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Home My WebLink AboutSAGE CREEK - PDP - 25-98B - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTow W, =11 IMM• Mv i� >� Ilia ■ul� A a —f ..... I r—z--1. I I -ROAD- 6"MW -ROAD- '� % �• 4 PROJECT T .� '� { 0 A SITE ., of r-----t „z " Z J � E• s / H COUNTY ROAD 36 ' 1 I EXISTIN CITY Uh ITS 1 I I C TY ROAD 34 Y VICINITY MAP Sage Creek Subdivislon Ft. Collins, CO Location shown is approximate. no scale Prepared by the SEAR -BROWN Group •r 209 & Meldn,m Ft Collis. CO 80521 ph: (970)482-5922 f c (970) 482-MOO April 1999 Al APPENDIX A VICINITY MAP VIII. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, interim revision January 1997. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. 3. McClellands Basin Master Drainage Plan, by Greenhorne and O'Mara, Inc., June 1986. 4. McClellands Basin 100-Year Master Plan Update (County Road 9 to Fairway Estates) for Proposed Modifications to the Oakridge Village Regional Detention Pond, April 1996. the onsite storm drain system will provide for the 2-year and the 100-year developed ' flows to reach the future detention ponds at the northern perimeter of this site. The detention ponds will outlet into the McClellands Basin Drainageway and the flows shall be carried east and south downstream to the Fossil Creek Reservoir Inlet Ditch as historically occurs. If, at the time of construction for some unforeseen reason, groundwater is encountered, a Colorado Department of Health Construction Dewatering Permit is required. C. Stormwater Quality Concept The proposed design has addressed the water quality aspect of stormwater runoff through the use of various Best Management Practices (BMPs) for the treatment of storm water. Volumes in Ponds A and B have been extended to accommodate Water Quality Capture Volume (WQCV, see calculation in the Appendix). D. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from the Sage Creek development. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standard shall be met. The proposed erosion control concepts presented in this report and shown on the erosion control plan are in compliance with the City of Fort Collins Erosion Control Criteria. VII. After overlot grading and utility installations have been completed, the parking/driveway surfaces shall receive curb, gutter, and pavement surfaces. The pavement structure shall be applied as soon as possible after the utilities are installed. After installation of the storm drains, riprap protection shall be installed at the outlets. If the disturbed areas will not be built on within one growing season, a permanent seed shall be applied. After seeding, a hay or straw mulch shall be applied over the seed at a minimum rate of 2 tons/acre, and the mulch shall be adequately anchored, tacked or crimped into the soil. In the event a portion of the roadway pavement surface and utilities will not be constructed for an extended period of time after overlot grading, a temporary vegetation seed and mulch shall also be applied to the roadway areas as discussed above. The grass lined detention ponds will be completed after other site infrastructure has been constructed. When the detention ponds are finished, they will include multi - staged outlet works and will be equipped with water quality riser pipes. The water quality riser pipes will allow the first flush of stormwater runoff to filter out of each detention pond over a forty (40) hour time period, thus allowing sediments and pollutants to settle out and not be transported directly into the McClellands Basin Drainageway, All construction activities must also comply with the State of Colorado permitting process for Stonnwater Discharges Associated with Construction Activity. A Colorado Department of Health NPDES permit must be obtained by the owner before construction grading can begin within this development. CONCLUSIONS A. 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. In addition, all computations are in compliance with the McClellands Basin Master Plan. B. 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 the existing and proposed drainage facilities at the northern and eastern property lines of the subject site. The combination of onsite street capacities in the curb and gutter and V. STORMWATER QUALITY A. General Concept The water quality of stormwater runoff must be addressed on all final design utility plans. The Sage Creek development is anticipating construction beginning in Spring 2000. Ponds A and B have been upsized to accommodate the Water Quality Capture Volume as required by the City of Ft. Collins (see calculations in the Appendix). The project will address all stormwater runoff quality concerns through the use of various Best Management Practices for the treatment of stormwater runoff. Best Management Practices (BMPs) for the treatment of storm water runoff include installation of silt fence, rough irregular surfaced soils during grading operations, WQCV, and straw or hay dry mulch of disturbed soils. VI. EROSION CONTROL A. General Concept This development lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. The