[Adopted 6-10-1985 by Ord. No. 51C]
The St. Mary's County Road Ordinance No. 76-7,
with Specifications and Standards for Highway and Street Construction,
as revised herein, is hereby adopted.
As used in this article, the following terms
shall have the meanings indicated:
The Construction Specifications of Leonardtown adopted herewith, revised and amended from time to time by Leonardtown, and described in § 128-28, Specifications and Standards for Highway and Street Construction. The construction specifications indicate requirements for construction methods and work quality.
The Design and Construction Standards of Leonardtown adopted herewith, revised and amended from time to time by Leonardtown and described in § 128-28, Specifications and Standards for Highway and Street Construction. The design and construction standards indicate dimensions and materials to be used for various items of work.
The Commissioners of Leonardtown.
[1][1]
Editor's Note: Pursuant to the 1989 Charter,
the Commissioners of Leonardtown are now the Mayor and Council of
the Town of Leonardtown.
A.
General requirements. No person shall improve any
road without first obtaining a permit from the Engineer. Such permit
shall be transferable upon application to Engineer's Office, and it
may be revoked if any provisions thereof or of this article are violated.
Willful refusal of any permittee to stop construction after receiving
notice of such revocation shall be deemed a violation of this article.
Before a permit is issued, the following requirements for application,
bond, fee, plans and right-of-way must be met.
B.
Permit application. Application for a permit for road
construction shall be made on forms provided by the Engineer and shall,
when required by the Engineer, be accompanied by special specifications
peculiar to the scope of work covered by the permit and suitable tracings
of detailed plans of the work.
C.
Right-of-way. If subdivision approval is applied for
with lots abutting road rights-of-way which are less than standard
width for the proposed type of roadway, the developer will be required
to dedicate the additional right-of-way and slope easements necessary
to obtain the necessary width as to the portion of the same that the
development fronts on.
D.
Alternate standards. Upon determination by the Engineer
that the standards and specifications are not feasible or practicable
for a particular project, he may require such alternate or additional
standards and specifications in accordance with good engineering principles
as may be deemed necessary, and such alternate or additional requirements
shall be part of and a condition of the permit.
E.
Permit expiration. Such permit shall automatically
expire 18 months after its issuance, unless extended, in writing,
by the Engineer, stating the reasons for extension. It shall be the
responsibility of the permittee to apply for an extension prior to
the expiration of the permit. The permittee shall notify the Engineer
within two days of the date the work commences.
A.
Required plans. The developer shall have prepared
and submitted to the Engineer suitable plans of the proposed work,
conforming to the following:
(1)
Proposed grade. The proposed road profile shall be
on plan and profile sheets showing the adjacent properties with lot
and block designations and topography on the plan view and, on the
profile section, the computed proposed grade with vertical curve information,
curb fillet profiles and existing ground lines at the center line
and both right-of-way lines.
(2)
Storm drainage. The storm drainage plan shall show
all storm drainage facilities in plan and profile, as well as property
lines, curb lines, utilities, ground profiles and other pertinent
features. Complete design data shall be submitted for all storm drainage.
(3)
Paving plans. Paving plans shall show rights-of-way,
road names, dimensions, topography, location map, North point, scale,
coordinates, datum, survey controls, curb and gutter, sidewalks, driveways,
types of paving, location of present and proposed inlets with their
gutter elevations and sufficient elevations at all road intersections
on the curb, gutter and paving to assure adequate drainage of the
intersection. Profiles of the curb and gutter at intersections may
be required. Other information which may be required is typical pavement
sections, grading plans, driveway profiles and ground cross sections.
B.
Additional data. The Engineer may require any necessary
additional data pertinent to the scope of the work covered by the
permit.
C.
Plan approval. Approval of the plans by the Engineer
shall be indicated by signature on the plan sheet. Plans may be approved
for various phases such as profile grade, storm drainage and paving
details.
D.
Plan signature. All plans submitted for approval must
be prepared and signed by a professional engineer or land surveyor
registered to practice in Maryland. All plans submitted for approval
shall conform to the standards and specifications of this article
unless prior approval has been given for exceptions.
The fee for issuance of a permit for road improvements
and the inspection of the work shall be as established by resolution
of the Commissioners of Leonardtown.
