Section 3 - Specifications and Technical Information / Plymouth, Indiana

I. Information Requirements

The following information and data provided by an Indiana licensed professional engineer, architect, or land surveyor engaged in storm drainage design shall be required.

A. Topographic and Soils Maps

A soils map of the proposed development indicating soils names and their hydrologic classification must be provided when Soil Conservation Service (SCS) hydrologic methods are used. In addition, a topographic map of the land to be subdivided and such adjoining land whose topography may affect the layout or drainage of the development must be provided.

The contour intervals shall be one foot when slopes are less than four percent and shall be two feet when the slope exceeds four percent. On this map, the following shall be shown:

The location of streams and other flood water runoff channels, the extent of the floodplains at the established 100 year flood elevation where available (regulatory floodway), and the limits of the floodway, all properly identified.
The normal shoreline of lakes, ponds, swamps and detention basins, their floodplains, and lines of inflow and outflow if any.
The location of regulated drains, farm drains, inlets and out-falls, if any of record.
Storm, sanitary, and combined sewers, and outfalls, if any of record.
Septic tank systems and outlets, if any of record.
Seeps, springs, flowing and other wells, that are visible or of record.

B. Preliminary Drainage Plan

A comprehensive plan, in preliminary form (or in combined preliminary and final form), designed to handle safely the storm water runoff and to retain/detain the increased storm water runoff, must be provided.

The plan shall provide or be accompanied by mapsor other descriptive materials indicating the feasibility of the drainage plan and showing the following:

The extent and area of each watershed affecting the design of retention/detention facilities as shown on USGS Quadrangle Maps or other more detailed maps as required by the Sanitary Board of Trustees.
The preliminary layout and design of proposed storm sewers, the outfall and outlet locations and approximate elevations, the receiving stream or channel and its 100 year return period water elevation.
The location and design of the proposed street system, especially including depressed pavements used to convey or temporarily store overflow from the heavier rainstorms, and the outlets for such overflow.
The locations, cross sections, and profiles of existing streams and floodplains to be maintained, and new channels to be constructed.
The materials, elevations, waterway openings, and the basis for design of proposed culverts and bridges.
Existing ponds and basins to be maintained, enlarged, or otherwise altered and new ponds or basins to be built and the basis of their design.
The estimated depth and amount of storage required in the new ponds or basins.
The estimated location and percentage of impervious surfaces existing and expected to be constructed when the development is completed.
Any interim plan which is to be incorporated into the development pending completion of the development and the final drainage plan.

C. Valley Cross Section

One or more typical cross sections must be provided showing all existing and proposed channels or other open drainage facilities carried to a point above the 100 year high water elevation; showing the elevation of the existing land and the proposed changes thereto, together with the high water elevations expected from the 100 year storm under the controlled conditions called for by this ordinance; and showing the relationship of structures, streets, and other facilities.

D. Site Plan

A plan drawn to scale showing dimensions of the site with existing and proposed storm drainage facilities must be provided.

E. Final Drainage Plans

The final plans shall provide or be accompanied by calculations, maps and/or other descriptive material showing the following:

The extent and area of each watershed tributary to the drainage channels in the development.
The street storm sewers and other storm drains to be built, the basis of their design, outfall and outlet locations and elevations, the receiving stream or channel and its high water elevation, and the functioning of the drains during high water conditions.
The parts of the proposed street system where pavements are planned to be depressed sufficiently to convey or temporarily store overflow from storm sewers and over the curb runoff resulting from the heavier rainstorms and the outlets for such overflow.
Existing streams and floodplains to be maintained, and new channels to be constructed, their locations, cross sections and profiles.
Proposed culverts and bridges to be built, their materials, elevations, waterway openings and basis of their design.
Existing storage basins and ponds to be maintained, enlarged, or otherwise altered and new basins or ponds to be built and the basis of their design.
The estimated location and percentage of impervious surfaces existing and expected to be constructed when the development is completed.
The slope, type and size of all sewers and other waterways.
For all storage basins, a plot or tabulation of storage volumes with corresponding water surface elevations and a plot or tabulation of the basin outflow rates for those water surface elevations.

F. Report

A report shall be submitted with the preliminary or final drainage plan that includes the following information:

A description of the proposed development;
The current land use conditions;
The method of hydraulic and hydrologic analysis used, including any assumptions or special condition;
The results of the analysis; and
The recommended drainage control facilities.
Hydraulic and hydrologic calculations, including input and output files, shall be included as appendices to the report.

G. Permission to Connect to Legal Drain

If plans include connection to a legal drain, written permission from the County Surveyor and/or the Marshall County Drainage Board shall be submitted with the preliminary or final drainage plan.

II. System Design Criteria

Plans shall show that provisions have been made for both retention and detention within the limits of the project/ development. The amount of retention shall be 25 gallons per one hundred square foot of hard surface area, as detailed in SECTION 3, III. In addition to this amount to be retained on the property, there shall be detention provided as detailed in SECTION 3, X. The detained amount may be released at the rate specified in SECTION 3, X.

For proposed improvements to an existing developed site, the Sanitary Board of Trustees may require that plans include additional remedial action to be performed at the site.

III. Storm Water Retention

The following shall govern the design of any improvement with respect to the retention of storm water runoff.

A. Acceptable Retention Methods

The portion of the increased storm water runoff resulting from a proposed development should be retained on-site by the provisions of appropriate wet or dry bottom reservoirs, drywells, vegetated shallow depressed areas, or other acceptable techniques. Retention basins shall be sized to hold the excess flows created by the development of the property as based on the amount of hard surface area, drives, parking lots, roofs, etc. This water shall not be released from the property, with the retention basins being utilized as ground water recharge areas.

B. Design Criteria

The design of storm water retention facilities shall be based on the amount of hard surface area. The holding capacity for retention facilities shall be 25 gallon per 100 square feet of hard surface area such as roofs, drives, parking lots, etc.

C. Drainage System Outlet

The site drainage collector system shall be designed to outlet into the site retention facility/facilities. Once the retention facility/facilities has been filled, the remainder of the runoff will then enter into the site detention facility/facilities and from there be released at a 10 year undeveloped release rate.

