Loading...
HomeMy WebLinkAboutTOWNHOMES AT TIMBER CREEK PUD - FINAL - 16-89O - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL STUDY THE TOWNHOMES AT TIMBER CREEK FINAL DRAINAGE AND EROSION CONTROL STUDY THE TOWNHOMES AT TIMBER CREEK Prepared for: BUENO DEVELOPMENT 3000 South College Avenue, Suite 103 PO Box 1845 Fort Collins, CO 80522 Prepared by: North Star Design 1200 Carousel Drive, Suite 201 Windsor, Colorado 80550 (970) 686-6939 September 14, 1999 Job Number 111-01 � North Star �fta. design September 14, 1999 Basil Hamdan City of Fort Collins Stormwater 700 Wood Street Fort Collins, CO 80522-0580 RE: Final Drainage and Erosion Control Study for the Townhomes at Timber Creek Dear Basil, I am pleased to submit for your review and approval, this Final Drainage and Erosion Control Study for the Townhomes at Timber Creek. This report for the final drainage design of the Townhomes at Timber Creek 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. 'ncerely, Patricia Kroetch, P.E. P� oPPpO REG�s�9 c`��ON 1►I. A ii 1200 Carousel Drive, Suite 201 Windsor, Colorado 80550 970-686-6939 Phone & Fax TABLE OF CONTENTS ... TABLEOF CONTENTS............................................................................................................... I I 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..........................................................................................1 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 Hydrologic Analysis of the Proposed Drainage Conditions....................................3 4.3 Specific Flow Routing.............................................................................................4 4.4 Drainage Summary ..................................................................................................5 4.5 Water Quality ...........................................................................................................6 5. EROSION CONTROL........................................................................................................6 5.1 General Concept.....................................................................................................6 5.2 Specific Details........................................................................................................6 6. CONCLUSIONS 6.1 Compliance with Standards....................................................................................7 6.2 Drainage Concept....................................................................................................7 7. REFERENCES....................................................................................................................8 APPENDICES A Vicinity Map B Hydrologic Computations C Erosion Control Calculations D Excerpts from Previous Reports E Figures and Tables iii 1. GENERAL LOCATION AND DESCRIPTION 1.1 Location The Townhomes at Timber Creek is a proposed 5.1 acre multi -family residential development. This project is located in the West half of Section 5, Township 6 North, Range 68 West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. The project is a portion of the Timber Creek P.U.D and is located in the northeast corner of the intersection of Timberline Road and Timber Creek Drive. The project is bounded on the south and east by the single-family portion of Timber Creek P.U.D., on the north by property owned by Poudre Valley Hospital currently under development and on the west by Timberline Road. 1.2 Description of Property The entire project consists of approximately 5 acres of land. The land is currently undeveloped and slopes to the south at approximately 1%. A drainage swale has been constructed along the north property line to divert off site flows to the east. The project will consist of 13 buildings containing 4 or 6 units each and detached garages. A private road will provide access to the site and will have some off street parking. 2. DRAINAGE BASINS AND SUB -BASINS 2.1 Major Basin Description The proposed development lies within the McClellands Drainage Basin. Runoff from the project area currently flows overland to Timber Creek Drive and is routed to the existing Detention Pond 373 in the southeast corner of Stetson Creek P.U.D. 2.2 Sub -basin Description This site encompasses basins 202 and 203 and portions of basins 204 and 205 as delineated in the Final Drainage and Erosion Control Study for Timber Creek P.U.D. by 1 RBD Engineering (see Appendix). The site has been graded to conform as nearly as possible to the basin delineation and runoff calculations previously completed with minor revisions due to existing fences impeding proposed flow paths along the south property line. A table comparing the values estimated by the RBD report and the values proposed with this development for area, C values, and runoff for the minor and major storms is included in Appendix B. These basins are shown on the Final Drainage and Erosion Control Plan in the back pocket of this report and a more detailed description of each basin is located in section 4.3 of this report. 