[Ord. No. 433 §5.1, 5-18-2005]
A.
The
following standards are regarded as guidelines for desirable development.
The size, shape and orientation of lots shall be designed to provide
desirable building sites and logically related to topography, natural
features, streets and adjacent land uses. Due regard shall be given
to natural features such as large trees, unusual rock formations,
watercourses and sites which have historical significance, scenic
view and similar assets, the preservation of which would add attractiveness
and value to the subdivision. The following minimum standards are
set forth as guides to these goals.
1.
Where additional widening strips are dedicated on existing streets,
calculations of the area of a lot should not include the dedicated
strips in determining the gross area of the lot. Dedicated widening
strips shall be required for all proposed subdivisions which front
along a State, County or City road. The area of all lots must be calculated
exclusive of the street rights-of-way.
2.
Where there is a question as to the suitability of a lot or lots
for their intended use due to factors such as rock formations, soil
conditions, steepness of terrain, flood conditions or other adverse
natural physical conditions, the Board of Aldermen may, after adequate
investigation, withhold approval of such lots until engineering studies
are presented to the Board of Aldermen which establish that the method
proposed to meet any such condition is adequate to avoid significant
danger to health, life or property.
3.
Alleys are undesirable except where alleys of adjoining subdivisions
would be closed off from access by the failure to provide alleys in
new subdivisions.
[Ord. No. 433 §5.2, 5-18-2005]
A.
Blocks
shall be designed so as to provide good circulation of traffic.
[Ord. No. 433 §5.3, 5-18-2005; Ord. No. 460 §5.3(g), 2-8-2006]
A.
The
size, shape, orientation and dimensions of lots shall be appropriate
for the location and physical character of the proposed subdivision
and for the type of development contemplated in compliance with these
regulations. The minimum lot size for residential use for any proposed
subdivision shall be not less than eight thousand four hundred (8,400)
square feet. Building lines shall be shown on all lots intended for
residential use and shall not be less than the setback required by
this Chapter.
1.
Depth. Excessive depth in relation to width shall
be avoided. (A proportion of 1:1 or 2:1 will normally be considered
appropriate, unless topography is such that other lot dimensions allow
for proper development.)
2.
Street access. Each proposed lot shall front upon
a street improved to the standards and specifications of the Warren
County Highway Department, unless the lots front on a private roadway.
3.
Width. Lots for residential purposes shall have
sufficient width at the building setback lines to permit compliance
with side yard or distance requirements of this Chapter or regulations
and still be adequate for a building of practicable width. The minimum
lot width required for a lot fronting on a circular turnaround shall
be measured along a line tangent to the setback line at a point midway
between the side lot lines.
4.
Double frontage. Lots with double frontage and reversed
frontage shall be avoided, except where necessary to provide separation
of development from traffic arteries or as otherwise required by topography
or similar conditions.
5.
Side lot lines. Side lot lines shall be at right
angles to straight street and radial to curved streets except when
said radial lot lines detract from desirability of the lot, in which
event some deviation may be allowed.
6.
Corner lots. Corner lots for residential use shall
be platted to permit compliance with the yard and setback requirements
for each side. The right-of-way radius on corner lots shall be a minimum
of twenty (20) feet or, in the case of a straight line, the line connecting
two (2) points twenty (20) feet distance from the intersection of
the projected lot lines.
7.
Properties outside of a platted subdivision. For
any property outside of a platted subdivision or which is not a manufactured
home, the setback requirements will be as follows.
a.
Five (5) feet, if the width of the front yard is less than sixty
(60) feet;
b.
Seven (7) feet, if the width of the front yard is at least sixty
(60) feet and less than seventy (70) feet;
c.
Ten (10) feet, if the width of the front yard is seventy (70) feet
or longer; and
d.
The front and back setback lines will be twenty (20) feet from the
property line.
[Ord. No. 433 §5.4, 5-18-2005]
A.
In
addition to the standards of this regulation, which are appropriate
to the platting of all subdivisions, the subdivider shall demonstrate
to the satisfaction of the Board of Aldermen that the street, parcel
and block pattern proposed is specifically adapted to the uses anticipated.
The following standards shall, therefore, be observed.
1.
Proposed industrial parcels shall be suitable in area and dimensions
to the types of industrial development anticipated.
2.
Street right-of-way and pavement shall be adequate to accommodate
the type of volume of traffic anticipated.
4.
Every effort shall be made to protect adjacent residential areas
from the proposed non-residential subdivision, including the provision
of extra depth in parcels adjacent to an existing or potential residential
development and provision for a permanently landscaped buffer strip
where indicated by the Board of Aldermen.
5.
Streets carrying non-residential traffic, especially truck traffic,
shall not be extended to the boundaries of adjacent residential areas
and not be connected to streets intended for predominantly residential
traffic.
[Ord. No. 433 §5.5, 5-18-2005]
A.
General Standards.
1.
Streets shall conform to existing topography as nearly as possible.
Streets shall intersect, as nearly as possible, at right angles. Street
jogs with centerline offsets of less than one hundred twenty-five
(125) feet are prohibited.
2.
Streets will not be approved which are subject to flooding or frequent
inundation.
3.
The system of streets designated for the subdivision, except in unusual
cases, must connect with any streets already dedicated in adjacent
subdivision and where no adjacent connections are platted, must in
general be the reasonable projection of streets in adjacent tracts
and must continue to the boundaries of the tract subdivided, so that
other subdivisions may connect therewith.
4.
The City Engineer may require a street to be dedicated to public
use in order to provide circulation.
B.
Street Right-Of-Way And Utility Easement Requirements.
1.
Highway and major thoroughfares. Highways and major
thoroughfares shall have widths as specified by the City of Truesdale,
Warren County and the Missouri Department of Transportation.
3.
Minor stub and cul-de-sac streets. Fifty-two (52) feet. All cul-de-sac and stub streets shall have a turnaround radius of fifty-two (52) feet. The Board of Aldermen may approve a "T" or "Y" shaped paved space instead of a required turning circle. Turnarounds may not be required on stub streets which are less than two hundred fifty (250) feet in length and are planned to be extended in the future. All stub streets in excess of two hundred fifty (250) feet in length must provide a temporary turnaround with three (3) standard specification, "Manual on Uniform Traffic Control Devices", end of roadway markers mounted on two (2) pound "U" channel signpost. Each marker shall consist of an eighteen (18) inch diamond reflector red panel. The bottom of each panel shall be mounted a minimum of four (4) feet above the elevation of the pavement surface and installed at terminus of pavement. Refer to Exhibit "A" to this Chapter 400 for general street standards.
4.
Utility easements. Utility easements where required
shall be a least ten (10) feet wide (five (5) feet on each side of
the lot line) along rear, front and side lot lines. Easements of adequate
width shall be provided for open drainage channels, where required.
Easements five (5) feet in width may be allowed for underground cable
installations. Telephone and electric power lines shall be located
underground, except in subdivisions where all of the lots are twenty
thousand (20,000) square feet or larger in size and then the developer
will have the option of underground or overhead utility lines.
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Note: In subdivisions with no through streets, a fifty-five
(55) foot pavement radius and a sixty-seven (67) foot right-of-way
radius will be required on at least one (1) cul-de-sac in order to
facilitate school bus circulation. For individual cul-de-sacs the
fifty-five (55) foot pavement radius and sixty-seven (67) foot right-of-way
radius shall only be required if the cul-de-sac exceeds one thousand
three hundred (1,300) feet in length.
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C.
Minimum Pavement Widths.
1.
Highways, major thoroughfare and collector streets. Thirty-eight (38) foot minimum. In the case of a major thoroughfare
requiring an improvement different than a thirty-eight (38) foot pavement,
the matter of financial and other arrangements for installing wide
pavements at the time shall be taken up by the developer with the
officials having jurisdiction.
2.
Minor, stub and cul-de-sac streets. Twenty-six (26). Refer to Exhibit "A" to this Chapter 400. The pavement of a turning circle at the end of a cul-de-sac street shall have a minimum outside diameter of eighty-four (84) feet.
3.
Alleys and service drives. Twenty (20) feet minimum.
4.
Sidewalks. Sidewalks shall be installed on both
sides of all major streets, collector streets, minor, dead-end and
cul-de-sac streets. Sidewalks shall have a minimum width of four (4)
feet in residential areas. In commercial and industrial areas sidewalks
may be required as deemed appropriate by the Board of Aldermen. The
City of Truesdale, Missouri, by these requirements does not accept
dedication of sidewalks.
[Ord. No. 433 §5.6, 5-18-2005]
A.
