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BUPN • • o � � y �O Oµ �<,,L�,',v�lgp� • I m � �1�I � � � AFC/�•y �r �O -:� �� II I z• y 1u • i P�c+'xL�'r m� r z • �.. 'MIL co Cf� p f D TTEm 2 �.tiV• M V • • c-.-+ 3 d r a� •h�y} //554 _Kii .4CJ�\ _ NMorrt xn i TSHORE .... 052 ODF APPENDIX A LOCATION MAP 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. 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. 12 Bucher, Willis & Ratliff Corporation x\i6K\WM.\�MWfITF➢I 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. 11 Bucher, Willis & Ratliff Corporation ¢�s 1a1 Vrwwx . J DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY 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 !i 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 1 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. Erosion control calculations, cost estimate, and schedule is included in the Appendix of this report. 10 Bucher, Willis & Ratliff Corporation Q�%i4�WM. pAAMAAi.I1N J' DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 1 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. IGeneral Description n The 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 comer and western portion of the site consist of poorly covered range type land. The slopes range from 0.5 to 3 percent. Soil Description �I In accordance with the Soil Conservation Service's (SCS) "Soil Survey of Fort Collins Area, r' 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. 9 Bucher, Willis & Ratliff Corporation '2VbY\WRC\DMP'RPIf1N iJ DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 4. RUNOFF DETENTION AND RELEASE Detention Area 1 Detention Area 1 is located southeast of the proposed retail building expansion and west of McDonalds. Flows are directed to this area from the surrounding parking area. This detention area has a proposed sump condition area inlet that acts as the outfall. The release C from this pond will be controlled by an orifice plate to be installed on the outfall pipe at the release. This area has been graded to provide for detention with the maximum ponding depth of 1 foot at the inlet location. In order to control this depth, the surrounding parking lot has been graded to allow for the overflow to be released into the parking areas on the south side of the existing McDonalds. Dentention Area 2 Detention Area 2 is located in the parking area south of the proposed retail building expansion. Detention Area 2 also includes the proposed 24" pipe which begins at the proposed inlet 1 at the northwest side of the site and wraps around the south side of the building and connects to the existing 15" pipe. Flows are directed to this area from the entire redeveloped site with the exception of Subbasins D1 and D9. This detention area has several proposed sump condition area inlet that connect to the outfall. The release from this pond will be controlled by the existing outfall pipe. This area has been graded to provide for detention with the maximum ponding depth of 1 foot at inlet No. 6. In order to control this depth, the parking lot has been graded to provide for an overflow to the south. `" Flow Rates Released to College Avenue Outfall System - Existing and Developed The proposed drainage system has been designed to discharge a maximum rate equal to the 2-year (existing conditions) historic rate to the College Avenue outfall system. Runoff detention and release calculations are included in the Appendix of this report. 1.1 Bucher, Willis & Ratliff Corporation .y4Wfi\ WMOMMAPI'.FM DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD where t, is the time of concentration in minutes, t; is the initial or overland flow time in minutes, and t, 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 )L0.5]/(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 Cf are as defined previously. All hydrologic calculations associated with the redeveloped sub -basins are attached in the Appendix of this report. 7 Bucher, Willis & Ratliff Corporation ?VON\WP!\OMMF1?.FW DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD Runoff from Sub -basin D5 is conveyed into a proposed sump area inlet to be located west of the existing building via roof and surface flow. Runoff from Sub -basin D6 is conveyed to proposed sump area inlet to be located near the south end of the storage units via roof and surface flow. Runoff from Sub -basin D7 is conveyed to proposed sump area inlet to be located near the mid point of the storage units via roof and surface flow. Runoff from Sub -basin D8 is conveyed to proposed sump area inlet to be located near the north end of the storage units via roof and surface flow. Runoff from Sub -basin D9 is conveyed to the existing swale at the northwest comer of the site via surface flow. Hydrologic Analysis of the Proposed Drainage Conditions ' The Rational Method was used to determine both 10-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=CfCIA where Q is the flow in cfs, A is the total area of the basin in acres, Cf 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 10-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. 