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HomeMy WebLinkAboutPADS AT HARMONY - PDP - 26-06 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI 1 E 1 i APPENDIX 1 L II 1-1 1 1 1 1 1 1 1 13 1 REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, Revised January 1997. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991, Revised January 1997. 3. McClellands Basin 100-Year Master Plan Update, by Icon Inc., Fort Collins, 4. Final Drainage and Erosion Control Report Poudre Valley Health Systems Harmony Campus Infrastructure Project Development Plan, Fort Collins, Colorado, May 12, 2004. 12 VII. CONCLUSIONS ' A. Compliance with Standards ' All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. The City of Fort Collins Storm water Utility will not maintain the on -site storm drainage facilities within the Pads at ' Harmony site. The owners of the Pads at Harmony site will maintain their on -site storm drainage facilities on a regular basis. B. Drainage Concept The proposed drainage concepts presented in this study and those shown on the final ' utility plans will adequately provide for the transmission of developed on -site runoff to the proposed detention ponds. The combination of on -site street capacities and the on -site storm sewer system will provide for the developed flows to reach the ' proposed detention ponds. The sizes, locations and release rates of these ponds will allow the Pads at Harmony site to develop in conformance with the Fox Meadows Drainage Master Planning concepts accepted by the City of Fort Collins. ' If groundwater is encountered at the time of construction, a Colorado Department of Health Construction Dewatering Permit will be required. C. Storm Water Ouality Storm water quality will be addressed through the use of gravel inlet filters, erosion control fence, grass -lined detention ponds, and extended detention with the Front ' Range Village development. D. Erosion Control Concept The proposed erosion control concepts will adequately provide for the control of wind and rainfall erosion from the Pads at Harmony site. 'Through the construction of the proposed erosion control concepts, the City of Fort Collins performance ' standards will be met. ' The Pads at Harmony site 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 erosion problems during construction, and after construction until the disturbed ground is re -vegetated or paved. There should be minimal to no erosion ' problems after completion of construction. The computed Erosion Control Performance Standards (PS) before and after construction is 80.4 and 94.6 respectively. Furthermore, the effectiveness values during and after construction are 95.6 and 98.3 respectively. These computed values meet the City of Fort Collins requirements and can be seen in Appendix C. ' An erosion control escrow cost estimate of $24,993 (price includes 50% contingency) is also included in Appendix C. This represents the cost to re -seed and provide the ' required erosion control methods for the site. B. Specific Details ' A silt fence will be installed prior to grading of the site, as shown on the drainage and erosion control plan. All other disturbed areas not in a roadway or greenbelt area ' shall have temporary vegetation seed applied within 30 days of initial disturbance. After seeding, a hay or straw mulch shall be applied over the seed at a rate of 1.5- tons/acre minimum, and the mulch shall be adequately anchored, tacked, or crimped ' into the soil. Those areas that are to be paved must have a 1-inch layer of gravel mulch applied at a rate of at least 135 tons/acre 30 days after overlot grading is ' completed. The pavement structure shall be applied within 30 days after the utilities have been installed. ' 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 1.5 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. All construction activities must also comply with the State of Colorado permitting ' process for Stormwater Discharges Associated with Construction Activity. A Colorado Department of Health NPDES permit has been obtained such that construction grading can continue within this development. Ito] southeast towards design point 106 and combines with that from basins 100,103, and 104 in the proposed manhole. The combined 32.9 cfs flow from basins 100, 103, 104, and 105 will be conveyed east in the proposed storm drain, then north through the Front Range Village site, and into the proposed detention pond in the northwest corner of the Front Range Village site. It is important to again note that this is contingent upon the agreement between the developers of the Front Range Village and The Pads at Harmony. Pond Sizing Pond sizing was computed using the modified FAA method from the Urban Drainage Website. Basins 100 and 104 were partially detained with a maximum outflow set at 5 cfs for each pond. This provided for partial detention of the site, thus reducing the flow to the Front Range Village detention pond. V. STORM WATER QUALITY A. General Concept Storm Water Quality will be provided through extended detention in the Front Range Village detention pond system. B. Specific Details Best Management Practices (BMP) for the treatment of storm water runoff will be provided through the use of gravel inlet filters, erosion control fence, and grass -lined detention ponds 1 and 2. Erosion control fence shall be installed where shown in the final plans. Gravel inlet filters shall be installed as shown on the erosion control plan. Erosion control calculations have been provided in Appendix C. VI. EROSION CONTROL A. General Concept Silt fence, tracking pads, straw bale check dams, mulching, and erosion control fabric ' will be utilized to minimize erosion on the Pads at Harmony site. Please see the Drainage and Erosion Control Exhibit located in the map pocket. 