipment and other service facilities
that are designed to be elevated at least one foot above the base flood elevation, so as to
prevent water from entering or accumulating within the components during conditions of
flooding;
(5) All new and replacement water supply systems shall be designed to minimize or
eliminate infiltration of flood waters into the system;
(6) New and replacement sanitary sewage systems shall be designed to minimize or
eliminate infiltration of flood waters into the system and discharge from the systems into
flood waters; and,
(7) On-site waste disposal systems shall be located to avoid impairment to them or
contamination from them during flooding.
(8) Compensating floodplain mitigation will be required for any fill placed below the riverine
base flood elevation and/or riverine 500-year floodplain elevation for any new construction or
substantial improvements, including fill placed in a Coastal AE zone that is below the riverine
100- or 500-year water surface elevations.
Sec. 94-87. - Specific standards.
In all areas of special flood hazards and moderate flood hazards where base flood
elevation and/or riverine 500-year floodplain elevation data has been provided as set forth in
(i)_section 94-38, (ii) subsection 94-62(8), or (iii) subsection 94-88(3), the following provisions are
required:
(1) Residential construction. New construction and substantial improvement of any
residential structure shall have the lowest floor (including basement), elevated one
foot above the base flood elevation or at or above the riverine 500-year floodplain
elevation, whichever is higher. A registered professional engineer, architect, or land
surveyor shall submit a certification to the floodplain administrator that the standard
of this subsection as proposed in section 94-64(1)(a), is satisfied.
(2) Nonresidential construction. New construction and substantial improvements of
any commercial, industrial or other nonresidential structure shall either have the
lowest floor (including basement) elevated to or above the base flood elevation or to
or above the riverine 500-year floodplain elevation, whichever is higher, or together
with attendant utility and sanitary facilities, be designed so that below the base
flood elevation or the riverine 500-year floodplain elevation, whichever is higher; the
structure is watertight with walls substantially impermeable to the passage of water
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and with structural components having the capability of resisting hydrostatic and
hydrodynamic loads and effects of buoyancy. A registered professional engineer or
architect shall develop and/or review structural design, specifications, and plans for
the construction, and shall certify that the design and methods of construction are
in accordance with accepted standards of practice as outlined in this subsection. A
record of such certification which includes the specific elevation (in relation to mean
sea level) to which such structures are floodproofed shall be maintained by the
floodplain administrator.
(3) Enclosures. New construction and substantial improvements, with fully
enclosed areas below the lowest floor that are usable solely for parking of vehicles,
building access or storage in an area other than a basement and which are subject
to flooding shall be designed to automatically equalize hydrostatic flood forces on
exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting
this requirement must either be certified by a registered professional engineer or
architect or meet or exceed the following minimum criteria:
a. A minimum of two openings on separate walls having a total net area of
not less than one square inch for every square foot of enclosed area
subject to flooding shall be provided.
b. The bottom of all openings shall be no higher than one foot above grade.
c. Openings may be equipped with screens, louvers, valves, or other
coverings or devices provided that they permit the automatic entry and exit
of floodwaters.
(4) Manufactured homes.
a. Require that all manufactured homes to be placed within zone A on a
community's FHBM or FIRM shall be installed using methods and practices
which minimize flood damage. For the purposes of this requirement,
manufactured homes must be elevated and anchored to resist flotation,
collapse, or lateral movement. Methods of anchoring may include, but are
not limited to, use of over-the-top or frame ties to ground anchors. This
requirement is in addition to applicable state and local anchoring
requirements for resisting wind forces.
b. Require that manufactured homes that are placed or substantially
improved within zones A1-30, AH, and AE on the community's FIRM on
sites (i) outside of a manufactured home park or subdivision, (ii) in a
new manufactured home park or subdivision, (iii) in an expansion to an
existing manufactured home park or subdivision, or (iv) in an existing
manufactured home park or subdivision on which a manufactured home
has incurred "substantial damage" as a result of a flood, be elevated on
a permanent foundation such that the lowest floor of the manufactured
home, as well as any electrical, heating, ventilation, plumbing, and air
conditioning equipment and other service facilities affixed thereto, is
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elevated at least one foot above the base flood elevation or at least one
foot above the riverine 500-year floodplain elevation, whichever is higher,
and be securely anchored to an adequately anchored foundation system to
resist flotation, collapse, and lateral movement.
c. Require that manufactured homes be placed or substantially improved on
sites in an existing manufactured home park or subdivision with zones A1-
30, AH and AE on the community's FIRM that are not subject to the
provisions of paragraph (4) of this section be elevated so that the lowest
floor of the manufactured home is at least one foot above the base flood
elevation or at or above the riverine 500-year floodplain elevation,
whichever is higher.
(5) Recreational vehicles. Require that recreational vehicles placed on sites within
zones A1-30, AH, and AE on the community's FIRM either (i) be on the site for
fewer than 180 consecutive days, or (ii) be fully licensed and ready for highway
use, or (iii) meet the permit requirements of section 94-64(1), and the elevation and
anchoring requirements for "manufactured homes" in paragraph (4) of this section.