D. Retention System Overflow Design

The retention facility shall have an overflow which discharges into the detention facility. If the facility is a combination retention/detention facility, the release rate shall be based on the 10 year undeveloped release rate (see SECTION 3, X., C.) after the required retention is held on the site.

E. Hard Surface Definition

Hard Surfaces are surfaces in which the water will run off the drainage area with very little or no ground infiltration. Areas include but are not limited to: building roof areas, asphalt surfaces, concrete surfaces, and compacted limestone surfaces.

F. Determination of Storage Volume

Following is the procedure for retention calculations.

Steps Procedure:

Determine total hard surface area in square feet = "A".
Divide the hard surface area by 100 square feet = "A/100".
Multiply this value (A/100) by 25 gallons.
This value is the required retention volume in gallons.
Multiply the required retention (gallons) by .1337 to obtain the required retention volume in cubic feet.

G. General Retention Basin Design Requirements

Basins shall be constructed to retain permanently on site 25 gallons per 100 square feet of hard surface area. The volume of storage provided in these basins, together with such storage as may be authorized in other on-site facilities, shall be sufficient to control the above runoff within the system.

The following design principles shall be observed:

The maximum volume of water stored and percolated into the soil shall not result in excessive storage durations.
The maximum planned depth of storm water stored (without a permanent pool) shall not exceed four feet.
All storm water retention facilities shall be separated by a sufficient amount from any building or structure to be occupied, so that 1) ingress/egress is not impeded and 2) the building or structure is not damaged by the storm water infiltration.
All excavated excess spoil may be spread so as to provide for aesthetic and recreational features such as sliding hills, sports fields, etc. Slopes no steeper than 6 horizontal to 1 vertical for safety, erosion control, stability, and ease of maintenance shall be permitted.
Safety screens having a maximum opening of 4 inches shall be provided for any pipe or opening to prevent children or large animals from crawling into the structures.
Danger signs shall be mounted at appropriate locations to warn of deep water, possible flooding conditions during storm periods and other dangers that exist. Fencing shall be provided if deemed necessary by the Sanitary Board of Trustees.
Outlet control structures shall be designed to operate as simply as possible and shall require little or no maintenance and/or attention for proper operation. They shall limit discharges into the detention facilities so as not to exceed the predetermined maximum authorized peak flow rate.
Emergency overflow facilities such as a weir or spillway shall be provided for the release of exceptional storm runoffs or in emergency conditions should the normal discharge devices become totally or partially inoperative. The overflow facility shall be of such design that its operation is automatic and does not require manual attention and its outlet flows into the detention facility.
Grass or other suitable vegetative cover shall be provided throughout the entire basin area. Grass should be cut regularly at approximately monthly intervals during the growing season or as required.
Debris and trash removal and other necessary maintenance shall be performed on a regular basis to assure continued operation in conformance to design.
A report shall be submitted with the preliminary or final plan as stated in Section 3, I., F.

H. Dry Bottom Basin Design Requirements

Retention basins which will not contain a permanent pool of water shall, whenever possible, be designed to serve a secondary or multipurpose function. Recreational facilities, aesthetic qualities (open spaces) or other types of use shall be considered in planning the retention facility.

I. Wet Bottom Basin Design Requirements

Where part of a retention basin will contain a permanent pool of water, all the items required for retention storage shall apply. A controlled positive outlet will be required to maintain the design water level in the wet bottom basin and may provide required detention storage above the design water level.

However, the following conditions shall apply:

Basins designed with permanent pools or containing permanent ponds shall have a water area of at least one-half acre. If fish are to be maintained in the pond, a minimum depth of approximately 10 feet shall be maintained over at least 25 percent of the pond area. The remaining pond area shall have no extensive shallow areas, except as required by subsection (3) below.
In excavated ponds, the underwater side slopes in the pond shall be stable. In the case of valley storage, natural slopes may be considered to be stable.
A safety ledge four to six feet in width is required and must be installed in all ponds approximately 30 to 36 inches below the permanent water level. In addition, a similar maintenance ledge 12 to 18 inches above the permanent water line shall be provided. The slope between the two ledges shall be stable and of a material such as stone or rip rap which will prevent erosion due to wave action.
A safety ramp exit from the pond is required in all cases and shall have a minimum width of 20 feet and exit slope to 6 horizontal to 1 vertical. The ramp shall be of a material that will prevent its deterioration due to vehicle use and/or wave action.
Periodic maintenance is required in ponds to control weed and larval growth. The pond shall also be designed to provide for the easy removal of sediment which will accumulate during periods of pond operation. A means of maintaining the designed water level of the pond during prolonged periods of dry weather is also required.
For emergency use, basin cleaning, or shoreline maintenance, facilities shall be provided or plans prepared for auxiliary equipment to permit emptying and drainage.
Facilities to enhance and maintain pond water quality shall be provided, if required to meet applicable water quality standards. Design calculations to substantiate the effectiveness of these aeration facilities shall be submitted with final engineering plans. Agreements for the perpetual operation and maintenance of aeration facilities shall be prepared to the satisfaction of the Sanitary Board of Trustees.

J. Facility Financial Responsibility

The construction cost of storm water control systems and facilities as required by this ordinance shall be accepted as part of the cost of land development. If general public use of the facility can be demonstrated, negotiations for public participation in the cost of such development may be considered.

K. Facility Maintenance Responsibility

Maintenance of retention/detention facilities during construction and thereafter, shall be the responsibility of the land developer/owner. Assignment of responsibility for maintaining facilities serving more than one lot or holding shall be documented by appropriate covenants to property deeds, unless responsibility is formally accepted by a public body, and shall be determined before the final drainage plans are approved.

Storm water retention and detention basins may be donated to the City or other unit of government designated by the City, for ownership and permanent maintenance providing:

The City or other governmental unit is willing to accept responsibility.
The facility has been designed and constructed according to all applicable provisions of this ordinance.
All improvements have been constructed, approved, and accepted by the governmental agency for the land area served by the drainage basin.
Retention ponds containing a permanent pool of water have all slopes between the riprap and high water line sodded and the remaining land area hydroseeded; are equipped with electrically driven aeration devices, if required to maintain proper aerobic conditions and sustain aquatic life; have a four-foot wide crushed limestone walkway at the high water line entirely around the body of water; provide suitable public access acceptable to the responsible governmental agency; and have the high water line not closer than 75 feet to any property line.
Dry retention ponds shall have all slopes, bottom of the basin and Areas above the high water line hydroseeded; and shall have the high water line not closer than 50 feet to any development boundary.