1 E 1 The historic release of the Pads at Harmony site was calculated using a "c" of 0.3, an intensity of 5 in/hr, and an area of 9.98 acres. This provides for a historic runoff of ' approximately 15 cfs. Utilizing the controlled release of 10 cfs between Ponds 1 and 2, the combined 100-year rational outflow from the north and south portions of the Pads at Harmony site is 32.90 cfs (northeast corner of the site as flow is routed north ' and through the Front Range Village Site). Therefore, the Pads at Harmony is increasing the historic runoff by approximately 17.9 cfs. Basins 100 & 104 ' Grading of the areas south of the proposed buildings will allow runoff to flow south towards the proposed 2' concrete trickle pans. The trickle pans will convey the storm flows east and into detention Ponds 1 and 2 (design points 100 and 104). It is important to note that 12" ADS storm drain pipes will be installed on the north side of the berms to allow runoff to flow south and into the proposed trickle pans. ' Ponds 1 and 2 will each have two basins for each pond, thus forming equalizer ponds. Proposed 15" storm drainpipes will be installed between the pond basins to allow pedestrian access flyover. The ponds will utilize 4:1 side slopes and dry ' stacked sandstone walls to keep pond sizes small, while meeting the detention requirements for the controlled releases. ' Ponds 1 and 2 will have CDOT Type D inlets installed in the east ends of the ponds. The inlets will have 15" outfall storm drains with orifice plates bolted to the inside of the inlets. The orifice plates will restrict flow out of the ponds to 5cfs (see ' calculations in Appendix B). These controlled releases will provide partial detention of the site, thus reducing the flows to the Front Range Village pond. Pond 1 will release 5 cfs north in the proposed 15" storm drain towards design point 103A, where the flow combines with that from basin 103. Pond 2 will also release 5 ' cfs north in the proposed 15" storm drain towards design point 106, where the flow combines with that from basin 100, 103, and 105. ' Basins 103 & 105 Basins 103 and 105 make up primarily the parking lots for the site. Basin 103 ' conveys its runoff northeast toward design point 103, where a 15' Type R Inlet (in sump) captures the 100-year flow. The flow is routed east in the proposed 24" storm drain to design point 103A, where the controlled flow from basin 100 combines with ' the flow from basin 103. The combined flow is routed east in the proposed 30" storm drain towards design point 106. t Meanwhile, basin 105 also conveys its flow northeast towards design point 105, where a 15' Type R Inlet (in sump) captures the 100-year flow. The flow is routed 3 ' The Pads at Harmony site accounts for approximately 9.05 acres. Storm flows from a portion of the north side of Harmony Road and also the south sides of the Pads at ' Harmony site will be conveyed to the two proposed detention ponds. The two ponds will provide partial detention for the site and release at 5.0 cfs (10 cfs total). ' The remaining portion of the Pads at Harmony site will be conveyed to two, proposed Type R Inlets in the northeast corners of the two parking lots. The captured runoff ' will be routed in the proposed storm drain to the northeast corner of the site. The runoff from the Type R Inlets, as well as the detained releases from the detention ponds will combine at the northeast corner of the Pads at Harmony site. The combined runoff is tentatively planned to be routed north and into the detention pond ' in the northwest corner of the Front Range Village site. It is important to note that the agreement to provide the remaining required detention ' and all of the water quality for the Pads at Harmony site, in the Front Range Village detention pond is solely between the developers of the two said properties. 1 B. Specific Details ' The Pads at Harmony site contains approximately 9.05 acres. The site has been broken down into 4 drainage basins. The south portion of the site (basins 100 and 104) contains the south half of the buildings, green space, and a segment of the north side of Harmony Road, adjacent to the site. ' The north portion of the site (basins 103 and 105) contains the parking lot and north - half of the buildings. Runoff from the south portion of the site and the north side of Harmony Road (basins 100 and 104) will be routed east along the north side of Harmony Road and into the two, proposed detention ponds. Runoff from the north portion of the site will be conveyed to two, proposed inlets in the northeast corners of the parking lots. ' Ultimately, the flows from the north and south portions of the site combine at the northeast corner of the site and are conveyed north, through the Front Range Village Site, and into the proposed detention pond in the northwest corner of the Front Range ' Village site. It is important to note that this is contingent upon the agreement between the developers of Front Range Village and Pads at Harmony properties. The proposed detention ponds will only provide partial detention and no water quality. Therefore, it is assumed that the agreement between the developers will ' provide that detention for basins 100 and 104 of the Pads at Harmony site and all of the water quality for the Pads at Harmony site (0.33 ac-ft) will be provided for in the Front Range Village development. 