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HomeMy WebLinkAboutFOSSIL CREEK ESTATES PUD PRELIMINARY - 50 92D - CORRESPONDENCE - RESPONSE TO STAFF REVIEW COMMENTSDecember 3, 1993 Project No: 1318-01-92 Rob Wilkinson City of Ft. Collins Natural Resources P.O. Box 580 Ft. Collins, Colorado 80522 Re: Fossil Creek Estates P.U.D.; Ft. Collins, Colorado Dear Rob, This letter is written in response to your comments and requests of our November 30 meeting. You will also find attached, a copy of our October 27 response letter to Kate Malers which addresses some of the issues which we discussed at our November 30 meeting. Apparently you did not get a copy of this response letter. This is for your reference only and supplements the latest drainage report, of which you apparently have a copy. Page 3 of the October 27 response letter addresses the lateral drainageway channel to Fossil Creek. The lateral drainageway to Fossil Creek which is located just west of the ridge, and protection of the wetland areas, seem to be the issues of greatest concern. Each issue, although related to one another will be discussed separately for clarification. The lateral drainageway would be most affected by the development of Fossil Creek Estates because it accepts the greatest amount of concentrated peak storm drainage flows from the development. All peak flow calculations, flow depths and lateral channel cross sections were provided with our revised drainage report as we were requested. This letter will expand our analysis and conclusions concerning the peak flows at other storm intensity levels, depths of flow in the channel, peak flow velocities at varying storm intensities and erodibility potential of the channel at varying storm intensities. We will also provide recommendations concerning possible improvements to the channel which would reduce erosion potential to the channel, if we feel these are necessary. We have made a visit to the site to establish the condition of the lateral drainageway channel and to establish the channel vegetation and other variables which may affect the channels performance during storms of varying return intervals and intensities. Existing channel conditions and variables have been documented and utilized to analyze and interpret the open channel hydraulics of the channel. The channel vegetation. consists of native wetland and dryland species which are well established. Most of the species noted are identified in the report provided by the Wetlands Consultant. You should have a copy of this report. The channel is currently in a stable condition. No signs of erosion or "headcutting" were apparent. 4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334 PAGE 2 December 3, 1993 Project No: 1318-01-92 Re: Fossil Creek Estates P.U.D.; Ft. Collins, Colorado * We have analyzed peak flow hydraulic performance at additional locations along the existing channel (refer to exhibit A for the calculations). The summary of peak flows, peak velocities and depths of flow for varying intensity storms, are as follows: 2-year storm 10-year storm 50-year storm 100-year storm 1.33 x Q . peak flow 22.70 cfs 41.05 cfs 67.83 cfs 85.24 cfs 113.27 cfs velocity 2.19 fps 2.58 fps 2.96 fps 3.15 fps 3_39 fps depth of flow 0.65 ft. 0.87 ft. 1.12 ft. 1.25 ft. 1.43 ft. Our conclusions are as follows: * The channel in its current condition, is stable and exhibits no apparent erosion problems. The increased flows to the channel, due to the development of Fossil Creek Estates, are maintained well within the limits of the channel up to 100-year storm frequency intensities and beyond. The maximum depth in the channel for a 100-year storm has been determined to be1.25 feet with a velocity of3 15 feet per second. For the existing channel vegetation, this velocity would not create the additional shear stress which would warrant additional downstream erosion protection measures. There are no channel improvements required to the lateral drainageway channel in our opinion. There are several items which we discussed at our November 30 meeting concerning protection and performance of the existing wetland areas. The following represents a summary of the action items which the owner is prepared to follow based on final recommendations of the subsurface hydro -geologic investigation report to be prepared by Resource Consultants and Engineers (RCE) of Fort Collins. The items may be implemented with design and construction of Fossil Creek Estates which will enhance, protect and hopefully improve wetland area performance. We stress that these are items which the owner is prepared to do based on final report recommendations. There will be extensive monitoring performed in the study area over the course of the next several months. A final report with accurate performance data will be available well in advance of final submittal for this phase of the Fossil Creek Estates development. Those items which we discussed, and are prepared to implement in the final design of this portion of Fossil Creek Estates (should the RCE report recommend it), are as follows: * Provide erosion control protection of the Cathy Fromme Natural Area and the wetlands areas during infrastructure and housing construction. A complete erosion protection plan will be provided with final design drawings according to the requirements of the City's Storm Water Utility and good engineering practice. * Identify and restrict construction to formal defined limits of allowable disturbance. * Implement water quality 'Best Management Practices" in order to ensure that surface runoff after development does not significantly affect the nature and quality of the wetland area. PAGE 3 December 3, 1993 Project No: 1318-01-92 Re: Fossil Creek Estates P.U.D.; Ft. Collins, Colorado * Mandate organic yard care chemicals in the subdivision covenants, controls and restrictions (CC and R). * Provide education to the potential homeowner's concerning the sensitivity of the wetland areas. Provide informational signage on 3 - rail equestrian style fencing to be installed around the perimeter of the wetland areas. The signage will address -the sensitivity of the wetlands areas. * Provide a means for bringing supplemental water from the upper ditch to wetlands area if studies indicate that a net water deficit exists * Create storm drainage discharge points within the limits of the surrounding lots in order to allow peak flow spreading to the wetland drainage areas prior to reaching the wetland areas. Also provide for the diffuse entry of surface flows and underdrain discharge to the wetland area along the rear lot lines. This system would need to be approved by the City's Storm Water Utility. If you have any additional questions, please call at 226-5334. Sincer, Brian W. Shear, Shear Engineering Corpora BWS / jmb attachments cc: Kirsten Whetstone; City of Fort Collins Planning Kerrie Ashbeck; City of Fort Collins Planning Carter Ewing; Fossil Creek Partners Jim Sell Design Paul Clopper, Resource Consultants and Engineers