A recreational vehicle is ready for highway use if it is on its wheels or jacking
system, is attached to the site only by quick disconnect type utilities and security
devices, and has no permanently attached additions.
Sec. 94-88. -Standards for development proposals.
(1) All subdivision proposals including the placement of manufactured home parks and
subdivisions shall be consistent with sections 94-33, 94-34, and 94-39.
(2) All proposals for the development of subdivisions including the placement of
manufactured home parks and subdivisions shall meet floodplain development permit
requirements of section 94-63; section 94-64; and the provisions of division 3 of this
ordinance.
(3 )_Base flood elevation and/or riverine 500-year floodplain elevation data shall be
generated for subdivision proposals and other proposed development including the
placement of manufactured home parks and subdivisions which is greater than 50 lots or
five acres, whichever is lesser, if not otherwise provided pursuant to section 94-38 or
subsection 94-62(8) of this article.
(4) All subdivision proposals including the placement of manufactured home parks and
subdivisions shall have adequate drainage provided to reduce exposure to flood hazards.
(5) All subdivision proposals including the placement of manufactured home parks and
subdivisions shall have public utilities and facilities such as sewer, gas, electrical and
water systems located and constructed to minimize or eliminate flood damage.
Sec. 94-89. - Standards for areas of shallow flooding.
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Located within the areas of special flood hazard established in section 94-38, are areas
designated as shallow flooding. These areas have special flood hazards associated with flood
depths of one to three feet where a clearly defined channel does not exist, where the path of
flooding is unpredictable, and where velocity flow may be evident. Such flooding is characterized
by ponding or sheet flow; therefore, the following provisions apply:
(1) All new construction and substantial improvements of residential structures
have the lowest floor (including basement) elevated to or above the base flood
elevation or the highest adjacent grade at least as high as the depth number
specified in feet on the community's FIRM (at least two feet if no depth number is
specified).
(2) All new construction and substantial improvements of nonresidential structures;
a. Have the lowest floor (including basement) elevated to or above the base
flood elevation or the highest adjacent grade at least as high as the depth
number specified in feet on the community's FIRM (at least two feet if no
depth number is specified), or
b. Together with attendant utility and sanitary facilities be designed so that
below the base specified flood depth in an AO zone, or below the base
flood elevation in an AH zone, level the structure is watertight with walls
substantially impermeable to the passage of water and with structural
components having the capability of resisting hydrostatic and hydrodynamic
loads of effects of buoyancy.
(3) A registered professional engineer or architect shall submit a certification to the
floodplain administrator that the standards of this section, as proposed in section
94-63 are satisfied.
(4) Require within zones AH or AO adequate drainage paths around structures on
slopes, to guide flood waters around and away from proposed structures.
Sec. 94-90. - Floodways.
Located within areas of special flood hazard established in section 94-38 of this chapter
are areas designated as floodways. Since the floodway is an extremely hazardous area due to the
velocity of flood waters which carry debris, potential projectiles and erosion potential, the following
provisions shall apply:
(1) Encroachments are prohibited, including fill, new construction, substantial
improvements and other development within the adopted regulatory floodway
unless it has been demonstrated through hydrologic and hydraulic analyses
performed in accordance with standard engineering practice that the proposed
encroachment would not result in any increase in flood levels within the community
during the occurrence of the base flood discharge.
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(2) If section 94-90(1) above is satisfied, all new construction and substantial
improvements shall comply with all applicable flood hazard reduction provisions of
division 3.
(3) Under the provisions of 44 CFR Chapter 1, Section 65.12, of the National Flood
Insurance Program Regulation, a community may permit encroachments within the
adopted regulatory floodway that would result in an increase in base flood
elevations, provided that the community first completes all of the provisions
required by Section 65.12.
Sec. 94-91. -Coastal high hazard areas.
Located within the areas of special flood hazard established in section 94-38 of this
chapter are areas designated as coastal high hazard areas (zones V1-30, VE, and/or V). These
areas have special flood hazards associated with high velocity waters from tidal surges and
hurricane wave wash; therefore, in addition to meeting all provisions outlined in this chapter, the
following provisions must also apply:
(1) Obtain the elevation (in relation to mean sea level) of the bottom of the lowest
structural member of the lowest floor (excluding pilings and columns) of all new and
substantially improved structures, and whether or not such structures contain a
basement. The floodplain administrator shall maintain a record of all such
information.
(2) All new construction shall be located landward of the reach of mean high tide.
(3) All new construction and substantial improvements shall be elevated on pilings
and columns so that:
(i)The bottom of the lowest horizontal structural member of the lowest floor
(excluding the pilings or columns) is elevated to or above the base flood
level;
(ii)The pile or column foundation and structure attached thereto is anchored
to resist flotation, collapse and lateral movement due to the effects of wind
and water loads acting simultaneously on all building components. Water
loading values used shall be those associated with the base flood. Wind
loading values used shall be those required by applicable state or local
building standards. A registered professional engineer or architect shall
develop or review the structural design, specifications and plans for the
construction, and shall certify that the design and methods of construction
to be used are in accordance with accepted standards of practice for
meeting the provisions of(3)(i) and (ii) of this section.
