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Home My WebLink AboutEAGLE CLIFFS - PDP - 22-02 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1 1 i 1 1 1 1 1 1 AK LEAF COURT •�CLE p� SETON STRE T 1 A SOUTHRIDGE GREENS BLVD W OORAL SITE < DEERCROF7 C PJ W J K I O j MUIRFIELD W F O O O � O 3 FOSSIL CREEK COMMUNITY PARK VICINITY MAP APPROXIMATE SCALE: 1" = 500' I 117 7 APPENDIX A 1 IN to ►irlrau"M r 1 r 1 1 7. REFERENCES 1. City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March, 1986. 2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria Manual", Volumes 1 and 2, dated March, 1969, and Volume 3 dated September, 1992. 7 ' fence installed. Vehicle tracking pads shall be installed at both connections to Southridge Greens Boulevard to control the mud being tracked onto the existing pavement. During overlot grading, disturbed areas are to be kept in a roughened condition and watered to reduce wind erosion. The detention area proposed on this site will discharge into Fossil Creek south of this site. ' This detention pond will be used as sediment basins during the construction process. ' 6. CONCLUSIONS ' 6.1 Compliance with Standards All computations that have been completed within this report are in compliance with the ' City of Fort Collins Erosion Control Reference Manual for Construction Sites and the Storm Drainage Design Criteria Manual. Requirements placed on the site as a result of the completion of the Master Plan Update have been followed. 6.2 Drainage Concept The proposed drainage concepts presented in this report and on the construction plans ' adequately provide for stormwater detention of improved areas. Conveyance elements have been designed to pass required flows and to minimize future maintenance. If, at the time of construction, groundwater is encountered, a Colorado Department of ' Health Construction Dewatering Permit will be required. �J 6 i ' • The backs of these lots abut the sewer easement and no filling will be allowed over the easement to force the entire lot to drain north into the street. The street is presently designed as low as possible. • All of the detention storage in the pond is above the 100-year WSEL of Fossil Creek (approximately the top of bank). The backs of these lots are basically at the top of bank elevation and well below the elevation of the detention pond. ' • Basin OS 1 has been detained to its 2-year historic rate in an attempt to offset Basin 4 draining undetained. 4.3 Drainage Summary The City of Fort Collins will be responsible for maintenance of the proposed storm drainage facilities located within the right-of-way. These facilities will be Class III RCP ' to conform to the City of Fort Collins criteria. The drainage facilities located outside of the right of way (including the detention pond, 12" storm drain system, pond outlet and ' underdrain) will be maintained by the owners of the site. ' 5. EROSION CONTROL 5.1 General Concept This site lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort ' Collins Zone Maps. The potential exists for silt movement from the site and into Fossil Creek. Potential also exists for tracking of mud onto existing streets which could then wash into existing stone systems. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and related calculations in Appendix E, the erosion control performance standard for the subject site is 78%. The erosion control plan gives a performance standard of 79%. The ' erosion control escrow amount is $11,550. 5.2 Specific Details To limit the amount of silt leaving the site several erosion control measures shall be ' implemented during construction. All inlets shall be protected with gravel filters, straw bales will be used where appropriate, and the south and east boundaries shall have silt ' 5 I 1 r I 11 I i fl 1 The storm sewer system has been designed to convey the 10-year flow for the basin. The 100-year flow will overtop the crown of the street and run east between the southerly two multi -family buildings to the detention pond. Basin 2 includes the outer group of lots and adjacent streets. The front portions of all of these lots drain to the street as well as the front of the northerly 2 multi -family buildings. The runoff from this basin drains to a 5' Type R inlet and storm sewer to the detention pond. The storm sewer system has been designed to convey the 10-year flow for the basin. The 100-year flow will run east between the southerly two multi -family buildings to the detention pond. There are several 18" catch basins and a 12" PVC storm system designed between the street and the multi family buildings. These facilities have not been sized as they are only for nuisance flows in the area. In the event of a large rainfall event, or the clogging of the system, flow will overtop the curb to the proposed Type R inlet. This system will be privately maintained and in the event of the system's failure, no damage will result to the adjacent buildings. The 5' Type R inlet has been sized