Agenda - Council - 10/22/1991 - Laserfiche WebLink

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,I I ! I I I I I I I ! I I i I I I I · Concern was expressed regarding potential high water elevation of the pond. The pond is designed by Hakanson Anderson Associates for an ultimate high water elevation of 885. This is three feet higher than normal water elevation. It is my understanding that the amount of storage is based upon four inches of run-off from the contributing drainage area under totally impermeable conditions (i.e., frozen ground). In addition, once the water level rose to within one foot of the high water level, additional ponding would occur in the 151st and Juniper Ridge Drive intersection area. · The citizens inquired as to what would be considered topsoil in performing the restoration work around the pond. The State Mn/DOT specification for topsoil will determine the acceptability of the material used for topsoil. · Questions were raised concerning the water quality of the pond and what role the City would have in maintaining water quality. It is the opinion of the City Engineer that the water quality anticipated for this pond will be similar to that found in other small, shallow ponds throughout the metro area, including both lined and unlined ponds. The potential for algae growth certainly is present. Perhaps the most significant factor causing algae growth relates to the amount of nutrients that are introduced into the pond facility which primarily would come from fertilization of lawns. It is the City's position that maintenance of water quality, should it deteriorate, would not be a City responsibility. The City would be responsible for maintenance of the drainage structures into the pond. · What assurance is there that the pond will not go dry during a drought period? To the City's knowledge, no detailed analysis or model of the pond has been prepared addressing precipitation and evaporation influences on the water level. However, within the area annual precipitation equals or exceeds the evaporation and transpiration from plants. In addition, the impervious area draining to the pond is greater than the pond surface from which evaporation will be occurring. As a result of these influences, it could be concluded that on an annual basis, there will be more water coming into the pond than there will be evaporating from the pond. Recommendations: It is a staff recommendation that resolution of the primary issues outlined above be made with the developer prior to the start of construction. I will be attempting to discuss with the developer the feasibility of potentially delaying initiating construction until these issues are resolved. Review Checklist: City Engineer City Administrator City Attorney CC: 10/22/91