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Home My WebLink AboutSPANJER OFFICE BUILDING - PDP - 25-01 - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORTVIz( CINITY MAP 1 "= 2000' Final Drainage Report Spanjer Office Building March 26, 2002 REFERENCES Northern Engineering Services, Inc 1) Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright Water Engineers, Inc., Denver, Colorado, Updated June 2001. 2) Erosion Control Reference Manual for Construction Sites, City of Fort Collins, Colorado, Hydrodynamics, Inc., January 1991. 3) Storm Drainage Design Criteria and Construction Standards. City of Fort Collins, Colorado, Updated April 1999. N IFinal Drainage Report Northern Engineering Services, Inc Spanjer Office Building March 26, 2002 5.2 Rainfall Erosion Control Plan The intent of the erosion control plan for this site includes the following guidelines. As f these measures can vary depending on the time of year construction activities take place, 1 as well as the construction window involved, we would look to the contractor to work closely with the City to insure the intent of the plan is generally complied with. The I proposed rainfall erosion control plan during construction will consist of temporary structural erosion control measures. A straw -bale sediment trap will be placed north of the 3' curb cut and concrete pan located in the entrance off the Frontage Road. A straw - bale dike will be place just north of WQCV Pond A. Gravel Outlet Filters will be installed at the outlets of both WQCV Ponds so the ponds can act as sediment traps I during construction., Silt fencing will be installed along the southern property boundary and along both Cameron Drive and the Frontage Road to prevent runoff particulates and windblown sediment from migrating off -site. It is our intent to restrict construction vehicular traffic to Cameron Drive. The measures proposed above will control surface erosion during the construction process, and prevent sediment from leaving the site. These structures are to remain in place until paving is completed and foundations and landscaping have been established. The proposed erosion control plan after construction will consist of all open space areas being revegetated as specified on the Landscape Plan. . VL CONCLUSIONS 6.1 Compliance with Standards All drainage design considerations are in accordance with the City of Fort Collins Storm Drainage Design Criteria Manual and the Urban Drainage and Flood Control District's Drainage Criteria Manual. The drainage system proposed within this report and the supporting construction documents provide adequate conveyance and water quality enhancement for the developed stormwater runoff from Spanjer Office Building. 5 Final Drainage Report Spanjer Office Building March 26, 2002 Northern Engineering Services, Inc 3.5.7 Sub -basin D-7 Also bound from the north by the parking lot of Lot 9, the 0.200 acres of sub -basin D-7 include the east side of Cameron Drive, the attached walk of Cameron Drive, and part of the entrance off said street. Runoff will sheet flow to Cameron Drive, to then be conveyed by curb and gutter to the existing creek. Both D-5 and D-7 release to the curb and gutter of Cameron Drive, creating 10- and 100-year event flows of 1.076 cfs and 2.794 cfs, respectively. 3.5.8 Sub -basin D-8 The 0.024 acres of Sub -basin D-8 are bound from the north by the parking lot of Lot 8 and bound from the south by the curb of the Frontage Road entrance. A small, grass -lined swale begins at the west end of the sub - basin and continues east to a 3' curb opening. Swale calculations are included in the appendix of this report. 3.6 Detention As mentioned above, the master drainage plans for this area do not require detention. Therefore, the entire site will be released un-detained to the existing creek north of Fossil Creek. A 60' wide drainage easement has been obtained to provide access to this existing drainage -way. Also, the impacts of this development do not significantly increase the flows downstream. IV. WATER QUALITY 4.1 Water Quality Measures and Criteria Two on -site water quality capture volumes (WQCV) are proposed to remove sediment and other pollutants from developed. runoff. Sub -basins D-2 and D-3 drain to WQCV Pond A at the east side of the site, sub -basin D-5 drains to WQCV Pond B at the west end of the site. Based on criteria for a 40-hour dry extended detention basin outlined in the Urban Storm Drainage Criteria Manual, Volume 3 — Best Management Practices by the Urban Drainage and Flood Control District (September 1999), the required water quality capture volume for Ponds A and B were determined to be approximately 163.9 and 328.8 cubic feet, respectively. These required WQCVs are achieved at an elevation of 4956.90 for Pond A and 4958.95 for Pond B. A steel orifice plate with vertical perforations will be built into both pond outlet structures to control the water quality capture volumes. V. EROSION CONTROL PLAN 5.1 Erosion Control Criteria This site lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. The desired effectiveness goal for this site was estimated to be approximately 78%. The erosion control plan presented here is intended to control both wind and rainfall erosion. The Erosion Control Reference Manual for Construction Sites (ECRM), City of Fort Collins, has been referenced for this erosion control plan. Final Drainage Report Spanjer Office Building March 26, 2002 Northern Engineering Services, Inc 3.5.1 Sub -basin D-1 Sub -basin D-1 represents 0.066 acres of the site, bounded by the high point of the site entrance from the Frontage Road, the Frontage Road attached walk, and the Frontage Road centerline. Flows will be conveyed by existing curb and gutter south to the existing creek. 