(A) Storm water regulations. It is not the intent of this chapter to take areas out of use for the sole purpose of storing excess storm water. Nor is it the purpose of this chapter to restrict land use or increase development costs. The basic purpose of this chapter is to eliminate the storage or transportation of excess storm water in or through habitable structures. The use of "natural" paths of storm water runoff to form the "by-pass" channel and the restriction of this channel to form storage areas is encouraged. Since political and ownership boundaries often make the use of "natural" drainage patterns difficult, the earthmoving that is accomplished to create the maximum land usage should also be planned to provide a "by-pass" channel for storm water that will not create a diversion of storm water drainage or radically change the watershed boundaries. The drainage scheme presented by those who wish to develop property in the city should be planned to accomplish all of the storm water controls of this chapter without major loss of land use.
(B) Soil erosion and sedimentation control. In regards to soil erosion and sedimentation control, the purpose of this chapter is to protect the public health, safety and welfare of the people of the city and the environment in which they live by guiding, regulating and controlling the design, construction, use and maintenance of any development or other activity which disturbs or breaks the topsoil or otherwise results in the movement of earth on land, or removes natural or cultivated vegetation, and which thereby creates the increased possibility of soil erosion, sediment deposits or flooding.
(Ord. 3270, passed 8-28-00)
The following definitions shall be applicable to this chapter:
BY-PASS CHANNEL. A channel formed in the topography of the earth's surface to carry storm water runoff through a specific area.
CLEARING. The cutting or destruction of trees, tree stumps of less than six inches in diameter, brush, or structures.
CONTROL STRUCTURE. A structure designed to control the volume of storm water runoff that passes through it during a specific length of time.
DEVELOPMENT. Any man-made change to improved or unimproved real estate, including but not limited to erection or removal of buildings or other structures, mining, dredging, filling, grading, paving, excavation, stripping, clearing, removal or drilling operations.
DRAINAGE. The removal of surface or ground water from a given area either by gravity or by pumping.
DRAINAGEWAY. A ditch, levee, watercourse, or other natural or artificial condition for the removal of surplus or excess surface water collecting or accumulating on the land.
DRY BOTTOM STORM WATER STORAGE AREA. A facility that is designed to be normally dry and contains water only when excess storm water runoff occurs.
EROSION. The natural wearing away of the land by the action of running water and/or wind.
EROSION, ACCELERATED. An increased wearing away of the land by the action of running water and/or wind resulting from the development of land, destruction of vegetative cover, or other activity of man.
EXCAVATE. Any act by which organic matter, earth, sand, gravel, rock or any other similar material is cut into, dug, quarried, uncovered, removed, displaced, relocated or bulldozed.
EXCAVATION. The condition resulting from excavating.
EXCESS STORM WATER. That portion of storm water runoff which exceeds the transportation capacity of storm sewers or natural drainage channels serving a specific watershed.
EXPOSED LAND. Land which has been stripped or from which vegetative cover and/or topsoil has been removed.
FILL. Any act by which earth, sand, gravel, rock, or any other material is deposited, placed, replaced, pushed, dumped, pulled, transported or moved by man to a new location.
GRADE, EXISTING. The vertical location of the existing ground or other surface prior to excavation or filling.
GRADE, FINAL. The vertical location of the ground or other surface after the grading work is completed in accordance with the erosion and sedimentation control plan.
GRADE, ROUGH. The vertical location of the ground or other surface after the commencement of grading but prior to the establishment of final grade.
GRADING. To excavate or fill or any combination thereof.
GROUND WATER RECHARGE. Replenishment of existing natural underground water supplies.
NATURAL DRAINAGE. Channels formed by the existing surface topography of the earth prior to changes made by unnatural causes.
PARCEL. All contiguous land under single ownership and/or unified control or all land included within a storm water control plan or an erosion and sedimentation control plan, whichever is greater.
POSITIVE GRAVITY OUTLET. A term used to describe the drainage of an area by means of natural gravity so that it lowers the free water surface to a point below the existing grade or invert of storm drains within the area.