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 ' 6 Bucher, Willis & Ratliff Corporation ' 2vcauwmoxnmaer.Flw J DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 3. DEVELOPED FLOWS Method The Rational Method was used to determine both the 10-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. Off -site Flows Off -site flows from the west generated between Burlington Northern Railroad and the west property line will flow from the south to the north along the west property line in a historic manner and will not impact the site. On -site Flows Drainage within the redeveloped area will surface flow to inlets and detention 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. A qualitative summary of the drainage patterns within each developed sub -basin is provided in the following paragraphs. Runoff from Sub -basin D1 is conveyed by surface flow towards the center of the basin where it is detained and released through an area inlet and piped to the existing outfall system located along the south property line. The proposed discharge location is consistent with the existing discharge location. Runoff from Sub -basin D2 is conveyed by surface flow towards the center of the basin where it is detained and released through an area inlet and piped to the existing outfall system. Runoff from Sub -basin D3 is conveyed into two existing sump area inlets in the paved area west of King Soopers via roof and surface flow. Runoff from Sub -basin D4 is conveyed into a proposed sump area inlet to be located west of the existing building via roof and surface flow. Bucher, Willis & Ratliff Corporation 2vsau�wmowwarcmv 5 1 I 1 1 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. 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. The drainage from the western portion of this site is conveyed to the north along the western edge of the existing asphalt parking area then to an existing swale, which starts at the northwest comer 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 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 Appendix of this report. Bucher, Willis & Ratliff Corporation g�vctss�wanon.�wxm mu 4 DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD Design Criteria 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. Runoff computations were prepared for the 10-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. The proposed University Center PUD will not have an impact on the Spring Creek Major Drainage Basin. 3 Bucher, Willis & Ratliff Corporation I I DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD 1 1. INTRODUCTION Project Location The University Center PUD is the proposed re -development of portions of the University 1 Mall. This project 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. This project is bounded on the south by existing commercial development (McDonalds and the K-Mart Plaza Expansion), on the west by the Burlington Northern Railroad, on the north by Montgomery Wards, and on the east by 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 corner 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 loams 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. 2 Bucher, Willis & Ratliff Corporation �y.Dtlf6 � W M�AAMRPf FA' 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 CRITERIA and CONSTRUCTION STANDARDS for the owners thereof. Daniel C. Blankenship, P.E. Colorado Registration No. 28198 For and On Behalf of Bucher, Willis & Ratliff Corporation 1 Bucher, Willis & Ratliff Corporation d\ W K\ W I!�OFNNAPf.FR+ 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. DETENTION............................................................... S 5. EROSION CONTROL....................................................... 9 6. MISCELLANEOUS......................................................... 11 7. REFERENCES............................................................. 12 APPENDIX A - LOCATION MAP APPENDIX B - HISTORIC FLOW CALCULATIONS - DEVELOPED FLOW CALCULATIONS - DETENTION CALCULATIONS APPENDIX C - EROSION CONTROL APPENDIX D - DRAINAGE, GRADING, AND EROSION CONTROL PLAN 101111D BUCHER, WILLIS & RATLIFF 101111111111L CORPORATION September 11, 1996 ICity of Fort Collins Stormwater Utility 235 Matthews Street Fort Collins, CO 80524 Re: Drainage and Erosion Control Report University Center PUD Fort Collins, Colorado Bucher, Willis & Ratliff Corporation is pleased to submit the attached Drainage and Erosion Control Report for University Center PUD for the City's review. The hydraulic and hydrologic evaluation of the site was performed in accordance with the City of Fort Collins' "Storm Drainage Design I Criteria and Construction Standards Manual" requirements. This report is a continuation of and revision to the "Final Drainage and Erosion Control Report - University Center PUD" prepared by JR Engineering, LTD., dated May 20, 1996. Bucher, Willis & Ratliff Corporation hereby acknowledges that said report prepared by JR Engineering was neither complete nor was approved by the City of Fort Collins. If you have any questions regarding the report, please call. Sincerely, BUCHER, WILLIS & RATLIFF CORPORATION Daniel C. Blankenship, P.E. Project Manager DCB/bhs Q: \ 96366\ WPC\ DRAINRPT. FIN 1 1743 WAZEE STREET, SUITE 200 1 DENVER, COLORADO 80202i1280 1 303/292-5056 1 FAX: 303/292-5668 1 1 DRAINAGE AND EROSION CONTROL REPORT UNIVERSITY CENTER PUD Prepared For: THE MULHERN GROUP 1730 BLAKE ST., SUITE 435 DENVER, CO 80202 Prepared By: BUCHER, WILLIS & RATLIFF CORPORATION/ 1743 Wazee Street, Suite 200 Denver, CO 80202 (303) 292-5056 September 11,1996 DIpD BUCHER, �VllliS & RAiLiff DAIS CORPORATION