A.
General. No permit for the construction of a road
shall be issued until the applicant, as principal, has posted cash
or bond with an approved corporate surety or an acceptable assignment
of funds in favor of the Commissioners of Leonardtown as conditioned
in subsequent sections or subsections of this article or an irrevocable
letter of credit issued by a financial institution approved by the
Town of Leonardtown. Where the estimated cost of the work is less
than $500, personal security will be accepted; provided, however,
that the cumulative total in such case for the applicant shall not
exceed $1,000 or more than two permits outstanding.
(1)
The permittee, his agents and servants shall comply
with all the applicable terms, conditions, provisions, requirements,
standards and specifications of this article.
(2)
The permittee, his agents and servants shall faithfully
complete the work for which the permit is issued.
(3)
The permittee, his agents and servants shall save
harmless the Town of Leonardtown from any expense incurred through
the failure of the permittee, his agents and servants to complete
the work as required by this article or from any damages growing out
of the negligence of the permittee, or his agents or servants.
B.
Performance bond. A cash or corporate bond or an irrevocable
letter of credit issued by a financial institution approved by the
Town of Leonardtown equal to the total cost of the project as estimated
by the Engineer, including an additional 10% of the cost for contingencies,
shall be furnished by the applicant, conditioned upon the satisfactory
completion of all work covered by the permit. Upon acceptance by Leonardtown
of the work covered by the permit, the Engineer shall certify such
performance bond as being discharged.
C.
Cash agreements. In lieu of filing a cash or corporate bond as required by Subsection B of this section, any person may enter into an agreement with the Commissioners of Leonardtown, such agreement to be approved by resolution of the Commissioners, providing that the permittee shall deposit in a depository approved by Leonardtown such sum of money as is estimated by the Engineer to be the total cost of the project. The agreement shall itemize the several phases of the work or construction. Upon completion of each step or phase, the permittee shall notify the Engineer that he is ready for an inspection. The Commissioners of Leonardtown are hereby authorized to refund to the permittee any installment due under the terms of the agreement upon the receipt of a certificate signed by the Engineer, certifying that the work has been performed by the permittee according to the standards, specifications and minimum requirements of this article, including any exception granted pursuant to § 128-25 hereof, and that the permittee is entitled to the installment due for completion of such work. Upon final completion of all work for which the permit is issued, a final certificate shall be issued, and upon acceptance of the road by the Commissioners of Leonardtown, the final payment shall be made to the permittee. The final draw of payment under the terms of the agreement shall in no event be less than 25% of the total cost of the project.
D.
Bond acceptance. Before acceptance, all grounds, irrevocable letters of credit or acceptable assignment of funds shall be approved by the Engineer, the Leonardtown Attorney and the Commissioners of Leonardtown. All bonds, irrevocable letters of credit or assignment of funds covering construction filed hereunder shall be released upon, but not before, acceptance of the completed road by Leonardtown in accordance with § 128-24 hereof.
A.
General. All construction shall conform to the requirements of these Rules and Regulations and to § 128-28, Specifications and Standards for Highway and Street Construction. The Engineer shall be responsible for the interpretation of the specifications and standards.
B.
Standards. The design and construction standards following herewith and as contained in the § 128-28, Specifications and Standards for Highway and Street Construction, are hereby prescribed. They may from time to time be amended or revised by official action of The Commissioners of Leonardtown, upon recommendations of the Engineer.
C.
Storm drainage. The construction of an adequate stormwater drainage system and/or facilities conforming to § 128-28, Specifications and Standards for Highway and Street Construction, shall be required in all cases.
D.
Curb, gutter and sidewalks. Concrete curb and gutter
and sidewalks shall be required along any road where the majority
of the individual lots abutting on such road have a frontage of less
than 150 feet or where any road abuts property being developed for
multidwelling residential use which is not being subdivided into individual
building lots or where urban construction is required by traffic conditions,
as determined by the Engineer.
E.
Connecting road. No road separated from a Leonardtown-maintained
road or a road maintained by any other public agency shall be improved
or accepted by Leonardtown unless a suitable connecting road to the
existing road is improved.
F.
Grade. All grades shall conform to § 128-28, Specifications and Standards for Highway and Street Construction.
G.