The
grades of streets shall not exceed the following, except where unusual
or exceptional conditions exist, the Board of Aldermen may modify
these requirements:
1.
Highway and major thoroughfares. Six percent (6%).
2.
Collector streets. Eight percent (8%).
3.
Minor streets, service drives and alleys. Twelve
percent (12%).
4.
Pedestrian ways or crosswalks. Five percent (5%).
5.
Minimum grade. In no event shall a minimum grade
be less than seventy-five hundredths percent (0.75%).
[Ord. No. 433 §5.7, 5-18-2005]
A.
Street
name signs meeting the requirements of the County Highway Department
shall be erected by the subdivider at all intersections.
B.
Stop
signs, yield signs, etc., non-illuminated, non-electric, reflectorized
shall conform to the current "Manual on Uniform Traffic Control Devices"
and be provided by the developer and determined by the County Highway
Engineer.
C.
Whenever
a new street is constructed along the approximate alignment or extension
of an existing street, its name shall be the same as that of the existing
one.
D.
Whenever
a cul-de-sac street serves not more than three (3) lots, the names
of the intersecting street shall apply to the cul-de-sac.
E.
To
avoid duplication and confusion the proposed names of all streets
shall be approved by the Warren County Highway Department prior to
both preliminary plat approval and such names being assigned or used.
[Ord. No. 433 §5.8, 5-18-2005]
A.
Public Street Construction. Street shall be graded to full width of the right-of-way and fully constructed of asphaltic concrete or Portland cement concrete pavements in accordance with the Standard Specifications of the County of Warren Highway Department. Refer to Exhibit "A" to this Chapter 400 for applicable construction standards. Before streets are constructed, soil tests on the subgrade shall be submitted and approved by the City Engineer. In all fill areas in the roadways, soil tests shall be submitted and approved by the City Engineer for every two (2) feet of fill. No traffic will be allowed on new concrete pavement for thirty (30) days or until it reaches a field cured strength of three thousand five hundred (3,500) psi. A Portland cement concrete street shall not be approved unless it reaches a strength of four thousand (4,000) psi.
B.
Improvement Of Existing Streets. For any development fronting
on an existing road or street, it shall be the responsibility of the
developer to bring the road or street up to County specifications
to the centerline of the road or street, plus an additional eight
(8) feet of width as per County specifications.
C.
Designation Of Private Streets. For any subdivision having
private streets, the developer must construct a sign at all entrances
of the subdivision, within fifty (50) feet of the centerline of the
road, which shall state: Private Streets Maintained by Property Owners.
These signs shall be installed where they are easily visible to anyone
entering the subdivision and maintained in good order by the developer
and/or subdivision trustees. The minimum size for each sign shall
be twelve (12) inches high by eighteen (18) inches wide with two (2)
inch high letters. There shall also be a sufficient contrast in the
coloring of the sign background as compared to the message lettering.
When private streets are built, they are to be built to public street
standards.
D.
Approval Of Subgrade. The City Engineer shall approve the
subgrade before any base course or surface is placed thereon. The
subgrade shall be so constructed that it will be uniform in density
throughout. The entire width and length will conform to line, grade
and cross section shown on the plans or as established by the engineer.
If any settling or washing occurs or where hauling results in ruts
or other objectionable irregularities, the contractor shall reshape
and reroll the subgrade before the base or surfacing is placed. Tolerance
allowed on all lines, grades and cross sections shall be plus or minus
four hundredths (±0.04) feet.
E.
Utility Work Prior To Base Construction. No base course
work may proceed on any street until all utility excavations (storm
and sanitary sewers, water, gas, electric, etc.) have been properly
backfilled with granular material, crushed stone or gravel mechanically
tamped in ten (10) inch lifts or jetted with water and allowed to
set for a length of time satisfactorily to the City Engineer.
[Ord. No. 433 §5.9, 5-18-2005]
A.
Sufficient
permanent and distinguished monuments shall be accurately placed throughout
the subdivision so that street alignment may be traced with accuracy.
Such monuments shall be in the form of iron pins or of something equal,
not less than one-half (½) inch in diameter and three (3) feet
long driven into the earth or spikes not less than six (6) inches
long driven into the pavement. Such monuments shall be installed by
the subdivider as soon as reasonably possible. The location of such
monuments shall be indicated on the final plat and shall be placed
in accordance with the following requirements:
[Ord. No. 433 §5.10, 5-18-2005]
A.
Storm
water sewers or channels provide the facility for removing and transporting
surface runoff produced from rainfall.
This Section gives the minimum technical design requirements
of the City storm drainage facilities. In general, the formulae presented
herein for hydraulic design represent "acceptable" procedures not
necessarily to the exclusion of other sound procedures and should
be discussed before submission of plans for approval and should be
justified. All construction details pertaining to storm sewer improvements
shall be prepared in accordance with the Metropolitan St. Louis Sewer
District (MSD) Standard Construction Specifications unless otherwise
noted.
B.
General Requirements Of Storm Sewer Construction. All storm
sewers shall meet the following general requirements:
1.
Size and shape. The minimum diameter of pipes for
storm water sewers shall be twelve (12) inches. Sewers shall not decrease
in size in the direction of the flow unless approved by the City.
Circular pipe sewers are preferred for storm water sewers, although
rectangular or elliptical conduits may be used with special permission.
2.
Materials. All materials shall conform to MSD Standard
Construction Specifications. Reinforced concrete pipe joints shall
be Type "A" or better, as required.
3.
Bedding. The project plans and specifications shall
indicate the specific type or types of bedding, cradling or encasement
required in the various parts of the storm sewer construction if different
than current MSD Standard Construction Specifications.
Special provisions shall be made for pipes laid within fills
or embankments and/or in shallow or partial trenches, either by specifying
extra strength pipe for the additional loads due to differential settlement
or by special construction methods, including ninety percent (90%)
modified proctor compaction of fill to prevent or to minimize such
additional loads.
Compacted granular backfill shall be required in all trench
excavation within public (or private) streets rights-of-way or areas
where street rights-of-way are anticipated to be dedicated for public
use. Under areas to be paved, the compacted granular backfill shall
be placed to the subgrade of the pavement. Under unpaved areas, the
compacted granular backfill shall be placed to within two (2) feet
of the finished surface.
Pipes having a cover of less than three (3) feet shall be encased
in concrete, unless otherwise directed by the City.
If the storm and sanitary sewers are parallel and in the same
trench, the upper pipe shall be placed on a shelf and the lower pipe
shall be bedded in compacted granular fill to the flow line of the
upper pipe.
C.
Concrete Pipe Or Conduit Strengths. Reinforced concrete
pipe shall be Class II, minimum. Any concrete pipe, conduit or culvert
beneath a street right-of-way, or with reasonable probability of being
so located, shall be a minimum of Class III, but also shall account
for all vertical loads, including the live load required by the highway
authority having jurisdiction. In no case shall the design provide
for less than HS-20 loading of the AASHTO. For other locations, the
minimum design live load shall be the HS-10 loading.
D.
Monolithic Structures. Monolithic reinforced concrete structures
shall be designed structurally as continuous rigid units.
E.
Alignment. Sewer alignments are normally limited by the
available easements which in turn should reflect proper alignment
requirements. Since changes in alignment affect certain hydraulic
losses, care in selecting possible alignments can minimize such losses
and use available head to the best advantage. Sewers shall be aligned:
1.
To be in a straight line between structures, such as manholes, inlets,
inlet manholes and junction chambers, for all pipe sewers thirty (30)
inches in diameter and smaller.
2.
To be parallel with or perpendicular to the centerlines of straight
streets unless otherwise unavoidable. Deviations may be made only
with approval of the City.
3.
To avoid meandering, off-setting and unnecessary angular changes.
4.
To make angular changes in alignment for sewers thirty (30) inches
in diameter or smaller in a manhole located at the angle point and
for sewers thirty-three (33) inches in diameter or larger, by a uniform
curve between two (2) tangents. Curves shall have a minimum radius
of ten (10) times the pipe diameter.
5.
To avoid angular changes in direction greater than necessary and
any exceeding ninety degrees (90°).
F.
Location. Storm sewer locations are determined primarily
by the requirements of service and purpose. It is also necessary to
consider accessibility for construction and maintenance, site availability
and competing uses and effects of easements on private property. Storm
sewers shall be located:
1.
To serve all property conveniently and to best advantage.
2.
In public streets, roads, alleys, right-of-way or in sewer easements
dedicated to the City.
3.
On private property along property lines or immediately adjacent
to public streets, avoiding diagonal crossings through the central
areas of the property.
4.