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 closely conform to previous calculations completed with the Final Drainage and Erosion Control Study for Timber Creek P. U.D. First Filing by RBD Engineering Consultants dated July 1, 1994. Detention for this site is provided in the Detention Pond 373 as noted in the above mentioned report. A majority of the runoff from this site will be collected in an inlet in Timber Creek Drive and conveyed to the detention pond via storm pipe. The streets and associated drainage systems surrounding the site are existing. The existing storm system was designed by RBD Engineering and was sized to convey the additional runoff resulting from the development of this site. 3.3 Hydrologic Criteria Runoff computations were prepared for the 2-year minor and 100-year major storm frequency utilizing the rational method. All hydrologic calculations associated with the basins are included in Appendix B of this 2 report. Time of concentration calculations for all sub -basins and a summary of the design flows at all Design Points associated with this site are included in Appendix B. Detention for this site is provided off site, therefore no discharge and storage calculations were performed. 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 the Appendix of this report. 4. DRAINAGE FACILITY DESIGN 4.1 General Concept The site was graded to maintain ("as closely as possible) the drainage patterns dictated in the Final Drainage Report for Timber Creek P.U.D. The majority of the runoff from the site will flow to the south and into an inlet in Timber Creek Drive. A portion of the site will drain east to Pole Pine Lane and be conveyed via gutter flow to a sidewalk culvert in Smallwood Drive. The runoff is then conveyed in a grass swale to the detention pond. 4.2 Hydrologic Analysis of the Proposed Drainage Conditions The Rational Method was used to determine both the 2-year and 100-year peak runoff values for each subbasin. The Rational Method utilizes the equation: Q=CIA (1) Where Q is the flow in cubic feet per second (cfs), A is the total area of the basin in acres, C is the runoff coefficient, and I is the rainfall intensity in inches per hour. "C" values were determined using Table 3-3 of the "City of Fort Collins Storm Drainage Criteria Manual" and I was determined from Figure 3-1. Although new rainfall criteria was accepted by the City of Fort Collins on March 26, 1999, this project is utilizing the rainfall intensity duration curve dated November, 1975. The original submittal date for this project was prior to the implementation date of the new rainfall criteria and is therefore, allowed to utilize the previous rainfall curves. 3 4.3 Specific Flow Routing A summary of the drainage patterns within each basin is provided in the following paragraphs. Subbasin 201 contains the east half of Timberline Road along the site frontage and a portion of the north half of Timber Creek Drive along the frontage. Runoff from Subbasin 201. is conveyed via gutter flow to the main entry of the site and into Subbasin 204. The runoff from this Basin was estimated with the RBD report to be 2.04 cfs in the 2 year event and 7.87 cfs in the 100 year event. The actual runoff from Basin 201 with this development will be reduced to 1.97 cfs in the 2 year storm and 7.35 cfs in the 100 year storm. Subbasin 202 contains the western portion of the site. Runoff from Subbasin 202 is conveyed via overland flow and swales to the interior street. The flow is then routed southwest in the street to the main entry where the runoff combines with runoff from Subbasin 201 and enters Subbasin 204. The runoff from this Basin was estimated with the RBD report to be 4.46 cfs in the 2 year event and 18.34 cfs in the 100 year event. The actual runoff from Basin 201 with this development will be increased slightly to 5.00 cfs in the 2 year storm and 19.56 efs in the 100 year storm. This increase is due to a higher C value than was estimated. Subbasin 203 contains the eastern portion of the site. Runoff from Subbasin 203 is conveyed vir-overland flow and swales to the interior street. The runoff is then routed east in the street to a concrete channel that conveys the flow to Pine Pole Lane. The runoff from this Basin was estimated with the RBD report to be 2.26 cfs in the 2 year event and 9.20 cfs in the 100 year event. The actual runoff from Basin 2.01 with this development will be higher than was estimated and will be 2.54 cfs in the 2 year storm and 9.92 cfs in the 100 year storm. This increase is due to an increase in area for this Basin and a slight increase in.the C value. Subbasin 204A contains the southern portion of the site. Runoff from Subbasin 204A is conveyed via a swale with a concrete pan to the Timber Creek Drive. The runoff is then 4 combined with runoff from Subbasin 204 and routed to the existing inlet at design point 4. Subbasin 204A deviates