Agenda Packets - 2008/11/24 - Laserfiche WebLink

Home Browse Search

November 24, 2008 Item No. 7H Page 3 Comments on the 1989 Drainage Study Staff shared the 1989 Study with Bonestroo. Bonestroo performed an initial review of the study, and essentially confirmed its findings. However, it appears that the improvements proposed in the 1989 Study may not be warranted to the level of a 5-year design standard, based on the perception of City Staff and residents living in this area. While residents in this area have complained of rear yard nuisance flooding following heavy rains, the improvements proposed in the 1989 Study appear to go well beyond what is necessary to address the rear yard nuisance flooding. Other concerns were noted with the 1989 Study as well. The Study assumed that the East Detention Pond would be constructed by a developer. However, under present conditions the City would need to acquire land and construct the pond itself. Also, the proposed improvements are very expensive. Finally, the improvements would be physically challenging. The proposed pipes are large diameter, and given the existing topography they would be extremely shallow, especially on Sherwood Road. It would be very difficult, and perhaps not even possible, to construct the proposed trunk storm sewer. In addition to these facts, the issue of storm water management has changed greatly since 1989. A Stormwater Infiltration Program (SIP) was adopted in 2008 by the City. With the discussion of the Spring Creek Regional Pond, the City has also recently indicated a preference for avoiding the acquisition of land and construction of large regional ponds. Proposed New Analysis Based on this information, Staff suggests that a new analysis be performed on the Ardan Avenue Drainage Subdistrict. The goals of the new analysis would be to eliminate the East Detention Pond and identify an alternate to the Sherwood Road storm sewer proposed in the 1989 Study, while still increasing the effectiveness of the storm sewer in comparison to the existing system. It is hoped the alternate improvements would also be lower cost than the improvements proposed in the 1989 Study. The new analysis would not be done to the level of detail of the 1989 Study. The intent would be to perform a more brief and practical analysis rather than a comprehensive study. Comprehensive issues would be addressed in the overall Local Surface Water Management Plan (LSWMP) for the City, which is currently being prepared. The findings of the new analysis would be incorporated into the LSWMP when it is completed. The scope of the proposed new analysis is shown in the attached letter from Bonestroo. It should be noted that an important part of the analysis would be to perform some specific site survey, to identify critical elevations of existing homes, garages, and other structures. That information would allow the existing level of flood protection provided for these structures to be determined. The improvements proposed by the new analysis would either maintain or improve the flood protection.