3.5.2 Sub -basin D-2 Containing 0.123 acres, D-2 conveys flows from a swale along the northerly property boundary to a 3' curb opening and pan, through another 3' .curb opening, around the commercial building to Water Quality Capture Volume Pond A, having a volume of 163.9 cubic feet and high water elevation of 4956.90. The pond's outlet structure releases flows to a 2' sidewalk chase, then to the curb and gutter of the Frontage Road. 3.5.3 Sub -basin D-3 Representing a very small section of the site, D-3 is 0.010 impervious acres that directs flows to an area drain and sump pit (by others) then pumped to Water Quality Capture Volume Pond A. Flows from sub -basins D-1, 2, 3, and 8 are conveyed by the Frontage Road curb & gutter to the existing creek, and will have combined release rates of 0.775 cfs and 1.991 cfs for the 10- and 100-year storm events, respectively. 3.5.4 Sub -basin D-4 Sub -basin D-4 is a very small grassy area of 0.012 acres. Stormwater will sheet flow from north to south to the existing Church. 3.5.5 Sub -basin D-5 D-5 is the largest of the sub -basins at 0.370 acres. Bound from the north by the existing parking lot of Lot 9, water will sheet flow around the storage building to the curb and gutter on the north side of the entrance off Cameron Drive. Flows are then conveyed to a concrete pan and curb and gutter, through a curb opening, and into Water Quality Capture Volume Pond B. Pond B has a volume of 328.8 cubic feet with a high water elevation of 4958.95, it's outlet structure releases to a 2' sidewalk chase conveying flows to the existing curb and gutter of Cameron Drive. 3.5.6 Sub -basin D-6 Having a pervious nominal area of 0.003 acres, water sheet flows north to south, to the existing Church. Final Drainage Report Spanjer Office Building March 26, 2002 Northern Engineering Services, Inc 2.3 Pre -development Drainage Patterns The existing topography is such that Lots 9 & 15 generally sheet flow across this site (shown in the appendix as historic basins H-3 and.114). The owner is concerned about not blocking their historic runoff, and will provide an interception swale along the northeasterly boundary of his site, and will allow runoff around his storage structure and through his parking lot to the existing Frontage Road. He would be willing to grant a drainage easement to the owners of these lots should the need ever arise. Lot 8 was developed into a small office complex with an attached parking lot south of the building. Drainage from this site is directed to the southeast across this parking lot, and directed by curb and gutter to a small concrete drainage pan that allows flows to enter the existing curb and gutter of the Frontage Road. M. POST -DEVELOPMENT CONDITIONS 3.1 Post -development Conditions The Spanjer Office Building development will include the following: • Storage Facility; • Commercial Building; • new attached walk along the west side of the Frontage Road; • drainage improvements and utility services. Portions of the asphalt surface of the Frontage Road near the property boundary will be replaced with this development. 3.2 Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual, (SDDCM) and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been referenced for this study. 3.3 Hydrologic Criteria The Rational Method has been used to estimate peak stormwater runoff within the developed site. The minor 10-year and major 100-year design storms have been used in the design of the proposed drainage system. Rainfall intensity data for the Rational Method has been taken from Figure 3-la updated by the City of Fort Collins in 1999. 3.4 Hydraulic Criteria The City of Fort Collins SDDCM has been referenced for all hydraulic calculations. 3.5 Drainage Patterns The site has been broken down into eight smaller sub -basins, a copy of the layout has been included in the appendix of this report. Sub -basins D-1, 2, 3, and 8 generally drain from northwest to southeast, and to the Frontage Road. Sub -basins D-5 and D-7 generally drain from northeast to southwest, and to Cameron Drive. Sub -basins D-4 and D-6 represent a small area of the site that will sheet flow to the existing Church. Final Drainage Report for Spanjer Office Building Fort Collins, Colorado March 26, 2002 L SITE LOCATION AND DESCRIPTION 1.1 Site Location The Spanjer Office Building site is Lot 7 of Cameron Park, located between Cameron Drive and the Frontage Road within the Cameron Park Development. The site can also be described as a portion of Section 2, Township 6 North, Range 69 West of the 6"' Principal Meridian in the City of Fort Collins, County of Larimer, State of Colorado. This site is also located within the Fossil Creek major drainage basin. 