[CC 1988 §24-65; Ord. No. 3457 §1, 5-21-2001]
This Chapter seeks to provide those standards, criteria, procedures
and controls necessary to minimize the harmful physical and economic
effects of erosion and flooding from stormwater within or directed
toward the City of De Soto. This is to be accomplished through the
requirement of special measures to mitigate erosion both during and
after development and the retention and controlled discharge of the
differential runoff from any property whereon any grading, excavation,
filling, or other disturbance of the natural vegetation or any construction,
erection or alteration of a building or structure is to be undertaken.
[CC 1988 §24-66; Ord. No. 3457 §1, 5-21-2001]
As used in this Chapter, the following terms shall have these
prescribed meanings:
Any tract of land in the City of De Soto whereon any grading,
excavation, filling, or other disturbance of the natural vegetation
or any construction, erection or alteration of a building or structure
has been undertaken.
Any tract of land in the City of De Soto.
Any tract of land in the City of De Soto whereon neither
grading, excavation, filling, or other disturbance of the natural
vegetation nor any construction, erection or alteration of a building
or structure has been undertaken.
[CC 1988 §24-67; Ord. No. 3457 §1, 5-21-2001; Ord. No. 3551 §1, 1-22-2004]
A.
General. An approved stormwater runoff control plan is required for all land development, subdivision and construction of buildings. Except as provided in Subsection (D) of this Section, it shall be unlawful for any person to develop or improve on any property within the City unless there is in force an approved stormwater runoff control plan issued as required under the provisions of this Chapter. The term "property", as used in this Section, shall be
defined as any tract of land in the City of De Soto.
B.
Construction Or Alteration Of Buildings. Except as provided
below, it shall be unlawful for any person to construct any new building
or structure or to enlarge or otherwise alter any existing building
or structure on any property within the City in such manner as to
change the land area covered by the building or structure unless there
is in force an approved stormwater runoff control plan issued as required
under the provisions herein.
C.
Change Or Disturbance Of Terrain. Except as provided in Subsection (D) of this Section, it shall be unlawful for any person to clear, grade, excavate, fill, remove topsoil from or change the contour of any land in the City unless there is in force an approved stormwater runoff control plan issued under the provisions of this Chapter.
D.
Exceptions. The provisions of this Section shall not apply
to:
1.
Any
reconstruction, repair or alteration of any existing building or structure
when no land, trees, shrubs, grass or other vegetation is to be disturbed,
destroyed or removed.
2.
Any
undeveloped property of less than one (1) acre zoned in an "A-1",
"R-1", "R-2" or single-family residential district.
3.
Any
already developed property zoned "A-1", "R-1", "R-2" or remaining
in a single-family residential use.
4.
The
clearing, grading, excavation, filling, removing topsoil from or changing
the contour of less than two thousand five hundred (2,500) square
feet of land.
5.
The
planting, trimming, pruning or removal of trees, shrubs, grass, weeds,
vegetation, ground cover or other plant material when such actions
are incidental to and part of the normal maintenance of land and property
in the City of De Soto.
6.
In considering
the applicability of these exceptions, the effective acreage for a
project, development or subdivision not limited to a fractional part
of the total concept. Rather, if a project is developed in phases
or small plats, the total acreage of the project, development or subdivision
will be considered. Furthermore, projects of less acreage than provided
for in this Chapter shall also provide retention if, in the judgment
of the City Engineer, conditions in the receiving system are inadequate,
or harmful effects can be anticipated if retention is not implemented.
[CC 1988 §24-68; Ord. No. 3457 §1, 5-21-2001; Ord. No. 3551 §2, 1-22-2004]
A.
General Standards.
1.
Zoning
classification and permitted land use determine the stormwater retention
requirements for any given property. Minimum lot size and percent
imperviousness are major factors in determining the future runoff
from a property. An additional volume of stormwater will be caused
to leave a property due to development thereon. The volume of stormwater
which must be retained in accordance with the provisions of this Chapter
is the difference between the volume of water expected to leave the
property in an undeveloped condition (roughly five percent (5%) impervious)
and the volume of water which will be caused to leave the property
due to all development (existing and proposed) thereon.
2.
