Retention ponds or reservoirs may be constructed. Such retention facilities shall be designed to retain a certain water level at all times and may, in addition to serving as part of the storm water drainage system of the village, be used for scenic and recreation purposes. Detailed engineering plans and specifications for retention or detention facilities shall be prepared by the design engineer for review by the village engineer and plan commission/board of appeals and approval by the village board. The design of retention or detention facilities shall be in accordance with the following guidelines: (Ord. 99-O-791, 6-7-1999; amd. Ord. 05-O-942, 11-7-2005)
A. Construction Pollution: There must not be any pollution of any kind entering the water area during or after construction.
B. Access: A plat of subdivision containing a lake, pond or other body of water shall provide for a fifteen foot (15') easement encircling the lake, pond or other body of water and terminating at a dedicated street. Such easement shall be deemed dedicated to the village for inspection and related purposes.
C. Control Gate: A mechanical control gate may be used at the outlet pipe.
D. Incoming Lines: The ends of all incoming storm sewer lines shall be below the normal pool elevation and shall be set in a concrete headwall or end section.
E. Bottom Slope; Safety Shelf: The bottom slope of the pool shall be four to one (4:1) from the maximum flood stage elevation to a point twenty feet (20') out from the normal pool elevation. A minimum six foot (6') safety shelf shall be provided.
F. Landscaping: The entire area shall be graded and seeded and the soil shall be stable enough to support mowing equipment and shall be landscaped. Minimum of five (5) trees, of two and one- half inch (21/2") diameter, shall be recommended.
G. Drainage Control: Storm drainage control shall be retained by the village.
H. Dams And Constructed Walls: All dams and constructed walls shall be designed by a registered engineer and, if of earth, shall have a maximum slope of two and five-tenths to one (2.5:1), be constructed of compacted clean earth fill and have an interior core wall of concrete on sheet steel.
I. Embankments: Shaped earth embankments shall have a maximum slope of four to one (4:1) and shall be compacted to remove all voids exposed by cutting and shall be cleared of all extraneous material and foliage below the designed water line. Erosion control fabric may be required by the village engineer.
J. Depth: Retention facilities shall maintain a minimum constant water depth of ten feet (10') over thirty percent (30%) of the surface water area, in addition to the depth of occasional water detained in the facility in storm situations.
K. Area: Retention and detention facilities smaller in area than three (3) acres shall not be permitted. Such area shall be measured at the constant water level.
L. Overflow Outlets: Overflow outlets shall be provided as necessary to keep the water level within a retention facility within its design limits. Materials and methods of construction for overflow piping shall be the same as for storm sewer construction as shown in section 6-5-3 of this chapter. Maximum overflow rate shall be designed in accordance with said section 6-5-3 of this chapter. Overflow spillways shall be of concrete and so constructed that no erosion of the dam or outfall shall occur.
M. Overflow Outfalls: Overflow outfalls shall be as specified in section 6-5-3 of this chapter for storm drainage outfalls.
N. Bank Stabilization And Landscaping: All cut embankments, earth dams or other surfaces shall be seeded or sodded, or in accordance with this section, to the designed occasional water level of the retention facility. From this point to the constant water level, sand or gravel may be used. Stabilization with stone, concrete or other material may be used if specifically approved by the village board. Trees shall not be planted on or within twenty feet (20') of any earth dam.
O. Drafting Pits/Fire Prevention: Where a retention pond or lake has a minimum depth of four feet (4'), the subdivider shall install a drafting pit manhole structure with a suction pipe with the inlet at the middle of the pond. The manhole drafting pit and outlet shall be installed within the right of way within the subdivision. The location of and specifications for the manhole drafting pit and the suction pipe shall be subject to the approval and direction of the village engineer. (Ord. 99-O-791, 6-7-1999)