Alignment. Roads shall be centered in the dedicated
public right-of-way wherever possible.
H.
Widths. Roads shall conform to the requirements of width, curb and gutter and sidewalks as contained in § 128-28, Specifications and Standards for Highway and Street Construction.
I.
Leonardtown roads. The developer is responsible for
constructing curbs and gutters, sidewalks, storm drainage, pavement
widening, driveway aprons, and sod adjacent to existing Leonardtown
roads as to the portion of the same the development fronts on if he
proposes development of the adjacent property. The level of improvements
shall be determined by the classification and function of the road
the development fronts on.
J.
Driveway entrances.
(1)
Driveway entrances shall be placed to obtain the optimum
or at least minimum sight distance.
(2)
Driveway entrances to residential properties shall
be according to the standard driveway design. No residential driveway
apron shall be constructed in or partially in any intersection curb
fillet.
(3)
Driveway entrances to commercial or industrial property
shall comply with the standard State Highway Administration driveway
design.
A.
Inspection.
(1)
Inspection services will be maintained at all times
by the Engineer to assure compliance with the permit.
(2)
The permittee shall notify the Engineer at least two
days before commencement of any construction thereunder, and, in the
event that there is an interruption of the work for a period of more
than 30 days, then the permittee shall notify the Engineer at the
end of each interruption of his intent to actively resume operations.
(3)
No paving, curb and gutter or sidewalk construction
or driveway entrances shall be started unless there has been a final
inspection and approval of the subgrade.
(4)
The permittee and his agents, servants and subcontractors
shall comply with all requirements of the Engineer pertaining to public
safety and the avoidance of unnecessary inconvenience to the public
during construction and compliance with the specifications.
(5)
The construction work materials, plans and specifications
shall at all times be open and available for inspection by duly authorized
officials and employees of the Town of Leonardtown.
B.
Construction requirements.
(1)
All roads to be constructed shall be graded to the
full width of the right-of-way.
(2)
Earthwork shall include clearing and grubbing, the
removal and replacement of all unsuitable material and the proper
preparation of subgrade.
(3)
Where necessary, adequate underdrains shall be installed
as directed.
(4)
No work on road pavement shall be started until all
underground utilities proposed to cross said road have been installed
and properly backfilled.
(5)
All materials used in construction shall conform in
every detail to the Leonardtown Standards and Specifications or as
otherwise approved and accepted by the Engineer.
(6)
The permittee shall be responsible for the maintenance
of vehicular and pedestrian traffic on the roadway and shall provide
materials, labor and equipment as necessary to properly maintain traffic.
Excavations or other hazards shall be properly barricaded at all times
and lighted at night, and proper connections shall be made to drives
and walks at occupied residences. The permittee is required to keep
the roadway shaped up by blading, as necessary, and to correct muddy
or soft subgrade by placing temporary gravel or stone. The permittee
is responsible for plowing snow sufficiently to maintain access to
inhabited residences or other facilities until the road is finally
accepted by Leonardtown. It shall be the responsibility of the permittee
to remove any dirt and debris deposited on streets in and adjacent
to the work area during the construction period.
(7)
A thick stand of permanent grass shall be obtained
by seeding or sodding. The seeded areas there shall be at least two
inches of topsoil.
(8)
Street signs shall be erected at all intersections.
These signs shall show the names of intersecting streets and be of
durable metal construction conforming to the Leonardtown standards.
(9)
Barricades shall be erected of an approved design.
(10)
Utility cuts.
(a)
No public utility or other person or organization
shall cut into the surface of any road in Leonardtown until a permit
for the same has been issued by the Engineer and essential notice
has been given, in writing, to the Engineer of the location, nature,
extent of the cut and the length of time it will be open.
(b)
In case of an emergency cut, notice shall be
given as soon as possible, but not more than 48 hours after it is
made.
(c)
In case of a cut, the person or organization
making it shall be responsible for restoring the roadbase and surface
to its former condition and repairing paving failures and settlements
due to the utility cut. Repairs to cut areas shall be made in conformance
with the applicable standards and specifications.
A.
Final approval. Final approval of construction work
under any permit shall be given by the Engineer after a field inspection
shows to his satisfaction that the work conforms in all respects to
the permit and includes all work required thereby.