potential exists for moderate erosion problems after completion of the Sage Creek improvements, due to some existing and proposed site slopes of greater than 2 percent. It is also anticipated that the project site improvements will be subject to both wind and rainfall erosion before new vegetation can take hold or before the new residential lots are developed. The Erosion Control Performance Standard (PS) during and after construction for this project was computed to be 80.7 and 95.0, respectively, per the criteria in the City of Fort Collins Erosion Control Reference Manual for Construction Sites. The ' Effectiveness (EFF) of the proposed erosion control plan was calculated to be 81.8 during construction and 96.3 after construction. Therefore, the erosion control plan below meets the City of Fort Collins' requirements. A copy of the calculation has ' been included in the Appendix. An erosion control escrow cost estimate of $66,300 is also included in the Erosion Control section of the Appendix. B. Specific Details Before grading or trenching begins within the project site, a sediment fence shall be installed at the northern and eastern perimeters (downstream perimeters) of the construction site. After overlot grading is completed, all disturbed areas not in a roadway area shall have temporary vegetation seed applied. After seeding, a hay or I' straw mulch shall be applied over the seed at a rate of 2 tons/acre minimum, and the mulch shall be adequately anchored, tacked, or crimped into the soil. 1 basin 110 is composed of rational basins Al-A16, A18-A27, PA. The total area of SWMM basin 110 is 19.00 acres and drains into detention pond #1 (Pond A). SWMM sub -basin 130 is composed of rational basins B1-B3, B5, B6, B14-B17, PB. The total area of SWMM basin 130 is 19.74 acres and drains into detention pond #2. SWMM sub -basin 140 is composed of rational basin B7. The total area of SWMM basin 140 is 0.22 acres and it drains into detention pond #2. Detention pond #1 will release to McClellands Basin Drainageway via a staged outlet control structure and approximately 170 L.F. of 30" RCP. The outlet works will be designed and constructed to limit the discharge into the McClellands Basin Drainageway to 0.2 cfs/acre for the 10-year storm and 0.5 cfs/acre for the 100-year storm (in accordance with the Master Plan for McClellands Basin). Based on these criteria, the total allowable release rate for the site is 23.80 cfs for the 100-year storm and 9.54 cfs for the 10-year storm. The basin widths for the site were determined by taking the average length of travel from the limit of the SWMM basin to the flow concentration point and dividing that into the area of the basin. The percent impervious values and slopes were determined from the site plan. A HEC-2 analysis was done of the existing condition McClellands Basin Drainageway. This analysis begins approximately 200 feet downstream of County Road 9 and concludes 100 feet upstream of the western property line. The existing corrugated metal pipe arch culvert under County Road 9 is 64 inches x 43 inches and is 43 feet in length. Based on the current Master Plan SWMM analysis the flow in the McClellands Basin Drainageway upstream of County Road 9 is 1002 cfs. The downstream flow of County Road 9 is 1,422 cfs based on the current Master Plan SWMM. Based on these flows the depth of flow over County Road 9 with the existing culvert is 1.16 feet. The elevation of the existing County Road 9 at the culvert crossing is 4905. A second HEC-2 analysis was done which included the proposed box culverts under County Road 9 and upstream at Corbett Drive. The same flow rates were used as in the existing condition HEC-2 analysis as stated previously. The proposed box culvert under County Road 9 shall be 6 feet high and 25 feet wide. The proposed box culvert under Corbett Drive will be three sided, with the creek as the bottom portion, left in its natural condition. This will remain the case until a 100-year event occurs. During a 100-year storm it is likely that the concrete sides of the box will be fully exposed. Based on this, the box culvert was modeled in its fully exposed size of 7 feet x 20 feet. With the proposed box culvert in County Road 9 the 100-year water surface elevation at County Road 9 is 4905.52. The low point in the proposed County Road 9 is approximately 4907.00. With the proposed box culvert under Corbett Drive the 100-year water surface elevation is 4911.53. The low point in the proposed Corbett Drive is approximately 4913.70. Inlet A4a intercepts 100-year design flows of approximately 6.5 cfs from basins Al and A14. These flows enter Storm Drain A2, which transports the flows through approximately 440 LF of 36" Reinforced Concrete Pipe (RCP), into Pond A. Inlet A4 intercepts 100-year design flows of approximately 5.2 cfs from basins Al2 and A15. These flows enter Storm Drain A2, which transports the flows through approximately 440 LF of 36" Reinforced Concrete Pipe (RCP), into Pond A. Inlets A4 and A4a are entering into the same 440 LF of 36" RCP. Inlet A5 intercepts 100 year