At a sufficient distance from existing and proposed building (including
footings) and underground utilities or other sewers to avoid encroachments
and reduce construction hazards.
5.
To avoid interference between other storm water sewers and house
connections to foul water or sanitary sewers.
6.
In unpaved or unimproved areas whenever possible.
7.
To avoid, whenever possible, any locations known to be or probably
to be beneath curbs, paving or other improvements particularly when
laid parallel to centerlines.
G.
Sinkhole Areas.
1.
Sinkhole report. Where improvements are proposed
in any area identified as sinkhole areas, a sinkhole report will be
required. This report is to be prepared by a professional engineer,
registered in the State of Missouri, with demonstrated expertise in
geotechnical engineering and shall bear his/her seal.
The sinkhole report shall verify the adaptability of grading
and improvements with the soil and geologic conditions available in
the sinkhole areas. Sinkhole(s) shall be inspected to determine its
functional capabilities with regard to handling drainage. The report
shall contain provisions for the sinkholes to be utilized as follows:
a.
All sinkhole crevices shall be located on the plan. Functioning sinkholes
may be utilized as a point of drainage discharge by a standard drainage
structure with a properly sized outfall pipe provided to an adequate
natural discharge point, such as a ditch, creek, river, etc.
b.
Non-functioning sinkholes and sinkholes under a proposed building
may be capped.
c.
If development affects sinkholes, they may be left in their natural
state, however, they will still require a properly sized outfall pipe
to an adequate natural discharge point.
d.
An overland flow path shall be required for all sinkholes assuming
the outfall pipe and sinkhole become blocked.
Where the topography will not allow for an overland flow path:
(1)
The storm sewer shall be designed for the 100-year, twenty-four
(24) hour storm;
(2)
If this storm pipe is smaller than thirty-six (36) inches in
diameter, a designated ponding area shall be identified, assuming
the pipe is blocked;
(3)
The ponding area shall be based on the 100-year, twenty-four
(24) hour storm; and
(4)
The low sill of all structures adjacent to the ponding area
shall be above the 100-year high-water elevation.
e.
Special siltation measures shall be installed during the excavation
of sinkholes and during the grading operations to prevent siltation
of the sinkhole crevice.
2.
Procedure for utilization of sinkholes.
a.
Excavation. Prior to filling operations in the vicinity
of a sinkhole, the earth in the bottom of the depression will be excavated
to expose the fissure(s) in the bedrock. The length of fissure exposed
will vary, but must include all unfilled voids or fissure widths greater
than one-half (½) inch maximum dimensions which are not filled
with plastic clay.
b.
Closing fissures. The fissure or void will be exposed
until bedrock in its natural attitude is encountered. The rock will
be cleared of loose material and the fissures will be hand packed
with quarry run rock of sufficient size to prevent entry of this rock
into the fissures and all the voids between this hand packed quarry
run rock filled with smaller rock so as to prevent the overlying material's
entry into the fissures. For a large opening, a structural (concrete)
dome will be constructed with vents to permit the flow of ground water.
c.
Placing filter material. Material of various gradations,
as approved, will be placed on top of the hand packed rock with careful
attention paid to the minimum thicknesses. The filter material must
permit either upward or downward flow without loss of the overlying
material.
The fill placed over the granular filter may include granular
material consisting of clean (no screenings) crushed limestone with
ten (10) inch maximum size and one (1) inch minimum size or an earth
fill compacted to a minimum density of ninety percent (90%) modified
proctor as determined by ADTM D-1557.
d.
Supervision. Periodic supervision of the cleaning
of the rock fissures must be furnished by the engineer who prepared
the soil report. Closing of the rock fissures will not begin until
the cleaning has been inspected and approved by that engineer.
During the placement and compaction of earth fill over the filter,
supervision by the engineer shall be continuous. Earth fill densities
will be determined during the placement and compaction of the fill
in sufficient number to ensure compliance with the specification.
The engineer is responsible for the quality of the work and to verify
that the specifications are met.
H.
Flowline. The flowline of storm sewers shall meet the following
requirements:
1.
The flowline shall be straight or without gradient change between
the inner walls of connected structures; that is, from manhole to
manhole, manhole to junction chamber, inlet to manhole or inlet to
inlet.
2.
Gradient changes in successive reaches normally shall be consistent
and regular. Gradient designations less than the nearest one-thousandth
(0.001) foot per foot, except under special circumstances and for
larger sewers, shall be avoided.
3.
Sewer depths shall be determined primarily by the requirements of
pipe or conduit size, utility obstructions, required connections,
future extensions and adequate cover.
4.
Storm water pipes discharging into lakes shall have the discharge
flowline a minimum of three (3) feet above the lake bottom at the
discharge point or no higher than the normal water line.
5.
A concrete cradle is required when the grade of a sewer is twenty
percent (20%) or greater. A special design and specification is required
for grades exceeding fifty percent (50%).
6.
For sewers with a design grade less than one percent (1%), field
verification of the sewer grade will be required for each installed
reach of sewer, prior to any surface restoration or installation of
any surface improvements.
7.
The City may require the submittal of revised hydraulic calculations
for any sewer reach having an as-built grade flatter than the design
grade by more than one-tenth percent (0.1%). Based on a review of
this hydraulic information, the City may require the removal and replacement
of any portion of the sewer required to ensure sufficient hydraulic
capacity of the system.
I.
Manholes. Manholes provide access to sewers for purposes
of inspection, maintenance and repair. They also serve as junction
structures for lines and as entry points for flow. Requirements of
sewer maintenance determine the main characteristics of manholes.
1.
For sewers thirty (30) inches in diameter or smaller, manholes shall
be located at changes in direction, changes in size of pipe, changes
in flowline gradient of pipes and at junction points with sewers and
inlet lines.
2.
Spacing of manholes shall not exceed four hundred (400) feet for
pipe sewers thirty-six (36) inches in diameter and smaller; five hundred
(500) feet for pipe sewers forty-two (42) inches in diameter and larger,
except under special approved conditions. Spacing shall be approximately
equal whenever possible.
3.
Manholes shall be avoided in driveways or sidewalks.
4.
Connections to existing structures may require rehabilitation or
reconstruction of the structure being utilized. This work will be
considered part of the project being proposed.
5.
When a project requires a manhole to be adjusted to grade, a maximum
of twelve (12) inches of rise is allowed if not previously adjusted.
When an adjustment to raise or lower a manhole is required, the method
of adjustment must be stated on the project plans and approved by
the City.
J.
Overlow/Design System.
1.
The "design" components of the drainage system include the inlets,
pipe, storm sewers and improved and unimproved channels that function
during typical rainfall events. The "overflow" system comprises the
major overflow routes such as swales, streets, floodplains, detention
basins and natural overflow and ponding areas.
2.
The purpose of the overflow system is to provide a drainage path
to safely pass flows which cannot be accommodated by the design system
without causing flooding of adjacent structures.
3.
The criteria for the design of the overflow and design systems shall
be as follows:
a.
The "design" system shall be designed in accordance with the Storm
Water Design Criteria Section.
b.
The "overflow" system shall be designed for the 100-year, 20-minute
event, assuming the "design" system is blocked. The capacity of the
"overflow" system shall be verified with hydraulic calculations at
critical cross sections. The "overflow" system shall be directed to
the detention facility or as approved by the City.
c.
The low sill of all structures adjacent to the "overflow" system
swales shall be above the 100-year high water elevation.
Where the topography will not allow for an overland flow path:
(1)
The storm sewer shall be designed for the 100-year, 20-minute
storm; and
(2)
If this storm pipe is smaller than thirty-six (36) inches in
diameter, a designated ponding area shall be identified, assuming
the pipe is blocked; and
(3)
The ponding area shall be based on the 100-year, 24-hour storm.
(4)
The low sill of all structures adjacent to the ponding area
shall be above the 100-year high water elevation.
d.
The "overflow" system shall be designated on the drainage area map
and on the grading plan.
e.
All overflow systems will be considered on a site-specific basis.
K.
Storm Water Design Criteria.
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Flow quantities. Flow quantities are to be
calculated by the "rational method" in which:
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Q = API
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Where:
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Q = runoff in cubic feet per second
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A = tributary area in acres
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I = average intensity of rainfall (inches per hour) for a given
period and a given frequency
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P = runoff factor based on runoff from previous and impervious
surfaces
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P (Runoff Factors) for various impervious conditions are shown in Table 4-1 following this Section 400.220.
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P.I. values for various impervious conditions are shown in Tables 4-2 to 4-4 following this Section 400.220.
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1.