B.
Acceptance. Final approval shall be certified to the
Town of Leonardtown by the Engineer. Actual acceptance into the Leonardtown
maintenance system for perpetual maintenance shall be only by order
of the Leonardtown Commissioners in each individual case.
C.
Partial acceptance. Final approval of a part, less than all, of the work covered by a permit may be requested and given, and such approved part may be accepted by Leonardtown, but no bond shall be released before all work called for by the permit is completed, unless another bond is posted to cover the remaining work. This bond will only be accepted on work that cannot be completed due to extenuating circumstances to be determined by the Engineer as specified under § 128-21B.
No attempt has been made to standardize any
construction on rights-of-way other than those mentioned herein. However,
each problem will be studied by the Engineer as an individual case,
and solution will be given for the special conditions. This applies
to bridges, culverts, and other structures and their appurtenances
or such conditions encountered on or contiguous to the project.
A.
The Engineer shall note all violations of or failure
to abide by the terms of this article by service of a stop-work order
on any person, firm or corporation in violation.
B.
Any person, firm or corporation who shall violate
any of the provisions of this article or fail to comply with any of
the requirements thereof or who shall improve any road in violation
of any plan submitted or permit issued hereunder, shall be guilty
of a misdemeanor and shall be liable to a fine not exceeding $1,000
or to imprisonment for a term not exceeding six months, or both.
[Amended 3-14-1994 by Ord. No. 78]
C.
Each day such violation shall be permitted to exist
shall constitute a separate offense.
D.
In addition to other remedies, the Commissioners of
Leonardtown may institute injunction, mandamus, abatement or other
appropriate action or proceedings to compel compliance with the provisions
of this article.
Any person aggrieved by any decision of the
Engineer or any agency acting under the provisions of this article
may within 30 days of the notice of the Engineer's decision request
a hearing before the Commissioners of Leonardtown. Any person aggrieved
by the action of the Commissioners of Leonardtown may appeal to the
Circuit Court within 30 days of the notice of the Commissioner's decision.
A.
Purpose. The purpose of these specifications is to
establish design criteria and specifications for the planning, construction,
improvement, maintenance and repair of public roads, including sidewalks,
curbs and gutters, and storm drainage facilities.
B.
Interpretation of standards. The provisions of these
specifications in their interpretation and application shall be construed
as minimum requirements. Should any requirements of these specifications
be found to be in conflict with those imposed by other provisions
of law, the more restrictive or higher standards shall prevail.
C.
Applicable documents.
(1)
The following publications shall be referred to as
necessary in the design of Leonardtown roads:
(d)
Highway Drainage Manual, Maryland Department
of Transportation, State Highway Administration, December 1981, as
amended (for design of open drainage systems).
(e)
County of Anne Arundel Design Manual, July 1972;
as amended (for design of closed drainage systems).
(f)
Maryland State Highway Administration Standard
Specifications for Construction Materials, Maryland Department of
Transportation, State Highway Administration, January 1982, as amended
(for construction methods and materials).
(g)
Maryland State Highway Administration Book of
Standards, January 1970, as amended (for construction detail).
(h)
Maryland State Highway Administration Rules
and Regulations for Commercial, Subdivision, Industrial and Residential
Entrances to State Highways, 1975, as amended.
(i)
A Policy on Geometric Design of Rural Highways
by the American Association of State Highway Transportation Officials
(AASHTO).
(j)
A Policy on Design of Urban Highways and Arterial
Streets (AASHTO).
(k)
Highway Capacity Manual - Highway Research Board
Special Report 1987, prepared by the National Academy of Sciences,
National Research Council Publications 1328.
(l)
Manual on Uniform Traffic Control Devices for
Streets and Highways, United States Department of Transportation,
Federal Highway Administration.
(2)
If a conflict should exist between these specifications
and the provisions of other Leonardtown ordinances and regulations,
the highest standards shall apply.
D.
Design specifications and standards.
(1)
General.
(a)
No construction, i.e., grading, etc., or the
installation of utilities will be permitted in the bed of any proposed
street until the street grade has been officially established, the
plat of the same has been approved by the Engineer and a road construction
permit is obtained.
