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Home My WebLink AboutUNIVERSITY CENTER PUD (UNIVERSITY MALL REDEVELOPMENT) - FINAL - 2-96A - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORT� z r v.....w 8Ei s+ M . ♦m C V LOW St r Q C l�W 8t r ROAD,. ggi 5pm P SPECT n sr " x we sa. �eu+e s• R W ? "ter Spep 0wk F— o- W yr r..ko- W „ G n��m qka im a "'SECTI❑ L 23 n.,, g€ $ ASITE — '""° v p0 Yr W. or S Pl.Is.bl DR KE R❑AD 6 b a � a j� °' t a 7±1 Mo' S VICINITY MAP N TS UNIVERSITY CENTER MALL 9-11-97 Suit BUCHIt, WLLIS & RATL§f 1743 WKNE SIR V DOMk COLO WO 8MM 303-292-M= APPENDIX A LOCATION MAP i� DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 7. REFERENCES 1. Preliminary Drainage and Erosion Control Report - University Center P.U.D.," prepared by JR Engineering, Ltd., Revised March 11, 1996. 2. "Final Drainage and Erosion Control Report - University Center P.U.D.," prepared by JR Engineering, Ltd., dated May 20,1996. 3. City of Fort Collins, Storm Drainage Design Criteria and Construction Standards," (SDDCCS), dated May 1984, revised April 29,1997. 4. Urban Drainage and Flood Control District, Urban Storm Drainage Criteria Manual," Volumes 1 and 2, dated March 1969, and Volume 3 dated September 1992. 5. "Drainage and Erosion Control Report - University Center P.U.D.," prepared by Bucher Willis and Ratliff Corporation, dated November 6, 1996. 13 I ' Bucher, Willis & Ratliff Corporation X \1)��S\IYPCpRP\OMINYP(CCC DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 6. MISCELLANEOUS Variances There are no variances requested with the development of the University Center PUD. Irrigation Ditches The proposed redevelopment of University Mall does not impact the outfall into the Sherwood Lateral which is the only irrigation ditch adjacent to the site. Ditch Company Approval Because this is the existing outfall for the drainage from this area and the proposed drainage plan does not impact the flows currently released into the Sherwood Lateral, ditch company approval is not required. Maintenance Agreements The developer will be responsible for the maintenance of all temporary drainage structures. 12 Bucher, Willis & Ratliff Corporation xnnus11 v.Rllnx WRI. DRAINAGE AND EROSION CONTROL REPORT IUNIVERSITY CENTER PUD Dust Abatement During the performance of the work or any operations appurtenant thereto, the Contractor shall carry out proper efficient measures wherever and as necessary to reduce ' dust nuisance, and to prevent dust nuisance, and to prevent dust which has originated from his operations from damaging crops, orchards, cultivated fields, and dwellings, or causing a nuisance to persons. The Contractor will be responsible for any damage resulting from dust originating from his operations. Tracking Mud on City Streets Wherever construction vehicles access routes or intersect paved public roads, provisions must be made to minimize the transport of sediment (mud) by runoff or vehicles tracking onto the paved surface. Stabilized construction entrances are required per the detail shown on the Plan, with base material consisting of 6" coarse aggregate. The contractor will be responsible for clearing mud tracked onto city streets on a daily basis. ' Maintenance All temporary and permanent erosion and sediment control practices must be ' maintained and repaired as needed to assure continued performance of their intended function. Maintenance is the responsibility of the contractor. Permanent Stabilization ' A vegetative cover shall be established within one and one-half years on disturbed areas and soil stockpiles not otherwise permanently stabilized. Vegetation shall not be considered established until a ground cover is achieved which is demonstrated to be ' mature enough to control soil erosion to the satisfaction of the City and to survive severe weather conditions. 11 Bucher, Willis & Ratliff Corporation 0.'\RiJ15\WVGORV\OIU INRI.I GOC DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 5. EROSION CONTROL Introduction This section represents the Erosion Control Report for the University Center PUD and was prepared to meet the regulatory requirements of the City of Fort Collins, Colorado. This.report was prepared following the guidelines and regulations within the SDDCCS Manual. General Description IThe proposed improvements comprise portions of the western and southwestern portions of the site, which totals 9.39 acres. The general topography of this site consists primarily of existing asphalt parking lot, buildings, and curb, gutter and sidewalk. The southwest corner and western portion of i the site consist of poorly covered range type land. The slopes range from 0.5 to 3 percent. Soil Description In accordance with the Soil Conservation Service's (SCS) "Soil Survey of Fort Collins Area, Colorado," the soils on -site consist of the following: Rainfall Wind Hydrologic Soil Designation Erodibility Zone Erodibility Zone Soil Group Nunn clay loam Slight to Moderate Slight to Moderate C Erosion and Sediment Control Measures Erosion and Sedimentation will be controlled on -site by the use of silt fence, gravel construction entrance, and inlet protection (gravel filters). The measures are designed to limit the overall sediment yield increase due to construction as required by the City of Fort Collins. 