Rainfall frequency. A 15-year rainfall frequency
is to be used in areas of the City. In the design of local storm sewer
systems, a twenty (20) minute time of concentration shall be used.
Figure 4-1 gives rainfall curves for 2-, 5-, 10-, 15- through 20-
and 100-year frequencies.
2.
Impervious percentages and land use. Minimum impervious
percentages to be used are as follows:
a.
For manufacturing and industrial areas: 100%*.
b.
For business and commercial areas: 100%*.
c.
For residential areas, including all areas for roofs of dwellings
and garages for driveways, streets and paved areas; for public and
private sidewalks; with adequate allowance in area for expected or
contingent increases in imperviousness:
In apartment, condominium and multiple-dwelling areas: 75%*.
In single-family areas:
¼ acre or less: 50%.
¼ acre to ½ acre: 40%.
½ acre to 1 acre: 35%.
1 acre or larger: 30%.
Playgrounds (non-paved): 20 — 35%*.
d.
For small, non-perpetual charter cemeteries: 30%.
For parks and large perpetual charter cemeteries: 5%.
*Note. Drainage areas may be broken into component
areas with the appropriate runoff factor applied to each component,
i.e., a proposed development may show one hundred percent (100%) impervious
for paved areas and five percent (5%) impervious for grassed areas.
The design engineer shall provide adequate detailed computations
for any proposed, expected or contingent increases in imperviousness
and shall make adequate allowances for changes in use. If consideration
is to be given to any other value than the above for such development,
the request must be made at the beginning of the project, must be
reasonable, fully supported and adequately presented and must be approved
in writing before its use is permitted.
Although areas generally will be developed in accordance with
current requirements, recognition must be given to the fact that ordinances
can be amended to change the currently proposed types of development
and any existing use. Under these circumstances the possibility and
the probability of residential areas having lot sizes changed or reclassified
to business, commercial or light manufacturing uses should be given
careful consideration.
e.
Average 20-minute values of P.I. (cfs per acre) to be used are as
follows:
|
Percent Imperviousness
|
20 Minute Duration
| ||
|---|---|---|---|
|
15 Year
|
20 Year
| ||
|
5
|
1.7
|
1.8
| |
|
10
|
1.8
|
1.9
| |
|
20
|
2.0
|
2.1
| |
|
30
|
2.2
|
2.3
| |
|
40
|
2.4
|
2.5
| |
|
50
|
2.6
|
2.7
| |
|
90
|
3.4
|
3.5
| |
|
100
|
3.5
|
3.7
| |
|
*Roofs
|
4.2
|
6.0
| |
|
*For direct connection to sewer
| |||
3.
Reduction in P.I. with time and area. Reduction
in P.I. values for the total time of concentration exceeding twenty
(20) minutes and for tributary areas exceeding three hundred (300)
acres will be allowed only in trunk sewers and main channels. The
reduced average P.I. value for the tributary area shall not be less
than the value determined as follows on the basis of:
a.
Time. As the time of concentration increases beyond twenty (20) minutes, select the appropriate P.I. value from Table 4-1 following this Section 400.220. The travel time through a drainage channel should be based on an improved concrete section. These reduced values shall be used unless a further reduction is allowed for the area.
b.
Area. As the total tributary area at any given location
in a channel increases in excess of three hundred (300) acres, the
P.I. value may be further reduced by multiplying it by an area coefficient
"Ka". (The area coefficient is obtained from data in a special study
of a major storm in the St. Louis area by the U.S. Corps of Engineers.)
The average rainfall rate, for a given storm, for a given period for
the tributary area, is less than the corresponding point value as
determined from recording rainfall gauges. The curve date is as follows:
|
Area (Abscissas)
|
"Ka" (Ordinates)
| |
|---|---|---|
|
300 to 449 acres
|
1.00
| |
|
450 to 549 acres
|
.99
| |
|
550 to 749 acres
|
.98
| |
|
750 to 999 acres
|
.97
| |
|
1,000 to 1,280 acres
|
.96
| |
|
1,281 to 1,600 acres
|
.95
| |
|
1,601 to 1,920 acres
|
.92
| |
|
1,921 to 2,240 acres
|
.91
|
L.
Hydraulic Grade Line For Closed Conduits.
1.
Computation methods. The hydraulic grade line is
a line coinciding with (a) the level of flowing water at any given
point along an open channel, or (b) the level to which water would
rise in a vertical tube connected to any point along a pipe or closed
conduit flowing under pressure.
The hydraulic grade line shall be computed to show its elevation
at all structures and junction points of flow in pipes, conduits and
open channels and shall provide for the losses and the differences
in elevations as required below. Since it is based on design flow
in a given size of pipe or conduit or channel, it is of importance
in determining minimum sizes of pipes within narrow limits. Sizes
larger than the required minimum generally provide extra capacity,
however, consideration still must be given to the respective pipe
system losses.
It is expected that the design will recognize the reality of
such "losses" occurring and make such allowances as good engineering
judgment requires.
a.
Friction loss. The hydraulic grade line is affected
by friction loss and by velocity head transformations and losses.
Friction loss is the head required to maintain the necessary flow
in a straight alignment against frictional resistance because of pipe
or channel roughness. It is determined by the equation:
|
|
hf = L x Sh
| |
|
|
Where:
| |
|
|
hf = difference in water surface elevation or head in feet in
length L
| |
|
|
L = length in feet of pipe or channel
| |
|
|
Sh = hydraulic slope required for a pipe
of given diameter or channel of given cross section and for a given
roughness "n", expressed as feet of slope per foot of length
| |
|
|
From Manning's formula: Sh = [V n / (1.486
R 0.667)] 2
| |
|
|
Where:
| |
|
|
R = hydraulic radius of pipe, conduit or channel (feet) (ratio
of flow area/wetted perimeter)
| |
|
|
V = velocity of flow in feet per second (fps)
| |
|
|
n = Manning's value for coefficient of roughness
| |
|
|
Use:
| |
|
|
n = .013 for pipes of concrete, vitrified clay and PVC pipe
| |
|
|
n = .012 for formed monolithic concrete, i.e., vertical wall
channels, box culverts and for R.C.P. over forty-eight (48) inches
in diameter
| |
|
|
n = .015 for concrete lining in ditch or channel inverts and
trapezoidal channels
| |
|
|
n = .020 for grouted riprap lining on ditch or channel side
slopes
| |
|
|
n = .033 for gabion walled channels
| |
b.
Curve loss. Curve loss in pipe flow is the additional
head required to maintain the required flow because of curved alignment
and is in addition to the friction loss of an equal length of straight
alignment. It should be determined from Figure 4-2 which includes
an example.
2.
Entrance loss at terminal inlets. Entrance loss
is the additional head required to maintain the required flow because
of resistance at the entrance. The entrance loss at a terminal inlet
is calculated by the formula:
|
|
Hti = (V2/2g)
| |
|
|
Where:
| |
|
|
V = Velocity in flow of outgoing pipe
| |
|
|
g = Acceleration of gravity (32.2 ft/sec/sec)
| |
3.
Turn loss. Head losses in structures due to change
in direction of flow (turns) in a structure will be determined in
accordance with the following:
|
Change in Direction of Flow (A)
|
Multiplier of Velocity Head of Water Being Turned (K)
| |
|---|---|---|
|
90 degrees
|
0.7
| |
|
60 degrees
|
0.55
| |
|
45 degrees
|
0.47
| |
|
30 degrees
|
0.35
| |
|
15 degrees
|
0.18
| |
|
0 degrees
|
0.0
| |
|
Other angles
|
By interpolation
|
 |
|
Formula:
| ||
|
|
HL = K(VL)2/2g
| |
|
Where:
| ||
|
|
HL = Feet of head lost in manhole due
to change in direction of lateral flow
| |
|
|
VL = Velocity of flow in lateral in ft/sec
| |
|
|
g = Acceleration of gravity (32.2 ft/sec/sec)
| |
|
|
K = Multiplier of velocity head of water being turned
| |
4.