(b)
All land within the right-of-way and all construction
easements (slope, drainage, etc.) shall be graded and stabilized using
methods and materials which will ensure stabilization and practicality
of maintenance. Methods and materials shall be specified.
(2)
Street classification.
(a)
Design standards are hereby issued for the following
functional classifications of streets and correspond to those classifications
presented in the plates contained herein:[4]
[1]
Place: a cul-de-sac or street, the primary purpose
of which is to provide access to and from adjacent dwellings to a
higher functional type street. Occasionally, a place will connect
with two or three small places. Places do not accommodate through
traffic movement.
[2]
Alley: a narrow roadway for access to the area
of commercial, multifamily or industrial structures.
[3]
Minor local: a street which provides access
to places and conducts traffic to a higher functional-type street.
[4]
Major local: a street which, in addition to
providing access to properties abutting thereon, carries traffic to
an activity center or higher classification street. It may be a loop
street or may link local and/or collector streets.
[5]
Minor collector: a principal traffic artery
within residential areas which may provide routes to local facilities
or serves as the main entrance to a sizable development or a combination
of developments.
[6]
Arterials: higher functional-type streets, i.e.,
not meeting functional definitions herein specified, shall meet retirements
set by the Engineer with consideration of the Leonardtown Master Plan,
Maryland Department of Transportation Standards, accepted design manuals
and transportation-traffic requirements projected for the site and
area in question.
[4]
Editor's Note: Said plates are included at
the end of this article.
(3)
Roadway typical section.
(a)
Soil conditions. Standards for construction
of pavement sections as set forth herein are based upon a minimum
subgrade value of CBR 5, (California Bearing Ratio). Where the subgrade
is less than CBR 5, reinforcing of sections will be required as directed
by the Engineer.
(b)
Paved driving surfaces shall be crowned with
a pitch from the center line of pavement of 1/4 inch to one foot (2%).
Gravel shoulders shall be graded to a pitch of 1/2 inch to one foot
(4%), from edge of pavement to edge of shoulder. Turf shoulders shall
be graded to a pitch of 3/4 inch to one foot (6%).
(c)
Sidewalks shall be provided along all streets
within urban areas. Within rural communities, sidewalks shall be required
along those streets used for pedestrian access to schools, parks and
shopping areas. Where a pedestrian walkway system will be superior
to traditional sidewalks in terms of safety, accessibility to all
lots in the development and physical design factors, a pedestrian
walkway system may be approved.
(d)
Typical street sections and road design standards
as depicted on plates continued herein are to complied with in the
design and construction of streets. Any need to modify these typical
sections shall be authorized upon the recommendation of the Engineer
and the approval of the Commissioners of Leonardtown.
(4)
Horizontal alignment (curvature).
(a)
The minimum stopping sight distance for the
various functional classifications of streets shall be as depicted
on tables contained herein.
(b)
Curves shall have sufficient length to provide
a smooth flowing alignment where possible (200 to 300 feet minimum).
(c)
Horizontal curve data shall be computed by the
arc definition of a circular curve.
(d)
A tangent length of at least 100 feet shall
be used between reverse curves, except in unusual situations.
(e)
Tangents should not be introduced between two
curves in the same direction unless the length of the tangent is greater
than 500 feet.
(5)
Vertical alignment (grade).
(a)
The maximum grade of streets shall be as indicated
on tables contained herein.
(b)
The minimum grade along rural streets shall
be 3/4% and 1/2% along urban streets.
(c)
Vertical curve lengths shall be designed to
provide at least the minimum stopping sight distance required for
the road design speed. Crest vertical curves shall be designed for
a minimum design speed of 30 miles per hour.
(d)
Vertical curves shall be used in changes of
grade exceeding 1%; the minimum length of vertical curves shall be
100 feet; grade breaks are to be shown on the profile, and high points
are to be shown in the plan.
(6)
Street intersections.
(a)
Standards for street intersections are depicted
on plates contained herein.
(b)
Right-angle intersections shall be used whenever
practical. No street shall intersect any other street at less than
a seventy-five-degree angle.
(c)
Minimum stopping sight distance shall be provided
at all intersections. No proposed street shall be permitted to intersect
an existing county road at a location that would result in undue interference
with or hazard to the free movement of normal traffic.