10 Bucher, Willis & Ratliff Corporation X:\lIX15\WPCORP\pXAINRFI.OLC DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD Flow Rates Released to College Avenue Outfall System - Existing and Developed The proposed drainage system has been designed to discharge at a rate not to exceed the 2 year release rate which is less than the historic rate (existing conditions) to the College Avenue outfall system for the major event. It is not anticipated that there will be additional impact to the College system based on this proposed design. 9 I Bucher, Willis & Ratliff Corporation N:\fi115\WpCONP\OMINAII.00L DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 4. RUNOFF DETENTION AND RELEASE Detention Ponds Detention Ponds 1 and 2 are located in the southeast portion of the proposed retail building expansion. Flows are directed to these areas from the surrounding parking lots. These detention areas have a sump type outlet structure that acts as the outfall. The release from these ponds will be controlled by orifice plates to be installed on the outfall pipe at the sump inlet. The FAA model was used to determine the required detention volumes for all ponds and calculations are presented in tables in Appendix C. POND SIZE FOR RESTRICTED OUTFLOW SIZE FOR 2 YEAR OUTFLOW DESIGNED CAPACITY 1 3748 cf 2791 cf 3530 cf 2 1169 867 1780 3 58070 55157 59170 The rate of release from Ponds 1 and 2 is restricted by the outflow capacity of manhole MH-1 at design point 1 of 1.64 cfs. Since this restricted outflow rate at MH-1 is less than the required historical 2 year flow of 2.48 cfs, we have designed the volume of Pond 1 to accommodate the 100 year storm at the 2 year release rate. This means that a portion of the 100 year storm volume for Pond 1 will flow offsite to the College Street storm system in an overland manner consistent with the allowable 2 year historical offsite flow. The spillway invert for Pond 1 is at elevation 5016 ft and spillway invert for Pond 2 is at elevation 5018 ft. Pond 2 is graded such that if the capacity is exceeded, it will spill over to Pond 1, then out to the S. College Ave. storm system. Detention Pond 3 is located in the western portion of the project. Details of the outlet structures and orifice sizes are shown on the Drainage, Grading and Erosion Control Plan. The spillway for Pond 3 is situated at elevation 5017.1 ft and spills to the railroad right-of-way property as flows in the rear of the retail buildings traveled historically. Bucher, Willis & Ratliff Corporation IL\!)CIS WYmPTONAINRTDL\' DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 7 I Bucher, Willis & Ratliff Corporation M:\9JJISWVCOPTORAINRT 0.Y DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD Hydrologic Analysis of the Developed Drainage Conditions The Rational Method was used to determine both 2-year and 100-year peak runoff values for each Sub -basin. Runoff coefficients were assigned utilizing Table 3-2 of the SDDCCS Manual. As stated above, the Rational Method was used for all hydrologic analyses for the project site. The Rational Method utilized the SDDCCS equation: Q=C fCIA where Q is the flow in cfs, A is the total area of the basin in acres, C f is the storm frequency adjustment factor, C is the runoff coefficient, and I is the rainfall intensity in inches per hour. The frequency adjustment factor, Cf is 1.0 for the initial 2-year storm and 1.25 for the major 100-year storm. The appropriate rainfall intensity information was developed based on rainfall intensity duration curves in the SDDCCS Manual (See attached Figure 3-1). In order to utilize the rainfall intensity curves, the time of concentration is required. The following equation was used to determine the time of concentration: t= ti+tt where t. is the time of concentration in minutes, ti is the initial or overland flow time in minutes, and tt is the travel time in the ditch, channel, or gutter in minutes. The initial or overland flow time is calculated with SDDCCS Manual equation: ti=[1.87(1.1- C Cf )Las]f(S)0.33 where L is the length of overland flow in feet (limited to a maximum of 500 feet), S is the average slope of the basin in percent, and C and C f are as defined previously. All hydrologic calculations associated with the redeveloped sub -basins are attached in the Appendix of this report. 