Junction chamber loss. A sewer junction occurs for
large pipes or conduits too large to be brought together in the usual
forty-two (42) inch diameter manhole or inlet where one (1) or more
branch sewers enter a main sewer. Allowances should be made for head
loss due to curvature of the paths and due to impact at the converging
streams.
|
|
Losses in a junction chamber for combining large flows shall
be minimized by setting flowline elevations so that pipe centerlines
(spring-lines) will be approximately in the same planes.
| |
|
|
At junction points for combining large storm flows, a manhole
with a slotted cover shall be provided.
| |
|
|
A computation method for determining junction chamber losses
is presented below:
| |
|
|
Hj = Δy + Vh1 Vh2
| |
|
|
Where:
| |
|
|
Hj = junction chamber loss (ft)
| |
|
|
Δy = change in hydraulic grade line through the junction
in feet
| |
|
|
Vhl = upstream velocity head
| |
|
|
Vh2 = downstream velocity head
| |
|
|
Where:
| |
|
|
Δy = [(Q2V2) - ((Q1V1) + {(Q3V3Cos e-3) + QnVnCos e-n)})]
| |
|
|
0.5 (A1+A2) g
| |
|
|
Where:
| |
|
|
Q2 = Discharge in cubic feet per second
(cfs) at the exiting conduit
| |
|
|
V2 = Velocity in feet per second (fps)
at the exiting conduit
| |
|
|
A2 = Cross-sectional area of flow in
square feet for the exiting conduit
| |
|
|
Q1 = Discharge in cfs for the incoming
pipe (main flow)
| |
|
|
V1 = Velocity in fps for the incoming
pipe (main flow)
| |
|
|
A1 = Cross sectional area of flow in
square feet for the incoming pipe (main flow)
| |
|
|
Q3, Qn = Discharge(s)
in cfs for the branch lateral(s)
| |
|
|
V3, Vn = Velocity(ies)
in fps for the branch lateral(s)
| |
|
|
Ө3, Өn = The angle between the axes of the exiting pipe and the branch
lateral(s)
| |
|
|
g = Acceleration of gravity (32.2 ft/sec/sec)
| |
|
|
Where:
| |
|
|
Ө = is the angle between the axes of the outfall and the
incoming laterals
| |
5.
Losses at junctions of several flows in manholes and/or inlets. The computation of losses in a manhole, inlet or inlet manhole with
several flows entering the structure should utilize the principle
of the conservation of energy. This involves both the elevation of
water surface and momentum (mass times the velocity head). Thus, at
a structure (manhole, inlet or inlet manhole) with laterals, the sum
of the energy content for inflows is equal to the sum of the energy
content of the outflows plus the additional energy required by the
turbulence of the flows passing through the structure.
 |
|
|
The upstream hydraulic grade line may be calculated as follows:
| |
|
|
Hu = [VD2/2g] - [((Qu/QD)(1-K)(Vu2/2g))
+ ((QL1/QD)(1-K)(VL12/2g)) + ((QLN/QD)(1-K)(VLN2/2g))] + HD
| |
|
|
Where:
| |
|
|
Hu = Upstream hydraulic grade line in
feet
| |
|
|
Qu = Upstream main line discharge in
cubic feet per second
| |
|
|
QD = Downstream main line discharge in
cubic feet per second
| |
|
|
QLI-QN = Lateral
discharges in cubic feet per second
| |
|
|
Vu = Upstream main line velocity in feet
per second
| |
|
|
VD = Downstream main line velocity in
feet per second
| |
|
|
VLI-VLN = Lateral
velocities in feet per second
| |
|
|
HD = Downstream hydraulic grade line
in feet
| |
|
|
K = Multiplier of velocity of water being turned
| |
|
|
G = Acceleration of gravity, 32.2 ft/sec/sec
| |
|
|
The above equation does not apply when two (2) almost equal
and opposing flows, each perpendicular to the downstream pipe, meet
and no other flows exist in the structure. In this case the head loss
is considered as the total velocity head of the downstream discharge.
| |
6.
Transition loss. The relative importance of the
transition loss is dependent on the velocity head of the flow. If
the velocity and velocity head of the flow are quite low, the transition
losses cannot be very great. However, even small losses may be significant
in flat terrain. The sewer design shall provide for the consideration
of the necessary transitions and resulting energy losses. The possibility
of objectionable deposits is to be considered in the design of transitions.
For design purposes it shall be assumed that the energy loss
and changes in depth, velocity and invert elevation, if any, occur
at the center of the transition. These changes shall be distributed
throughout the length of the transition in actual detailing. The designer
shall carry the energy head, piezometric head (depth in an open channel)
and invert as elevations and work from the energy grade line. Because
of inherent differences in the flow, transitions for closed conduits
will be considered separately from those for open channels.
a.
Closed conduits. Transitions in small sewers may
be confined within a manhole. Special structures may be required for
larger sewers. If a sewer is flowing surcharged, the form and friction
losses are independent of the invert slope; therefore, the transition
may vary at the slopes of the adjacent conduits. The energy loss in
a transition shall be expressed as a coefficient multiplied by the
change in velocity head (ΔV2/2g)
in which ΔV is the change in velocity before and after the transition.
The coefficient may vary from zero (0) to one (1), depending on the
design of the transition.
If the areas before and after a transition are known, it is
often convenient to express the transition loss in terms of the area
ratios and either the velocity upstream or downstream.
For an expansion:
HL = K(V1-V2)2/2g ≈ [K(Vi)2/2g][1-A1/A2)]2
in which HL is the energy loss; K is
a coefficient equal to 1.0 for a sudden expansion and approximately
0.2 for a well-designed transition and the subscripts 1 and 2 denote
the upstream and downstream sections, respectively, i.e., A1 = area before transition and A2 = area after transition.
HL = [K(V2)2/2g][(1/Cc)-1]2 ≈ [K(V2)2/2g][1-A2/A1)]2
in which K is a coefficient equal to 0.5 for a well designed
transition, Cc is a coefficient of contraction
and the other terms and subscripts are similar to the previous equation.
Losses in closed conduits of constant area are expressed in terms
of (V2/2g).
The above equations may be applies to approximate the energy
loss through a manhole for a circular pipe flowing full. If the invert
is fully developed, that is, semi-circular on the bottom and vertical
on the sides from one-half (½) depth up to the top of the pipe,
for the expansion (A1/A2) = 0.88 and for the contraction (A2/A1) = 0.88 the expansion is sudden; therefore, K = 1.
The contraction may be rounded if the downstream pipe has a bell or
socket. In this case, K may be assumed to be 0.2.
The expansion energy loss is 0.014 [K(V1)2/2g] and the contraction energy loss
is 0.010 [K(V2)2/2g]. If the invert is fully developed, the manhole loss is small,
but if the invert is only developed for one-half (½) of the
depth or not all, the losses will be of considerable magnitude.
b.
Open channel transitions. The hydraulics of open
channel transitions are further complicated by possible changes in
depth. As a first (1st) approximation to the energy loss, unless a
jump occurs, the equations given above may be used with a trial and
error solution for the unknown area and velocity. The K value for
a well-designed expansion should probably be increased to 0.3 or 0.4.
Whether the properties of the upstream and downstream section will
be known will depend on the characteristics of the flow and the channel,
but can be determined by a profile analysis. In transitions for super
critical flow, additional factors shall be considered. Standing waves
of considerable magnitude will be estimated to provide a proper channel
depth. In addition, in long transitions, air entrainment will cause
bulking of the flow with resultant greater depths of the air-water
mixture.
7.
Hydraulic grade line limits. The hydraulic grade
line shall not rise above the following limits as determined by flow
quantities calculated per the storm water design criteria previously
described.
a.
The hydraulic grade line at any inlet or storm manhole shall not
be higher than two (2) feet below the inlet sill or top of manhole.
b.
Storm sewers shall not flow with greater than three (3) feet of head.
c.
The hydraulic grade line for combined sewers shall not rise above
the pipe intrados.
8.
Inlets. Inlets function entirely as entry points
for storm water flow. They also may be constructed to serve as a manhole
on separate storm water sewers and are then termed inlet manholes.
Steep gradients may give such low inlet capacities that additional
inlets should be located at more favorable grade locations or special
inlets designed for steep gradients must be used. Provision must be
made to control by-pass flow and to provide additional capacity in
the inlet and line affected by such increased flow. Six (6) inch,
open-throat inlets should be used at all times.
Grated inlets, without an open throat or other provision for
overflow shall be avoided except under exceptional conditions and
are prohibited in grade pockets. Any exceptions shall be used only
with City approval.
Curb inlets shall be placed in street intersections or driveways
such that no part of the inlet structure or sump is within the curb
rounding.
a.
Inlets are shown in the Standard Details of Sewer Construction. The
minimum depth of a terminal inlet is four (4) feet from the top of
the flowline of the outlet pipe. Greater depth shall be used for intermediate
inlets if necessary for the required depth of the hydraulic grade
line. Trapped inlets shall have the depth shown in the Standard Details
of Sewer Construction.
b.
Inlet capacity should not be less than the quantity flow tributary
to the inlet and by-pass flow shall be avoided whenever possible.