assuming that all of the drainage in this basin flows to this inlet. Basin 3 includes the back portions of the multi -family units, the majority of the driveways for these units and the detention and water quality pond. All of the flow in this area will reach the pond by overland flow, roof drains, or curb cuts and sidewalk culverts. Another 12" PVC and 18" catch basin is proposed within this basin. As discussed above, this system was not sized, in the even of a failure; flow would overtop the sidewalk prior to damaging the adjacent structure. The detention and water quality pond will outlet in a 15" RCP to the invert of Fossil Creek. Every effort has been made to minimize the disturbance around the creek. All calculations related to the pond are in Appendix D of this report. Basin 4 includes the entire southerly portion of the site. It includes the back portion of the lots described in Basin 2 and a portion of the south multi -family building. The additional impervious area in this basin is small in comparison with the other 3 basins. Runoff from this basin will sheet flow directly into Fossil Creek. This basin cannot be detained for the following reasons: 4 4. to determine the required volume. Water quality volume was calculated using the method recommended in the "Urban Storm Drainage Criteria Manual". 3.4 Hydraulic Criteria All hydraulic calculations within this report have been prepared in accordance with the City of Fort Collins Drainage Criteria and are included in Appendix C of this report. DRAINAGE FACILITY DESIGN 4.1 General Concept The majority of the runoff from the site will drain to the south and west to the proposed detention pond. A small portion of Southridge Greens Boulevard which presently drains directly to Fossil Creek will now be intercepted and routed through the detention pond. In conversations with the City, it was agreed that this off -site flow could pass through the detention pond undetained, but the multi family area on the south was to be regraded to drain to the pond. After reviewing the grading of the multi -family area, it was determined that it will not be possible to drain this area to the pond. Because of this, the flow off of Southridge Greens Boulevard will be detained and will not be pass -through flow in the detention area. The lots on the south side of the site abut the existing sanitary sewer easement. In this area, no filling or other grading will be allowed. The backs of these lots will drain directly to Fossil Creek undetained. 4.2 Specific Flow Routing A summary of the drainage patterns within each basin is provided in the following paragraphs. Basin 1 is in the central portion of the site and includes 13 single-family lots and the adjacent streets. This basin intercepts the flow off of the south half of Southridge Greens Boulevard adjacent to the site (Basin OS1). The lots in this basin drain to the streets and to the backs of the lots where a shallow grass swale and underdrain are located. The runoff from this basin drains to a 5' Type R inlet and storm sewer to the detention pond. 3 ' site flow to this site will be a small portion of Southridge Greens Boulevard which will ' enter the site through the proposed streets. 3. DRAINAGE DESIGN CRITERIA 3.1 Regulations This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage Design Criteria Manual' specifications. Where applicable, the criteria established in the ' "Urban Storm Drainage Criteria Manual' (UDFCD), 1984, developed by the Denver Regional Council of Governments, has been used. ' 3.2 Development Criteria Reference and Constraints ' The runoff from this site has been routed to conform to the requirements discussed with the City Stormwater Department. It is assumed that these requirements will become ' requirements for all future development in the Fossil Creek Basin. In conversations with the Department, it was stated that the 2-year historic release would be required for the ' site. The proposed plan detains to that rate for all of the area that is captured by the detention pond. ' The elevation of the 100-year Fossil Creek Floodplain and the existing sanitary sewer on the south side of the site are the only constraints on the site with respect to drainage and ' grading design. 1 3.3 Hydrologic Criteria ' Runoff computations were prepared for the 10-year minor and 100-year major storm frequency utilizing the rational method. 