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(a) Purpose. The following provisions in this Section are established to preserve and provide properly located public sites and facilities for drainage and stormwater management as the community develops, and to insure that the costs of providing and developing such public sites are equitably apportioned on the basis of serving the need for the management of increased stormwater quantities resulting from land development.
(b) Drainage System Required.
(1) As required by Section 14-1-58, a drainage system shall be designed and constructed by the subdivider to provide for the proper drainage of the surface water of the land division and the drainage area of which it is a part. A Final Plat shall not be approved until the subdivider shall submit plans, profiles and specifications as specified in this Section, which have been prepared by a registered professional engineer and approved or modified by the Village Board, upon the recommendations of the Plan Commission and Village Engineer.
(2) Lots shall be laid out so as to provide positive drainage away from all buildings, and individual lot drainage shall be coordinated with the general storm drainage pattern for the area. Drainage shall be designed so as to avoid concentration of storm drainage water from each lot to adjacent lots.
(3) The Plan Commission shall not recommend for approval any subdivision plat which does not provide adequate means for stormwater or floodwater runoff. Any stormwater drainage system will be separate and independent of any sanitary sewer system. Storm sewers, where necessary, shall be designed in accordance with all governmental regulations, and a copy of design computations for engineering capacities shall accompany plans submitted by the planning engineer for the final plat. When calculations indicate that curb capacities are exceeded at a point, no further allowance shall be made for flow beyond that point, and basins shall be used to intercept flow at that point.
(c) Drainage System Plans.
(1) The subdivider shall submit to the Village at the time of filing a Preliminary Plat a preliminary drainage plan or engineering report on the ability of existing watercourse channels, storm sewers, culverts and other improvements pertaining to drainage or flood control within the subdivision to handle the additional runoff which would be generated by the development of the land within the subdivision. Additional information shall be submitted to adequately indicate that provision has been made for disposal of surface water without any damage to the developed or undeveloped land downstream or below the proposed subdivision. The report shall also include:
a. Estimates of the quantity of storm water entering the subdivision naturally from areas outside the subdivision.
b. Quantities of flow at each inlet or culvert.
c. Location, sizes and grades of required culverts, storm drainage sewers and other required appurtenances.
(2) A grading plan for the streets, blocks and lots shall be submitted by the subdivider for the area within the subdivision.
(3) The design criteria for storm drainage systems shall be based upon information provided by the Village Engineer.
(4) Material and construction specifications for all drainage projects (i.e., pipe, culverts, seed, sod, etc.) shall be in compliance with specifications provided by the Village Engineer.
(d) Drainage System Requirements. The subdivider shall install all the storm drainage facilities indicated on the plans required in Subsection (a) of this Section necessary to serve, and resulting from, the phase of the land division under development:
(1) Street Drainage. All streets shall be provided with an adequate storm drainage system. The street storm system shall serve as the minor drainage system and shall be designed to carry street, adjacent land and building storm water drainage. Storm water shall not be permitted to be run into the sanitary sewer system within the proposed subdivision.
(2) Off-Street Drainage. The design of the off-street major drainage system shall include the entire watershed affecting the land division and shall be extended to a watercourse or ditch adequate to receive the storm drainage. When the drainage system is outside of the street right-of-way, the subdivider shall make provisions for dedicating an easement pursuant to Subsection (e) of the Village to provide for the future maintenance of said system.
(e) Protection of Drainage Systems. The subdivider shall adequately protect all ditches to the satisfaction of the Village Engineer. Ditches and open channels shall be seeded, sodded or paved depending upon grades and soil types. (Generally ditches or channels with grades up to one percent [1%] shall be seeded; those with grades up to four percent [4%] shall be sodded and those with grades over four percent [4%] shall be paved.)
(f) Drainage Easements. Where a land division is traversed by a watercourse, drainageway, channel or stream:
(1) There shall be provided a storm water easement or drainage right-of-way conforming substantially to the lines of such watercourse and such further width or construction, or both, as will be adequate for the purpose and as may be necessary to comply with this Section; or
(2) The watercourse, drainageway, channel or stream may be relocated in such a manner that the maintenance of adequate drainage will be assured and the same provided with a storm water easement or drainage right-of-way conforming to the lines of the relocated watercourse, and such further width or construction, or both, as will be adequate for the purpose and may be necessary to comply with this Section; or
(3) Wherever possible, drainage shall be maintained in an easement by an open channel with landscaped banks and adequate width for maximum potential volume flow. In all cases, such easements shall be of a minimum width established at the high water mark or, in the absence of such specification, not less than thirty (30) feet.