Inlets at low points or grade pockets should have extra capacity
to compensate for possible flow by-pass of upstream inlets.
Figure 4-3 shows inlet capacity/maximum gutter capacity with
a given gutter line grade and flow.
c.
Connections to existing structures may require rehabilitation or
reconstruction of the structure being utilized. This work will be
considered part of the project being proposed.
9.
Open channels.
*Note: This Section contains sole excerpts relating to design
and are attributed to "Open Channel Hydraulics" by Ven Te Chow, a
McGraw-Hill work published in 1959.
All open channels shall meet the following requirements:
a.
Size and shape. Open channels shall not decrease
in size in the direction of flow. Open channels shall be vertical
walled except in special cases where other approved materials are
being considered.
b.
Materials. Channels may be constructed with reinforced
concrete or other approved material. However, the City shall have
the right to approve or disapprove any channel material and shall
select the appropriate channel material if a proposed material is
rejected. Swales shall be sodded unless velocities are excessive (greater
than five (5) fps or where velocities are less than two (2) fps causing
deposition of soil particles, then concrete swales may be used).
c.
Bedding. Special provisions shall be made for channels
or paved swales laid over fill on non-supportive soils to support
the channel on paved swales. Pipes extended to the channel in a fill
area shall have compacted crushed limestone bedding for support.
d.
Structural considerations. Provision must be made
for all loads on the channels.
e.
Alignment. Open channel alignments may be limited
by available easements, physical topography, existing utilities, buildings,
residential development, maintenance access and roadways.
f.
Locations. Storm channel locations are determined
primarily by natural drainage conditions. It is also necessary to
consider accessibility for construction and maintenance, site availability
and competing uses and evaluation effects of easements on private
property.
Storm channels shall be located:
(1)
To serve all adjacent property conveniently and to best advantage.
(2)
In easements or rights-of-way dedicated to the City.
(3)
In easements on common ground when feasible.
(4)
On private property along property lines or immediately adjacent
to public streets, avoiding crossings through the property.
(5)
At a sufficient distance from existing and proposed buildings
(including footings) and underground utilities or sewers to avoid
future problems of flooding or erosion.
(6)
To avoid interference between storm water sewers and house connections
to foul-water or sanitary sewers.
(7)
In unpaved or unimproved areas whenever possible.
(8)
Crossing perpendicular to streets, unless unavoidable.
g.
Flowline. The flowline of open channels shall meet
the following requirements:
(1)
Gradient changes shall be kept to a minimum and be consistent
and regular.
(2)
Gradient designations less than the nearest one-thousandth (0.001)
foot per foot shall be avoided.
(3)
Channel and swale depths shall be determined primarily by the
requirements of the channel size, utility obstructions and any required
connections.
h.
Other open channel considerations and requirements.
(1)
All natural channels and ditches shall be improved unless otherwise
authorized by the district.
(2)
Drainage within private property should be controlled to prevent
damage to the property crossed. Swales or broad shallow grass-lined
ditches with non-erosive slopes are generally located at or near rear
lots and along common property lines. If a paved gutter is utilized,
then appropriate erosion protection shall be used at both ends.
(3)
Drainage channels and watercourses draining through a subdivision
shall be enclosed if the required pipe size does not exceed sixty
(60) inches. When it is undesirable or impractical to enclose a channel
with a pipe across a road or street, a suitable bridge or culvert
shall be required.
(4)
For flows greater than four (4) cfs, area inlets or inlet manholes
are required to intercept the gutter or swale flow.
(5)
All improved concrete channels shall have a forty-eight (48)
inch chain link fence on each side of the channel or other protective
measurers as directed by the City.
(6)
Channels and watercourses draining large areas shall be located
in rights-of-way or easements previously approved by the City as a
part of an adequate overall plan for drainage.
i.
Design limitations.
(1)
The flow quantity shall be calculated by the method presented
in this Chapter of this Title.
(2)
If the channel is within an area designated in a community's
Flood Insurance Study, then the channel shall also meet all City floodplain
requirements.
(3)
Other agencies of jurisdiction may have requirements which must
be met. A U.S. Army Corps of Engineers permit may be required for
any construction affecting a watercourse.
j.
Hydraulic grade line.
(1)
Computation methods. In open channels, the
water surface is identical with the hydraulic grade line. The hydraulic
grade line shall be computed throughout the channel reach to show
its elevation at junctions with incoming pipes or channels and at
the ends of the channel reach under consideration. It shall also provide
for the losses and differences in elevations as required below. Since
it is based on design flow in a given channel, it is of importance
in determining minimum sizes within narrow limits. The depth at which
the actual flows will occur is controlled by the two (2) end conditions
of the reach considered and by the relationship between the energy
available and by the energy required to overcome the losses that are
encountered along the channel.
There are several methods of calculating "losses" in channel
design. The following procedures are presented for the engineers'
information and consideration.
It is required that the designs recognized the reality of such
"losses" occurring and make such allowances as good engineering judgment
indicates.
(a)
Control sections. The engineer should locate
all possible control sections for the reach in question. A control
section refers to any section at which the depth of flow is known
or can be controlled to a required stage. At the control section,
flow must pass through a control depth which may be the critical depth,
the normal depth or any other known depth. Three (3) types of control
sections include:
(b)
Friction loss. The friction loss may be calculated
by the same procedure as is presented in this Section of this Chapter.
(2)
Flow in curved channels. The centrifugal force
caused by flow around a curve produces a rise in the water surface
on the outside wall and a lowering of the inner wall. This phenomenon
is called super elevation. The flows tend to behave differently according
to the state of flow.
In subcritical flow, friction effects are of importance, whereby
in super critical flow, the formation of cross waves is of major concern.
(a)
Curve losses. Curve losses may be estimated
from Figure 4-2 by replacing (D), diameter, with (b), width of channel.
(b)
Super elevations. In addition to curve losses,
an evaluation of super elevations should be considered and, if required,
allowance made in the tip elevation of the outside wall. Equations
are presented below which may be used to determine the super elevation
at channel bends.
(3)
Trapezoidal channels.
|
Sub-critical Flow:
| ||
|
ΔHW = 1.15 (V2/2grc) [b + D (ZL + ZR)]
| ||
|
Super-critical flow:
| ||
|
ΔHW = 2.6 (V2/2grc) [b + D (ZL + ZR)]
| ||
(4)
Rectangular channels.
|
|
Sub-critical flow:
|
|
|
ΔHW = (V2b/2grc)
|
|
|
Super-critical flow:
|
|
|
ΔHw = (V2b/grc)
|
|
|
Where:
|
|
|
ΔHw = Change in water height above
the centerline water surface
|
|
|
V = Average velocity of design flow in Fps
|
|
|
g = Acceleration of gravity (32.2 ft/sec/sec)
|
|
|
rc = Radius of curve on horizontal alignment
in feet
|
|
|
b = Base width of channel in feet
|
|
|
D = Depth of flow in straight channel
|
|
|
ZL = Left side slope (ft/ft)
|
|
|
ZR = Right side slope (ft/ft)
|
(5)
Transition. Transitions should be designed
to accomplish the required change in cross section with as little
flow disturbance as possible.
The following features are to be considered in design of transition
structures.
(a)
Proportioning. For a well designed transition,
the following rules should be used:
(6)
Losses. The energy loss in a transition consists
of the friction loss and the conversion loss. The friction loss may
be estimated by the Manning Formula. The conversion loss is generally
expressed in terms of the change in velocity head between the entrance
and exit sections of the structure.
|
|
Ht = Kt ΔHH
| |
|
|
Where:
| |
|
|
Ht = Conversion loss
| |
|
|
Kt = Coefficient of head loss in transition
| |
|
|
ΔHH = Absolute change in velocity
head
| |
|
|
Average design values for Kt are presented
in the table below:
|
|
Type of Transition
|
Contracting Section
|
Expanding Section
| |
|---|---|---|---|
|
Warped
|
0.10
|
0.20
| |
|
Wedge
|
0.20
|
0.50
| |
|
Cylinder-quadrant
|
0.15
|
0.25
| |
|
Straight line
|
0.30
|
0.50
| |
|
Square end
|
0.40
|
0.75
|
|
See Figure 4-4 for sketches of each type of transition.
|
(a)
Freeboard. A transition shall have a minimum
of one (1) foot of freeboard above the hydraulic grade line.
(b)
Hydraulic jump. The existence of a hydraulic
jump in a transition may become objectionable and the design of the
transition should be check for such.
(c)
Sudden enlargement and contraction. A sudden
enlargement results when an intense shearing action occurs between
incoming high-velocity jet and the surrounding water. As a result,
much of the kinetic energy of the jet is dissipated by eddy action.
