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1 J <br /> Memo <br /> Stantec <br /> To: Darren Amundsen � From: Robert Monk ' <br /> File: 400 Willow Drive South Date: 11/23/11 <br /> Reference: 400 Willow Drive South Routing Analysis <br /> This memo summarizes routing issues from the review of stormwater calculations submitted by <br /> Gronberg&Associates, Inc. for 400 Willow Drive South. <br /> The following materials were reviewed as part of the submittal: <br /> • Site Plans <br /> • HydroCAD models for proposed conditions <br /> "t.i.r,�:` .rh� <br /> HvdroCAD Routinq <br /> • The submitted HydroCAD routing demonstrates three subcatchments (A1-A3)each being routed <br /> directly to three corresponding ponds (1 P-3P). In turn, each pond is then routed to the next, i.e. <br /> 1 P to 2P, and 2P to 3P. Additionally, there is a subcatchment(A4)for which no routing <br /> information has been included. <br /> Plan Routina <br /> Pre-development conditions demonstrate three watershed areas(Area 1 —Northwest,Area 2— <br /> Southwest,Area 3—East) each draining to a corresponding wetland(Wetland A—East,Wetland <br /> �B—Southwest,Wetland C-Northwest). Wetland B is then routed (via 12" HDPE pipe)to <br /> Wetland C. <br /> Proposed conditions demonstrate Area 1 draining to both pond 1 P (HydroCAD) and Wetland C. <br /> Pond 1 P is then routed (via 6" RCPpipe)to Wetland C. Area 2 drains directly to Wetland B <br /> which is then routed (via 12" HDPE pipe)to Wetland C. No outlet from Wetland C is shown on <br /> the proposed plans. Area 3 drains partially to Wetland A and partially to pond 1 P. <br /> Comments <br /> 1. Ponds 2P and 3P are not clearly defined on the plan sheets, thus no routing pattern could be <br /> established. If being used for ponding purposes, each wetland should be given a designation <br /> similar to that used in HydroCAD. <br /> 2. HydroCAD pond P2 and P3 elevations and conveyances do not match any pond elevations <br /> and conveyances on plan sheets. <br /> 3. Pre-development HydroCAD modeling was absent from the submittal. <br /> 4. Pre-and post-development watershed boundaries are not individually delineated for use in <br /> HydroCAD. <br /> i. Existing drainage areas (not submitted)are as follows:Area 1 —2.4 ac,Area 2—2.9 <br /> ac,Area 3—8.5 ac. �� <br /> ii. The catchment areas modeled in HydroCAD are as follows:A1 —2.061 ac,A2— <br /> 1.261 ac,A3—2.748 ac, and A4—7.665 ac. Areas used in HydroCAD modeling are <br /> not delineated on plans. <br /> t1ld�:�er�Enld�id�e�r���0�4��hlAll��crosofl\windowsltemporary internet <br /> fil es�wntent outl ook\sbpn5sp 1k100wi11 owdrive_stortmvatertouti n�112311.docx <br />