L. Inspections

All public and privately owned retention storage facilities can be inspected by representatives of the City not less often than once every 2 years. If inspected, a certified inspection report covering physical conditions, available storage capacity and operational condition of key facility elements will be provided to the owner.

M. Corrective Measures

If deficiencies are found by the inspector, the owner of the retention/detention facility will be required to take the necessary measures to correct such deficiencies. If the owner fails to do so, the City will undertake the work and collect from the owner using lien rights, if necessary.

N. Joint Development of Control Systems

Storm water control systems may be planned and constructed jointly by two or more developers as long as compliance with this Ordinance is maintained.

O. Installation of Control Systems

Runoff and erosion control systems shall be installed as soon as possible during the course of site development. Retention/ detention basins shall be designed with an additional (six) percent of available capacity to allow for sediment accumulation resulting from development and to permit the pond to function for reasonable periods between cleanings. Basins should be designed to collect sediment and debris in specific locations so that removal costs are kept to a minimum.

P. Retention Facilities in Floodplains

If retention storage is provided within a floodplain, only the net increase in storage volume above that which naturally existed on the floodplain shall be credited to the development. No credit will be granted for volumes below the elevation of the regulatory flood at the location unless compensatory storage is also provided.

Q. Off-Site Drainage Provisions

When the allowable runoff is released in an area that is susceptible to flooding, the developer may be required to construct appropriate storm drains through such area to avert increased flood hazard caused by the concentration of allowable runoff at one point instead of the natural overland distribution. The requirement of off-site drains shall be at the discretion of the Sanitary Board of Trustees.

IV. Determination of Runoff Quantities

Runoff quantities shall be computed for the area of the parcel under development plus the area of the watershed flowing into the parcel under development.

The quantity of runoff which is generated as the result of a given rainfall intensity may be calculated as follows:

A. For Areas up to and including 200 acres, the Rational Method may be used. In the Rational Method, the peak rate of runoff, Q, in cubic feet per second is computed as:

Q = CIA

where: C = runoff coefficient, representing the characteristics of the drainage area and defined as the ratio of runoff to rainfall. I = average intensity of rainfall in inches per hour for a duration equal to the time of concentration (tc) for a selected rainfall frequency. A = tributary drainage area in acres. Guidance to selection of the runoff coefficient "C" is provided by Table 1 and Table 1A which show values for different types of surface and local soil characteristics. The composite "C" value used for a given drainage area with various surface types shall be the weighted average value for the total area calculated from a breakdown of individual Areas having different surface types.

Table 2 provides runoff coefficients and inlet times for different land use classifications. In the instance of undeveloped land situated in an upstream area, a coefficient or coefficients shall be used for this area in its present or existing state of development.

Rainfall intensity shall be determined from the rainfall frequency curves shown in Figure 1 or from data shown in Table 3. The time of concentration (tc) to be used shall be the sum of the inlet time and drainage area to the point under consideration. The flow time in the storm sewers may be estimated by the distance in feet divided by velocity of flow in feet per second. The velocity shall be determined by the Manning Formula.

Inlet time is the combined time required for the runoff to reach the inlet of the storm sewer. It includes overland flow time and flow time through established surface drainage channels such as swales, and ditches, and sheet flow across such Areas as lawns, fields, and other graded surfaces. It may be computed by using Figure 2.

B. The runoff rate for Areas in excess of 200 acres shall be determined by methods described in SECTION 3, X., F.

Table 1 - Urban Runoff Coefficients (1)

Type of Surface Pavement	Runoff Coefficient "C"
Asphalt and Concrete	0.70 to 0.95
Brick	0.70 to 0.85
Roofs	0.75 to 0.95

Lawns (Sandy soil)
Flat (0-2% Slope)	0.05 to 0.10
Average (2-7% Slope)	0.10 to 0.15
Steep (7% & Greater)	0.15 to 0.20

Lawns (Heavy soil)
Flat (0-2% Slope)	0.13 to 0.17
Average (2-7% Slope)	0.18 to 0.22
Steep (7% & Greater)	0.25 to 0.35
Water Impoundment	1.0

(1) HERPICO; Stormwater Drainage Manual; July, 1994.

The coefficients of this tabulation are applicable to storms of 5 to 10 year frequencies. Coefficients for less frequent higher intensity storms shall be modified as follows (Note that "C" should never be greater than 1.):

Return Period (yrs)	Multiply "C" by
25	1.1
50	1.2
100	1.25

(2) Marshall County, Indiana, Storm Drainage and Sediment Control Ordinance, October 1993.Â

TABLE 1A
Rural Runoff Coefficients (1)
Type of Surface Runoff Coefficient "C"
Vegetation and Topography Open Sandy Silt Clay and Silt Loam Tight Clay
Flat (0-5% Slope)
Rolling (5-10% Slope)
Steep (greater than 10%)
Woodland
Flat
Rolling
Steep 0.10
0.25
0.30 0.30
0.35
0.50 0.40
0.50
0.60
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Pasture
Flat
Rolling
Steep 0.10
0.16
0.22 0.30
0.36
0.42 0.40
0.55
0.60
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Cultivated
Flat
Rolling
Steep 0.30
0.40
0.52 0.50
0.60
0.72 0.60
0.70
0.82

(1) HERPICO; Stormwater Drainage Manual; July, 1994.

Return Period (Yrs.)	Multiply "C" by
25	1.1
50	1.2
100	1.25

(2) Marshall County, Indiana, Storm Drainage and Sediment Control Ordinance, October 1993.

