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Home My WebLink AboutLAUREL STREET LOFTS - PDP/FDP - 25-00 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTQ z U VICINITY MAP A i I 1 1 I 1 1 1 1 B 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. 3 4 McClellands Basin 100 Year Master Plan Update by RBD, Inc. Engineering Consultants dated April 1, 1996. Final Drainage and Erosion Control Study for the Oakridge Business Park P.U.D. 215` Filing by RBD, Inc. Engineering Consultants dated February 15, 1996. 6 adequately provide for the detention and transmission of developed on -site runoff to the existing streets and into the existing storm system. The impact of the development of this site on existing downstream facilities is very minor and therefore on site detention is not being proposed. If, at the time of construction, groundwater is encountered, a Colorado Department of Health Construction Dewatering Permit would be required. 6.3 Erosion Control Concept Since the site is less than 5.0 acres, a NPDES permit is not required. During construction, erosion control shall be maintained to minimize erosion on this site and transport of silt downstream. 5 4.4 Variance Requests A variance is being requested to forgo the detention requirement for this site due to the ' increase rainfall criteria adopted by the City of Fort Collins in 1999. The amount of increase to the runoff for this site (from the existing condition to the developed condition) is approximately 1.0 cfs and when viewed in the context of the overall basin, this increase is very minor. 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 the ' existing storm system during construction. Silt fence is being utilized to minimize this potential during construction. This project is an infill project and construction will utilize the majority of the site. Because of this, most Best Management Practices (BMP's) are not effective and therefore very few erosion control measures are being proposed. Most of the construction traffic (concrete trucks, etc) will utilize the existing alleys and will not enter the site thus minimizing the possibility of mud tracking. Silt fence is utilized until the majority of the pavement is installed to minimize wind and stormwater erosion. Watering of disturbed areas is being proposed to also minimize the wind erosion. The erosion control escrow amount is S 1530. 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 Storm Drainage Design Criteria Manual. 6.2 Drainage Concept The proposed drainage concepts presented in this report and on the construction plans 1 4 I 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. 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 also included in Appendix C of this report. ' 4. DRAINAGE FACILITY DESIGN ' 4.1 General Concept The runoff from this site is split by the new building. The building will have a peak ed roof with the peak running north -south. Half of the runoff will flow to a pan on the west side of the building and be conveyed to the alley on the north. The remaining portion of the site will flow east and be conveyed north in the alley. 1 4.2 Specific Flow Routing A summary of the drainage patterns within each basin is provided in the following paragraphs. Subbasin 1 contains the east half of the site and runoff from this basin flows to the center of the alley along the east perimeter of the site. Flows then continue north and off site. Subbasin 2 contains the west half of the site. Runoff from Subbasin 2 is collected in a concrete pan and is conveyed north to the alley along the north perimeter of the site. The flow is combined with runoff from Subbasin 1 and is then released to the north. 4.3 Drainage Summary The storm conveyance system is a surface system and has been designed for minimum maintenance. The City of Fort Collins will be responsible for maintenance of the existing adjacent alleys utilized as drainage conveyance. The drainage facilities located on this site (concrete pan) will be maintained by the owners of the site. 3 I site is not within the area that is prone to flooding and was not mapped with the RCE ' study. Portions of the Old Town Master Drainage Plan are included in appendix E. 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 existing site constraints. Since this is an `in fill' project with all of the adjacent alleys, street and buildings already ' constructed, there is very little room for variances from existing site conditions. The streets and associated drainage systems surrounding the site are existing. The nearest storm system is approximately 200' east of this site in Laurel Street but this site is intended to release to the north in the alley. As currently proposed, this site will receive only minor off -site flows from the adjacent property to the east. The adjacent site generally slopes to the north but a small portion of the east side of the site will tend to n flow east into the subject site and be conveyed north to the alley. No detention is proposed for this site. The existing site (based on the rainfall criteria adopted by the City of Fort Collins on March 26, 1999) generates approximately 0.16 cfs runoff in the 2 year storm and 0.76 cfs in the 100 year storm event. The site as it is proposed will generate approximately 0.40 cfs in the 2 year event and 1.80 cfs in the 100 year event. Although this is more than double the existing runoff, the additional runoff in the 100 year event is only 1.0 cfs. This increase, when viewed on a basin wide level, is very insignificant and will have a very minor impact on downstream conveyances. 3.3 Hydrologic Criteria ' Runoff computations were prepared for the 2-year minor and 100-year major storm frequency utilizing the rational method. 2 I 2 GENERAL LOCATION AND DESCRIPTION 1.1 Location This site is located in Old Town Fort Collins. This project is located in Block 96 of Harrison's Addition in the Northeast Quarter of Section 14, Township 5 North, Range 67 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 north of Laurel Street between Meldrum Street and Sherwood Street. The project is bounded on the south by Laurel Street and the CSU Campus and on the east, north and west by existing housing occupied mainly by CSU students. 1.2 Description of Property The entire project consists of approximately 0.18 acres of land. The land is currently undeveloped and slopes to the north and east at approximately 1%. The site currently drains overland to the alleys on the north and east sides of the site. The project will consist of a single building, several short driveways and two decks. The site will access off the alleys on the north and east. DRAINAGE BASINS AND SUB -BASINS 2.1 Major Basin Description The proposed development lies within the Old Town Drainage Basin. More specifically, the site is a portion of Basin 211 in District 5 of the Old Town Master Drainage Plan, as prepared by RCE Inc., dated January 7, 1993. An excerpt of the drainage schematic is shown in Appendix E. 2.2 Sub -basin Description Basin 211 of the Old Town Master Drainage Plan flows north in the street to Myrtle Street where it is intercepted in storm pipe and conveyed east and north to the Poudre River. The Old Town Basin is subject to areas of flooding along the major conveyances and these areas were mapped by RCE in the Old Town Master Drainage Basin Plan. This I TABLE OF CONTENTS ' TABLE OF CONTENTS...............................................................................................................iii 1. GENERAL LOCATION AND DESCRIPTION 1.1 Location................................................................................................................... I 1.2 Description of Property ............................................................................................1 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 ..................................................................................................3 4.4 Variance Requests....................................................................................................4 5. EROSION CONTROL n5.1 General Concept......................................................................................................4 6. CONCLUSIONS 6.1 Compliance with Standards....................................................................................4 6.2 Drainage Concept....................................................................................................4 6.3 Water Quality and Erosion Control Concept...........................................................5 7. REFERENCES....................................................................................................................6 APPENDICES A Vicinity Map B Hydrologic Computations & Erosion Control C Figures and Tables D Excerpts from Previous Reports North Star off, design _ August 16, 2000 Basil Hamdan City of Fort Collins Stormwater 700 Wood Street Fort Collins, CO 80522-0580 RE: Final Drainage Report for Laurel Street Apartments Dear Basil, I am pleased to submit for your review and approval, this Final Drainage Report for Laurel Street Apartments with revisions to address your comments. I certify that this report for the drainage design of Laurel Street Apartments 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, ' Patricia Kroetch, P.E. North Star Design, Inc. ' ii 1 194 W. Ash Street, Suite B Windsor, Colorado 80550 970-686-693S Phone • 970-686-1188 Fax FINAL DRAINAGE AND EROSION CONTROL REPORT LAUREL STREET APARTMENTS 9 Prepared for: VANTAGE PROPERTIES 3555 Stanford Road, Suite 202 Fort Collins, CO 80525 Prepared by: North Star Design, Inc. 1194 W. Ash Street, Suite B Windsor, Colorado 80550 (970)686-6939 August 16, 2000 Job Number 136-01