(4) Provide that all new construction and substantial improvements have the space
below the lowest floor either free of obstruction or constructed with non-supporting
breakaway walls, open wood lattice-work, or insect screening intended to collapse
under wind and water loads without causing collapse, displacement, or other
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structural damage to the elevated portion of the building or supporting foundation
system.
For the purpose of this section, a breakaway wall shall have a design safe loading
resistance of not less than ten and no more than 20 pounds per square foot. Use of
breakaway walls which exceed a design safe loading resistance of 20 pounds per
square foot (either by design or when so required by local or state codes) may be
permitted only if a registered professional engineer or architect certifies that the
designs proposed meet the following conditions:
(i)Breakaway wall collapse shall result from a water load less than that
which would occur during the base flood; and
(ii)The elevated portion of the building and supporting foundation system
shall not be subject to collapse, displacement, or other structural damage
due to the effects of wind and water loads acting simultaneously on all
building components (structural and nonstructural). Water loading values
used shall be those associated with the base flood. Wind loading values
used shall be those required by applicable state or local building standards.
Such enclosed space shall be useable solely for parking of vehicles,
building access, or storage. Such space shall not be used for human
habitation.
(5) Prohibit the use of fill for structural support of buildings.
(6) Prohibit manmade alteration of sand dunes and mangrove stands that increase
potential flood damage.
(7) Manufactured homes. Require that manufactured homes placed or substantially
improved within zone V1-30, V, and VE on the community's FIRM on sites (i)
outside of a manufactured home park or subdivision, (ii) in a new manufactured
home park or subdivision, (iii) in an expansion to an existing manufactured home
park or subdivision, or (iv) in an existing manufactured home park or subdivision on
which a manufactured home has incurred "substantial damage" as the result of a
flood, meet the standards of paragraphs (1) through (6) of this section and that
manufactured homes placed or substantially improved on other sites in an existing
manufactured home park or subdivision within zones V1-30, V, and VE on the
community's FIRM meet the requirements of subsection_94-87(4) of this article.
(8) Recreational vehicles. Require that recreational vehicles placed on sites within
zones V1-30, V, and VE on the community's FIRM either (i) be on the site for fewer
than 180 consecutive days, or (ii) be fully licensed and ready for highway use, or
(iii) meet the requirements in_section 94-63 of this article and paragraphs (1)
through (6) of this section. A recreational vehicle is ready for highway use if it is on
its wheels or jacking system, is attached to the site only by quick disconnect type
utilities and security devices, and has no permanently attached additions.
Sec. 94-92. -Coastal AE zone.
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Located within the special flood hazard area established in section 94-87 of this article are
areas within the AE flood zone designated for limited to moderate wave action. These areas have
special flood hazards associated with high velocity waters from tidal surges and hurricane wave
wash; therefore, all development must meet the criteria set forth in section 94-91 and subsection 94-
87(3) of this article.
Sec. 94-93. - Penalties for noncompliance.
No structure or land shall hereafter be constructed, located, extended, converted, or
altered without full compliance with the terms of this article and other applicable regulations.
Violation of the provisions of this article by failure to comply with any of its requirements (including
violations of conditions and safeguards established in connection with conditions) shall constitute
a misdemeanor. Any person who violates this article or fails to comply with any of its requirements
shall upon conviction thereof be fined not more than $2,000.00 for each violation, with each day
constituting a separate violation, and in addition shall pay all costs and expenses involved in the
case. Nothing herein contained shall prevent City of La Porte from taking such other lawful action
as is necessary to prevent or remedy any violation.
Section 2. Any person, as defined in Section 1.07 (27), Texas Penal Code, who shall violate any
provision of the ordinance, shall be deemed guilty of a misdemeanor and upon conviction shall
be punished by a fine not to exceed TWO THOUSAND DOLLARS ($2,000.00).
Section 3. Each and every provision, paragraph, sentence and clause of this Ordinance has been
separately considered and passed by the City Council of the City of La Porte, Texas, and each said
provision would have been separately passed without any other provision, and if any provision
hereof shall be ineffective, invalid or unconstitutional, for any cause, it shall not impair or affect the
remaining portion, or any part thereof, but the valid portion shall be in force just as if it had been
passed alone.
Section 4. All ordinances or parts of ordinances in conflict herewith are hereby repealed to the
extent of such conflict only.
Section 5. The City Council officially finds, determines, recites and declares that a sufficient
written notice of the date, hour, place and subject of this meeting of the City Council is posted at
a place convenient to the public at the City Hall of the city for the time required by law
preceding this meeting, as required by Chapter 551, Tx. Gov't Code; and that this meeting has
been open to the public as required by law at all times during which this ordinance and the
subject matter thereof has been discussed, considered and formally acted upon. The City Council
further ratifies, approves and confirms such written notice and the contents and posting thereof.