(d)
Approach grades to all street intersections
shall be given careful considerations. The grade of the preference
street shall be continued through the intersection and the approach
leveling area of at least 75 feet (measured from the intersection
of the center lines), within which the grade shall not exceed a maximum
of 4%. In cases where the intersection involves collector- or arterial-type
streets, the design criteria established by the State Highway Administration
and contained in the Rules and Regulations for Commercial, Subdivisions,
Industrial and Residential Entrances shall apply.
(e)
Acceleration, deceleration, channelization and
bypass lanes at an entrance to or within a proposed development may
be required. The necessity for such shall be based upon the ultimate
size of the proposed development and the potential function of the
streets and roads.
(f)
Streets shall not normally intersect roads classified
as minor collector at intervals less then 750 feet.
(7)
Superelevation.
(a)
Horizontal curves of streets in subdivisions
or commercial and industrial developments shall not normally be superelevated.
(b)
The maximum rate of superelevation for streets
shall be 6%.
(c)
Superelevated pavements shall be rotated around
the center line, except where this procedure would adversely affect
adequate storm drainage design.
(d)
Normally, 2/3 of the superelevation transition
is accomplished on the tangent. The Design Engineer shall provide
the necessary superelevation tables.
(9)
Entrances and driveways.
(10)
Curbs, gutters and islands.
(a)
Where required, concrete curb and gutter shall
conform to the standards shown on plates contained herein.
(b)
The minimum grade of a concrete gutter shall
be 1/2 of 1%.
(c)
All islands must be concrete curbed. The pitch
of the gutter plan may be reversed for drainage purposes, such as
with a superelevation section or the high side of a crown section
at the median island.
(d)
The minimum curb tangent length between entrances
and property lines shall be five feet.
(e)
The minimum curb radius rounding shall be 2
1/2 feet.
(f)
Valley gutters shall be used only where approved
but will normally be permitted where no more than two cubic feet per
second flow across an intersection.
(11)
Cross sections and quantities.
(a)
When required, cross sections shall be taken
at least every 50 feet and at all noticeable terrain breaks. The center
line and profile grade line shall be stationed correspondingly.
(b)
The Design Engineer shall provide quantity and
construction cost estimates. These estimates shall include all quantities
for grading, paving, curb and gutter, etc., and shall be tabulated
as directed.
(12)
Street and traffic control. Street name signs
and traffic control signs shall be installed by the developer as directed
by the Town Engineer. Installation shall be in accordance with the
Manual on Uniform Traffic Control Devices, as currently amended, and
the plates contained herein. Street name signs and appropriate traffic
control signs must be installed prior to the issuance of a certificate
of occupancy for any lot on that street.
(13)
Guardrailings.
(a)
Guardrailing shall be erected on roadways at
points of extreme hazard to a vehicle leaving the traveled portion
of the trafficway. Generally, this potential hazard develops at fills
over eight feet in vertical depth from the edge of the shoulder to
the toe of the slope when the slope ratio is steeper than 4:1.
(b)
Guardrailing shall be placed as shown on the
plates depicting typical roadway sections.
(c)
Where roadway construction ends in fill areas,
guardrail W-beam barricades shall be erected.
(14)
Shoulders. Where shoulders and open drainage
sections are applicable, the shoulder section shall be as shown in
the plates depicting typical sections.
E.
Construction specifications.
(1)
All material specifications, methods of construction
and methods of measurements shall be accordance with the Standard
Specifications for Construction Materials, Maryland Department of
Transportation, State Highway Administration, January 1982, as amended.
(2)
If, in the event an item(s) proposed to be constructed
is not contained in the State Highway Administration Specifications,
the Design Engineer shall submit special provisions to the Town Engineer
for approval.
F.
Storm drainage.
(1)
General.
(a)
Stormwater runoff is to be collected and conveyed
in closed conduit systems (inlets, pipes and connectors) and open
channel systems (ditches, streams, culverts, rivers, improved open
channels).
(b)
Existing storm drainage systems which are considered
inadequate to accommodate the proposed development must be improved
prior to development.
(c)
Changes to the limits of natural drainage basins
are prohibited, and, in general, runoff after development shall drain
to the same outfall as before development.
(2)
Methods of computation.
