STATEMENT OR PURPOSE.
As urban development continues to transform previous watersheds into highly impervious urban areas, the problem of handling the ever-increasing storm water runoff on these watersheds is becoming more pronounced. In recent years, much attention has been focused on detention basins as a means of controlling the storm water runoff by detaining the water in the basin and releasing it at a rate compatible with downstream conditions. Some basins have a multi-purpose function, containing sport facilities, lakes and a park-like atmosphere during dry periods. The recommendations presented in this report are intended to serve this function. By following the recommendations, the detention basin can be designed so as to obtain the maximum recreational aesthetic benefits for the surrounding community while serving as an effective flood control mechanism.
(a) Planning Guidelines.
(1) Detention basins serve to capture and temporarily store the surface water runoffs that result from urban development. This temporary storage allows for the release of the storm runoff at discharge rates which are acceptable to the receiving waterway. On-site provision for detention storage would follow these approaches:
A. The release rate and volume of detention storage would be based on previously mentioned design requirements and standards.
B. Recreational uses should be maximized where possible and feasible.
C. Any development which the drainage exits the corporation limits of the Village and enters onto County, Township or State jurisdiction shall be reviewed by the appropriate government official. A statement of comments must be submitted by that official in writing.
D. Storm water runoff of the pre-developed "sheet flow" characteristics versus postdeveloped "point source" release of the storm water exiting the site shall be taken into design consideration. Runoff from a proposed development shall provide downstream energy dissipation.
E. Storm water design shall take into consideration and provide adequate drainage for neighboring upstream property surface or subsurface water entering onto the proposed development or site. Offsite water may flow through the property and is not subject to storm control.
F. All storm tiles found entering a proposed development or found while excavating needs to be investigated. If the storm tile is found to be in working condition, the storm tile must be replaced with new within the development.
G. If a storm tile is going to be abandoned, it must be totally excavated and destroyed within the development.
(b) Detention Basins.
(1) The bottom of the basin shall have a minimum slope of one percent (1%).
(c) Retention Basins.
(1) In order to provide for better management of the water, retention basins shall have a permanent water area of at least one-half acre. The permanent water area shall have an average water depth of four (4) feet and no extensive shallow areas.
(2) In excavated lakes, the underwater side slopes shall be stable.
(3) A safety ledge of two (2)-foot-deep, five (5)-feet-wide is required around the perimeter of the basin.
(d) Detention and Retention Basins.
(1) All developments/site improvements requiring detention/retentions shall have a homeowners' association established as a part of the plat restrictions. The association shall be responsible for all pond and drainage swale maintenance.
(2) There shall be a minimum three-foot-wide berm at a two percent (2%) slope between the right-of-way and the top of the basin slope.
(3) Slopes on the sides of the basin shall have a maximum slope of 3 to 1. This includes both sides of any constructed levy.
(4) The minimum diameter of any outlet conduit shall be one (1) foot.
(5) Safety measures shall be provided for any pipe or opening to prevent children or large animals from crawling into structures.
(6) Danger signs should be mounted at appropriate locations to warn of deep water, possible flood conditions that exist during storm periods, and other dangers that exist.
(7) Retention pond design and maintenance shall include algae control with pond additives. Fountains shall also be considered but are optional.
(8) Grass or other suitable vegetative cover shall be maintained throughout the entire basin area. Grass shall be cut regularly, no less than five times a year, by the homeowners' association.
(9) Debris, trash removal and other necessary maintenance shall be performed after each storm to assure continued operation in conformance with the design.
(10) There shall be a minimum of one (1)-foot freeboard between the 100-year storm elevations and the top of the levy or embankment containing the basin.
(11) All basins shall have an emergency overflow.
(12) The Village shall be notified prior to any adjustments to the approved outlet structure to any detention or retention basin. No adjustment shall be made until approved by the Village.
(13) The surface area opening for catch basin inlets shall be equal to or greater than the design overland flow contributing water to that basin.
(14) Detention/Retention basin shall be located within an easement and have a means of access available to the Village.
(15) The site developer may pass on maintenance responsibilities to the respective owner/homeowners' association via a maintenance agreement. The maintenance agreement must be approved by the Village and an approved copy must be submitted to the Village for their records.
(e) "As-built" drawings will be required for all basins to assure compliance with all applicable requirements. This requirement shall include calculations to confirm that the basin and outlet were constructed to function as designed.
(Ord. 2021-08. Passed 12-13-21.)