Runoff
rates for all categories of projects shall be evaluated by the rational
formula. The runoff coefficients in the following table for a storm
event with a twenty-five (25) year (frequency) and an assumed twenty
(20) minute inlet time shall be used to calculate runoff volumes.
|
Average C.I. Factors in Cubic Feet Per Second Per Acre
(CFS/Acre) 20 Minute Inlet Time
| ||||||
|---|---|---|---|---|---|---|
|
Zoning District
|
Use
|
% Imp.1
|
C
|
C.I. Factors2
| ||
|
25-Yr
|
50-Yr
|
100-Yr
| ||||
|
A-1 Agricultural
|
All uses
|
5
|
0.37
|
2.00
|
2.18
|
2.37
|
|
R-1 Residential
|
One-family dwelling
All other uses
|
45
60
|
0.54
0.60
|
2.92
3.24
|
3.19
3.54
|
3.46
3.84
|
|
R-2 Residential
|
One-family dwelling
All other uses
|
47
75
|
0.548
0.665
|
2.96
3.59
|
3.23
3.92
|
3.51
4.26
|
|
R-3 Residential
|
Two-family dwelling
All other uses
|
60
75
|
0.600
0.665
|
3.24
3.59
|
3.54
3.92
|
3.84
4.26
|
|
R-4 Residential
|
Multiple-family dwelling
All other uses
|
70
75
|
0.645
0.665
|
3.48
3.59
|
3.81
3.92
|
4.13
4.26
|
|
C-1 Commercial
|
Office and professional
All other uses
|
Same as R-4
85
|
Same as R-4
0.705
|
Same as R-4
3.81
|
Same as R-4
4.16
|
Same as R-4
4.51
|
|
C-2 Commercial
|
Downtown
All other uses
|
Same as C-1
85
|
Same as C-1
0.705
|
Same as C-1
3.81
|
Same as C-1
4.16
|
Same as C-1
4.51
|
|
C-3 Commercial
|
General
|
Same as C-1 and C-2
|
Same as C-1 and C-2
|
Same as C-1 and C-2
|
Same as C-1 and C-2
|
Same as C-1 and C-2
|
|
M-1 Manufacturing
|
Light
|
90
|
0.73
|
3.94
|
4.31
|
4.67
|
|
M-2 Manufacturing
|
General
|
90
|
0.73
|
3.94
|
4.31
|
4.67
|
|
PUD — Planned Unit Development
|
As determined on a site-by-site basis.
| |||||
|
NOTES:
|
|---|
|
1 The percent impervious (% Imp.)
values were based upon the minimum lot size requirements for each
use.
|
|
2 The C.I. factors were derived from
the U.S. Weather Bureau Technical Paper No. 40: "Rainfall Frequency
Atlas of the United States for durations from thirty (30) minutes
to twenty-four (24) hours and return periods from one (1) to one hundred
(100) years."
|
B.
Retention Facilities. In general, retention facilities shall
be provided with obvious and effective control strategies. The following
shall be considered in determining the effectiveness and safety of
these facilities in relation to the intent and purpose of this Section.
1.
(Volume
of runoff from the developed property) = C.I. factor x area of property
(in acres) x 30 minutes x 60 seconds/minute.
2.
(Volume
of runoff from the property in undeveloped condition) = 2.00 cfs/acre
x area of property (in acres) x 30 minutes x 60 seconds/minute.
3.
Volume
of retention for the developed property = (Volume of runoff from developed
property) - (Volume of runoff from the property in an undeveloped
condition).
4.
Tributary
(Q) peak runoff to basin.
5.
Balanced
maximum outflow rate from the low-flow structure.
6.
Ratios
of inflow to outflow rates.
7.
Sizing
of the overflow facilities.
8.
Stability
of retention dikes.
9.
Safety
features.
10.
Maintenance
features.
C.
Open Dry Reservoirs.
1.
Wet
weather ponds or dry reservoirs shall be designed with proper safety,
stability and ease of maintenance features and shall not retain stormwater
to a depth greater than four (4) feet if specifically permitted by
site plan review by the Planning and Zoning Commission in consideration
of a special demonstrated need and special provisions to avoid safety
hazards of such greater hazards of such greater depths.
2.