(g) Dedication of Drainageways. Whenever a parcel is to be subdivided or consolidated and embraces any part of a drainageway identified on a Village Comprehensive Storm Water Management Plan, master plan and/or official map or any portion thereof, such part of said existing or proposed public drainageway shall be platted and dedicated by the subdivider as an easement or right-of-way in the location and at the size indicated along with all other streets and public ways in the land division. Whenever any parcel is to be subdivided or consolidated and is part of a drainage district established under the authority of Chapter 88, Wis. Stats., the subdivider shall petition the Circuit Court to transfer the jurisdiction of that portion of the drainage district being subdivided or consolidated to the Village in accordance with Chapter 88.83, Wis. Stats.
(h) Dedication/Preservation of Storm Water Management Facilities. The subdivider shall dedicate sufficient land area for the storage of storm water to meet the needs to be created by the proposed land development and in accordance with the standards for on-site detention and as determined by the Village Engineer. Whenever a proposed storm water management facility (e.g., detention or retention basin) shown on the Comprehensive Storm Water Management Plan, master plan and/or official map is located, in whole or in part, within the proposed land division, ground areas for providing the required storage capacity in such proposed public facility shall be dedicated to the public to the requirements o the master plan and/ or official map. Storage areas necessary to serve areas outside the land division shall be held in reserve for a period of five (5) years from the date of final plat approval for future acquisition by the Village or other appropriate agency having the authority to purchase said property. The subdivider and Village shall enter into an agreement with the Village to provide for the purchase of the lands held in reserve prior to the conclusion of the five (5) year reserve period.
(i) Storm Drainage Facilities.
(1) The subdivider, at his cost, shall install all drainage facilities identified in the Erosion Control Plan or determined by the Village Engineer as being necessary for the management of all lands and roadways within the development. In addition, drainage capacity through the development from other areas shall be provided in accordance with a Comprehensive Surface Water Management Study, if applicable. All required storm drainage facilities shall be constructed and operational prior to acceptance of any dedications and/or public improvements served by the storm drainage facilities.
(2) The subdivider shall submit to the Village Engineer for his review and approval a report on the ability of existing watercourse channels, storm sewers, culverts and other improvements pertaining to drainage or flood control within the land division to handle the additional runoff which would be generated by the development of the land within the land division. Additional information shall be submitted to adequately indicate that provision has been made for disposal of surface water without any damage to the developed or undeveloped land downstream or below the proposed land division. The report shall also include:
a. Estimates of the quantity of storm water entering the land division naturally from areas outside the land division.
b. Quantities of flow at each inlet or culvert.
c. Location, sizes and grades of required culverts, storm drainage sewers and other required appurtenances.
(3) A grading plan for the streets, blocks and lots shall be submitted by the subdivider for the area within the land division.
(4) The design criteria for storm drainage systems shall be reviewed by the Village Engineer and approved or modified.
(5) Material and construction specifications for all drainage projects (i.e., pipe, culverts, seed, code, etc.) shall be in compliance with standards and specifications provided by Village ordinance and/or the Village Engineer.
(j) Minor Drainage System. The subdivider shall install all minor drainage system components necessary to reduce inconvenience and damages from frequent storms. Minor drainage components shall include all inlets, piping, gutters, channels, ditching, pumping and other facilities designed to accommodate the post-development runoff resulting from a two (2) year, twenty-four (24) hour rainfall [ten (10) year, twenty-four (24) hour rainfall for commercial zoning district] event as determined in the most current edition of the Soils Conservation Service Technical Release 55 (TR 55). Temporary accumulations of storm runoff from ponding or flowing water, in or near minor system components, shall be permitted providing such accumulations do not encroach on any traffic lane of any collector or arterial street, nor on the center twenty-four (24) feet of any local street, except on cul-de-sac or permanently dead-end streets serving less than ten (10) dwelling units, where such accumulations may not overtop the curb. In drainageways and drainageway easements, accumulations of water shall not inundate beyond the limits of the drainageway or drainageway easement. Cross- street drainage channels (valley gutters) shall not be permitted except on cul-de-sac or permanent dead-end streets serving less than ten (10) dwelling units and where the minimum grade in the valley gutter and street gutter between the valley gutter and the next downstream drainage inlet is not less than one percent (1.00%).
(k) Major Drainage System. The subdivider shall install all major drainage system components necessary to reduce inconvenience and damages from infrequent storms. Major system components shall include large channels and drainageways, streets, easements and other paths and shall be capable of accommodating post- development runoff in excess of that accommodated by minor system components resulting from twenty-four (24) hour rainfall events for storms with return frequencies greater than two (2) years up to and including the one hundred (100) year return event (as identified in TR 55). On local and collector streets and drainageways and drainage easements, accumulations of water shall not inundate any buildings at the ground line, unless such buildings are flood-proofed. On arterial streets and in commercial zoning districts, accumulations of water shall not inundate any buildings at the ground line, unless such buildings are flood- proofed and the depth of water at the street crown shall not exceed six (6) inches to permit operation of emergency vehicles.