Table 2
Runoff Coefficients "C"
By Land Use and Typical Inlet Times(1)
Land Use Runoff Coefficients (1) Inlet Time (2)
Flat Rolling Steep (minutes)
Commercial (CBD) 0.75 0.83 0.91 5
Commercial (Neighborhood) 0.54 0.60 0.66 Â
Industrial 0.63 0.70 0.77 5-10
Garden Apartments 0.54 0.60 0.66
Churches 0.54 0.60 0.66
Schools 0.31 0.35 0.39 10-15
Semi Detached Residential 0.45 0.50 0.55
Detached Residential 0.40 0.45 0.50
Quarter Acre Lots 0.36 0.40 0.44
Half Acre Lots 0.31 0.35 0.39
Parkland 0.18 0.20 0.22 To Be Computed

Flat terrain 0-2% slopes.
Rolling terrain 2-7% slopes.
Steep terrain greater than 7% slopes.
Interpolation, extrapolation and adjustment for local conditions shall all be based on engineering experience and judgment.
The coefficients of this tabulation are applicable to storms of 5 to 10 year frequencies. Coefficients for less frequent higher intensity storms shall be modified as follows ("C" should never be greater than 1):

Return Period (Yrs.)	Multiply "C" by
25	1.1
50	1.2
100	1.25

(1) Marshall County, Indiana, Storm Drainage and Sediment Control Ordinance, October 1993.

TABLE 3
RAINFALL INTENSITIES FOR VARIOUS RETURN
PERIODS AND STORM DURATIONS FOR SOUTH BEND, INDIANA (1)
Return Period (yrs)
Time (hrs) 2 5 10 20 50 100
Extrapolated from HYDRAIN 0.083 5.063 5.898 6.443 7.009 7.716 8.233
0.167 3.961 4.713 5.212 5.738 6.405 6.900
0.25 3.195 3.889 4.357 4.855 5.495 5.973
0.5 2.184 2.726 3.098 3.501 4.026 4.423
-----------------------------------------------------------------
Actual Data
from Analysis 1 - 1.119 1.460 1.686 1.903 2.183 2.393
2 - 0.707 0.916 1.054 1.187 1.359 1.488
3 - 0.531 0.692 0.798 0.900 1.032 1.130
4 - 0.420 0.542 0.624 0.701 0.802 0.878
5 - 0.351 0.452 0.519 0.583 0.666 0.728
6 - 0.303 0.387 0.443 0.495 0.565 0.616
7 - 0.272 0.348 0.399 0.448 0.512 0.559
8 - 0.244 0.315 0.362 0.407 0.465 0.508
9 - 0.220 0.283 0.326 0.366 0.418 0.458
10 - 0.201 0.260 0.299 0.336 0.385 0.421
11 - 0.185 0.240 0.277 0.312 0.357 0.391
12 - 0.172 0.223 0.257 0.290 0.332 0.364
13 - 0.162 0.210 0.241 0.271 0.311 0.340
14 - 0.154 0.200 0.230 0.259 0.296 0.324
15 - 0.146 0.190 0.219 0.247 0.283 0.310
16 - 0.138 0.180 0.207 0.234 0.268 0.293
17 - 0.132 0.171 0.198 0.223 0.256 0.280
18 - 0.126 0.163 0.188 0.212 0.243 0.266
19 - 0.121 0.157 0.180 0.203 0.233 0.255
20 - 0.115 0.149 0.172 0.194 0.223 0.244
21 - 0.110 0.143 0.165 0.186 0.214 0.234
22 - 0.106 0.138 0.159 0.179 0.205 0.225
23 - 0.102 0.133 0.173 0.198 0.217 0.217
24 - 0.099 0.128 0.148 0.167 0.191 0.210
25 - 0.096 0.124 0.143 0.162 0.185 0.203
26 - 0.093 0.120 0.138 0.155 0.177 0.193
27 - 0.090 0.116 0.133 0.149 0.170 0.186
28 - 0.088 0.112 0.129 0.145 0.165 0.180
29 - 0.086 0.110 .0126 0.142 0.162 0.176
30 - 0.084 0.107 0.123 0.138 0.158 0.172
31 - 0.082 0.106 0.121 0.136 0.156 0.171
32 - 0.080 0.103 0.118 0.132 0.151 0.165
33 - 0.078 0.100 0.114 0.128 0.147 0.160
34 - 0.076 0.097 0.112 0.125 0.143 0.156
35 - 0.074 0.095 0.109 0.122 0.139 0.152
36 - 0.072 0.092 0.105 0.118 0.134 0.146

Table 9. Intensity-duration-frequency tables for South Bend with data extrapolated from HYDRAIN for durations smaller than 1 hour.

(1) Marshall County, Indiana, Storm Drainage and Sediment Control Ordinance, October 1993.

V. Amount of Runoff to be Accommodated by Various Parts of Drainage Facility

Various parts of drainage facility must accommodate runoff water as follows:

A. The minor drainage system such as inlets, catch basins, street gutters, swales, sewers, and small channels which collect storm water must accommodate peak runoff from a 10-year return period storm. Rainfall duration shall be equal to the time of concentration or one hour if the time of concentration is less than one hour. A first quartile storm distribution shall be used for computer modeling. These minimum requirements must be satisfied:

The allowable spread of water on Collector Streets is limited to maintaining two clear 10 foot moving lanes of traffic. One lane is to be maintained on Local Roads, while Places can have a water spread equal to one-half of their width.
Open channels carrying peak flows greater than 30 cubic feet per second shall be capable of accommodating peak runoff for a 50-year return period storm within the drainage easement.
Culverts shall be capable of accommodating peak runoff from a 50-year return period storm when crossing under a road which is part of the Indiana Department of Transportation rural functional classification system and are classified as principal or minor arterial, major or minor collector roads.

B. Major drainage systems are defined in SECTION 1, XI., subsection DD and shall be designed in accordance with Indiana Department of Natural Resources Standards as described in SECTION 1, X.

VI. Storm Sewer Design Standards

All storm sewers, whether private or public, and whether constructed on private or public property shall conform to the design standards and other requirements contained herein.

A. Manning's Equation

The hydraulic capacity of storm sewers shall be determined using Manning's Equation:

V = mean velocity of flow in feet per second
R = the hydraulic radius in feet
S = the slope of the energy grade line in feet per foot
n = roughness coefficient

The hydraulic radius, R, is defined as the cross sectional area of flow divided by the wetted flow surface or wetted perimeter. Typical "n" values and maximum permissible velocities for storm sewer materials are listed in Table 4. Roughness coefficient (n) values for other sewer materials can be found in standard hydraulics tests and references.

