STORM WATER DRAINAGE STANDARDS

 

 

The following provisions are established to preserve and provide for the orderly and adequately sized storm water drainage facilities for the management of increased storm water quantities resulting from increased urbanization. The Surface Water Drainage Requirements, most recently adopted Winnebago County Town/County Zoning Ordinance, are referenced here to identify the minimum design requirements for all developments subject to this zoning ordinance.

 

(1) Minor Drainage System:

Minor drainage system components shall include and consist of all inlets, piping, gutters, channels, ditching, pumping and conveyance facilities to intercept and transport drainage from individual lots and roadways to a central, common location where a major drainage system would begin.  In general terms, roadway drainage requiring piping or drainage structures smaller than 24-inches in diameter would be classified as part of the minor drainage system.

 

(2) Major Drainage System:

Major drainage system components shall include and consist of all channels, ditching, piping and conveyance facilities to transport drainage from minor drainage system facilities to the point or location of discharge.  In general terms, drainage values requiring piping larger than 24-inches in diameter would be classified as part of the major drainage system.

 

(3) Drainage Calculations:

 

(a)    Storm water drainage computations shall be submitted to the Town Engineer for approval.  The computations shall be accompanied by a drainage area plan showing all major drainage basins and sub-basins within the development and contributing areas outside of the development.

 

(b)   Rate of runoff computations shall be made for the use of sizing road culverts, drainage structures, detention areas, ditches and storm sewers.  The Soil Conservation Service Technical Release 55 (TR55) method shall be required.  Use of other methods of runoff computations shall require written permission of the Town Engineer.

 

(c)    Road culverts shall be designed using the standard procedures and graphs shown in the Hydraulic Engineering Circulars published by the Federal Highway Administration.

 

(d)   Detention and retention basins or areas shall be designed using the flood routing procedure conforming to the storage equation of It-S=Ot:

 

                        I = inflow in cfs

                        t = time

                        S = change in storage in feet;

                        O = outflow in cfs

 

(e)    Drainage ditches and storm sewers shall be designed using the Manning equation and the methods outlined in the State of Wisconsin Department of Transportation Facilities Development Manual.

 

(4)  Open Channel Systems:

 

(a) General:

 

Where open channels are utilized, they shall be designed so as to minimize maintenance requirements and maximum safety.  Drainage easements (in lieu of dedications) may be utilized to accommodate open channels provided adequate access for maintenance of the drainage is also provided.

 

(b) Design Details:

 

All ditch slide slopes shall not exceed a 3:1 slope.  The minimum depth of road ditches below the finished grade of the centerline shall be 18-inches deep, except that at a high point of the ditch, the depth may be a minimum of 12-inches.  The maximum depth of road ditches below the finished grade of the centerline shall be 60 inches deep. There shall be a minimum of 46-feet in width between the centerline of the road ditches.

 

            (c) Grade:

 

The minimum grade for any ditch invert shall not be less than 2.0% in the direction of flow.  Where the grade is less than 2.0% but greater than 1.5%, additional facilities shall be provided consisting of a minimum of a 6-inch diameter sump pump collector system.  Where the grade is less than l.5% but greater than 1.0%, additional facilities shall be provided consisting of a storm sewer system capable of handling storm water runoff generated from a ten (10) year frequency rainfall event.  In addition, there shall be provisions within the design layout of the subdivision or area to be serviced by this storm sewer for the conveyance of the runoff volume in excess of the ten (10) year return frequency rainfall event so as to provide protection of major structures, building and roadways from flooding and ponding in excess of 2-feet. No new drainage way shall be designed at less than 1.0% grade.

 

Minor drainage system facilities shall be provided with a french drain system located below the ditch invert consisting of a 6-inch minimum diameter perforated tile, gravel and drainage filter fabric envelope.  This underdrain system shall be designed to accommodate the flows from sump pump discharge from adjacent properties.  This drain system shall also be designed to discharge with a free fall to an open drainage way.

 

Major drainage system facilities shall be provided with a similar french drain system located below the ditch invert or shall have a concrete paved invert of sufficient size and capacity to convey the required runoff volume.

 

            (d) Ditch Lining:

 

All ditches not having a concrete paved invert section shall be dressed with a minimum of 3-inches of top soil, carefully graded to the established line and elevations.

 

(e)    Seeding:

 

The seed bed shall be prepared by raking to remove lumps, stones, rocks and debris.  The seed shall be composed of seeds of the purity, germination and proportions, by weight, as given below:

 

 

TABLE OF SEED MIXTURES

 

                                                    Seed            Mixtures

 

                                                     in., %             Min., %        No. 1,           No. 2,

Species                                        Purity           Germination         %                 %

 

Kentucky Bluegrass                      85                      80                     45             20

Creeping Red-Fescue                   97                      80                    35              55

Perennial Ryegrass                        95                      90                      5              10       

White Clover                                95                      90                     15              ---

Empire Birdsfoot Trefoil                95                      80                     --              15

 

Seed Mixture No. 1 is intended for use on projects where loam, heavy clay average or moisture soils predominate.  Seed Mixture No. 1 shall be sown at a rate of 1-1/2 pounds per 1,000 square feet.  Seed Mixture No. 2 is intended for use on projects where light, dry, sandy or gravelly soils predominate.  Seed Mixture No. 2 shall be sown at a rate of 2 pounds per 1,000 square feet.