0 I Bucher, Willis & Ratliff Corporation P:\9i�15\IVVCpRP\ONAINRF(P'C DRAINAGE AND EROSION CONTROL REPORT ' UNIVERSITY CENTER PUD 3. DEVELOPED FLOWS ' Method The Rational Method was used to determine both the 2-year and 100-year developed flows for the sub -basins impacted by the redevelopment. A detailed description of the hydrologic analysis is provided later in this section. Flow Characteristics Drainage within the redeveloped area will surface flow to detention pond areas. The ' existing drainage patterns have been maintained where possible. All grading has been designed to carry flows away from structures to the proposed drainage facilities. Flow patterns are illustrated on the Drainage, Grading and Erosion Control Plan in the pocket at the back of this report. Onsite flows generated from the west between Burlington Northern Railroad and the west ' property line will be diverted along the western property line to the north and outfall to a natural swale on the railroad property. A qualitative summary of the drainage patterns within each developed sub -basin is provided in the following paragraphs. Detention and release rates are described in Section 4, "Runoff Detention and Release'. ' Sub -basin Al is 0.83 acres in area and is located on the east side of the proposed building expansion in the parking area. This sub -basin drains to Pond 1 which is located within the north -south driveway. Sub -basin A2 is 0.26 acres in area and is located on the south side of the proposed building expansion in the parking area. This sub -basin drains to Pond 2 which is located within the east -west drive lane. Sub -basin B is 8.43 acres in area and consists of the parking and landscaped areas west of the proposed and existing buildings and also the rooftop for King Soopers and Tenants A through E. The detention for this sub -basin is located along the west property line within a landscaped area. 5 Bucher, Willis & Ratliff Corporation zvr�iswxoxa�ortnivxvr ooc DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD ' 2. HISTORIC (EXISTING) DRAINAGE For the purposes of this report, the historic flows for the site are considered to be the current existing drainage flows. A discussion of the drainage patterns was presented in the Drainage and Erosion Control Report for the University Center PUD, dated November 6, 1996, and is presented here again. In general, the existing drainage patterns for this site consist of the routing of flows to existing area inlets in the following areas: the east parking area of this site; the loading ramps at the rear of King Soopers; the existing businesses on the north and south; and the existing dirt area in the southwest corner of this site. Onsite drainage patterns occur from the Berlington Northern Railroad property along the southwestern portion of the site which are then conveyed to the north along the western edge of the existing asphalt parking area behind King Soopers, then flows to an existing offsite swale which starts at the northwest corner of this site within existing railroad right- of-way (To our knowledge, this swale is not contained in an existing easement.) The flows then leave said swale and are conveyed in the low area between the previously existing storage units and the railroad, and outfalls into the existing Sherwood Lateral. ' The proposed re -development of portions of this site will not result in changes to the flows and drainage structures on the east side of this site. Those areas that are not impacted by the redevelopment have not been included in this report. The historic runoff calculations are included in the Appendices of this report I L 1 ' Bucher, Willis & Ratliff Corporation IL-\fJ�15\I4iCDY1�\UMINNV� P^L 1 IDRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD Design Criteria I This report was prepared to meet or exceed the submittal requirements established in the City of Fort Collins' "Storm Drainage Design Criteria and Construction Standards" (SDDCCS), dated May 1984 and updated April 29, 1997. An additional update of the SDDCCS manual is expected to be completed by the City of Fort Collins by the first part of 1998. Runoff computations were prepared for the 2-year and 100-year storm frequency utilizing the rational method. Where applicable, the criteria established in the "Urban Storm Drainage Criteria Manual" (UDFCD), 1984, developed by the Denver Regional Council of Governments, has been utilized. Master Drainage Basin This site falls within the Spring Creek Major Drainage Basin and a report entitled "Spring Creek Master Drainageway Plan" was prepared by Engineering Professionals, Inc. in March 1988. It is not anticipated that the proposed University Center PUD will have a negative impact on the Spring Creek Major Drainage Basin. 