Where part of a stormwater basin will contain a permanent pool of water, all the items required for stormwater storage shall apply except that the system of drains with a positive gravity outlet required to maintain a dry-bottom basin will not be required. A controlled positive outlet will be required to maintain the design water level in the wet-bottom basin and provide required temporary storage above the design water level (permanent pool). However, the following additional conditions shall apply:
(A) Stormwater basins shall be designed in compliance with the City of Crawfordsville’s standard detail.
(B) In the case of valley storage, natural slopes may be considered stable.
(C) A safety ledge shall be provided per the city’s standard detail must be installed in all ponds.
(D) There shall be two feet of freeboard from the routed 100-year pool to the top of bank.
(E) There shall be a minimum easement width around the pond of 20 feet, with an additional easement area adjacent to the pond large enough to serve as a staging area for maintenance equipment such as dredges and dump trucks.
(F) Periodic maintenance is required in ponds to control weed and larval growth. The pond shall also be designed to provide for the easy removal of sediment that will accumulate during periods of pond operation. A means of maintaining the designed water level of the pond during prolonged periods of dry weather is also required.
(G) Aeration facilities to enhance and maintain pond water quality shall be provided for all ponds with a surface area of less than one acre.
(H) Design calculations to substantiate the effectiveness of these aeration facilities shall be submitted with final engineering plans. Agreements for the perpetual operation and maintenance of aeration facilities shall be prepared to the satisfaction of the Board.
(I) If fish are to be maintained in the pond, a minimum depth of approximately ten feet shall be maintained over at least 25% of the pond area. The remaining pond areas shall have no extensive shallow areas.
(J) If fish are not to be maintained, the minimum depth shall be with eight feet over at least 25% of the pond at permanent water level, or where a limiting layer prevents excavation to that depth, a minimum of six feet over at least 50% of the area shall be required.
(K) In excavated ponds, the underwater side slopes in the pond shall be stable. In the case of valley storage, natural slopes may be considered stable.
(L) A safety ledge a minimum of six feet in width and a 10:1 slope is required and must be installed in all ponds approximately 30 inches below the permanent water level.
(M) Erosion control measures must be installed to prevent erosion from wave action and wet-dry cycles.
(Ord. 2-2010, passed 3-8-10)