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GEICO OFFICE BUILDING - PDP - PDP130039 - REPORTS - DRAINAGE REPORT
PRELIMINARY DRAINAGE AND EROSION CONTROL REPORT GEICO OFFICE BUILDING Fort Collins, Colorado March 5, 2014 Prepared for: Steve Allen Local Geico Office 115 E. Harmony Rd, Suite 110 Fort Collins CO 80525 Prepared by: 200 South College Avenue, Suite 100 Fort Collins, Colorado 80524 Phone: 970.221.4158 Fax: 970.221.4159 www.northernengineering.com Project Number: 959-001 3 This Drainage Report is consciously provided as a PDF. Please consider the environment before printing this document in its entirety. When a hard copy is absolutely necessary, we recommend double-sided printing. March 5, 2014 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Preliminary Drainage and Erosion Control Report for Geico Office Building Dear Staff: Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for your review. This report accompanies the 10.16.12 Basic Development Review submittal for the proposed Geico Office Building. Comments from the Basic Development Review Letter dated May 13 , 2013 have been addressed. Written responses thereto can be found in the comprehensive response to comments letter on file with Current Planning. This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM), and serves to document the stormwater impacts associated with the proposed Engines Geico Office Building project. We understand that review by the City is to assure general compliance with standardized criteria contained in the FCSCM. If you should have any questions as you review this report, please feel free to contact us. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Bud Curtiss, PE Cody Snowdon Principle Project Engineer Geico Office Building Preliminary Drainage Report TABLE OF CONTENTS I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1 A. Location ....................................................................................................................................... 1 B. Description of Property ................................................................................................................ 2 C. Floodplain .................................................................................................................................... 3 II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 4 A. Major Basin Description ............................................................................................................... 4 B. Sub-Basin Description .................................................................................................................. 4 III. DRAINAGE DESIGN CRITERIA ................................................................................... 4 A. Regulations .................................................................................................................................. 4 B. Four Step Process ........................................................................................................................ 4 C. Development Criteria Reference and Constraints ......................................................................... 5 D. Hydrological Criteria .................................................................................................................... 6 E. Hydraulic Criteria ......................................................................................................................... 6 F. Floodplain Regulations Compliance .............................................................................................. 6 G. Modifications of Criteria .............................................................................................................. 6 IV. DRAINAGE FACILITY DESIGN .................................................................................... 6 A. General Concept .......................................................................................................................... 6 B. Specific Details ............................................................................................................................. 7 V. CONCLUSIONS ........................................................................................................ 9 A. Compliance with Standards .......................................................................................................... 9 B. Drainage Concept ........................................................................................................................ 9 References ....................................................................................................................... 10 APPENDICES: APPENDIX A – Hydrologic Computations APPENDIX B – Hydraulic Computations B.1 – Storm Sewers B.2 – Inlets B.3 – Detention Facilities APPENDIX C – Water Quality Design Computations APPENDIX D – Erosion Control Report Geico Office Building Preliminary Drainage Report LIST OF TABLES AND FIGURES: Figure 1 – Aerial Photograph ................................................................................................ 2 Figure 2 – Proposed Site Plan ............................................................................................... 