1.2 Site Description The Spanjer Office Building site is approximately 0.45 acres and has historically been undeveloped. The site consists mainly of native grasses, and generally slopes from the north to the south at approximately 6%. Plans for this site include a commercial building with associated parking. H. PRE -DEVELOPMENT CONDITIONS 2.1 Historic Drainage As mentioned above, the site is presently undeveloped, and consists mainly of native grasses and vegetation. Cameron Drive along the westerly side of the project has been built, as well as the Frontage Road along the easterly boundary of the project. A church has been built on Lot 6, south of this project, and a small office building and parking lot has been built on Lot 8, north of this project. 2.2 Historic Basins The site was broken into 2 historic basins, designated as H-1 and H-2. H-1 represented the westerly end of the site, which presently sheet flows generally towards the Church and Cameron Drive. H-2 represents the easterly end of the site, which also generally sheet flows to from the northwest to the southeast across the existing Church and to the Frontage Road. Both the Frontage Road and Cameron Drive have existing 24" culvert under College Ave. The developer of the Fossil Creek Office Park has obtained a 60' drainage easement from the termination point of the Frontage Road to Fossil Creek for the purposes of conveying stormwater runoff thereby eliminating the need for onsite detention. It is our understanding that this existing 60' wide drainage easement is for all the lots in Cameron Park. Table of Contents VICINITY MAP Page L SITE LOCATION AND DESCRIPTION 1.1 Site Location.................................................................................... 1 1.2 Site Description................................................................................ 1 H. PRE -DEVELOPMENT CONDITIONS 2.1 Historic Drainage............................................................................. 1 2.2 Historic Basins............................................................................... 1 2.3 Pre -development Drainage Patterns ................................................ 2 III. POST -DEVELOPMENT CONDITIONS 3.1 Post -development Conditions.......................................................... 2 3.2 Design Criteria and References....................................................... 2 3.3 Hydrologic Criteria.......................................................................... 2 3.4 Hydraulic Criteria............................................................................ 2 3.5 Drainage Patterns............................................................................ 2 3.6 Detention.......................................................................................... 4 IV. WATER QUALITY 4.1 Water Quality Measures and Criteria .............................................. 4 V. EROSION CONTROL PLAN 5.1 Erosion Control Criteria................................................................. 4 5.2 Rainfall Erosion Control Plan.......................................................... 5 VL CONCLUSIONS 6.1 Compliance with Standards............................................................. 5 REFERENCES.......................................................................................... 6 APPENDICES APPENDIX A- Hydrology Calculations APPENDIX B - Water Quality Calculations APPENDIX C - Street Capacity Calculations APPENDIX D- Erosion Control Calculations APPENDIX E- Weir, Swale, and Riprap Calculations i NE NORTHERN ENGINEERING SERVICES, INC. March 26, 2002 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Spanjer Office Building Fort Collins, Colorado Project Number: 01-042.02 Dear Staff. Northern Engineering Services, Inc. is pleased to submit this Final Drainage Report for the Spanjer Office Building site for your review. We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Storm Drainage Design Criteria and Construction Standards. This report was prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual. If you should have any questions or comments as you review this report, please feel free to contact us at your convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Kimberly J Walsh Project Engineer Roger A. gurtiss, P.E. t Project ManagerNice President 27362 1 420 SOUTH HOWES, SUITE 202 / FORT COLLINS, COLORADO 80521 / 970.221.4158 / FAX 970.221.4159 Final Drainage Report for Spanjer Office Building Fort Collins, Colorado March 26, 2002 Prepared For: Spanjer Construction Corp. PO Box 9644 Office 5731 Bueno Drive, #C Fort Collins, Colorado 80525 Prepared By: NORTHERN @NGI NEERING lowmw SERVICES, INC. Northern Engineering Services, Inc 420 S. Howes, Suite 202 Fort Collins, Colorado 90621 Phone: (970) 221 -41 SS Project Number: SPA (01-042.02) Third Submittal