Agenda Packets - 2009/02/08 - Laserfiche WebLink

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February 9, 2009 Item No. 11B 1 Page 2 Bonestroo Staff had met with RCWD Staff prior to preparing the permit application for the project, to determine the application requirements. Historically, for projects consisting of trail or sidewalk improvements, RCWD had waived the rate control portions of their rules. This was the case on the previous City project for County Road 10 Trail Segments 9 & 10, as well as for the Silver Lake Road Sidewalk project. During the initial meeting, RCWD Staff indicated that they felt rate control would again not be a requirement for the permit on Trail Segments 1-5. However, they did reserve final judgment until they actually performed the detailed review of the permit application submittal materials. The permit application materials were submitted to RCWD on December 19, 2008. The initial review report was received from the RCWD Engineer on January 9, 2008. The report stated that the rate control portion of the rule would be applied to this project. Rate control was being required due to potential impacts to the drainage system downstream of the outlet for the storm sewer beneath Woodale Drive. As a result of the RCWD review, the plan needed to be revised to provide rate control. In addition, detailed storm water modeling and analysis was required by RCWD for both the existing and proposed conditions to show the proposed rate control method would work. Bonestroo Staff had not performed the detailed storm water analysis prior to this, in an effort to save the City the cost of this analysis. The analysis was not necessary prior to this permit requirement. The solution to the rate control requirement is straightforward and relatively inexpensive. The existing end section of the storm sewer beneath Woodale Drive can be removed and replaced with a new structure with a smaller diameter opening. No easements are required for the work, the work is readily accessible from County Road 10, and the work is similar to other storm sewer work already included in the project. Construction cost for the storm sewer revision is estimated at approximately $3,000. The construction plans were revised to show the rate control modification to the storm sewer, and the revised plans were submitted to RCWD. Upon review, RCWD found this to be acceptable. The permit application for the project was considered at the RCWD Board meeting of January 28, 2009, and conditional approval (CAPROC) was granted. Issue Identified – Trail Overtopping The detailed storm water modeling was performed for both the existing condition, as well as the proposed condition with the storm sewer modification. When the results of the analysis were reviewed, Bonestroo Staff discovered that during very large storm events, the high water level of the existing storm water pond is predicted to exceed the proposed trail elevation. In other words, during large storms, a portion of the trail would be lower than the pond, and the trail would be overtopped with water for a period of time.