3 Figure 3 – Existing Floodplains ............................................................................................. 3 MAP POCKET: C400 - Drainage Exhibit Geico Office Building Preliminary Drainage Report 1 I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map 2. The Geico Office Building site is located in the southwest quarter of Section 31, Township 7 North, Range 68 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. 3. The project site is located just northwest of the intersection of Harmony Road and Timberline Road. 4. Currently the existing lot does not have any stormwater or water quality facilities. All runoff from the site is routed via overland and discharged directly into the Dixon Canyon Lateral. Harmony Road is slightly elevated to the project site creating a ridge line running east and west along the right-of-way line. There are currently two drive cuts into Harmony Road. The west drive cut is slightly graded back to Harmony, but flows within the gutter above 0.7 feet will overtop the sidewalk and be routed through the site and into Dixon Canyon Lateral. The east drive cut is graded back towards the site and any drainage within the northern section of Harmony is currently routed through the site and into Dixon Canyon Lateral. The overall site grades from the south to the north. 5. The project is currently border to the south by Harmony Road, west by a commercial building, north by Dixon Canyon Lateral and east by Timberline Road. Geico Office Building Preliminary Drainage Report 2 B. Description of Property 1. The Geico Office Building property is approximately 0.55 net acres. Figure 1 – Aerial Photograph 2. The Geico Office Building project consists of two properties, 2024 & 2016 East Harmony Road. The 2024 East Harmony Road or western property consisted of tow building used for commercial use. A single drive access point exists from East Harmony Road. The areas in front of the two buildings consist of gravel parking area and the remaining property consists of over grown weeds. Stormwater is routed though the site from south to north via overland flow and is discharged directly into Dixon Canyon Lateral. Earlier this year, the existing buildings were deconstructed because of the “Dangerous Building Issue” policy through the City. The 2016 East Harmony Road or eastern property currently consists of a commercial office building with associated outbuildings. There is an existing drive access point from East Harmony Road. The area to the west of the building consists of a paved parking area with associated landscaped areas. Stormwater is routed though the site from south to north via overland flow and is discharged directly into Dixon Canyon Lateral. 3. According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey, 74 percent of the site consists of Nunn clay, which falls into Hydrologic Soil Groups B, while the remaining site consists of Fort Collins loam, which falls into Hydrologic Soil Groups B. More site-specific exploration found primarily sandy lean clays with a groundwater encountered 15 to 17 feet below existing site grades. See the Geotechnical Engineering Report by EEC (EEC Project No. 1132073) for additional information. 4. The proposed development will include the deconstruction of the existing commercial building on the western property and the existing paved parking area. The proposed site will a new commercial building located to the east of the project along Timberline road. It will include two drive access points from Harmony and an associated parking lot. The majority of the parking lot will be paved with permeable pavers and will act as the projects water quality and detention facility. Geico Office Building Preliminary Drainage Report 3 Figure 2– Proposed Site Plan 5. The project is bordered to the north by Dixon Canyon Lateral Irrigation Ditch. There is an existing private irrigation system associated with the existing property to the west. No other irrigation facilities are known at this time. 6. The project site is within the Harmony Corridor District (H-C) Zoning District. The proposed project is not requesting a change in the land use. C. Floodplain 1. The subject property is not located in a FEMA or City regulatory floodplain. 2. The FEMA Panel 08069C1000F has not been printed for this location. It is noted that the vertical datum utilized for site survey work is the City of Fort Collins Benchmark #1-96 (Elevation = 4941.81, Fort Collins NVGD 29 – Unadjusted) Figure 3 – Existing Floodplains Geico Office Building Preliminary Drainage Report 4 II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. The Geico Office Building project is located within the Fox Meadows Basin, which is located between East Horsetooth Road and East Harmony Road from north to south and approximately South Lemay Avenue and Fossil Creek Reservoir Inlet Ditch from west to east. B. Sub-Basin Description 1. The subject property historically drains away from the existing buildings. Stormwater is routed through the site via overland flow and discharges directly into the Dixon Canyon Lateral (0.7 cfs for the 2-year storm and 3.2 cfs for the 100-year event – onsite only). A more detailed description of the projects proposed drainage patterns follows in Section IV.A.4., below. 