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HomeMy WebLinkAboutSPRING CREEK CENTER PUD FINAL - 17 90D - CORRESPONDENCE - MEETING COMMUNICATION11 Ll June 9, 1998 Mr.. Basil Harridan City of Fort Collins Stormwater Utility 235Mathews P.O. Box 580 Ft. Collins, CO 80522-0580 re: Spring Creek Center Fort Collins, Colorado Project No. 9734.03 Dear Libby? E N G I N E E R I'N G 5.,1E- R V. 1 C_'`E, S I N C` In a June 1 meeting with the City of Fort Collins Stormwater Utility regarding Spring Creek Center, the most recent City comments were discussed. Further discussions were held at a meeting with yourself and Mary Wohnrade of Northern Engineering on June 5. The following are the resolutions of the thirteen items on the City's list, dated May 15. (The comments themselves are attached and are not reproduced here:): We will move the swale as requested. Other design concerns may be raised once the swale revisions are under way. 2. This item has already been done. 3. This item has already been done. 4. This item has already been done. 5. The City agreed that the water quality design is for stormwater runoff only. Potential future gasoline spills at the two pads allocated to service stations will be designed when those sites develop. Three water quality ponds had been designed per City standards but, in order to restrict outflows to the required 40-hour detention period, the orifice was unreasonably small. Stormwater requested that two of the ponds be replaced with an oil/sand separator and that the remaining pond orifice be sized for a larger opening. 6. This item has already been done. 7. This item has already been done. 8. The City agreed that we can leave the pipes as -is and to use buried rip rap for erosion protection. 420 SOUTH HOWES, SUITE 202, FORT (OLLINS, (OLORADO 80521, (970) 221-4158, FAX (970) 221-4159 _+ Spring Creek Center t June 5, 1998 Page 2 of 2 9. At a meeting earlier in the project; the City had agreed to use the FIS discharge. The City, therefore, agreed to leave the calculations as -is. 10. In order to avoid placing a large temporary culvert under Timberline, the 100-year storm flows which currently over top the railroad embankment are being allowed to continue to flow across Timberline into the existing swale. The required median in Timberline will direct this flow into the swale, but may cause a small rise in the water surface elevation at that location. The City has asked that a new HEC-2 model of the area west of Timberline is to be prepared to analyze the impacts of the median on that area. 11. This item has already been done. 12. After discussing this item at the second meeting; the City agreed that the design is acceptable.. 13. The City agreed that the topography is acceptable as -is. The above represents our understanding of the discussions that were held concerning the design of the Spring Creek Center. We would like very much to bring this project to closure with this round of comments. If you have any comments regarding these issues, please contact this office by June 15 so that we may re -submit the plans on the schedule we had discussed.. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Michael F. Jones, P.E. Principal Attachment: Stormwater comments, 5-15-98 cc; Libby Glass, W. W. Reynolds Eldon Ward, Cityscape Lucia LiIley, March & Liley Mike Ludwig, Current Planning Mike Dean, Engineering Review M coNTME d'T SKEET Cun-ent PWwIng DATE: s- /S -� DEFT: Stormwater4. PROJECT: .SP+7179 Cfee h CPin fp/ P 1. The diversion swale along the west side is shown to be within the right -of --way. The swale should be located outside the right-of-way. This comment was mad with the previous comments. RESPONSE: 2. The swale 12 calculations show the 500-year flow will not be contained within the swale. Please contain the 500-year flow in the swale to not inundate the gas stations. RESPONSE:. 3. Please evaluate culvert 12 and the overtopping in this location. The flow must be contained within the channel. RESPONSE: WGLsUMI OU ML7o 1V DiGM WM UMM VWMAd Mi/lp Gv�/wig l�o✓ f'MM OkIV. w, Reynolds Qtp of Fost comas 4. There were two stage -storage calculations for pond 3. Please provide the correct calculations in the report and remove the other. RESPONSE: 5. Please revise the water quality outlet design to match the procedure shown in section 5 of the UDFCD Vol. 3. The water quality outlets shown on the plans are under sized. The open area determined from Figure 5-2 is the open area per row. Please see detail. RESPONSE: O �7 ;V c 6. The inlet sizing calculations for design points 6 and 7 must apply an 800/6 clogging factor. RESPONSE: 7. Two of the water quality ponds will be within the proposed parking lots. The ponds are designed to detain the "first flush" for 40 hours. Therefore the ponds will be full of water quite frequently. These ponds are not intended for parking lot detention. Please provide the water quality ponds in grass open space areas. RESPONSE: — J 8. The outfall pipes to Spring Creek should meet the elevation of the bed of the creek. Please revise the profiles 7 and 8 to enter the creek at the bed elevation. RESPONSE: . 1 � -r ,..., .:,,�_ 9. Please verify the discharge used for the 500-year overflow of Timberline Drive. The FIS 500-year discharge should not be used. The 100-year discharge of 2400 cfs from the 1988 Master Plan was used for the 100-year overtopping. Therefore, it is logical that the 500-year discharge from the 1988 Master Plan should also be used. It should be noted that the most updated 1998 Spring Creek model shows less discharge than the 1988 model for the 100-year event so this means that the 1988 Master Plan 500-year would also be less than the 1998 Master Plan 500-year. RESPONSE: L-�- E 0 10. The median is Timberline Road is shown to divert the overtopping to the diversion swale. However, there is a concern that this median will cause more ponding on the property west of Timberline because the low point in Timberline will be raised. The improvements with this.site must not cause an adverse impact on off -site properties. RESPONSE: _1 Lam. *c.. ..,^ ,,)_- t r i is s j 5 tD 11. Please provide supporting documentation for the weir coefficients used for the split flow analysis. RESPONSE: 12. Further explanation and justification is needed for removing part of the flow at station 2000 that overtops Timberline Drive from the existing and proposed models. Please provide justification that flow will be diverted in the swale along Timberline Drive back into Spring Creek. Please see comments in the HEC-2 output. RESPONSE: IDJ 13. The cross -sections show that City aerial topography was used to develop the cross - sections. Please show this topography to support the cross -sections. RESPONSE: n ; ., Please refer to the redline plan and report for additional review comments.