B. Minimum Size

The minimum size of all storm sewers shall be 12 inches. Rate of release for detention storage shall be controlled by an orifice plate or other devices, subject to approval of the Sanitary Board of Trustees, where the 12 inch pipe will not limit rate of release as required.

C. Grade

Sewer grade shall be such that, in general, a minimum of two feet of cover is maintained over the top of the pipe. Pipe cover less than the minimum may be used only upon approval of the Sanitary Board of Trustees. Uniform slopes shall be maintained between inlets, manholes and inlets to manholes. Final grade shall be set with full consideration of the capacity required, sedimentation problems and other design parameters. Minimum and maximum allowable slopes shall be those capable of producing velocities of 2.5 and 15 feet per second, respectively, when the sewer is flowing full.

D. Alignment

Storm sewers shall be straight between manholes insofar as possible. Deflection of pipe sections shall not be permitted.

Table 4

Typical Values of Manning's "n"

Material	Manning's n	Desirable Maximum Velocities
Closed Conduits
Concrete	0.013	15 f.p.s.
Vitrified Clay	0.013	15 f.p.s.
Brick	0.015	15 f.p.s.
Cast Iron	0.013	15 f.p.s.

Circular Corrugate Metal Pipe (Annular Corrugations, 2-2/3 x 1/2 in.)
12"	0.011
18"	0.013
24"	0.015
36"	0.018
48"	0.020
60" or larger	0.021

Corrugated Plyethylene Smooth Interior Pipe	0.012	15 f.p.s.
Concrete Culverts	0.013

Open Channels
Concrete, Trowel Finish	0.013
Concrete, Broom or Float Finish	0.015
Gunite	0.018
Riprap Placed	0.030
Riprap Dumped	0.035
Gabion	0.028
New Earth (Uniform, Sodded, Clay)	0.025
Existing Earth (Fairly Uniform, w/Some Weeds)	0.030
Dense Growth of Weeds	0.040

Dense Weeds and Brush	0.040
Swale with Grass	0.035

E. Manholes

Manholes shall be installed to provide access to continuous underground storm sewers for the purpose of inspection and maintenance.

Manholes shall be provided at the following locations:

Where two or more storm sewers converge.
At the point of beginning or at the end of a curve, and at the point of reverse curvature (PC, PT, PRC).
Where pipe size changes.
Where an abrupt change in alignment occurs.
Where a change in grade occurs.
At suitable intervals in straight sections of sewer.

The maximum distance between storm sewer manholes shall be as follows:

Size of pipe (inches)	Maximum Distance (feet)
12 thru 42	400
48 and larger	500

F. Inlets

Inlets or drainage structures shall be utilized to collect surface water through grated openings and convey it to storm sewers, channels, or culverts. Inlet design and spacing shall be in accordance with Section 7-400 of the Indiana Department of Transportation's Road Design Manual - Volume 1 or other approved design procedure. The inlet grate opening provided must be adequate to pass the design 10 year flow with 50% of the sag inlet Areas clogged. An overload channel from sag inlets to the overflow channel or basin shall be provided at sag inlets, so that the maximum depth of water that might be ponded in the street sag shall not exceed 7 inches.

VII. Workmanship and Materials of Storm Sewers

A. Workmanship

The specifications for the construction of storm sewers shall not be less stringent than those set forth in the latest edition of the Indiana Department of Transportation's "Standard Specifications"; additionally, ductile iron pipe shall be laid in accordance with American Water Works Association (AWWA) C-600, and plastic pipe shall in laid in accordance with the American Society of Testing Materials (ASTM) D-2321.

B. Materials

Storm sewer manholes and inlets shall be constructed of masonry, cast-in-place concrete or precast reinforced concrete. Material and construction shall conform to Indiana Department of Transportation's "Standard Specifications", Section 720.

Pipe and fittings used in storm sewer construction shall be ductile iron pipe (AWWA C-151), concrete pipe (ASTM C-76), acrylonitrile-butadiene-styrene pipe (ASTM D-2751), or polyvinyl chloride pipe (ASTM D-2729). Other pipe and fittings not specified herein may be used only when specifically authorized by the Sanitary Board of Trustees. Pipe joints shall be flexible and watertight and shall conform to the requirements of Section 715.02 - Materials, of the latest edition of the Indiana Department of Transportation's "Standard Specifications".

C. Special Hydraulic Structures

Special hydraulic structures required to control the flow of water in storm runoff drainage systems include junction chambers, drop manholes, inverted siphons, stilling basins, and other special structures. The use of these structures shall be limited to those locations justified by prudent planning and by careful and thorough hydraulic engineering analysis.

VIII. Open Channel Design Standards

All open channels, whether private or public, and whether constructed on private or public land, shall conform to the design standards and other design requirements contained herein.

A. Manning's Equation

The waterway for channels shall be determined using Manning's Equation.

Mannings Equation 2 link

Where: A = Waterway area of channel in square feet
Q = Discharge in cubic feet per second (cfs)
V, R, S & n are explained in Paragraph VI.,A.

B. Channel Cross Section and Grade

The required channel cross section and grade are determined by the design capacity, the material in which the channel is to be constructed, and the requirements for maintenance. A minimum depth may be required to provide adequate outlets for subsurface drains, tributary ditches, or streams. The channel grade shall be such that the velocity in the channel is high enough to prevent siltation but low enough to prevent erosion. Velocities less than 1.5 feet per second should be avoided because siltation will take place and ultimately reduce the channel cross section. The maximum permissible velocities in vegetal-lined channels are shown in Table 5. Developments through which the channel is to be constructed must be considered in design of the channel section.

C. Side Slopes

Earthen channel side slopes shall be no steeper than 3 to 1. Flatter slopes may be required to prevent erosion and for ease of maintenance. Where channels will be lined, side slopes shall be no steeper than 1.5 to 1 with adequate provisions made for weep holes.

Side slopes steeper than 1.5 to 1 may be used for lined channels provided that the side lining and structural retaining wall are designed and constructed with provisions for live and dead load surcharge.

D. Channel Stability

1. Characteristics of a stable channel are:

It neither aggrades nor degrades beyond tolerable limits.
The channel banks do not erode to the extent that the channel cross section is changed appreciably.
Excessive sediment bars do not develop.
Excessive erosion does not occur around culverts, bridges or elsewhere.
Gullies do not form or enlarge due to the entry of uncontrolled surface flow to the channel.