2. No drainage is routed onto the property from the east, west or north. Due to an existing drive access cut from Harmony Road, all of the drainage conveyed through the northern curb and gutter is discharged directly onto the property. Through the widening design done by the City of Fort Collins, this existing drive cut is located at the high point within the curb and gutter and the amount of runoff that is conveyed to the existing drive cut is minimal. This stormwater is routed through the site and discharged directly into the Dixon Canyon Lateral. III. DRAINAGE DESIGN CRITERIA A. Regulations There are no optional provisions outside of the FCSCM proposed with the Geico Office Building project. B. Four Step Process The overall stormwater management strategy employed with the Geico Office Building project utilizes the “Four Step Process” to minimize adverse impacts of urbanization on receiving waters. The following is a description of how the proposed development has incorporated each step. Step 1 – Employ Runoff Reduction Practices Several techniques have been utilized with the proposed development to facilitate the reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the current use by implementing multiple Low Impact Development (LID) strategies including: Conserving existing amenities in the site including the existing vegetated along the Dixon Canyon Lateral. Providing large vegetated open areas throughout the site to reduce the overall impervious area and to minimize directly connected impervious areas (MDCIA). Routing flows, to the extent feasible, through vegetated swales and grass buffers to increase time of concentration, promote infiltration and provide initial water quality. Providing permeable paver areas with underground detention area to increase time of concentration promote infiltration and provide water quality. Geico Office Building Preliminary Drainage Report 5 Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with Slow Release The efforts taken in Step 1 will facilitate the reduction of runoff; however, this development will still generate stormwater runoff that will require additional BMPs and water quality. Stormwater generated from the proposed building will be routed through landscaped swales and into a proposed storm collection system. This storm collection system is proposed to discharge directly into the permeable paver area and routed through this section to achieve water quality. The stormwater generated from the proposed parking area will be routed via overland flow to the permeable paver area. Step 3 – Stabilize Drainageways The project site currently discharges to the Dixon Canyon Lateral. While these drainage patterns are being maintained with the proposed grading, measures have been proposed to decrease the amount of run-off discharging into Dixon Canyon Lateral as well as the quality of the storm water being released. The existing onsite area is releasing 0.7 cfs for the 2-year event and 3.2 cfs for the 100-year event undetained and untreated. Currently the existing drive cut is located within a high point of Harmony Road and a minimal amount of runoff generated from Harmony Road and routed through the site. Within the proposed design, the runoff from Harmony Road is being rerouted to remain within the street section. The western half of the drive access will drain to the west and the eastern half of the drive access will drain east. The additional runoff that will be generated from closing the drive access is negligible. Water quality will be provided through a permeable paver section and will treat all runoff generated by onsite site improvements. Furthermore, this project will pay onetime stormwater development fees, as well as ongoing monthly stormwater utility fees, both of which help achieve City-wide drainageway stability. Step 4 – Implement Site Specific and Other Source Control BMPs. The Geico Office Building project includes a new building with an associated drive and parking area, all of which will require the need for site specific source controls including: A localized trash enclosure at the rear of the building for the disposal of office waste. C. Development Criteria Reference and Constraints 1. There are no known drainage studies for the existing properties. 2. There are no known drainage studies for any adjacent properties that will have any effect on the Geico Office Building project. 3. The subject property is essentially an "in-fill" development project as the property is surrounded by currently developed properties. As such, several constraints have been identified during the course of this analysis that will impact the proposed drainage system including: Existing elevations along the south and east property lines adjacent to Harmony Road and Timberline Road will be maintained. Existing elevations along the west property lines will be maintained. Existing elevations and vegetation on the north side of the subject property will be preserved. As previously mentioned, overall drainage patterns of the existing site will be maintained. Geico Office Building Preliminary Drainage Report 6 D. Hydrological Criteria 1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations associated with the Regency Lakeview development. Tabulated data contained in Table RA-7 has been utilized for Rational Method runoff calculations. 