RECOGNIZED AGENCY. An agency or governmental unit that has statistically and consistently examined local and climatic and geologic conditions and maintained records as they apply to storm water runoff, e.g., U.S. Weather Bureau, University of Illinois Engineering Experiment Station, Illinois State Water Survey, etc.
REMOVAL. Removing vegetation (including ground cover) to the ground and complete extraction of tree stumps by cutting, burning, chemical application or other means.
SAFE STORM DRAINAGE CAPACITY. A term used to describe the quantity of storm water runoff that can be transported by a channel or conduit without having the water surface rise above the level of the earth's surface over the conduit, or adjacent to the waterway.
SEDIMENTATION. The process of forming and depositing of suspended matter carried in suspension in water through the action of gravity. It is usually accomplished by reducing the velocity of the water below the point where it can transport the suspended material.
SETTLING. See SEDIMENTATION.
STORM WATER RUNOFF. Water that results from precipitation which is not absorbed by the soil or plant material.
STORM WATER RUNOFF RELEASE RATE. The rate at which storm water runoff is released from dominant to servient land.
STORM WATER STORAGE AREA. Areas designated to store excess storm water.
STRIPPING. Any activity which relocates topsoil and tree stumps with diameters of six inches or more from the site, or relocated topsoil for storage for later use on the site.
STRUCTURE. Any object which is constructed or erected and which requires permanent location on the land or attachment to an object having permanent location on the land. The term STRUCTURE is intended to include, but not be limited to, such objects as buildings, fences, parking lots, concrete or asphalt slabs, decks and patios.
STRUCTURE, HYDRAULIC. Any engineering structure for the purpose of regulation and control of water.
STRUCTURE, TEMPORARY. Any structure used to retard erosion or limit the flow of water, constructed of nondurable materials in a manner to insure temporary control of waterflow rates for beneficial use over as short a period as one or two seasons.
TRIBUTARY WATERSHED. All of the area that contributes storm water runoff to a given point.
WATERCOURSE. A channel in which a flow of water occurs, either continuously or intermittently, and if the latter, with some degree of regularity. Such flow must be in a definite direction and cover a prescribed area. Watercourses may be either natural or artificial, and both may occur either on the surface or underground.
WATERCOURSE, ARTIFICIAL. A surface or underground watercourse constructed by man.
WATERCOURSE, NATURAL. A surface or underground watercourse created by natural forces and conditions.
WATERCOURSE, UNDERGROUND. A geological formation which contains water moving in a known direction and defined channel.
(Ord. 3270, passed 8-28-00)
Drainage schemes for control of storm water shall comply with the following regulations.
(A) The controlled release and storage of excess storm water runoff shall be required in combination for all developments except single-family residential developments that contain an area less than one acre.
(B) The controlled release rate of storm water runoff from all developments described in subsection (A), hereof, shall not exceed the existing "safe" storm drainage capacity of the natural downstream outlet channel or storm sewer system. The rate at which storm water runoff is delivered to a designated storm water storage area shall be unrestricted.
(C) Storm water channels.
(1) A "natural" or surface channel system shall be designed with adequate capacity to convey through the development the storm water runoff from all tributary upstream areas. This "by-pass" channel shall be designed to carry the peak rate of runoff from a 100-year frequency rain event, assuming all storm sewers are blocked and that the upstream areas are fully developed and have been saturated with antecedent rainfall. No habitable structures shall be constructed within this floodway, however, streets and parking or playground areas and utility easements shall be considered compatible uses.
(2) Design of this floodway system shall also take into consideration control of storm water velocity to prevent erosion or other damage to the facility which will restrict its primary use. Depths of flow shall be kept to a minimum and retention of channel configurations shall be totally under Municipal control. In the event that the area within this "by-pass" channel is reshaped or restricted for use as a floodway, the Municipality will cause to have any restrictions removed at the expense of the party or parties causing said restriction.