3 Bucher, Willis & Ratliff Corporation .\11115111P ORR\OMINR1. I DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 1. INTRODUCTION Project Location The University Center PUD is a proposed re -development of a portion of the University Center Mall. The project site is located in the Southeast One -Quarter of Section 23, Township 7 North, Range 69 West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. The project site is bounded on the south by existing commercial development (K-Mart Plaza Expansion), on the west by the Burlington Northern Railroad, on the north by Montgomery Wards, and on the east by McDonalds and College Avenue. Site Characteristics The general topography of the site consists primarily of existing asphalt parking lot, buildings, and curb, gutter and sidewalk. The southwest comer and western portion of the site consists of poorly covered range type land. The slopes range from 0.5 to 3 percent. Soils The soils for this site are comprised of the Nunn clay loams. The Nunn clay loam complex consists of nearly level soils on high terraces and fans. Pertinent characteristics of this soil include slow to medium runoff and a slight to moderate hazard of wind and water erosion. Nunn clay loams are categorized in Hydrologic Group C. The source for this soil data is the "Soil Survey for Larimer County Area, Colorado," prepared by the United States Department of Agriculture Soil Conservation Service. Purpose and Scope of Report This report defines the.proposed drainage and erosion control plan for University Center PUD, including consideration of all on -site and tributary off -site runoff. Bucher, Willis & Ratliff Corporation X:\!i�IS WVNXAOMINXVl.0.Y DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD CERTIFICATION I hereby certify that the Drainage and Erosion Control Report for University Center PUD was prepared by me or under my direct supervision in accordance with the provisions of the City of Fort Collins STORM DRAINAGE DESIGN CRITERIA and CONSTRUCTION STANDARDS for the owners thereof. James R. Swanson, P.E. Colorado Registration No. 24639 For and On Behalf of Bucher, Willis & Ratliff Corporation 1 Bucher, Willis & Ratliff Corporation x 11N ISM IVPQIPP\OMIN.1I DRAINAGE AND EROSION CONTROL REPORT for UNIVERSITY CENTER PUD TABLE OF CONTENTS CERTIFICATION.................................................................. 1 1. INTRODUCTION........................................................... 2 2. HISTORIC (EXISTING) DRAINAGE .......................................... 4 3. DEVELOPED FLOWS ....................................................... 5 4. RUNOFF DETENTION AND RELEASE ...................................... 8 5. EROSION CONTROL ...................................................... 10 6. MISCELLANEOUS......................................................... 12 7. REFERENCES............................................................. 13 APPENDIX A - LOCATION MAP APPENDIX B -HYDROLOGIC CALCULATIONS HISTORIC (EXISTING) APPENDIX C- HYDROLOGIC CALCULATIONS DEVELOPED APPENDIX D -DRAINAGE, GRADING, AND EROSION CONTROL PLAN 01111D BUCHER, WILLIS & RATLIFF 1111111111111k6. CORPORATIO N Engineers. Planners & Architects October 27, 1997 Mr. Basil Hamdan City of Fort Collins Stormwater Utility 235 Matthews Street Fort Collins, CO 80522 Re: University Mall Drainage Report Dear Basil: Enclosed please find the revised Drainage Report for University Center Mall. The Site Plan has ' changed considerably since the last report was submitted on November 6, 1996. This report reflects these changes, along with addressing the comments by the City from the last submittal which were received in December, 1996. With the proposed design, the developed discharges to the College ' Ave. system and offsite flows to the railroad property will be less than the current (historic) discharge. I Once again, we have made a genuine effort to comprehensively address the comments from the City of Fort Collins. If you have any questions on the proposed design, please do not hesitate to call. We are more than happy to work with you, as it is our intent to provide a plan that meets the ' City's requirements. Thank you for your assistance. ISincerely, IBUCHER, WILLIS & RATLIFF CORPORATION ' Andrew J. Walsh, P.E. Project Engineer ' AJW/ajw M\VJ\IS\\V�p0.f\pMAI\RIT.OJC 1743 WAZEE STREET, SUITE 200 1 DENVER, COLORADO 80202-1280 1 303/292-5056 1 FAX: 303/292-5668 DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD Prepared For: DPC Development Company 7000 E. Belleview Ave., Suite 290 . Greenwood Village, CO 80111 Prepared By: BUCHER, WILLIS & RATLIFF CORPORATION 1743 Wazee Street, Suite 200 Denver, CO 80202 (303)292-5056 October 27,1997 Hp BUCHER, WILLIS & MR111 ilk CORPORATION