2. The Rational Method has been employed to compute stormwater runoff utilizing coefficients contained in Tables RO-11 and RO-12 of the FCSCM. 3. The Rational Formula-based Modified Federal Aviation Administration (FAA) procedure has been utilized for detention storage calculations. 4. Three separate design storms have been utilized to address distinct drainage scenarios. A fourth design storm has also been computed for comparison purposes. The first design storm considered is the 80th percentile rain event, which has been employed to design the project’s water quality features. The second event analyzed is the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third event considered is the “Major Storm,” which has a 100-year recurrence interval. The fourth storm computed, for comparison purposes only, is the 10-year event. 5. No other assumptions or calculation methods have been used with this development that are not referenced by current City of Fort Collins criteria. E. Hydraulic Criteria 1. As previously noted, the subject property historically drains directly to the Dixon Canyon Lateral. The majority of the site drains stormwater via overland and swale flow. 2. All drainage facilities proposed with the Geico Office Building project are designed in accordance with criteria outlined in the FCSCM and/or the Urban Drainage and Flood Control District’s (UDFCD) Urban Storm Drainage Criteria Manual. 3. As stated in Section I.C.1, above, the subject property is not located within a FEMA regulatory floodplain. 4. The Geico Office Building project does not propose to modify any natural drainageways. F. Floodplain Regulations Compliance 1. As previously mentioned, all structures are located outside of any FEMA 100-year floodplain, and thus are not subject to any floodplain regulations. G. Modifications of Criteria 1. The proposed Engines and Energy Conversion Lab development is not requesting any modifications to criteria at this time. IV. DRAINAGE FACILITY DESIGN A. General Concept 1. The main objectives of the Geico Office Building drainage design are to maintain existing drainage patterns and ensure no adverse impacts to any adjacent properties, and to maintain the detention concepts as outlined within the “Fox Meadows Master Geico Office Building Preliminary Drainage Report 7 Drainage Plan Update,” by Icon Engineering, August 1999. 2. The existing site does have off-site from Harmony Road. The existing runoff will be rerouted to remain within the existing Harmony Road street section. 3. A list of tables and figures used within this report can be found in the Table of Contents at the front of the document. The tables and figures are located within the sections to which the content best applies. 4. The Geico Office Building project divided the site into four (4) major drainage basins, designated as Basins A, OS, OE and ON. The project further subdivided Basin A in to four (4) sub-basins, designated as Basins A1, A2, A3, and A4. The drainage patterns anticipated for each basin and sub-basin are further described below. Basin A Basin A consists of the improvements within the project area. Basin A1 encompasses the most areas within Basin A. This basin includes all of the proposed parking area and a portion of the proposed sidewalk. Runoff through this basin is routed through a combination of overland and gutter. Runoff from this basin is primarily routed across the proposed permeable pavers and underground detention. The portion of runoff that is not intercepted by the permeable paver system will be intercepted by a proposed curb inlet. An orifice plate is proposed within the curb inlet to restrict the released flow from the underground and above ground detention. Basin A2 is composed of the northwest quarter of the building and the building frontage. The stormwater is routed via overland and swale flow. All runoff from this basin is intercepted by a stormwater collection system that discharges directly into the permeable paver system discussed above. Basin A3 is composed of the southwest quarter of the building and the building frontage. The stormwater is routed via overland and swale flow. All runoff from this basin is intercepted by a stormwater collection system that discharges directly into the permeable paver system discussed above. Basin A4 is composed of the eastern half of the building and the landscaped areas around the building. The stormwater is routed via overland and swale flow. All runoff from this basin is intercepted by a stormwater collection system that discharges directly into the permeable paver system discussed above. Basin OS Basin OS1 consists primarily of the sidewalk within the public ROW. This area was redesigned to eliminate the drainage running through the project site from Harmony Road. Basin ON Basin ON1 consists of the northern property boundary. No improvements are proposed in this area and historic drainage patterns will be maintained. Basin OE Basin OE1 consists of the eastern property boundary. No improvements are proposed in this area and historic drainage patterns will be maintained. A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report. B. Specific Details 1. The main drainage problem associated with this project site is the deficiency of water Geico Office Building Preliminary Drainage Report 8 quality present within the existing site and the amount of offsite runoff being conveyed onto the property from Harmony Road. Currently the entire site drains overland and discharges directly into the Dixon Canyon Lateral without water quality. The existing two outbuildings also drain directly into Dixon Canyon Lateral without any water quality. The proposed site will mitigate this issue by instituting the following water quality devices: All of the runoff generated from the proposed building will be routed through a landscape area. All improvements generated from the site will be routed through a permeable paver detention system. 