2. Channel stability shall be determined for an aged condition and the velocity shall be based on the design flow or the bank full flow, whichever is greater, using "n" values for various channel linings as shown in Table 4. In no case is it necessary to check channel stability for discharges greater than that from a 100 year return period storm.

3. Channel stability must be checked for conditions immediately after construction. For this stability analysis, the velocity shall be calculated for the expected flow from a ten-year return period storm on the watershed, or the bank full flow, whichever is smaller. The "n" value for newly constructed channels in fine-grained soils and sands may be determined in accordance with the National Engineering Handbook 5, Supplement B, Soil Conservation Service and shall not exceed 0.025. The allowable velocity in the newly constructed channel may be increased by a maximum of 20 percent to reflect the effects of vegetation to be established under the following conditions:

The soil and site in which the channel is to be constructed are suitable for rapid establishment and support of erosion controlling vegetation.
Species of erosion controlling vegetation adapted to the area, and proven methods of establishment are shown.
The channel design includes detailed plans for establishment of vegetation on the channel side slopes.

Table 5

Maximum Permissible Velocities in Vegetal-Lined Channels (1)

Permissible Velocity	Slope Range (2) (Percent)	Erosion Resistant Soils (ft. per sec)	Easily Eroded Soils (ft. per sec.)
Cover	0-5	8	6
Bermuda	5-10	7	5
Grass	Over 10	6	4

Bahia
Buffalo grass
Kentucky bluegrass	0-5	7	5
Smooth brome	5-10	6	4
Blue grama	Over 10	5	3

Grass mixtures (2)	0-5	5	4
Reed canarygrass	5-10	4	3

Lespediza sericea
Weeping lovegrass
Yellow bluestem (3)	0-5	3.4	2.5
Redtop
Alfalfa
Red fescue

Common lespedeza (4)	0-5	3.5	2.5
Sudangrass (5)

(1) Use velocities exceeding 5 feet per second only where good covers and proper maintenance can be obtained.

(2) Do not use on slopes steeper than 10 percent except for vegetated side slopes in combination with a stone, concrete, or highly resistant vegetative center section.

(3) Do not use on slopes steeper than 5 percent except for vegetated side slopes in combination with stone, concrete, or highly resistant vegetative center section.

(4) Annuals--use on mild slopes or as temporary protection until permanent covers are established.

(5) Use on slopes steeper than 5 percent is not recommended.

(1) From Soil Conservation Service, SCS-TP-61, Handbook of Channel Design for Soil & Water Conservation.

E. Drainage of Waterways

Vegetated waterways that are subject to low flows of long duration or where wet conditions prevail shall be drained with a tile system or by other means such as paved gutters. Tile lines may be outletted through a drop structure at the end of the waterway or through a standard tile outlet.

F. Establishment of New Regulated Drain

The Marshall County Drainage Board may mandate that storm drains and detention basins in residential subdivisions become regulated drains to insure the proper maintenance of the system. If the Board mandates the establishment of a new Regulated Drain, each developer must provide the necessary information and meet the requirements of the 1965 Indiana Drainage Code, as amended, for the establishment of a new Regulated Drain. The Marshall County Drainage Board shall determine the necessary easements for adequate maintenance of any new Regulated Drain.

G. Appurtenant Structures

The design of channels will provide all structures required for the proper functioning of the channel and the laterals thereto and travelways for operation and maintenance. Recessed inlets and structures needed for entry of surface and subsurface flow into channels without significant erosion or degradation shall be included in the design of channel improvements. The design is also to provide the necessary flood gates, water level control devices, and any other appurtenance affecting the functioning of the channels and the attainment of the purpose for which they are built.

The effect of channel improvements on existing culverts, bridges, buried cables, pipelines, and inlet structures for surface and subsurface drainage on the channel being improved and laterals thereto shall be evaluated to determine the need for modification or replacement. Culverts and bridges which are modified or added as part of channel improvement projects shall meet reasonable standards for the type of structure, and shall have a minimum capacity equal to the design discharge or governmental agency design requirements, whichever is greater.

H. Disposition of Spoils

Spoil material resulting from clearing, grubbing and channel excavation shall be disposed in such a manner which will:

Minimize overbank wash.
Provide for the free flow of water between the channel and floodplain unless the valley routing and water surface profile are based on continuous dikes being installed.
Not hinder the development of travelways for maintenance.
Leave the right-of-way in the best condition feasible, consistent with the project purposes, for productive use by the owner.
Improve the aesthetic appearance of the site to the extent feasible.
Be approved by the Indiana Department of Natural Resources or US Army Corps of Engineers (whichever is applicable) if deposited in the floodway.

IX. Construction and Materials of Open Channels

A. Construction

Specifications shall be in keeping with the current standards of engineering practice and shall describe the requirements for proper installation of the project to achieve its intended purpose.

B. Materials

Materials acceptable for use as channel lining are:

Grass
Revetment Riprap
Concrete
Hand-laid Riprap
Precast Cement Concrete Riprap
Grouted Riprap
Gabions

Other lining materials shall receive specific approval of the Sanitary Board of Trustees. Materials shall comply with the latest edition of the Indiana Department of Transportation's "Standard Specifications".

X. Storm Water Detention

The following shall govern the design of any improvement with respect to the detention of stormwater runoff.

A. Acceptable Detention Methods

The increased stormwater runoff resulting from a proposed development should be detained on-site by the provisions of appropriate wet or dry bottom reservoirs, by storage on flat roofs, parking lots, streets, lawns, or other acceptable techniques. Measures which retard the rate of overland flow and the velocity in runoff channels shall also be used to control the runoff rate partially. Detention basins shall be sized to store excess flows from storms with a one hundred (100) year return period. Control devices shall limit the discharge to a rate no greater than that prescribed by this ordinance (see SECTION 3, X., E. and F.).

B. Design Storm

Design of storm water detention facilities shall be based on a return period of once in 100 years. The storage volume and outflow rate shall be sufficient to handle storm water runoff from a 24 hour duration storm, as defined in SECTION 3, X., E. and F. Rainfall intensity-duration-frequency relationships shall be those given in Table 3.