Section 6. This Ordinance shall be effective fourteen (14) days after its passage and approval.
The City Secretary shall give notice of the passage of this ordinance by causing the caption
19
hereof to be published in the official newspaper of the City of La Porte at least once within ten
(10) days after the passage of this ordinance.
PASSED AND APPROVED this the ''��.` day of �� 2021.
CITY OF LA P. 'TE, TEXAS
By: �� .�
ouis ' . Rigby,yor
A EST:
e Woodward, City
APPROVED AS TO FORM:
Clark Askins, Assistant City Attorney
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CHAPTER 5
STORMWATER DESIGN CRITERIA
5.1 GENERAL PROVISIONS
Drainage Criteria for development within the City of La Porte, and where applicable within La Porte’s
Extraterritorial Jurisdiction (E.T.J.) is dependent upon the size and type of development, the conditions
within the individual watershed, the conditions or design of the receiving stream, bayou, channel, roadside
swale, culvert, or roadway.
The basic objective of this policy is to minimize the threat of flooding to areas within the City and its E.T.J.
and to minimize the effect of continued development on individual watersheds.
1. The City believes that the best long-term means of accomplishing its objective is a continued
program of improvement and extension of the Harris County Flood Control District’s system of
open channels. This statement recognizes the technical reality that an essential prerequisite to an
effective flood control program is a system of open channels capable of carrying storm runoff of
any type in Harris County to Galveston Bay without adversely impacting existing urban areas
adjacent to the channels.
2. The City recognizes that both District’s and City’s existing open channel system is, in many
instances, inadequate to accomplish the goal of eliminating existing flooding conditions for
existing levels of urban development, or for ultimate development in the watershed.
3. The City therefore recommends that where required, certain additional flood control facilities be
utilized to supplement the open channel system. Such flood control facilities shall be designed to
preclude flooding in areas that do not presently flood and not increase flood levels where flooding
now occurs. Specifically, the City supports the use of storm water detention to supplement the
open channel system until long-term channel improvements can be completed, or as permanent
facilities where additional open channel improvements are not feasible. The result will be that
new development will limit or restrict the impact downstream.
5.1.1 All the drainage plans and construction shall meet or exceed the requirements of the City of La
Porte, Harris County Flood Control, Harris County, TxDOT, or any other entities having
jurisdiction over a facility (i.e. roadway, channel, etc.).
5.1.2 Unless otherwise provided for in these policies, development shall follow the Harris County Flood
Control District Criteria Manual for the design of Flood Control and Drainage Facilities in Harris
County, Texas.
5.1.3 If application of the policies and criteria contained in this document conflict with the City’s duties
under the Flood Hazard Prevention Ordinance, the regulations of the Flood Hazard Prevention
Ordinance shall apply.
5.1.4 Drainage structures shall be constructed in such locations and of such size and dimensions to
adequately serve the development and the contributing drainage area. In new developments, the
developer shall provide all the necessary easements and rights-of-way required for drainage
structures, including storm sewer and open or lined channels.
5.2 CONSTRUCTION PLAN REQUIREMENTS
5.2.1 A drainage map shall be included in the construction plans. The drainage area map shall include:
Stormwater Criteria Page 1 of 10
A. Drainage areas, including areas draining from off-site onto or adjoining the project
B. Design storm runoff, based on the type of facility and storm frequency listed in Section
5.4.
C. 100 – year runoff sheet flow pattern.
D. Route of overland flow including the overflow to a drainage channel or detention facility
E. Water surface profiles for the 25-year and/or 100-year storms in the outfall channel. All
available information will be considered when making this determination.
F. Flow per inlet
G. Maximum ponding elevation
H. For bridge designs the 100-year WSEL must be shown on the plans and the low chord of
the bridge must be a minimum of eighteen inches above the 100-year WSEL.
5.2.2 Detailed drainage calculations shall be submitted with the construction plans.
5.2.3 A lot grading plan should demonstrate that the finished grading plan will drain to approved
collection and discharge points and that the overland flow of water from adjacent properties will
not be impacted. In no instance will plans be approved without specific detail as to how the 100-
year event will sheet flow from the development to the outfall without adversely impacting
structures.
5.2.4 The hydraulic gradient for the design storm may be shown on the construction drawings.
Calculations for the elevation for the hydraulic gradient shall be provided with the design storm
drainage calculations. The hydraulic gradient must be below the gutter line for the design storm.
The tailwater elevations based on a 25-year frequency in the outfall channel shall be used for
calculations of the hydraulic gradient. If the 25-year WSEL is not available then use 80% of the
ultimate channel height. In areas which are tidally influenced the mean high tide elevation will be
used unless it is lower than the 25-year WSEL, in which case the higher value will be used. In
instances where the 25-year WSEL in the receiving channel is lower than the top of pipe then the
top of pipe shall be used as the starting point for HGL calculations.
5.3 USE OF PREVIOUSLY DESIGNED AND INSTALLED INFRASTRUCTURE
Situations where previously installed infrastructure is in place but not yet utilized to its design
capacity will be considered on a case by case basis. The developers engineer shall after
consultation with the City, prepare a report that:
a. outline the original design criteria
b. evaluates the impact of the original design on the receiving stream, adjoining
properties and/or the 100 year Floodplain.