 

In areas where the soils are potentially highly erosive, the Town Board may require a specially designed seed mixture and seeding rate as recommended in 630.2.1.5.1.2 of the State of Wisconsin Department of Transportation Standard Specifications for Road and Bridge Construction, latest Edition.

 

(f) Mulching:

 

All seeded areas must be mulched.  Mulching material shall consist of any straw or hay in an air condition or wood excelsior fiber, wood chips or other suitable material of a similar nature which is substantially free of noxious weed seeds and objectionable foreign matter.

 

Mulch shall be placed on a given area within three (3) days after the seeding has been completed.  The mulching material shall be uniformly spread over the seeded areas to a loose depth of no less than 1-inch.

 

In ditches which shall be especially susceptible to erosion, the Town Engineer may order the use of excelsior mat or jute netting over seeded areas.

 

(g)   All open drainage ways and culverts shall be designed to convey the runoff generated from a twenty-five (25) year return frequency rainfall event as required to meet the provisions of the Surface Water Drainage Section of Winnebago County Zoning Ordinance.

 

(5)  Drainage Piping System:

 

   (a) Culvert Pipes:

 

All drainage piping shall be no smaller than 15-inches in diameter.  All drainage piping located beneath or crossing a Town roadway shall be constructed of Class 3 reinforced concrete unless the depth of cover is less than 2-feet where the pipe shall be Class 5 reinforced concrete.  Prefabricated end sections shall be provided at the ends of all culvert pipes.  In areas of high susceptibility of erosion to the embankment at the ends of the culverts, the Town Engineer may order the use of rip-rap, headwall or slope paving at the ends of the culvert.  All culverts shall be a minimum of 40-feet in length.  The culvert length shall be increased as is necessary to provide a stable embankment slope of no steeper than two (2) (horizontal) to one (1) (vertical).

 

(b)  Storm Sewer:

 

Storm sewers shall be constructed per the requirements as set forth in the Standard Specifications for Sewer & Water Construction in Wisconsin, Fourth Edition, March 1, 1980.  All storm sewer pipes shall be one of the following materials:

 

            -   Reinforced concrete for all sizes

            -   PVC SDR 3S for sizes less than 15-inches

            -   ABS truss pipe for sizes less than 15-inches

 

(c) Protection:

 

Open drainage piping and culverts with any opening dimension in excess of 18-inches shall be equipped with debris grates having an exposed area of at least 18-inches, shall be equipped with debris grates having an exposed area of at least five (5) times the pipe opening area to avoid backwater accumulations from trash buildup and unsafe stream velocities and a maximum opening size of 6-inches.  Drainage piping outfalls with any opening dimension in excess of 36-inches shall be protected from unauthorized entry by fencing, partial or total submergence of the outlet, debris grates or other methods approved by the Town Engineer unless in such a location as to render routine maintenance operations impossible.  Outfalls and their channels shall be protected from damages due to scour and erosion to the satisfaction of the Town Engineer.

 

(d) All underground storm sewer systems shall be designed to convey the runoff generated from a ten (10) year frequency rainfall event.  In addition, there shall be provisions within the design layout of the subdivision or area to be serviced by this storm sewer for the conveyance of the runoff volume in excess of the ten (10) year return frequency rainfall event so as to provide protection of major structures, building and roadways from flooding and ponding in excess of 2-feet.

 

(6) Disruption of Drainage:

 

It shall be unlawful for any person, firm, corporation or public utility to fill or obstruct any ditch alongside a Town road, any drainage easement or any creek, stream, river or canal with any dirt, debris or construction, without prior written approval of the Town Board.

 

(a)           It shall be unlawful for any person, firm, corporation of public utility to landscape, cultivate, plow or remove soil from their property in such a manner as to obstruct or fill any ditch, drainage easement, creek, stream, river or canal without prior written approval of the Town Board.

 

(b)           Any person, firm, corporation or public utility who fills or obstructs or causes to be filled or obstructed any ditch, drainage easement, creek, stream, river or canal in violation of (a) or (b) above shall, on written order from the Street Department, correct such violation and restore the affected ditch, drainage easement, creek, stream, river or canal at their own expense.  If corrective and restorative action is not commenced within ten (10) days after receipt of such written order or completed within such reasonable time as the Street Department shall specify in writing, the Town of Menasha may proceed with such work as is necessary for said corporation and restoration may charge the costs of the work to the violator, to be collected through legal action or the levying of a special tax or assessment.

 

(c)                      Failure to comply with the provisions of this section shall constitute a public nuisance.

 

(d)                     Any person, firm, corporation or public utility violating the terms of this section shall be guilty of a violation and upon adjudication to that effect, shall be subject to a forfeiture of not less than fifty & no/100 dollars ($50.00) nor more than one hundred & no/100 dollars ($100.00) and in default of payment of such forfeiture, shall be subjected to imprisonment in the county jail for not less than ten (10) days nor more than thirty (30) days.