1 All hydrologic calculations associated with the basins are included in Appendix B of this report. Standard Form 8 (SF-8) provides time of concentration calculations for all sub - basins. Standard Form 9 (SF-9) provides a summary of the design flows for all Sub - basins and Design Points associated with this site. ' Detention volume was calculated based on the 2-year historic release rate for the area draining to the detention pond. The FAA method for detention pond sizing was utilized 2 I GENERAL LOCATION AND DESCRIPTION ' 1.1 Location This site is located in southeast Fort Collins. This project is located in the Northeast Quarter of Section 12, Township 6 North, Range 69 West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. See the location map in Appendix ' A. ' The project is located in the southwest corner of the intersection of Southridge Greens Boulevard and Lemay Avenue; in the past, this site has been known as Huntington Hills, Parcel A. The project is bounded on the north by Southridge Greens Boulevard, on the east by Lemay Avenue, and on the south and west by Fossil Creek and Fossil Creek Community Park. 1.2 Description of Property The entire project consists of approximately 10 acres of land of which only 8 is developable because of buffers for Fossil Creek and a sanitary sewer which is on the southerly boundary of the property. The land is currently undeveloped and slopes to the south at a range of approximately 1% to 4%. 1 ' 2. DRAINAGE BASINS AND SUB -BASINS 2.1 Major Basin Description The proposed development lies within the Fossil Creek Master Drainage Basin. The Updated Master Drainage Plan for this Basin has just been completed by ICON Engineering, Inc. The 100-year floodplain from the updated report is reflected in the ' plans for this project. In the past the Fossil Creek Basin did not have detention requirements. Per conversations with Basil Hamdan, development in this basin will ' require detention to the 2-year historic rate. 2.2 Sub -basin Description This site drains to Fossil Creek independent of any of the surrounding land. The only off- ' t FJ TABLE OF CONTENTS ' TABLE OF CONTENTS............................................................................................................... iii 1. GENERAL LOCATION AND DESCRIPTION 1.1 Location...................................................................................................................1 1.2 Description of Property............................................................................................I ' 2. DRAINAGE BASINS AND SUB -BASINS 2.1 Major Basin Description..........................................................................................I ' 2.2 Sub -Basin Description.............................................................................................1 3. DRAINAGE DESIGN CRITERIA ' 3.1 Regulations..............................................................................................................2 3.2 Development Criteria Reference and Constraints....................................................2 3.3 Hydrologic Criteria..................................................................................................2 ' 3.4 Hydraulic Criteria....................................................................................................3 4. DRAINAGE FACILITY DESIGN 4.1 General Concept.......................................................................................................3 4.2 Specific Flow Routing.............................................................................................3 ' 4.3 Drainage Summary ...................................................................................................5 5. EROSION CONTROL ' 5.1 General Concept......................................................................................................5 5.2 Specific Details........................................................................................................5 ' 6. CONCLUSIONS 6.1 Compliance with Standards....................................................................................6 6.2 Drainage Concept.....................................................................................................6 7. REFERENCES....................................................................................................................7 APPENDICES A Vicinity Map ' B Hydrologic Computations C Hydraulic Calculations D Detention Pond Sizing E Erosion Control Calculations F Figures and Tables iii North Star A%m, design, inc. April 22, 2002 Basil Hamdan ' City of Fort Collins Stormwater 700 Wood Street Fort Collins, CO 80522-0580 ' RE: Final Drainage and Erosion Control Study for Eagle Cliffs Dear Basil, I am pleased to submit for your review and approval, this Final Drainage and Erosion Control ' Study for Eagle Cliffs, a single and multi -family residential project. I certify that this report for the drainage design was prepared in accordance with the criteria in the City of Fort Collins Storm Drainage Manual. I appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. ' Sincerely, �PPpO RE v '• ( ry 1 ' 34288 amp Michael Oberlander, P.E., L.S.I. ��FSS� ..... I ii ' 700 Automation Drive, Unit I Windsor, Colorado 80550 970-686-6939 Phone • 970-686-1188 Fax 1 1 1 1 1 1 1 1 1 FINAL DRAINAGE AND EROSION CONTROL STUDY EAGLE CLIFFS Prepared for: EAGLE CLIFFS, LLC 2655 Midpoint Drive Fort Collins, CO 80525 Prepared by: North Star Design 700 Automation Drive, Unit I Windsor, Colorado 80550 (970)686-6939 April 22, 2002 Job Number 120-14