from the original overall drainage report for Timber Creek Subdivision. The area contained in 204A should be contained in Subbasins 204 and 205 but, due to existing fences impeding proposed flow paths, a portion of each subbasin has been rerouted. The total runoff from Subbasins 204A, 204 (as revised) and 205 (as revised) does not exceed the total allowable runoff in the overall drainage report for 204 (original) and 205 (original). The total runoff estimated for Basins 204 and 205 was 5.01 efs in the 2 year event and 19.54 cfs in the 100 year event. The total runoff for Basins 204A, 204 and 205 proposed with this development is 4.72 in the 2 year storm and 17.73 cfs in the 100 year storm. Subbasin 204 contains 3 existing single-family lots. Runoff from Subbasin 204 is conveyed to Timber Creek Drive via existing side lot swales along Lots 1, 2 and 3. The runoff then combines with flow from Subbasins 201, 202 and 204A and into the existing inlet at design point 4. Subbasin 205 contains 12 existing single-family lots. Runoff from Subbasin 205 is conveyed to Timber Creek Drive via existing side lot swales. The runoff then flows into the existing inlet at design point 5. 4.4 Drainage Summary There were not any drainage problems encountered on this site. Proposed drainage patterns were delineated in order to minimize impact on existing housing. Basins were modified slightly from the predicted basin layout in the RBD report but total runoff from the site is within restrictions outlined in that report. The storm conveyance system is primarily a surface system and has been designed for minimum maintenance. The City of Fort Collins will be responsible for maintenance of storm drainage facilities located within the right-of-way. The drainage facilities located on this site will be maintained by the The Townhomes at Timber Creek Master Association.. 5 4.5 Water Quality This site is a portion of the overall Timber Creek Subdivision and shares detention facilities with the overall subdivision. Water quality measures were not implemented in the remainder of the Timber Creek Subdivision and therefore are not being proposed with this site. The effects of any water quality measures implemented on this site would not be evident after runoff from this site is combined with the runoff from the remainder of the subdivision at the detention area. 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. Potential also exists for tracking of mud onto existing streets which could then wash into existing storm systems. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and related calculations in Appendix D, the erosion control performance standard for the subject site is 76.7%. The erosion control plan gives a performance standard of 77.0%. The erosion control escrow amount is 54936. 5.2 Specific Details To limit the amount of silt leaving the site several erosion control measures shall be implemented during construction. The west boundary shall have silt fence installed and gravel filters shall be installed at the metal sidewalk culverts to reduce sediment leaving the site. All area to be sodded or seeded shall have a straw mulch applied and maintained until a grass cover can be established. A vehicle tracking pad shall be installed at the entry onto Timber Creek Drive to control he mud being tracked onto the existing pavement. Any mud tracked onto the public streets shall be cleaned on a daily basis. During overlot grading, disturbed areas are to be kept in a roughened condition and watered to reduce wind erosion. 6 6. CONCLUSIONS 6.1 Compliance with Standards All computations that have been completed within this report are in compliance with the Storm Drainage Design Criteria Manual and the City of Fort Collins Erosion Control Reference Manual for Construction Sites. 6.2 Drainage Concept The proposed drainage concepts presented in this report and on the construction plans adequately provide for the transmission of developed on -site runoff to Timber Creek Drive or Pine Pole Lane where the runoff will be conveyed in existing facilities to the existing downstream detention facility. The onsite street capacities and off site storm drain system will provide for the 2- year and the 100- year developed flows to reach the existing detention facility. The existing receiving detention facility has been sized to accommodate developed runoff from this site. If, at the time of construction, groundwater is encountered, a Colorado Department of Health Construction Dewatering Permit would be required. 7 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. Guo, James C.Y., PhD, P.E. "Street Hydraulics and Inlets Sizing using the Computer Model UDINLET". University of Colorado at Denver, January 1995. 4. StormCAD v.1.5, Storm Sewer Design & Analysis Software by Haestad Method, 1997. 8 APPENDIX A VICINITY MAP I'lT:�IJ�81 WATOX i HORSETOO TH ROAD PROJS31 CT T E CITY LIMITS O 9 COUNTY ROAD J6 FOSSIL CREEK RE SERVCJI VICINITY MAP APPROXIMATE SCALE: 1" = 2000'