Maximum
side slopes for grass-edged reservoirs shall not exceed one (1) foot
vertical for two (2) feet horizontal (2:1) unless adequate measures
are included to provide for the stability of these slopes.
3.
In no
case shall the limits of maximum ponding elevation be closer than
thirty (30) feet horizontally from any building and less than two
(2) feet vertically below the lowest sill elevation.
4.
The
entire reservoir area shall be seeded, fertilized and mulched, sodded
or paved prior to release of escrows.
D.
Permanent Lakes Used For Retention.
1.
Permanent
lakes with fluctuating volume controls may be used as retention areas
provided that the limits of maximum ponding elevations are no closer
than thirty (30) feet horizontally from any building and less than
two (2) feet below the lowest sill elevation of any building.
2.
Maximum
fluctuation from permanent pool elevation to maximum ponding elevation
shall be three (3) feet.
3.
Special
consideration shall be given to measures to ensure the safety of small
children in the design of permanent lakes especially when located
in residential areas.
E.
Parking Lots Used For Retention.
1.
Retention
is permitted in parking lots to maximum depth of twelve (12) inches.
2.
In no
case should the maximum limits of ponding be designed closer than
ten (10) feet from a building unless proper provision is made for
the waterproofing of the building and for pedestrian accessibility.
3.
The
minimum freeboard from the maximum ponding elevation to the lowest
sill elevation shall be two (2) feet.
4.
Closed retention tanks. Facilities which are fully enclosed
to detain stormwater may be of any depth.
F.
Discharge Systems.
1.
The
design discharge (Q) for the low-flow pipe shall not exceed the twenty-five
(25) year (frequency) twenty (20) minute duration (inlet time), runoff
from the tributary area for five percent (5%) imperviousness (2.0
c.f.s. per acre). The maximum discharge shall be designated to take
place under total anticipated design-head conditions.
2.
Low-flow
pipes shall not be smaller than four (4) inches in diameter to minimize
maintenance and operating problems, except in parking lot and roof
retention where minimum size of opening shall be designed specifically
for each condition. The low-flow pipe shall be provided with a bar-screen
on a minimum 2:1 slope to reduce blockage by debris.
3.
The
overflow opening or spillway shall be designed to accept the total
peak runoff of the improved tributary area with discharge velocity
not to exceed five (5) feet per second unless special provisions are
made.
4.
Proper
engineering judgment shall be exercised in analysis of secondary routing
of discharge of greater intensity than the design twenty-five (25)
year frequency in order to avoid economic losses or damage downstream.
Review with twenty-five (25) and fifty (50) year frequency is recommended.
5.
Sizing
of the system below the control structure shall be for the total improved
peak runoff tributary to the structure with no allowance for retention
with discharge velocity not to exceed five (5) feet per second unless
special provisions are made.
[CC 1988 §24-69; Ord. No. 3457 §1, 5-21-2001]
A.
All stormwater
discharge pipes shall be computed on a twenty-five (25) year rainfall
frequency at a minimum.
B.
Construction And Maintenance Of Stormwater And Erosion Control Facilities.
1.
Retention
facilities, when mandatory, are to be built in conjunction with the
storm sewer installation and/or grading. Since these facilities are
intended to control increased runoff, they must be partially or fully
operational soon after the clearing of the vegetation.
2.
Silt
and debris connected both with early construction and with general
erosion from the site and elsewhere in the watershed after construction
shall be removed periodically from the retention area and control
structure in order to maintain full storage capacity.
3.
The
responsibility of maintenance of the retention facilities in subdivision
projects shall remain with the developer until such time as applicable
escrows are released. Upon release of escrows the maintenance responsibility
shall be vested in the trustees of the subdivision by virtue of the
trust indenture. The indenture of the trust shall clearly indicate
resident responsibility for maintenance in cases of projects without
common ground.
4.
The
responsibility of maintenance of the retention facilities in single
owner development projects shall remain with the general contractor
until final inspection of the development is performed and approved.
Upon approval of the project, the maintenance of retention facilities
shall be vested with the owner of the property.
C.
Submission, Review And Approval Of Required Stormwater Runoff Control
Plans.
1.