C. Allowable Release Rate

The allowable release rate of storm water originating from a proposed development shall not exceed the amount specified in SECTION 1, II. - Storm Water Control Policy, and as described in SECTION 3, X., E. and F.

In the event the storm sewer system is inadequate to accommodate the release rate provided above, then the allowable release rate shall be reduced to that rate permitted by the capacity of the receiving storm sewer system, and additional detention as determined by the Sanitary Board of Engineers shall be required to store that portion of the runoff exceeding the capacity of the receiving sewers or waterways.

If more than one detention basin is involved in the development of the area upstream of the limiting restriction, the allowable release rate from any one detention basin shall be in direct proportion to the ratio of its drainage area to the drainage area of the entire watershed upstream of the restriction.

D. Drainage System Overflow Design

Drainage systems shall have adequate capacity to convey the storm water runoff from all upstream tributary Areas through the development under consideration for a storm of 100 year design return period calculated on the basis of the upstream land in its present state of development. An allowance, equivalent to the reduction in flow rate provided, shall be made for upstream detention when such upstream detention and release rate have previously been approved by the Sanitary Board of Trustees and evidence of its construction can be shown.

E. Determination of Storage Volume - Rational Method

For Areas of two hundred (200) acres or less, the Rational Method may be used to determine the required volume of storm water storage. The following eleven step procedure may be used to determine the required volume of storage. Other design methods may also be used, subject to approval of the Sanitary Board of Trustees, and as described in SECTION 3, X., F.

Steps Procedure:

Determine total drainage area in acres "A".
Determine composite runoff coefficient "Cu" based on existing land use (undeveloped).
Determine time of concentration "tc" in minutes based on existing conditions.
Determine rainfall intensity "Iu" in inches per hour, based on time of concentration and using FIGURE 1 or from data given in Table 3 for the ten (10) year return period.
Compute runoff based on existing land use (undeveloped), and ten (10) year return period:
Qu = CuIuA
Determine composite runoff coefficient "Cd" based on developed conditions and a one hundred (100) year return period.
Determine the one hundred (100) year return period rainfall intensity "Id" for various storm durations "td" up through the time of concentration for the developed area using Table 3.
Determine developed inflow rates "Qd" for various storm durations "td", measured in hours.
Qd = CdIdA
Compute a storage rate "Std" for various storm durations "td" up through the time of concentration of the developed area.
Std = Qd - Qu
Compute required storage volume "SR" in acre-feet for each storm duration "td". This assumes a triangular hydrograph of duration (2*td) hours with the peak flow of Std at td hours.
SR = Std (td/12)
Select the largest storage volume computed in step 10 for detention basin design.

F. Determination of Storage Volume - Other Methods

Methods other than the rational method for determining runoff and routing of storm water may be used to determine the storage volume required to control stormwater runoff. The procedures or methods used must receive the prior approval of the Sanitary Board of Trustees. The ILLUDAS, TR-20 and TR-55 models are approved by the Sanitary Board of Trustees for appropriate use in analysis of the runoff and routing of storm water. The use of these models or other approved procedures can be defined in a seven step procedure to determine the required storage volume of the detention basin(s).

Step Procedure:

Calibrate the hydrologic/hydraulic model that is to be used for prediction of runoff and routing of storm water.
For each storm duration listed in Table 3, perform steps three through six.
Determine the ten (10) year, undeveloped peak flow. Denote this flow by Qu10.
Determine the one hundred (100) year runoff hydrograph (Hd100) for developed conditions.
Determine the hydrograph that must be stored (Hs100) by subtracting a flow up to Qu10 from the hydrograph (Hd100) found in step 4.
Determine the volume of water (Vs) to be stored by calculating the area under the hydrograph Hs100.
The detention basin must be designed to store the largest volume (Vs) found for any storm duration analyzed in step 6.

G. General Detention Basin Design Requirements:

Basins shall be constructed to detain temporarily the storm water runoff which exceeds the maximum peak flow rate authorized by this Ordinance. The volume of storage provided in these basins, together with such storage as may be authorized in other on-site facilities shall be sufficient to control excess runoff from the one hundred (100) year storm.

The following design principles shall be observed:

The maximum volume of water stored and subsequently released at the design release rate shall not result in a storage duration in excess of 48 hours unless additional storms occur within the period.
The maximum planned depth of storm water stored (without a permanent pool) shall not exceed four feet.
All storm water detention facilities shall be separated by not less than 75 feet from any building or structure to be occupied.
All excavated excess spoil may be spread so as to provide for aesthetic and recreational features such as sliding hills, sports fields, etc. Slopes no steeper than 6 horizontal to 1 vertical for safety, erosion control, stability, and ease of maintenance shall be permitted.
Safety screens having a maximum opening of 4 inches shall be provided for any pipe or opening to prevent children or large animals from crawling into the structures.
Danger signs shall be mounted at appropriate locations to warn of deep water, possible flooding conditions during storm periods and other dangers that exist. Fencing shall be provided if deemed necessary by the Sanitary Board of Trustees.
Outlet control structures shall be designed to operate as simply as possible and shall require little or no maintenance and/or attention for proper operation. They shall limit discharges into existing or planned downstream channels or conduits so as not to exceed the predetermined maximum authorized peak flow rate.
Emergency overflow facilities such as a weir or spillway shall be provided for the release of exceptional storm runoffs or in emergency conditions should the normal discharge devices become totally or partially inoperative. The overflow facility shall be of such design that its operation is automatic and does not require manual attention.
Grass or other suitable vegetative cover shall be provided throughout the entire basin area. Grass should be cut regularly at approximately monthly intervals during the growing season or as required.
Debris and trash removal and other necessary maintenance shall be performed on a regular basis to assure continued operation in conformance to design.
A report shall be submitted with the preliminary or final plan as stated in SECTION 3, I., F.

H. Dry Bottom Basin Design Requirements

Detention basins which will not contain a permanent pool of water shall comply with the following requirements:

Provisions shall be incorporated to facilitate complete interior drainage of dry bottom basins, to include the provisions of natural grades to outlet structures, longitudinal and transverse grades to perimeter drainage facilities, paved gutters, or the installation of subsurface drains.
The detention basin shall, whenever possible, be designed to serve a secondary or multipurpose function. Recreational facilities, aesthetic qualities (open spaces) or other types of use shall be considered in planning the detention facility.