Based on the report, the City Engineer may allow full or partial use of the previously installed
infrastructure and may require it to be supplemented with detention or other facilities.
5.4 STORM FREQUENCY, RUNOFF AND DATUM
A. Storm Frequency
All drainage improvements shall be designed for the following storm frequencies based
on Atlas 14 rainfall data for Harris County Region 3.
Type of Facility
Road Side Ditches and Culverts 5 year
Storm Sewers 5 year
Ditches & Culverts Drainage 100 acres and more 25 year
Bridges 100 year
Creeks 100 year
Stormwater Criteria Page 2 of 10
Detention Facilities Refer to Section 5.5
B. Storm Runoff
Design flow of storm water runoff is to be calculated using the Rational Method.
The Rational Method is based on the direct relationship between rainfall and runoff, and
the method is expressed by the following equation:
Q = CIA, where
Q is the storm flow at a given point in cubic feet per second (c.f.s).
C is a coefficient of runoff (see Table 1).
I is the average intensity of rainfall in inches per hour for a period equal to the
time of flow from the farthermost point of the drainage area to the point under
consideration. (See figure 1, I-D-F Curves and Figure 2, Determination of Time
of Concentration)
A is the drainage area in acres
The size and shape of the watershed must be determined for each installation. The area
of each watershed may be determined through the use of planimetric-topographic maps of
the area, supplemented by field surveys in areas where topographic data has changed or
where the contour interval is insufficient to adequately determine the direction of flow.
The outline of the drainage area contributing to the system being designed and outline of
the sub-drainage area contributing to each inlet point shall be determined.
When calculating the peak flow rate of storm water runoff, rainfall intensity will be
determined from the rainfall intensity, duration and frequency curves, shown in Figure 1.
The storm frequency used for this determination will be according to the facility to be
designed as listed in Section A.
1. Runoff Coefficients and Time of Concentration
Runoff coefficients, as shown in Table 1, shall be the minimum used, based on
total development under existing land zoning regulations. Where land uses
other than those listed in Table 1 are planned, a coefficient shall be developed
utilizing values comparable to those shown. Larger coefficients may be used if
considered appropriate to the project by the City Engineer.
The time of concentration is defined as the longest time, without unreasonable
delay, that will be required for a drop of water to flow from the upper limit of a
drainage area to the point of concentration. The time of concentration to any
point in a storm drainage system is a combination of the “inlet time” and the
time of flow in the drain. The inlet time is the time for water to flow over the
surface of the ground to the storm drain inlet. Because the area tributary to most
storm sewer inlets is relatively small, it is customary in practice to determine the
inlet time on the basis of experience under similar conditions. Inlet time
decreases as the slope and the imperviousness of the surface increases, and it
increases as the distance over which the water has to travel and retention by the
contact surfaces.
Time of concentration shall be computed from Figure 2 and in no case shall the
inlet time be more that the time shown in Table 1.
Stormwater Criteria Page 3 of 10
Table 1
Zone Zoning District Name Runoff Maximum Inlet
Coefficient “C” Time in Minutes
R-1 Low Density Residential 0.50 15
R-2 Mid Density Residential 0.60 15
R-3 High Density Residential 0.80 10
MH Manufactured Housing District 0.55 15
NC Neighborhood Commercial District 0.80 10
GC General Commercial District 0.85 10
BI Business Industrial Park District 0.85 10
LI Light Industrial 0.85 10
HI Heavy Industrial 0.85 10
PUD Planned Unit Development District variable 10 to 15
Miscellaneous Land Uses
Land Use Runoff Coefficient “C”
Church 0.70 to 0.90
School 0.50 to 0.90
Park 0.30 to 0.70
C. Datum
All drainage plans shall be prepared based on North American Vertical Datum of 1988,
2001 adjustment, consistent with National Flood Insurance Program, Flood Insurance
Study for the City of La Porte.
5.5 REQUIRED DETENTION
Detention will be required to mitigate increase in flows. Minimum detention rates are described in the table
below. Minimum storage rate does not apply for single family residential structure and/or accessory
buildings proposed on an existing lot.
Hydrograph timing may not be used as a substitute for detention when detention is required.
5.5.1 Design Standards for Detention Basins
Detention requirements for developments less than 50 acres shall be according to the following table. For
developed areas of 10 acres or less, the required volume equals the total development area times the
appropriate storage coefficient. For areas greater than 10 acres and less than 50 acres the volume is
determined by applying Harris County Flood Control District criteria for small watersheds.
Table 2 (Also, See Figure 4)
Developed Area Storage Coefficient
0 to 1 acres 0.20 acre ft. / acre
1 to 10 acres 0.55 acre ft. / acre
10 to 50 acres per HCFCD criteria
Stormwater Criteria Page 4 of 10
For developments which are larger than 50 acres, Harris county Flood Control District and/or the City
Engineer shall approve the detention facility criteria, however, a minimum detention storage rate of 0.55
acre-ft/acre will be required.