Requirements for building or grading permit. No permit shall
be issued to construct, erect or alter any building or structure or
to clear, grade, excavate, fill, remove topsoil from or change the
contour of any property within the City until a stormwater runoff
control plan has been submitted and approved by the City of De Soto
in accordance with the provisions of this Chapter, except as provided
in 425.030(D).
D.
Procedure.
1.
Application
for an approved stormwater runoff control plan, as required, shall
be submitted to the City Manager by the owner of the land prior to
the time any work subject to this Chapter is begun on the land.
2.
Upon
receipt of any application and plan, the City Manager with the advice
of the City Engineer shall consider the plan in light of the provisions
of this Chapter and shall approve the plan, disapprove the plan or
approve the plan with modifications, noting thereon any changes that
will be required.
3.
The
City shall promptly notify the applicant of the City's decision on
a plan. Failure of the City Manager to act on any plans submitted
within forty-five (45) days after they have been properly filed should
be deemed to constitute approval of the plans. Any approved plan shall
be issued, dated, and bear the manual signature of the City Manager.
E.
Submission Requirements.
1.
All
plans and specifications submitted for review and/or approval shall
be prepared by or under the direct supervision of a registered professional
engineer licensed in the State of Missouri and shall meet the minimum
standards and requirements of the City and other applicable authorities.
Each of the plan, profile and special drawing sheets for a project
shall bear a legible stamp of the professional engineer in charge.
2.
In order
to facilitate review of plans, all projects shall be submitted with
a letter of transmittal which shall include the name of project, name
and address of owner or developer, name, address and telephone number
of engineer, and clarification as to the purpose of submittal.
[CC 1988 §24-70; Ord. No. 3457 §1, 5-21-2001]
The stormwater runoff control plan shall be subject to all provisions
of this Chapter relating to enforcement, violations and penalties.
In addition, a corporate surety bond, conditioned upon carrying out
all and every part of approved plans for at least the sum estimated
to be the full costs of carrying out such plans, or a cash escrow,
upon the same conditions and in the same amount, shall be furnished
the City whenever such costs exceed five hundred dollars ($500.00).
The bond or escrow shall be released upon proper completion of all
of the requirements of such approved plans.
[CC 1988 §24-71; Ord. No. 3457 §1, 5-21-2001]
This Chapter shall be enforced by the City Manager with the
assistance and cooperation of other officials including the City Engineer.
If the City Manager finds that any of the provisions of this Chapter
are being violated, he/she shall notify in writing the person responsible
for such violation, indicating the nature of the violation and ordering
the action necessary to correct it. He/she shall take any other action
authorized by law to ensure compliance with or to prevent violation
of the provisions of this Chapter.
[CC 1988 §24-72; Ord. No. 3457 §1, 5-21-2001]
A.
Violations
of this Chapter shall include, but are not limited to, the following:
1.
Any
activity of proceeding not in accordance with the procedures, requirements,
standards or other provisions of this Chapter.
2.
No owner,
or agent of the owner, or any land located within a subdivision of
the City of De Soto shall knowingly or with intent to defraud, transfer,
sell, agree to sell, or negotiate to sell that land by reference to
or by other use of a plat of any purported subdivision of the land
before the final subdivision plat has been approved by the Planning
and Zoning Commission and City Councilmen in accordance with this
Chapter and recorded by the Recorder of Deeds of the County.
3.
Failure
to obtain the approvals and permits required by this Chapter and to
comply with their terms and conditions.
B.
Those
chargeable, singly or jointly, with violations of this Chapter shall
include, but are not limited to, the following:
1.
Those
who commit, assist in, or otherwise participate in a violation.
2.
The
owner or other persons who maintain the building, premises, property,
or other place where the violation has been committed or exists.
3.
The
developer, agent, architect, contractor, or any other person who performs
work or enters into a contract for work in violation of this Chapter.
C.
Wherever
in this Chapter any act is prohibited or is declared to be unlawful
or an offense or misdemeanor, upon conviction of a violation of any
such provision of this Chapter, the violator shall be punished by
a fine not exceeding five hundred dollars ($500.00) or by imprisonment
in the City or County Jail not to exceed ninety (90) days, or by both
such fine and imprisonment. Each day any violation of this Chapter
shall continue shall constitute, except where otherwise prohibited,
a separate offense.