design flows of approximately 1.4 cfs from basin All. ' These flows enter Storm Drain A2, which transports the flows through approximately 65 LF of 36" Reinforced Concrete Pipe (RCP), into Pond A. Inlet B2 intercepts 100 year design flows of approximately 50.05 cfs from basins B1, B2, B6, B14-17. These flows enter Storm Drain B2-3, which transports the flows through approximately 88 LF of 30" Reinforced Concrete Pipe (RCP), into Pond B. ' Inlet B3 intercepts 100 year design flows of approximately 8.1 cfs from basin B3. These flows enter Storm Drain B2-3, which transports the flows through ' approximately 60 LF of 30" Reinforced Concrete Pipe (RCP), into Pond B. ' Inlet B 1 intercepts 100 year design flows of approximately 17.4 cfs from basin B 16. These flows enter Storm Drain B 16, which transports the flows through approximately 260 LF of 2 1 " Reinforced Concrete Pipe (RCP), into Pond B. ' Basin Il shall maintain historic flows to McClellands Basin Drainage way. The 100 year flows from this basin is approximately 0.48 cfs which are not historically nor developed channelized flows and therefore are considered incidental flows to the McClellands Basin Drainage way. A SWMM analysis of the proposed Sage Creek development has been done. When the model is finalized and approved it can be inserted into the Master Plan update currently being prepared by the City's consultant. The results of the SWMM analysis are included in the Appendix. The site was broken into 4 basins as shown on the SWMM schematic. SWMM sub -basin 120 is composed of rational basins B4, B8- B13. The total area of the SWMM basin is 8.78 acres and it drains into detention pond #2 (Pond B). Pond #2 releases to McClellands Basin Drainage way via a staged outlet control structure and approximately 170 L.F. of 30" RCP. The outlet works will be designed and constructed to limit the discharge into the McClellands Basin Drainage way to 0.2 cfs/acre for the 10-year storm and 0.5 cfs/acre for the 100- year storm (in accordance with the Master Plan for McClellands Basin). Based on these criteria, the total allowable release rate for the site is 28.2 cfs for the 100-year storm and 11.4 cfs for the 10-year storm. SWMM sub -basin 100 is composed of McClellands Basin. The total area of the SWMM basin is 6.83 acres. SWMM sub- D. 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. fE. Variances from Criteria INo variances are being sought for the proposed project site. IV. DRAINAGE FACILITY DESIGN A. General Concept All on -site runoff produced by the proposed Sage Creek development will be routed ' to one of the two proposed detention ponds via curb and gutter, cross -pans, sidewalk chases, inlets, and underground storm drains. The outflow from the detention ponds will be released into the McClellands Basin Drainageway and will then be conveyed ' under County Road 9 through a pair of box culverts (to be designed and constructed by the Harvest Park development). The McClellands Basin Drainageway enters the Fossil Creek Reservoir Inlet Ditch approximately 1.2 miles southwest of the site. ' A SWMM analysis was done of the site in order to determine the volume requirements of the proposed detention ponds on the site. A HEC-2 analysis has ' been done of the McClellands Basin Drainageway in order to determine the existing and proposed flood plain limits adjacent to the site. B. Specific Details The proposed Sage Creek development contains a total area of approximately 53.5 t acres, which has been divided into forty eight (48) sub -basins for Rational Method runoff analysis. Basin designations with an `A' prefix drain to Pond A, basin designations with a `B' prefix drain to Pond B. All basins drain to the north and/or east, and are routed through on -site detention facilities, and eventually into the McClellands Basin Drainageway. Please refer to Appendix B and the Drainage and Erosion Control Plan in the back of this report. Inlet A2 intercepts 100 year design flows of approximately 24.8 cfs from drainage basins and Al — A6. These flows enter Storm Drain A2, which transports the flows through approximately 805 LF of 30" and 36" reinforced concrete pipe (RCP), into Pond A. The initial 65 LF of pipe is 24"x38" Horizontal Elliptical Reinforced . Concrete Pipe (HERCP) due to small cover amounts with 30" circular at Inlet A2. I I i i Drainageway eventually drains into the Fossil Creek Reservoir Inlet Ditch, which transmits water to the Fossil Creek Reservoir. B. Sub -basin Description The area encompassed by the proposed Sage Creek development has been divided into 48 sub -basins for Rational Method calculations. Runoff is routed to one of two detention ponds (Ponds A and B). Ponds A and B will be located 100 feet south of the existing McClellands Basin Drainageway. These on -site basins are proposed to be developed with residential housing and street improvements, including improvements to County Road 9 and County Road 36. These sub -basins are shown on the Drainage and Erosion Control Plan in the back pocket of this report. This development will also include improvements to the portions of County Road 9 and County Road 36 that are adjacent to the site. A majority of the runoff from the roads will be directed onto the site and detained in the proposed detention ponds, in accordance with City of Fort Collins directives. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. B. Development Criteria Reference and Constraints The criteria and constraints from the McClellands Basin 100-year Master Plan and subsequent update, dated April 1, 1996 are being utilized in this Final Drainage Study. With this development, on site detention will be provided and flows will be released into the McClellands Basin Drainageway at the rates defined by the Master Plan. ' C. Hydrologic Criteria The Rational Method for determining surface runoff was used for the project site. The recently adopted 2-year and 100-year storm event intensities provided by the City of Fort Collins were used in calculating runoff values. Regional hydrologic modeling was completed using SWMM. These calculations and criteria are included in the Appendix of this report. II FINAL DRAINAGE AND EROSION CONTROL STUDY FOR SAGE CREEK FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location Sage Creek is bounded by County Road 9 on the east, private residences with large lots on the west, the McClellands Basin Drainageway and the Harvest Creek Subdivision on the north, and by County Road 36 on the south. The site location can also be described as situated in the south half of the southeast 1/4 of Section 5, Township 7 North, Range 68 West of the 6th Principal Meridian, City of Fort Collins, Larimer County, Colorado. A map showing the site location is included in the Appendix. B. Description of Property Sage Creek contains approximately 53.5 acres of land, of which a majority is currently cultivated farmland. The property is being proposed as a residential development within the City of Fort Collins Zoning. There is one existing concrete lined irrigation channel located in the western half of the site. This channel has been used historically for irrigation of the existing adjacent farmland only and has not been a drainage conveyance for storm events. The removal of this channel will not affect any of the surrounding farm irrigation channels. The channel will be removed with the Sage Creek development. The topography generally slopes north-northeast towards the existing McClellands Basin Drainageway at approximately 0.6 — 4.5 percent. McClellands Basin Drainageway runs from west to east along the northern edge of the project boundary. II. DRAINAGE BASINS A. Major Basin Description The Sage Creek development lies within McClellands Basin. The McClellands Basin Drainageway flows in a generally southeast direction, and runs from west to east along the northern edge of the project boundary. The McClellands Basin APPENDIXA: VICINITY MAP.........................................................................................................................................................................A APPENDIX B: RATIONAL METHOD HYDROLOGY....................................................................................................................................B APPENDIXC: SWMM ANALYSIS AND POND DESIGN.............................................................................................................................. C APPENDIXD: HEC-2 ANALYSIS..................................................................................................................................................................... D APPENDIXE. PONDS, INLETS AND STORM DRAINS.................................................................................................................................E APPENDIXF: RIPRAP DESIGN........................................................................................................................................................................F APPENDIXG: STREET CAPACITY CALCULATIONS.................................................................................................................a.............. G APPENDIXH: EROSION CONTROL AND WATER QUALITY.................................................................................................................. H APPENDIX1: TABLES AND FIGURES............................................................................................................................................................1 APPENDIX 2: HEC-2 FLOOD PLAIN MAP, SWMM BASIN MAP................................................................................. BACK POCKET 1 APPENDIX 3: DRAINAGE AND EROSION CONTROL PLAN DRAWING SHEET ..................................................... BACK POCKET 2 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION................................................................................................................I A. LOCATION......................................................................................................................................................................... I B. DESCRIPTION OF PROPERTY............................................................................................................................................. I H. DRAINAGE BASINS...........................................................................................................................................................1 A. MAJOR BASIN DESCRIPTION............................................................................................................................................. 