5.2.2 Outlet Sizing
1. The outlet structure shall be designed using the orifice equation as follows:
½
Q = CA x (2gh)
Where,
C = 0.8
A = cross sectional area
g = 32.2 feet / sec^2
h = head differential
For head differential use 2’ or the 100-year water surface in pond minus the 25-year
water surface in receiving channel, if available.
2. Minimum restrictor shall be 6” diameter.
5.5.3 Additional Standards for Detention Basins
The detention facility shall be designed for easy maintenance. For smaller developments the designer is
encouraged to use parking lots, underground piping, swales, green spaces, etc. to achieve the volume
required.
For larger developments every consideration shall be given to designing of the facility for multipurpose
use, such as playgrounds, ballfields, miniparks, required green spaces, etc. to assure that maintenance will
be accomplished. The design shall include the following:
1. an earthen detention basin shall have minimum side slopes of 4:1 and a minimum bottom width
of ten feet;
2. the bottom of the detention basin shall have a minimum 0.50% cross slope to facilitate quick
drainage.
3. a v-shaped trickle channel a minimum of 5’ wide, six-inch thick, reinforced concrete shall be
constructed through the detention basin at a longitudinal slope of 0.20% to accommodate low flow
and facilitate rapid drainage. For developments less than 3 acres, the trickle channel may be 2 feet
wide and 4” thick.
4. a minimum 12-foot wide maintenance berm shall be provided around the perimeter of the
detention facility.
5. ingress and egress for maintenance including a dedicated right-of-way if required, shall be
provided to the detention basin and clearly shown on the construction drawings or site plan
subdivision plat.
6. the detention basins, slopes, bottom, maintenance berm, and other associated right-of-way shall
be final graded with a minimum of 6” top soil then hydro-mulch or drill-seeded and watered to
facilitate full grass coverage.
7. parties responsible for maintenance of the detention facility must be shown on the plat and or
plans.
8. Pumped detention systems may be allowed with specific approval from the City Engineer.
5.5.4 Ownership and Maintenance of Facilities
The City will not accept maintenance of on site facilities that serve only one tract or development, unless it
is determined to have other public benefits, is recommended by staff and approved by the Planning and
Zoning Commission.
Stormwater Criteria Page 5 of 10
Harris County Flood Control District may, at their discretion, accept maintenance of facilities, provided
they are designed in accordance with the District’s criteria manual. Requests for Harris County Flood
Control District to assume maintenance of any facility should be coordinated with the City prior to any
development approvals.
5.6 ADDITIONAL DESIGN REQUIREMENTS
5.6.1 Discharge Points
The developer shall terminate all drainage improvements at a discharge point approved by the City. The
developer shall design and construct such discharge point, or outlet, to prevent damage to or overflowing
into adjacent property. The City may require creek improvement, channel lining, energy dissipaters or
other improvements for such outlet to prevent erosion or increase the flow capacity.
Finished elevations of new pavement, parking areas, or other improvements shall be designed so that each
succeeding high point is lower when moving in a downstream direction. This ensures the 100-year
discharge has an unobstructed path to the discharge point whether discharging to a channel or detention
pond.
5.6.2 Public Streets as Drainage Facilities
1. Maximum depth of water to be allowed in local streets during design flow shall be at the top
crown, or top of curb, whichever is less.
2. Maximum spread of water in collector streets during design flow shall allow for one clear lane
of traffic (12 feet wide).
3. Maximum spread of water in arterial streets during design flow shall allow for two clear lanes
of traffic (24 feet wide).
4. The street is to be designed to convey the 100-year event to the outfall point by successively
lower high points. A dedicated easement must be provided at the terminus to allow the 100-year
event to sheet flow to the ultimate outfall. In lieu of sheet flow it is allowable for the developer to
construct an underground system to convey the 100-year event.
5.6.3 Drainage Channels and Structures
1. The developer shall install an underground storm drain on curb and gutter streets beginning at
the point where calculated storm water runoff is of such quantity that it exceeds the height
specified above. The developer shall construct the storm drain system from the point to an
approved outlet.
2. For non-curb and gutter streets, the developer may use open channel (channel or ditch) methods
to dispose of storm water specified above. Such channels may be in dedicated draining easements
outside the standard street right-of-way upon City approval of the location and alignment of such
easements. Alternatively, the developer may widen the street right-of-way to accommodate an
open channel of greater capacity than the standard street/ditch section.
3. If the developer locates the channel in a widened street right-of-way, the City shall approve the
right-of-way width and channel configuration. The depth of flow in the channel shall not exceed
one (1) foot as measured from the ditch flowline to the point on the roadway established as the
high water level in this section.
4. The developer shall design and construct all channels to terminate at an approved outlet.
5.6.4 Habitable Structures
The developer shall provide adequate means for storm water run-off in excess of the “design storm”
capacity (i.e., 3, 10-year storm) to flow around habitable structures.