The head loss at a sudden enlargement, HLe is:
|
HLe = Ke (V2/2g)
| ||
|
Where:
| ||
|
Ke = Coefficient of head loss for enlargements
= 1
| ||
|
V = Change in velocities between incoming and outgoing sections
| ||
|
g = Acceleration of gravity (32.2 ft/sec/sec)
| ||
|
The flow in a sudden contraction is first contracted and then
expanded resulting in high losses as compared to a sudden enlargement.
Thus the head loss at a sudden contraction, HLc is:
| ||
|
HLc = Kc(ΔV2/2g)
| ||
|
Where:
| ||
|
Kc = Coefficient of head loss for contractions
= 0.5
| ||
|
V = Change in velocities between incoming and outgoing sections
| ||
|
g = Acceleration of gravity, ft/sec/sec
| ||
(7)
Constrictions. A constriction results in a
sudden reduction in channel cross section. The effect of the constriction
on the flow depends mainly on the boundary geometry, the discharge
and the state of flow. When the flow is subcritical, the constriction
will induce a backwater effect that extends a long distance upstream.
If the flow is super critical, the disturbance is usually local and
will only affect the water adjacent to the upstream side of the constriction.
A control section may or may not exist at a constriction. The control
section, when it exists, may be at either side of the constriction
(upstream or downstream), depending on whether the slope of the constricted
channel is steep or mild. The entrance and outlet of the constriction
then acts as a contraction and an expansion, respectfully.
(8)
Obstructions. An obstruction in open-channel
flow creates at least two (2) paths of flow in the channel. Typical
obstructions include bridge piers, pile trestles and trash racks.
The flow through an obstruction may be subcritical or super critical.
k.
Hydraulic jump. When flow changes from the super
critical to subcritical state, a hydraulic jump may occur. A study
should be made on the height and location of the jump and for discharges
less than the design discharge to ensure adequate wall heights extend
over the full ranges of discharge.
l.
Open channel junctions.
(1)
General. Consideration shall be given in the
design of open-channel junctions to the geometry of the confluence
of flows in order to minimize undesirable hydraulic effects due to
super critical velocities.
(2)
Confluence design criteria.
(a)
The momentum equation can be applied to the confluence design
if the below stated criteria is used.
(b)
The design water surface elevations in the two (2) joining channels
should be approximately equal at the upstream end of the confluence.
(c)
The angle of the junction intersection can vary from zero degrees
(0°) through twelve degrees (12°).
(d)
The width of the main channel shall be expanded below the junction
to maintain approximate flow depths throughout the junction.
(e)
Flow depths should not exceed ninety percent (90%) of the critical
depth.
m.
Erosion protection. Grouted rock blankets, minimum
one (1) foot thick, shall be required at each end of the improved
channel. The minimum length of the grouted rock blanket shall be twenty-five
(25) feet. A grouted rock toe wall, minimum two (2) feet deep, shall
be constructed at the free end of each blanket.
n.
Sanitary sewer crossings. The characteristics of
any sanitary sewer crossing shall be given consideration in the design
of the channel floor.
M.
Culverts. The design of culverts shall include consideration
of many factors relating to requirements of hydrology, hydraulics,
physical environment, imposed exterior loads, construction and maintenance.
With the design discharge and general layout requirements determined,
the design requires detailed consideration of such hydraulic factors
as shape and slope of approach and exit channels, allowable head at
entrance (and ponding capacity, if appreciable), tail-water levels,
hydraulic and energy grade lines and erosion potential.
1.
Hydraulic design. The hydraulic design of a culvert
for a specified design discharge involves:
a.
Selection of a type and size;
b.
Determination of the position of hydraulic control; and
c.
Hydraulic computations to determine whether acceptable headwater
depths and outfall conditions will result. Hydraulic computations
will be carried out by standard methods based on pressure, energy,
momentum and loss considerations.
(1)
Entrances and headwalls — outlets and end-walls. Where an existing culvert is to be extended, the possibility for
maintaining or improving existing capacity should be investigated.
Marked improvement may be obtained by proper entrance design. All
culverts shall be designed for possible extension unless there are
extenuating circumstances.
N.
Bridges. Bridges shall be designed to meet the current criteria
of the governing agencies.
1.
Waterway capacity and backwater effects. Sufficient
capacity will be provided to pass the runoff from the design storm
determined in accordance with principles given elsewhere in this manual.
2.
Clearance. The lowest point of the bridge superstructure
shall have a (freeboard) clearance of two (2) feet above design water
surface elevation for the 15-year frequency and one (1) foot for the
100-year frequency.
3.
Waterway alignment. The bridge waterway will be
aligned to result in the least obstruction to stream flow, except
that for natural streams, consideration will be given to future realignment
and improvement of the channel.
4.
Erosion protection. To preclude failure by scouring,
abutment and pier footings usually will be placed either to a depth
of not less than five (5) feet below the anticipated depth of scour
or on firm rock if such is encountered at a higher elevation. Large
multi-span structures crossing alluvial streams may require extensive
pile foundations. To protect the channel, revetment on channel sides
and/or bottom consisting of concrete or grouted rock blanket should
be placed as required. Other governing authorities should be contacted
regarding their design requirements.
O.
Outlet Erosion Protection. If outlet velocities exceed five
(5) fps, an appropriate erosion protection must be provided. Erosion
protection may be required at outlets where velocities are less than
five (5) fps if soil conditions warrant.
For paved channels, a cutoff wall will be required at the termini
with appropriate protection. The cutoff wall shall extend a minimum
depth of two (2) feet into the existing ground line.
P.
Limitations On Areas Draining Across Sidewalks Or Driveways. Area inlets shall be required to intercept overland flows greater
than one (1) cfs to prevent that flow from crossing sidewalks or curbs.
Q.
Storm Water Detention. When required:
1.
The requirement of storm water detention shall be required for all
projects submitted to the City for review and approval. Detention
facilities shall be provided and designed in accordance with the requirements
of this Section.
3.
When existing detention facilities are going to be used to accommodate
additional runoff from building or parking lot expansions or subdivision
additions, the facilities shall be retrofitted to meet the current
detention requirements for the drainage area which is tributary to
the facility. Projects which cannot meet this requirement due to physical
constraints will be evaluated on a case-by-case basis.
R.
Design Considerations.
1.
The 2-year and 100-year, twenty-four (24) hour inflow hydrographs
shall be determined by using Technical Release 55 (TR-55), "Urban
Hydrology for Small Watersheds" from the Natural Resources Conservation
Service, formerly "Small Watersheds" from the Natural Resources Conservation
Service, formerly Soil Conservation Service (SCS). The inflow hydrograph
shall be developed based on the actual flow and timing characteristics
upstream of the detention facility. The rainfall distribution shall
be Type II.
2.
Storm water shall be detained on site or off site as approved and
released at a rate not to exceed the allowable release rates for the
2-year and 100-year, 24-hour events, as determined by the City for
the watershed in question. The allowable release rates are 0.4 CFS/AC
(2-year) and one and eight-tenths (1.8) CFS/AC (100-year). Note that
storm water pipes, downstream from the control structure, shall be
sized to carry the runoff from the 15-year, 20-minute design storm
for the total tributary upstream watershed. No reduction in outfall
pipe size shall be permitted because of detention.
3.
The volume of detention may be provided through permanent detention
facilities such as dry basins or ponds, permanent ponds of lakes,
underground storage facilities or in parking lots. The engineer shall
make every effort to locate the detention facility at or near the
lowest point of the project such that all of the on-site runoff will
be directed into the detention facility.
Flows from off-site upstream areas should be by-passed around
the detention facility to ensure that the proposed detention facility
will function as designed and will provide effective control of downstream
flows with development in place. If off-site flows are directed into
a detention facility, the allowable release rates shall not be modified
without City approval. Modifying the release rate to accommodate off-site
flows may reduce or eliminate the effectiveness of the detention facility,
because it will no longer control the increased volume of runoff during
the critical time period of the watershed.
4.
Detention basin volume will be based on routing the post development
2-year and 100-year, 24-hour inflow hydrographs through the detention
facility while satisfying the appropriate allowable release rate.
The routing computations shall be based on an application of the continuity
principle (i.e., level pool routing).
5.
Design of underground basins.
a.
Adequate access for basin maintenance and inspection shall be provided.
A means of visual inspection from the ground surface of the low flow
device, overflow weir and outlet structure is necessary. Access also
shall be provided to allow for cleaning of the low flow device from
the ground surface.
b.