(3) Should the development contain an existing "natural" waterway, this land configuration shall be preserved as part of the "by-pass" channel system. Construction of a "low flow" system of storm sewers to carry the minor storm runoff and reshaping of the channel with a maximum of six horizontal to one vertical (6:1) side slopes and bottom of a width adequate to facilitate maintenance and carry the flood runoff without eroding velocities shall be included in the plans for land development.
(D) The required volume for storm water detention shall be calculated on the basis of the runoff from a 25-year frequency rain event of any duration as published by a recognized agency. This volume of storage shall be provided for the fully developed watershed that is tributary to the area designated for detention purposes. The storm water release rate shall be considered when calculating the storm water storage capacity and the control structure designed to maintain a relatively uniform flow rate regardless of the depth of storm water in the storage area.
(E) Dry bottom storm water storage areas.
(1) Dry bottom storm water storage areas shall be designed to serve a secondary purpose for recreation, open space or other types of uses that will not be adversely affected by occasional or intermittent flooding. A method of carrying the low flow through these areas shall be provided in addition to a system of drains, and both shall be provided with a positive gravity outlet to a natural channel or storm sewer with adequate capacity as described in § 157.002 hereof.
(2) The combination of storage of water from a 25-year storm and the design release rate shall not result in a storage duration in excess of 72 hours. Maximum depth of planned storm water storage shall not exceed four feet unless the existing natural ground contours and other conditions lend to greater storage depth, which shall be approved by the municipality. Minimum grades for turf areas shall be 2% and maximum slopes shall be 10% (ten units horizontally to one unit vertically). Storage area side slopes shall be kept as close to the natural land contours as practical and a 10% slope or less shall be used wherever possible. If slopes greater than 10% are necessary to meet storage requirements or area restrictions, approval shall be obtained from the Municipality and suitable erosion control provided in addition to the protection required to insure public health, safety and welfare.
(3) Outlet control structures shall be designed as simply as possible and shall require little or no attention for proper operation. Outlet control structures shall also be designed in consideration of the safety of adjacent persons and property. When necessary, said structures will have features to restrict access to unwanted parties. Each storm water storage area shall be provided with a method of emergency overflow in the event that a storm in excess of the 25-year frequency storm occurs. This emergency overflow facility shall be designed to function without attention and shall become part of the "natural" or surface channel system described in § 157.002 hereof. Hydraulic calculations shall be submitted to substantiate all design features.
(4) Both outlet control structures and emergency overflow facilities shall be designed and constructed to fully protect the public health, safety and welfare. Storm water runoff velocities shall be kept at a minimum and turbulent conditions at an outfall control structure will not be permitted without complete protection for the public safety. The use of restrictive fences shall be kept to a minimum and used only as a last resort when no other method is feasible.
(F) Rooftop and paved storm water storage areas.
(1) Rooftop storage shall be designed with permanent-type control inlets and parapet walls to contain runoff on the rooftop. Emergency overflow areas shall be provided to insure that the weight of water stored will not exceed the structural capacity of the roof.
(2) Paved surfaces that are to serve as storm water storage areas shall have minimum grades of 1% and shall be restricted to storage depths of one foot maximum. Release rates and storage volume requirements for paved storage areas remain the same as outlined in § 157.002 hereof. If a portion of an area within a storm water storage area is to be paved for parking or recreational purposes, the paved surface shall be placed at the highest elevation within the storage area as possible. Maximum parking lot grades shall not exceed normal design parameters of 3% to 5%.
(G) Plans and approval required. Plans, specifications and all calculations for storm water runoff control as required hereunder shall be submitted to the city for review and approval prior to the approval of a final plat, in the case of subdivisions, or issuance of a building permit, in the case of planned unit developments, commercial, industrial, or qualifying residential construction. Final engineering plans and calculations shall show complete details for all of the items covered in this chapter and shall be submitted for review and approved prior to the start of construction.
(H) Control facilities constructed first. Where development of a property presents the threat of flooding or damage by flash runoff to downstream residents, the facilities for storm water runoff control shall be constructed prior to any earthmoving or drainage construction on the project site.
(Ord. 3270, passed 8-28-00)
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