I. Wet Bottom Basin Design Requirements

Where part of a detention basin will contain a permanent pool of water, all the items required for detention storage shall apply except that the system of drains with a positive gravity outlet required to maintain a dry bottom basin will not be required. A controlled positive outlet will be required to maintain the design water level in the wet bottom basin and provide required detention storage above the design water level.

However, the following conditions shall apply:

Basins designed with permanent pools or containing permanent ponds shall have a water area of at least one-half acre. If fish are to be maintained in the pond, a minimum depth of approximately 10 feet shall be maintained over at least 25 percent of the pond area. The remaining pond area shall have no extensive shallow areas, except as required by subsection (3) below.
In excavated ponds, the underwater side slopes in the pond shall be stable. In the case of valley storage, natural slopes may be considered to be stable.
A safety ledge four to six feet in width is required and must be installed in all ponds approximately 30 to 36 inches below the permanent water level. In addition, a similar maintenance ledge 12 to 18 inches above the permanent water line shall be provided. The slope between the two ledges shall be stable and of a material such as stone or riprap which will prevent erosion due to wave action.
A safety ramp exit from the pond is required in all cases and shall have a minimum width of 20 feet and exit slope of 6 horizontal to 1 vertical. The ramp shall be of a material that will prevent its deterioration due to vehicle use and/or wave action.
Periodic maintenance is required in ponds to control weed and larval growth. The pond shall also be designed to provide for the easy removal of sediment which will accumulate during periods of pond operation. A means of maintaining the designed water level of the pond during prolonged periods of dry weather is also required.
For emergency use, basin cleaning, or shoreline maintenance, facilities shall be provided or plans prepared for auxiliary equipment to permit emptying and drainage.
Facilities to enhance and maintain pond water quality shall be provided, if required to meet applicable water quality standards. Design calculations to substantiate the effectiveness of these aeration facilities shall be submitted with final engineering plans. Agreements for the perpetual operation and maintenance of aeration facilities shall be prepared to the satisfaction of the Sanitary Board of Trustees.

J. Roof Top Storage

Detention storage requirements may be met in total or in part by detention on flat roofs. Details of such designs are to be included in the building permit application and shall include the depth and volume of storage, details of outlet devices and downdrains, and elevations of emergency overflow provisions.

K. Parking Lot Storage

Paved parking lots may be designed to provide temporary detention storage of storm waters on all or a portion of their surfaces. Outlets will be designed so as to empty the stored waters slowly. Depths of storage must be limited to a maximum depth of 7 inches so as to prevent damage to parked vehicles and so that access to parked vehicles is not impaired. Ponding should, in general, be confined to those positions of the parking lots farthest from the area served.

L. Facility Financial Responsibility

M. Facility Maintenance Responsibility

Maintenance of detention/retention facilities during construction and thereafter, shall be the responsibility of the land developer/owner. Assignment of responsibility for maintaining facilities serving more than one lot or holding shall be documented by appropriate covenants to property deeds, unless responsibility is formally accepted by a public body, and shall be determined before the final drainage plans are approved.

Storm water detention and retention basins may be donated to the City or other unit of government designated by the City, for ownership and permanent maintenance providing:

The City or other governmental unit is willing to accept responsibility.
The facility has been designed and constructed according to all applicable provisions of this ordinance.
All improvements have been constructed, approved, and accepted by the governmental agency for the land area served by the drainage basin.
Detention ponds containing a permanent pool of water have all slopes between the riprap and high water line sodded and the remaining land area hydroseeded; are equipped with electrically driven aeration devices, if required to maintain proper aerobic conditions and sustain aquatic life; have a four-foot wide crushed limestone walkway at the high water line entirely around the body of water; provide suitable public access acceptable to the responsible governmental agency; and have the high water line not closer than 75 feet to any property line.
Dry detention ponds shall have all slopes, bottom of the basin and Areas above the high water line hydroseeded; and shall have the high water line not closer than 50 feet to any development boundary.

N. Inspections

All public and privately owned detention storage facilities can be inspected by representatives of the City not less often than once every 2 years. If inspected, a certified inspection report covering physical conditions, available storage capacity and operational condition of key facility elements will be provided to the owner.

O. Corrective Measures

If deficiencies are found by the inspector, the owner of the detention/retention facility will be required to take the necessary measures to correct such deficiencies. If the owner fails to do so, the City will undertake the work and collect from the owner using lien rights, if necessary.

P. Joint Development of Control Systems

Storm water control systems may be planned and constructed jointly by two or more developers as long as compliance with this Ordinance is maintained.

Q. Installation of Control Systems

Runoff and erosion control systems shall be installed as soon as possible during the course of site development. Detention/ retention basins shall be designed with an additional (six) percent of available capacity to allow for sediment accumulation resulting from development and to permit the pond to function for reasonable periods between cleanings. Basins should be designed to collect sediment and debris in specific locations so that removal costs are kept to a minimum.

R. Detention Facilities in Floodplains

If detention storage is provided within a floodplain, only the net increase in storage volume above that which naturally existed on the floodplain shall be credited to the development. No credit will be granted for volumes below the elevation of the regulatory flood at the location unless compensatory storage is also provided.

S. Off-Site Drainage Provisions

XI. Other Requirements

A. Sump Pumps

Sump pumps installed to receive and discharge groundwaters or other storm waters shall be connected to the storm sewer where possible or discharged into a designated storm drainage channel. Sump pumps installed to receive and discharge floor drain flow or other sanitary sewage shall be connected to the sanitary sewers. A sump pump shall be used for one function only, either the discharge of storm waters or the discharge of sanitary sewage.

B. Down Spouts

All down spouts or roof drains shall discharge onto the ground or be connected to the storm sewer. No down spouts or roof drains shall be connected to the sanitary sewers.

C. Footing Drains

Footing drains shall be connected to storm sewers where possible or designated storm drainage channels. No footing drains or drainage tile shall be connected to the sanitary sewer.

D. Basement Floor Drains

Basement floor drains shall be connected to the sanitary sewers.

Section 3 - Specifications and Technical Information

I. Information Requirements

II. System Design Criteria

III. Storm Water Retention

IV. Determination of Runoff Quantities

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