1 B. SUB -BASIN DESCRIPTION...................................................................................................................................................2 III. DRAINAGE DESIGN CRITERIA................................................................................................................................2 A. REGULATIONS...................................................................................................................................................................2 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS..............................................................................................2 C. HYDROLOGIC CRITERIA...................................................................................................................................................2 D. HYDRAULIC CRITERIA......................................................................................................................................................3 E. VARIANCES FROM CRITERIA.............................................................................................................................................3 IV. DRAINAGE FACILITY DESIGN......................................................................................................................................3 A. GENERAL CONCEPT..........................................................................................................................................................3 B. SPECIFIC DETAILS.............................................................................................................................................................3 V. STORMWATER QUALITY...............................................................................................................................................6 A. GENERAL CONCEPT..........................................................................................................................................................6 VI. EROSION CONTROL.........................................................................................................................................................6 A. GENERAL CONCEPT..........................................................................................................................................................6 B. SPECIFIC DETAILS.............................................................................................................................................................6 VII. CONCLUSIONS..............................................................................................................................................................7 A. COMPLIANCE WITH STANDARDS.......................................................................................................................................7 B. DRAINAGE CONCEPT.........................................................................................................................................................7 C. STORMWATER QUALITY CONCEPT................................................................................................................................... H D. EROSION CONTROL CONCEPT.......................................................................................................................................... H VIII. REFERENCES................................................................................................................................................................9 THE SEAR -BROWN GROUP FULL -SERVICE DESIGN PROFESSIONALS 209 SOUTH MELDRUM FORT COLLINS, COLORADO 80521-2603 970-482-5922 FAX:970-482-6368 August 20, 1999 Mr. Basil Hamdan City of Fort Collins Water Utilities--Stormwater 700 Wood Street Fort Collins, Colorado 80522 RE: Final Development Plan Drainage and Erosion Control Study for Sage Creek Dear Basil: ' We are pleased to submit to you, for your review and approval, this Final Development Plan Drainage and Erosion Control Study for Sage Creek. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, The Sear -Brown Group Prepared by: Lee Cunning, P.E. Design Engineer Max McGowan, P.E. Design Engineeer Andrea H. Faucett, P.E. HEC 2 consultant cc: File 434-021A Jim Postle, The James Company Reviewed by: Kevin W. Gingery, P.E. Engineering Manager David K. Thaemert, P.E. Water Resource Engineer NEW YORK • PENNSYLVANIA COLORADO • UTAH • WYOMING STANDARDS IN EXCELLENCE EQUAL OPPORTUNITY EMPLOYER < _. I 1. I I i Final Development Plan Drainage and Erosion Control Study Sage Creek, Fort Collins, Colorado August 20, 1999 THE SEAR -BROWN GROUP Standards in Excellence I