(a)
In the design of a storm drainage system, the
present runoff and future runoff from the development and from the
area draining thereto shall be determined on the basis of full development
of the watershed in accordance with current zoning for the area. A
registered professional engineer or land surveyor, as appropriate,
shall design the stormwater system and certify that the system is
adequate to collect and convey stormwater runoff from the development
and any area contributing thereto and shall attest to the effects
of the stormwater runoff to neighboring lands. The following data
shall be submitted:
[1]
A map at a scale not smaller than one inch equals
2,000 feet or as otherwise specified, outlining the entire drainage
area that contributes to the watercourses which pass through the development.
Also, a drainage area map at a scale of one inch equals 200 feet or
larger showing the areas draining to each element of the proposed
storm drain systems of the development.
[2]
A plan showing the facilities to be provided,
along with flow data and computations developed in the design and
the tentative layout of the drainage facilities.
[3]
Runoff calculations and assumptions shall be
provided in acceptable format for both closed and open systems, giving
area, size, quantity, velocity, slope and depth of flows and hydraulic
gradient.
(b)
The rational method shall, unless otherwise
approved, be used to determine quantities of stormwater runoff. Normally,
the ten-year-frequency storm shall be used in the design for storm
drainage. The time of concentrations and runoff coefficients shall
be determined in accordance with accepted practice and shall be based
upon established sources considering topographic and ground cover
conditions.
(c)
The minimum size of any culvert or storm drain
shall be 18 inches by 11 inches or an equivalent-size pipe.
(d)
Storm drains crossing water mains and sanitary
sewers shall be constructed with a minimum clearance of 12 inches.
Clearance shall be measured between outsides of pipes. A minimum of
six inches' base material shall be between a storm drain pipe and
the surface material in a private driveway and at least 12 inches
in a public street or roadway.
(3)
Closed stormwater runoff systems.
(a)
Closed runoff systems shall generally be required
where curb and gutter (urban) street sections are required.
[1]
Wherever possible, existing natural drainageways
shall be preserved as a supplementary element to closed drainage systems.
In all cases, closed systems shall discharge into existing natural
drainageways as soon as is practical.
[2]
Where, as a function of net development densities,
closed drainage systems are not essential to serve portions of developments
dedicated to permanent open space or portions developed at densities
less than one dwelling unit per acre, the use of existing natural
or open ditch drainageway systems may be approved. This recommendation
and approval shall be based upon findings that:
(b)
Closed systems shall be designed to carry ten-year-frequency
storms, provided that surcharge overflow from twenty-year storms can
be carried without damage in public streets, alleys and rights-of-way
to a suitable outfall. In sumps and other critical areas where overflow
is not permissible, twenty-year flows shall govern. The easement or
fee simple right-of-way required shall extend at least five feet beyond
the outside limits of the pipe and shall in no case be less than 20
feet in width.
(4)
Open runoff systems.
(a)
Where development density is equivalent to one
dwelling unit or less per acre and the existing or modified natural
channels can safely handle stormwater runoff, an open system utilizing
drainage ditches, culverts and natural channels may be utilized. In
certain cases, where quantity of flow, topographic, soil or natural
channel conditions preclude open systems, then the system shall be
fully or partially enclosed as required.
(b)
Normally, open ditch and culvert systems shall
be designed for a ten-year-frequency storm, culverts in excess of
24 inches in diameter for a minimum twenty-five-year storm.
(c)
For floodplains, bridges, major structures,
stream channels, etc., the design criteria shall be established individually.
(d)
Roadside drainage shall not be disrupted by
private driveways. A minimum 18 inches by 11 inches corrugated metal
pipe (arch type) is required to permit the free flow of water at those
points where a driveway intersects the roadside drainageway. When
a paved driveway is located near the crest of a vertical curve, valley
gutters may be provided as approved.
(e)
The shape and length of culverts and the grading
of culvert inlets and outlets shall be designed to facilitate periodic
maintenance to remove obstruction.
(f)
Where a development is traversed by a natural
drainage course or stream, there shall be provided a drainage easement,
a minimum of 50 feet in width, conforming substantially with the drainage
of such watercourse for the purpose of maintaining, improving or protecting
such drainage facilities. This easement area shall be designed to
the one-hundred-year floodplain level.