Stormwater Criteria Page 6 of 10
a.) The developer shall provide a grading/drainage plan which shows that all building sites can
provide a finished floor elevation:
(1) At least one foot (1’) above the top of the curb using the highest point along the
portion of such curb fronting the building site, or
(2) At least one foot (1’) above the crown of the road elevation, using the highest point
along the portion of such road fronting the building site.
(3) At least one foot above the ground elevation along all sides of the building site.
b.) In addition to paragraph (a) above, the developer shall provide a grading/drainage plan which
meets or exceeds the provisions of Chapter 94, Code of Ordinances, Flood Hazard Reduction.
c.) The developer shall design and construct all streets to minimize any fill required to bring
building pads into compliance with this code.
d.) Alternate methods of building protection may be accepted by the City upon submittal of
detailed information, review and approval by the City Engineer.
5.6.5 Drainage System Criteria
If an underground drainage system is required, and a 60-inch or smaller pipe will handle the
design flow, pipe shall be used. If a 60-inch pipe is not adequate, the developer has the option to
use concrete pipe or natural and/or a lined open drainage channel. If pipe is selected, the
maximum allowable velocity shall be 8fps in the pipe. Lining materials, if used, shall be approved
by the City.
5.6.6 Public storm sewers are defined as sewers and appurtenances that provide drainage for a public
right-of-way, or more than one private tract, and are located in public right-of-way or easement,
private storm sewers provide internal drainage for a reserve or other tract. Private storm or sewer
connections to public storm sewers shall occur at a manhole or at the back of an inlet as approved
by the City Engineer. All private storm sewers within the public right-of-way shall be constructed
in conformance with the Standards.
5.6.7 All construction shall conform with the City of La Porte Construction Details.
5.6.8 All storm sewers shall meet or exceed the requirements of the “Drainage Criteria Manual for
Harris County, Texas” and the requirements of the City of La Porte.
5.6.9 All storm sewer shall be sized based on Atlas 14 rainfall data as described in Section 5.4. Any
new development proposed to discharge to a City of La Porte conveyance system (i.e. storm sewer
system, roadside ditch, etc.) will require detention at a minimum storage rate of 0.55 acre-ft/acre.
5.7 LOCATION OF STORM SEWER
5.7.1 Public storm sewers shall be located within a public street right-of-way or storm sewer easement,
dedicated to the public and adjoining a public street right-of-way. Storm sewers through side lot
drainage easements are highly discouraged. Limited use may be approved at the discretion of the
City Engineer. If approved, a minimum twenty-foot (20’) wide easement is required (10’ on each
lot).
5.7.2 Recommended alignment within a public street right-of-way.
A. Boulevard pavement section with median – along centerline of the right-of-way.
B. Undivided pavement section five feet (5’) inside the right-of-way. For storm sewer
located in a public street right-of-way, a minimum of two-foot (2’) shall be maintained
inside the right-of-way line to the outside edge of the storm sewer unless otherwise
accompanied by an adjacent easement.
C. Alternate locations for a storm sewer will be permitted by the City Engineer.
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5.7.3 Recommended alignment within an exclusive storm sewer easement.
A. Storm sewers placed in easements shall conform to the requirements of Section 2.4.5
B. Storm sewers within easements shall be placed no closer than five feet (5’) measured
from the outside edge of the pipe to the edge of an easement, except when adjoining
another easement or public right-of-way where the distance may be reduced to two feet
(2’). The storm sewer shall be placed in the center of the easement. When the storm
sewer easement adjoins a public right-of-way, the easement may be reduced to a
minimum of ten feet (10’) and the storm sewer may be aligned close to the right-of-way
line, as long as required clearances are met, with specific approval of the City Engineer.
5.8 STORM SEWER MATERIALS
5.8.1 Storm sewer and culvert pipe shall be precast reinforced concrete pipe, unless specifically
approved by the City Engineer. Concrete pipe shall be manufactured in conformance with the
requirements of ASTM C 76, “Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe,”
current revision. Reinforced concrete pipe shall be Class III or stronger. The design engineer
shall provide for increased pipe strength when conditions of the proposed installation exceed the
allowable load for Class III pipe. All concrete pipe constructed in water-bearing soil or forty-two
inches (42”) in diameter or larger, shall have rubber gasket joints meeting the requirements of
ANSI/ASTM C 443, “Joints for Circular Concrete Sewer and Culvert pipe, Using Rubber
Gaskets”, current revision. Concrete pipe with diameter of less than forty-two inches (42”) may
be installed using pipe with tongue and groove type joint and Ram-nek, or approved equal, as a
joint filler. When specifically approved by the City Engineer, reinforced concrete arch and
elliptical pipe conforming to ASTM C506 and ASTM C507, respectively, current revision, may be
installed in lieu of circular pipe. Reinforced concrete box culverts shall meet the minimum
requirements of ASTM C789, “Precast Reinforced Concrete Box Sections for Culverts, Storm
Drains, and Sewers”, current revision. Pipe joints for arch and elliptical pipe and box culverts
shall be sealed using Ram-nek or approved equal.