1 7 I 1 ' III. DRAINAGE BASIN 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 City of Fort Collins Master Plan and the Fox ' Meadows Basin Drainage Master Plan Update will be utilized in this Drainage Study. C. Hydrologic Criteria Since the Pads at Harmony site is only 9.05 acres, the modified FAA method was used to size the detention ponds for the site. Furthermore, rational calculations have ' been provided in Appendix B for the site, as well as storm drain sizing using UDInlet, and UDSewer. ' D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of ' Fort Collins Storm Drainage Criteria. Detention pond sizing was computed using the modified FAA method. ' F. Variance A variance for 0.70' and 0.75' of freeboard for Ponds 1 and 2 respectively is being requested to minimize the height of walls in the detention ponds and provide a more aesthetic look with the surrounding grading. " IV. DRAINAGE FACILITY DESIGN ' A. General Concept The purpose of this report is to address the storm drainage flows from the ' development of the Pads at Harmony site. 1 6 ' II. 1 FINAL DRAINAGE AND EROSION CONTROL REPORT FOR THE PADS AT HARMONY, FIRST FILING FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION A. Location The Pads at Harmony site is located north of Harmony Road, east of Timberline Road, and is split down the middle by Snow Mesa Drive, in southeastern Fort Collins, Colorado. The site is shown on the Vicinity Map in Appendix A. More particularly, the site is situated in the northwesterly portion of Section 5, Township 6 North, Range 68 West of the Sixth P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The Pads at Harmony site is located north of the PVH Harmony Campus and accounts for approximately 9.05 acres. The Pads at Harmony site currently consists of native grass and was previously a prairie dog colony. The site generally slopes to the northeast at approximately 1.1%. The planned development will consist of commercial property. DRAINAGE BASINS A. B. Major Basin Description The Pads at Harmony site lies within the Fox Meadows Drainage Basin. The project drainage will be partially detained, and flows directed to a detention pond in Front Range Village (adjacent property to the east). Please see the Final Drainage and Erosion Control Front Range Village, Fort Collins, Colorado for basin modeling. The existing site conveys flows overland to the northeast and into an existing field east of the Pads at Harmony site. The field to the east is currently under development review under the name "Front Range Village". Sub -Basin Description Historic drainage patterns will be held for the Pads at Harmony site, with flows being conveyed to the northeast. The runoff from the Pads at Harmony site will be conveyed, via storm drain, to the proposed detention pond in the northwest corner of the Front Range Village development. 5 APPENDIX PAGE VICINITY MAP A RATIONAL CALCULATIONS, UDINLET, UDSEWER B STORM DRAIN SIZING, & POND SIZING DRAINAGE & EROSION CONTROL PLAN DRAWING & EROSION C CONTROL CALCULATIONS 1 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION A. LOCATION 5 B. DESCRIPTION OF PROPERTY 5 II. DRAINAGE BASINS A. MAJOR BASIN DESCRIPTION 5 B. SUB -BASIN DESCRIPTION 5 III. DRAINAGE DESIGN CRITERIA 6 A. REGULATIONS 6 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 6 C. HYDROLOGICAL CRITERIA 6 D. HYDRAULIC CRITERIA E. VARIANCE . 6 IV. DRAINAGE FACILITY DESIGN 6 A. GENERAL CONCEPT 6 B. SPECIFIC DETAILS 7 V. STORM WATER QUALITY 9 A. GENERAL CONCEPT 9 B. SPECIFIC DETAILS 9 VI. EROSION CONTROL 9 A. GENERAL CONCEPT 9 B. SPECIFIC DETAILS 10 VII. CONCLUSIONS 11 A. COMPLIANCE WITH STANDARDS I I B. DRAINAGE CONCEPT 11 C. STORM WATER QUALITY 11 D. EROSION CONTROL CONCEPT 11 REFERENCES 12 APPENDICES 13 ' Stantec Consulting Inc 209 South Meldrum Street Fort Collins CO 80521-2603 Tel: (970) 482-5922 Fax: (970) 482-6368 stantK.com Stantec 1 August 30, Mr. Basil Hamdan ' City of Fort Collins Water Utilities --Storm water 700 Wood Street Fort Collins, Colorado 80521 RE: Final Drainage and Erosion Control Report for The Pads at Harmony, First Filing. ' Dear Basil: ' We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Report for The Pads at Harmony, First Filing. 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, Stantec ' Prepared by: ' John Gooch, EIT Jim Allen -Morley, P.E. Project Engineer Project Manager 1 1 1 1 OM-� Final ` Drainage and Erosion Control Report The Pads at Harmony, Filing 1 Stantec Fort Collins, Colorado August 30, 2006