A. An adequate system of stormwater drainage designed for five (5) year rain shall be constructed and installed, consisting of pipes, tiles, manholes, inlets, catch basins and other necessary facilities, that will adequately drain the entire subdivision, protect roadway pavement and prevent the accumulation of stormwater at any place under normal conditions. Open ditches shall be avoided if possible. The stormwater drainage system shall be separate and independent of the sanitary sewer system. Materials and methods of construction shall conform to specifications adopted by resolution by the village president and board of trustees. Such drainage system shall be subject to approval by the village engineer.
B. All street pavements in the subdivision shall be provided with drainage inlets discharging directly into a storm sewer system which shall conduct such stormwater to an established watercourse or outfall sewer. Inlets shall be placed on each side of the pavement in the gutter lines at all low points at street intersections (except when such intersection is located at the high point) and at intervals along the gutter line not exceeding four hundred feet (400') between inlets and shall be connected only to catch basins. The catch basins shall be connected only to manholes.
C. All street pavements in subdivisions shall be bounded with combination portland cement concrete curb and gutter. The curb and gutter may be deleted only with the permission of the Planning and Zoning commission.
D. Design of storm sewers shall be based on a flow computed on the basis of the following formula:
Q = CIA
Where:
Q | is stormwater runoff in cubic feet per second from the drainage areas. |
C | is a coefficient representing the ratio of runoff to rainfall. C shall not be less than 0.35 for residential, 0.50 for multi-family and 0.75 for business areas in small or short drainage systems. |
I | is the intensity of rainfall in inches per hour for a duration equal to the time of concentration. The value of I will depend on the rainfall intensity curve for the village vicinity in a 10-year storm frequency. |
A | is the drainage area in acres including all tributary areas. |
E. Minimum velocity shall be two feet (2') per second, and the maximum velocity shall be ten feet (10') per second.
F. The minimum sewer size shall be ten inches (10").
G. Provisions must be made in the design of the storm sewer for the runoff which will come on the subject land from tributary lands through natural watercourses. In calculating the runoff from tributary lands, consideration shall be given to the character of the developed land in determining the C factor. For undeveloped land, the C factor shall be no less than 0.35. Such designs shall provide adequate capacity for receiving such drainage from tributary areas on a basis of the ultimate development of such tributary areas. No increase in stormwater runoff shall be directed to any existing watercourse or drainage system unless the village engineer shall have determined that the receiving watercourse or drainage system shall have adequate capacity to receive such increased flow.
H. All storm sewers and connection pipes between inlets, catch basins and storm sewers which are constructed beneath existing or proposed paving improvements shall be backfilled in lifts of twelve inches (12") with stone screenings or trench backfill, as defined in the state standard specifications. Reinforced RCP pipe shall be used in all pavements.
I. Backyard swales may be permitted subject to the following:
1. No continuous swale shall have a length exceeding eight hundred feet (800') unless approved by the village engineer.
2. The minimum grade of flow line shall be five-tenths of one percent (0.5%).
3. At no point in the swale shall the flow line be more than three feet (3') below the finished grade of the topsoil at the foundation of the building opposite the swale.
4. No change in alignment of a backyard swale shall exceed forty five degrees (45°).
5. All such swales or drainage easement areas shall be sodded.
J. Lots and blocks shall be so sloped in final grading that stormwater runoff will be away from the building foundation and from the rear of the lot to the proposed pavement or sewer systems. Where swales are allowed, only the runoff from the rear yard shall drain toward the swales. Grading will be done so as to keep runoff from running onto adjoining lots to a minimum.
K. No sump pump shall be so installed and connected so as to discharge stormwater runoff onto adjoining property or upon any street or public way, nor shall any such sump pump be connected to a sanitary sewer. Building construction on parcels which are proximate to storm sewers shall cause footing drains from such structures to be connected to the storm sewer system. Building construction on parcels which are proximate to a retention pond may be required to cause footing drains from such structures to be discharged into the retention pond rather than to be connected to a storm sewer system. (1978 Code § 7-4-6; amd. Ord. 2023-56, 9-7-2023)