(l) Drainage Piping Systems.
(1) Unless otherwise approved by the Village Engineer, all drainage piping of twelve (12) inches diameter and greater in street rights-of-way shall be constructed of Class Three (3) reinforced concrete pipe. Piping materials outside of rights-of-way shall be subject to approval of the Village Engineer. Open drainage inlet pipes or culverts with any opening dimension in excess of eighteen (18) inches shall be equipped with debris grates having an exposed area at least seven (7) times the pipe opening area to avoid backwater accumulations from trash buildup and unsafe stream velocities and a maximum opening size of six (6) inches. Drainage piping outfalls with any opening dimension in excess of thirty-six (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 Village 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 Village Engineer.
(2) When, on the basis of the soils information, the Village Engineer determines that the ground water elevation is less than nine (9) feet below the proposed street centerline elevation and the adjacent lots have access to a storm drainage piping system, the subdivider shall be required to provide approved sump pump laterals from the storm sewer piping system to the property line of each lot for connection to by the property owner.
(3) Agricultural drain tiles which are disturbed during construction shall be restored, reconnected or connected to public storm drainage facilities.
(m) Open Channel Systems.
(1) Where open channels are utilized in either the minor or major drainage system, they shall be designed so as to minimize maintenance requirements and maximize safety. Drainage easements (in lieu of dedications) shall be utilized to accommodate open channels provided adequate access by the Village for maintenance of drainage capacity. Side slopes shall not exceed a four-to-one (4:1) slope. Drainageways with grades of 0.75% or less, or where subject to high ground water, continuous flows, or other conditions as determined by the Village Engineer that would hamper maintenance operations due to consistently wet conditions, shall have a paved concrete invert of not less than eight (8) feet wide and side slopes to a point one (1) foot above the channel invert.
(2) In areas where invert paving is not required, the drainageway bottom shall be grass. If the drainageway has a bare soil bottom or the natural grasses in the drainageway are disturbed due to development operations, the drainageway bottom shall be sodded and securely staked to one (1) foot above the elevation of inundation resulting from a predevelopment five (5) year, twenty-four (24) hour storm event. Other disturbed areas shall be seeded and prepared in accordance with the Village's Erosion Control requirements. Velocities for grass-lined channels shall not exceed those presented in the Village's Surface Water Management Study, if one is adopted.
(n) Standards for On-Site Detention Storage. The subdivider may employ on-site detention to control erosion and sedimentation, reduce the post-development peak runoff rate or temporarily store storm water runoff due to inadequate down- stream drainage facilities. The detention (storage) facilities shall be subject to regulation in accordance with the following standards:
(1) Where on-site detention is temporarily employed for erosion and sedimentation control, the detention facilities shall safety contain the predevelopment runoff from a twenty-five (25) year storm event of twenty-four (24) hour duration within the limits of the facility.
(2) Where on-site detention is permanently employed to reduce the postdevelopment peak runoff, the detention facility shall safety contain the post-development runoff from a twenty-five (25) year storm event of twenty-four (24) hour duration within the limits of the facility.
(3) Detention facility peak discharge rates for the maximum storm required to be contained shall not exceed the predevelopment peak discharge rate from a five (5) year storm event of twenty-four (24) hour duration or the capacity of the downstream drainage facilities, whichever is less.
(4) All temporary detention facilities shall safety contain or pass the runoff from any storm of any duration which exceeds the maximum storm required to be contained up to the one hundred (100) year storm event of twenty-four (24) hour duration.
(5) All permanent detention facilities shall safety contain the runoff from the one hundred (100) year storm event of twenty-four (24) hour duration on both public and, if necessary, private properties without inundating any building at the ground elevation, the travel lanes of any arterial street, the center ten (10) feet of any collector street or the top of the curb on any local street.
(6) Determination of on-site detention volumes shall be computed by procedures established by the United States Soil Conservation Service in the most current edition of its technical publication entitled "Urban Hydrology for Small Watersheds, TR-55," and as accepted and approved by the Village Engineer.
(7) The storage of storm water runoff shall not encroach on any public park (except parks designed with detention facilities) or any private lands outside the land division unless an easement providing for such storage has been approved and recorded for said lands.
(8) All detention facilities shall be designed with the safety of the general public and any considerations for ease of maintenance as top proprieties.
(9) Any wet detention facilities shall include riprap to not less than two (2) feet above the normal pool elevation for protection from wave action.
(10) The sides of all detention facilities shall have a maximum slope ratio of four to one (4:1) (horizontal to vertical), with flatter slopes being required where determined practical by the Village Engineer.
(11) The Village Board, upon recommendation by the Village Engineer, may require the installation of fencing or other such security measures in detention facilities with excessively long down times or permanent water features, or other features requiring additional security for safety reasons.