5.8.2 Storm sewer outfalls into open channels shall be constructed using corrugated steel pipe.
Corrugated steel pipe shall be manufactured in conformance with the requirements of
AASHTO Designation M-36-82, current revision. Pipe material shall be Aluminized Steel Type
2, meeting the requirements of AASHTO Designation M-27-79I, current revision, or Pre-coated
Galvanized Steel, AASHTO M-246, 10 mil coating on both sides. All pipe shall have a full
double coating, Type A, in accordance with AASHTO Designation M-190, current revision. Pipe
joints and fittings shall meet the minimum requirements of these specifications and shall have an
O-ring gasket seal meeting the requirements of AASHTO C-361, current revision. (See City of La
Porte Construction Details).
5.8.3 Storm sewer outfalls shall have a slope protection to prevent erosion. Slope protection may be
constructed of slope paving or rip rap. Slope paving shall be four-inch (4”) five (5) sack concrete
with six-inch by six-inch (6” x 6”) welded wire mesh (W14 x W14) or three eighths inch (3/8”)
steel rebar on twenty-four-inch (24”) centers, each way. Rip rap shall be a minimum of six-inch
(6”) broken concrete rubble with no exposed steel or well-rounded stone and shall be a minimum
of eighteen inches (18”) thick. Slope protection texturing shall be required where public access
likely. Refer to the Construction Details for minimum dimensions.
5.9 ADDITIONAL REQUIREMENTS
5.9.1 Minimum depth of storm sewer (measured to the top of pipe) shall be twenty-four (24”) below the
top of curb or finished grade, whichever is lower. Minimum size storm sewer for main and
inlet lead shall be twenty-four inches (24”).
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5.9.2 Storm sewers shall be bedded using cement stabilized sand (see specification in Section 4.2.3) as
shown in the City of La Porte Construction Details.
5.9.3 Pipe requirements.
A. Reinforced concrete pipe installed at a depth greater than thirty feet (30’) shall be designed by the
engineer for the specific installation and approved by the City Engineer, Reinforced concrete pipe
shall be designed in accordance with the American Concrete Pipe Association, “Concrete Pipe
Design Manual”, Maximum cover on the pipe shall be measured from the top of pipe to the
ultimate finished grade or natural ground, whichever is greater.
B. Corrugated steel pipe shall have a minimum thickness as follows:
PIPE SIZE MINIMUM THICKNESS
(Inches) Corrugations (Inches)
242-2/3” X 1/2” 0.052
30- 482-2/3” X 1/21 0.064
54- 723’t X 1” or 511 X 1” 0.064
78- 102311 X 1” or 5” X 1” 0.079
Bedding for corrugated steel pipe shall be cement-stabilized sand. Corrugated steel pipe less than
or equal to fifty-four inches (54”) in diameter and less than thirty feet (30’) deep shall have the
minimum thickness given above.
C. Design storm flow in a street shall not exceed the capacity of the street, for the water surface equal
to the top or curb and shall not exceed the inlet capacity. Design storm flow shall meet Harris
County criteria.
D. All bridges must be a minimum of eighteen inches (18”) above the 100-year water surface
elevation or in accordance with the Federal Emergency Management Agency (FEMA)
regulations, latest revisions, or HCFCD requirements, whichever is greater.
5.9.4 Storm sewers less than forty-two inches (42”) in diameter shall be constructed on a straight
horizontal and vertical alignment between manholes. Storm sewers greater than or equal to forty-
two inches (42”) in diameter may be laid along a curve using manufactured bends of less than or
equal to 11¼’.
5.10 APPURTENANCES
5.10.1 Manholes
A. Manholes shall be placed at all changes in alignment, grade and size of the storm sewers;
at the intersection of two or more storm sewers; at all inlet leads; and at the end of all
storm sewers.
B. Maximum spacing between manholes shall be four hundred feet
(400’).
C. Manhole covers shall be cast iron, traffic bearing, type ring and cover with the words
“storm sewer” cast into the cover.
5.10.2 Inlets
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A. Curb inlets shall be spaced and sized to intercept the calculated runoff for the design
storm. The water surface elevation at the inlet shall be less than or equal to the gutter for
the design storm flow.
B. Maximum travel distance of water in the street to a curb inlet shall be three hundred feet
(300’) on a major thoroughfare and in a commercial area. The maximum travel distance
of water in the street permitted in a single-family residential area shall be four hundred
feet (400’).
C. No Valley Gutter without prior approval.
D. Curb inlets should be on the intersecting side street at intersections with a major
thoroughfare. The City Engineer shall specifically approve locations at intersections.
E. Grated inlets will not be permitted in an open ditch.
F. Backslope swale interceptors shall be placed in accordance with the requirements of
Harris County.
G. Curb inlets shall have solid inlet lids. Grate or Curb and Grate inlets shall not be allowed
for residential subdivisions. Curb inlets shall be recessed, unless otherwise directed by
the City Engineer.
H. Backfill around inlets and to top of first stage inlet with cement stabilized sand.
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