The basin should have sufficient volume and spillway capacity to
pass/contain the 100-year, 24-hour event with the low flow outlet
blocked.
6.
The engineer must submit the following for review of a detention
facility:
a.
Elevation vs. discharge tables or curves for all frequencies.
b.
Elevation vs. storage tables or curves for all frequencies.
c.
Inflow calculations and data for all frequencies.
d.
Hydraulic grade line computations for pipes entering and leaving
the basin for all frequencies.
e.
If the embankment contains fill material, a geotechnical report may
be required.
f.
Site plan showing appropriate design information.
g.
Structural calculations for the outlet control structures (if required).
h.
Cross sections defining the size, shape and depth of the detention
basin shall be required. At a minimum, three (3) sections, one (1)
at each end and one (1) in the middle of the basin will be required.
These sections will be used to compute the as-built volume of
the basin and thus must be tied to a known physical structure or baseline.
7.
All ends of pipes discharging into a dry basin or pond shall be connected
with the low-flow pipe or control structure by means of a paved swale.
The paved swale shall be non-reinforced concrete, six (6) inches thick,
with a minimum two percent (2%) slope to the center and a minimum
two-tenths percent (0.2%) longitudinal slope. Paved swales shall be
a minimum of six (6) inches deep and four (4) feet wide or 1.3 times
the diameter of the pipe entering the basin, whichever is greater,
and be keyed to structure or channel. The bottom of the basin shall
be sloped a minimum of two percent (2%) towards the concrete swale.
8.
Railroad tie walls cannot be used where water will be in contact
with the railroad tie wall.
9.
Permanent detention ponds or lakes are to be designed to minimize
fluctuating lake levels. Maximum fluctuation from the permanent pool
elevation to the maximum ponding elevation shall be three (3) feet.
10.
The maximum side slopes for dry basins or ponds and the fluctuating
area of permanent ponds or lakes shall be 3:1 (three (3) feet horizontal,
one (1) foot vertical) without fencing.
11.
Dry basins or ponds and the fluctuating areas of permanent ponds
or lakes are to be sodded and kept mowed.
12.
Control structures and overflow structures are to be reinforced concrete.
13.
The outflow pipe shall be sized for the developed flow rate.
14.
In basins with concrete walls or rock blanket covered slopes, the
bottoms should be paved or provisions made for moving equipment to
reach the bottom (ramps, etc.).
S.
Maximum Depths.
1.
The maximum depth of water in a dry detention basin or pond shall
not exceed eight (8) feet. Projects which need a deeper basin to attain
the required detention volume due to physical constraints may be evaluated
on a case-by-case basis. The design and construction of dams greater
than eight (8) feet or as directed by the City must be sealed and
certified by a professional engineer registered in the State of Missouri
with demonstrated expertise in geotechnical engineering.
2.
Parking lots used for automobiles shall have a maximum depth of eight
(8) inches of water.
3.
Parking lots used for trucks or truck trailers shall have a maximum
depth of water of twelve (12) inches.
T.
Limits Of Maximum Ponding.
1.
The maximum ponding elevation shall be calculated based on a routing
of the design storm (100-year, twenty-four (24) hour event) assuming
the low flow outlet is blocked with water ponded to the overflow structure's
sill.
2.
The limits of maximum ponding in dry basins or ponds and permanent
lakes or ponds shall not be closer than thirty (30) feet horizontally
to any building and not less than two (2) feet vertically below the
lowest sill elevation of any building.
3.
The limits of maximum ponding in parking lots shall not be closer
than ten (10) feet horizontally from any building and not less than
one (1) foot vertically below the lowest sill elevation of any building.
4.
A minimum of one (1) foot of freeboard shall be provided from the
top of the basin to the maximum ponding elevation.
U.
Easement Required. In subdivisions, the detention basin,
access roads or paths, control structures and outfall pipes are to
be located in easements dedicated to the subdivision trustees.
V.
Detention Basin Fencing. A four (4) foot (minimum height)
approved fence shall be provided around the perimeter of any basin
where the side slopes exceed 3:1 (three (3) feet horizontal, one (1)
foot vertical).
W.
Detention Basin Elevation. The low elevation of the detention
basin shall be above the 15-year, 20-minute hydraulic elevation of
the receiving channel or pipe system and shall be above the 100-year
floodplain elevation.
X.
Dam Permit Requirements. Dam with a height of thirty-five
(35) feet or greater will require approval from the Missouri Department
of Natural Resources.
[Ord. No. 433 §5.11, 5-18-2005]
A.
All
buildings, structures and use of land in the incorporated area of
the City of Truesdale, Missouri, shall hereafter be required to have
an adequate, safe and sanitary disposal system for all human waste.
Disposal of sewage or other liquidated wastes shall conform to the
methods outlined herein:
1.
Where a public sanitary sewer main is reasonably accessible, in the
opinion of the Board of Aldermen, the subdivision shall be provided
with a complete sanitary sewer system connected with such sewer main,
including a lateral connection for each lot. Such systems and connections
shall comply with the regulations of the Missouri State Board of Health,
Missouri Department of Natural Resources, City of Truesdale, Missouri,
and appropriate sewer district.
2.
It shall be the responsibility of the developer/applicant to comply
with all requirements of the City of Truesdale, Missouri, and appropriate
sewer district. Verification of the service shall be provided at the
time of submission of the preliminary plat.
3.
Where no sewers are accessible and no plans for a sewer have been
prepared and approved, the developer shall either install a sewage
collection and disposal system in accordance with the requirements
of the preceding paragraph or individual disposal devices may be installed
on each lot within the subdivision; provided that no individual disposal
device should be permitted unless the lots to be served have sufficient
area to allow adequate soil absorption for on-site sewage disposal.
The Board of Aldermen may modify lot area requirements in relations
to soil conditions and other pertinent facts and findings in any particular
subdivision. All such individual devices and systems shall be constructed
and maintained in accordance with the regulations and requirements
of the Missouri Department of Natural Resources. In no case shall
there exist on lots of less than three (3) acres in area individual
sanitary sewage disposal systems.
[Ord. No. 433 §5.12, 5-18-2005]
Where a public water supply main is reasonably accessible, in
the judgment of the Board of Aldermen, the subdivision shall be provided
with a complete water distribution system adequate to serve the area
being platted, including a connection for each lot and appropriately
spaced fire hydrants. In no case shall there exist on lots of less
than three (3) acres in area individual water systems unless a public
water system is not reasonably accessible in the judgment of the Board
of Aldermen. The waste system shall be designed by an engineer and
approved by the City of Truesdale, Missouri, and the appropriate water
company serving the area of the proposed development.
[Ord. No. 433 §5.13, 5-18-2005]
A.
Prior
to starting any of the work covered by the above plans, after approval
thereof, the developer shall make arrangements to provide for inspection
of the work by the City, to assure compliance with the plans and specifications
as approved. The developer will be invoiced monthly for time and expense
provided by the City for inspection services, escrow administration
and resident concern investigations.
B.
The
City or the City's duly authorized representative shall make all necessary
inspections of all pavement construction, along with all roadway-related
storm sewer construction.
C.
Twenty-four
(24) hours' notice shall be given to the City regarding any requested
inspection.
[Ord. No. 433 §5.14, 5-18-2005]
A.
The
construction of all improvements required by these rules and regulations
shall be completed within two (2) years from the date of approval
of the final plat by the Board of Aldermen, unless good cause can
be shown for the granting of an extension of time by authority of
the Board of Aldermen upon recommendation by the City Engineer.
B.
The
final release of ten percent (10%) of the escrow on all public improvements
cannot be made at the end of the one (1) year warranty period until
a final inspection is made and all corrected items are completed.
[Ord. No. 433 §5.15, 5-18-2005]
Where the subdivision contains sewers, sewage treatment plants,
waste supply systems or other physical facilities that are necessary
or desirable for the welfare of the area or that are of common use
or benefit and which are not or cannot be satisfactorily maintained
by an existing public agency, provision shall be made which is acceptable
to the agency having jurisdiction over the location and maintenance
of such facilities for the proper and continuous operations, maintenance
and supervision of such facilities.
[Ord. No. 433 §5.16, 5-18-2005]
Trust indentures will be required by the Board of Aldermen regarding
maintenance of common areas, private roads and other applicable amenities.
[Ord. No. 433 §5.17, 5-18-2005; Ord.
No. 699 §1, 11-13-2013]
All lots, regardless of use, shall comply with the following
setback requirements:
Front yard: 20 feet from property line.
Rear yard: 20 feet from property line.
Side yard: 10 feet from property line.