2. A hybrid approach was utilized to compute the maximum allowable release rate associated with the FAA detention sizing calculations. The 100-year peak runoff rate was calculated for the pre-development impervious areas for the eastern lot. This essentially “grandfathers” the existing impervious areas by allowing the respective 100-year peak discharge to be added to the maximum allowable release rate. The release rate for the remaining undeveloped land (pre-development pervious areas and the entire western lot) was established by calculating the prescribed 0.23 cfs per acre. The total of these two discharges (i.e., 1.07 cfs and 0.14 cfs) establishes the overall maximum allowable release rate, 1.21 cfs, from the project site. The allowable release rate of 0.60 cfs utilized within the FAA procedure detention storage computations (Refer to Appendix A for these calculations) and was established by subtracting the undetained release of 0.61 cfs, from the overall maximum allowable release rate. This hybrid approach ensures that all increased impervious areas are over-detained down to 0.23 cfs per acre. 3. The FAA method was used to size the on-site pond for quantity detention. Calculations for this area, based on the characteristics of basin A and adjusted release rate, indicated a detention volume of 3365 cu. Ft. This includes the 406 cu.ft. of Water Quality Capture Volume (WQCV). During the water quality events the water quality capture volume will release over 12-hours. This section is considered a no- infiltration section because the in-situ soils in this area are USCS Nunn Clay Loam. 4. The storage volume available within the reservoir areas (i.e., No. 57 and No. 2 open- graded aggregate) of the MBP section is ±3712 cu. ft. The MBP section is designed with an increased No. 2, open-graded aggregate, material depth in order to provide storage for storm events in excess of the water quality (80th percentile) storm event. In addition to the volume within the MBP section, parking lot detention is designed to account for an additional 203 cu. ft. 5. There is a Nyloplast Drain Basin located on the southern, eastern and a portion of the western building boundary. These area inlets are designed to intercept local flows, as well as the flow generated by the proposed buildings. These basins will convey runoff through landscape areas before discharging into the drain system. The drain basin is connected directly to the MBP section; therefore, runoff conveyed through the drain system will be treated. 6. The emergency spillway will be located at the low point on the northern side of the parking area. The spillway will utilize the low point within the curb with an elevation 1’ lower than the lowest finish floor elevation. In the event that an emergency overflow occurs, the drainage will flow to the north, into the existing irrigation lateral. Geico Office Building Preliminary Drainage Report 9 V. CONCLUSIONS A. Compliance with Standards 1. The drainage design proposed with the Geico Office Building project complies with the City of Fort Collins’ Stormwater Criteria Manual. 2. The drainage design proposed with the Geico Office Building project complies with the City of Fort Collins’ Master Drainage Plan for the Fox Meadows. 3. There are no regulatory floodplains associated with the Geico Office Building development. 4. The drainage plan and stormwater management measures proposed with the Geico Office Building development are compliant with all applicable State and Federal regulations governing stormwater discharge. B. Drainage Concept 1. The drainage design proposed with this project will effectively limit any potential damage or erosion associated with its stormwater runoff. Geico Office Building will detain for the pervious area converted to impervious areas to release at the existing 0.23 cfs per acre during the 100-year event. 2. The proposed Geico Office Building development will not have any impact on the Master Drainage Plan recommendations for the Fox Meadows. Geico Office Building Preliminary Drainage Report 10 References 1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities, November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services. 2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No. 174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code. 3. Subsurface Exploration Report, Geico Insurance Office Building 2024 East Harmony Road, October 14, 2013, Earth Engineering Consultants, Inc.(EEC Project No. 1132073). 4. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007. 5. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service, United States Department of Agriculture. 6. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008. Geico Office Building Preliminary Drainage Report 11 APPENDIX A HYDROLOGIC COMPUTATIONS Geico Office Building CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: Geico Office Building Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: C. Snowdon Asphalt ……....……………...……….....…...……………….………………………………….0.. 95 100% Date: Concrete …….......……………….….……….………………..….………………………………… 0.95 90% Gravel ……….…………………….….…………………………..……………………………….0.. 50 40% Roofs …….…….………………..……………….…………………………………………….. 0.95 90% Pavers…………………………...………………..…………………………………………….. 0.40 22% Lawns and Landscaping Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0% Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf = 1.00 100-year Cf = 1.25 Basin ID Basin Area (s.f.) Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Roofs (ac) Area of Gravel (ac) Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. H1impervious 6174 0.14 0.00 0.00 0.08 0.06 0.00 0.76 0.76 0.96 69% H1pervious 18106 0.42 0.00 0.00 0.00 0.00 0.42 0.15 0.15 0.19 0% Harmony 73938 1.70 1.61 0.09 0.00 0.00 0.00 0.95 0.95 1.00 99% H1 24280 0.56 0.11 0.05 0.11 0.07 0.21 0.59 0.59 0.73 51% December 20, 2013 10-year Cf = 1.00 **Soil Classification of site is Sandy Loam** Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I. HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Engines Energy Conversion Lab Overland Flow, Time of Concentration: Project: Geico Office Building Calculations By: Date: Gutter/Swale Flow, Time of Concentration: Tt = L / 60V Tc = Ti + Tt (Equation RO-2) Velocity (Gutter Flow), V = 20·S½ Velocity (Swale Flow), V = 15·S½ NOTE: C-value for overland flows over grassy surfaces; C = 0.25 Is Length >500' ? C*Cf (2-yr Cf=1.00) C*Cf (10-yr Cf=1.00) C*Cf (100-yr Cf=1.25) Length, L (ft) Slope, S (%) Ti 2-yr (min) Ti 10-yr (min) Ti 100-yr (min) Length, L (ft) Slope, S (%) Velocity, V (ft/s) Tt (min) Length, L (ft) Slope, S (%) Velocity, V (ft/s) Tt (min) 2-yr Engines Energy Conversion Lab Rational Method Equation: Project: Geico Office Building Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: h1 H1impervious 0.14 11 11 10 0.76 0.76 0.96 2.17 3.71 7.88 0.24 0.40 1.07 h2 H1pervious 0.42 11 11 10 0.15 0.15 0.19 2.17 3.71 7.88 0.14 0.23 0.61 h3 H1pervious 1.70 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 4.60 7.85 16.89 h1 H1 0.56 11 11 10 0.59 0.59 0.73 2.17 3.71 7.88 0.71 1.21 3.22 100-yr Tc (min) Flow, Q2 (cfs) Flow, Q10 (cfs) Flow, Q100 (cfs) C2 C10 C100 Released Undetained to ditch Allowable release rate: 1.07 + 0.14 = 1.21 HISTORIC RUNOFF COMPUTATIONS Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) Notes C. Snowdon December 20, 2013 Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1 Design Point Basin(s) Area, A (acres) 2-yr Tc (min) 10-yr Tc (min) Q C f C i A Page 3 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Hist-Direct-Runoff Engines Energy Conversion Lab CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: Geico Office Building Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: Asphalt ……....……………...……….....…...……………….………………………………….0.. 95 100% Date: Concrete …….......……………….….……….………………..….………………………………… 0.95 90% Gravel ……….…………………….….…………………………..……………………………….0.. 50 40% Roofs …….…….………………..……………….…………………………………………….. 0.95 90% Pavers…………………………...………………..…………………………………………….. 0.40 22% Lawns and Landscaping Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0% Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf = 1.00 100-year Cf = 1.25 Basin ID Basin Area (s.f.) Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Roofs (ac) Area of Gravel (ac) Area of Pavers (ac) Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. A1 11277 0.259 0.132 0.048 0.000 0.000 0.039 0.040 0.74 0.74 0.93 68% A2 1050 0.024 0.000 0.000 0.021 0.000 0.000 0.004 0.83 0.83 1.00 77% A3 1142 0.026 0.000 0.000 0.022 0.000 0.000 0.004 0.82 0.82 1.00 75% A4 4057 0.093 0.000 0.003 0.043 0.000 0.000 0.047 0.54 0.54 0.68 44% OE1 784 0.018 0.000 0.000 0.000 0.000 0.000 0.018 0.15 0.15 0.19 0% ON1 3509 0.081 0.000 0.004 0.000 0.000 0.000 0.077 0.19 0.19 0.24 4% Engines Energy Conversion Lab Overland Flow, Time of Concentration: Project: Geico Office Building Calculations By: Date: Gutter/Swale Flow, Time of Concentration: Tt = L / 60V Tc = Ti + Tt (Equation RO-2) Velocity (Gutter Flow), V = 20·S½ Velocity (Swale Flow), V = 15·S½ NOTE: C-value for overland flows over grassy surfaces; C = 0.25 Is Length >500' ? C*Cf (2-yr Cf=1.00) C*Cf (10-yr Cf=1.00) C*Cf (100-yr Cf=1.25) Length, L (ft) Slope, S (%) Ti 2-yr (min) Ti 10-yr (min) Ti 100-yr (min) Length, L (ft) Slope, S (%) Velocity, V (ft/s) Tt (min) Length, L (ft) Slope, S (%) Velocity, V (ft/s) Tt (min) 2-yr Engines Energy Conversion Lab Rational Method Equation: Project: Geico Office Building Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: a1 A1 0.26 5 5 5 0.74 0.74 0.93 2.85 4.87 9.95 0.5 0.9 2.4 Q100 = 0.60 cfs a2 A2 0.02 5 5 5 0.83 0.83 1.00 2.85 4.87 9.95 0.1 0.1 0.2 a3 A3 0.03 5 5 5 0.82 0.82 1.00 2.85 4.87 9.95 0.1 0.1 0.3 a4 A4 0.09 5 5 5 0.54 0.54 0.68 2.85 4.87 9.95 0.1 0.2 0.6 oe1 OE1 0.02 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.0 0.0 0.03 on1 ON1 0.08 5 5 5 0.19 0.19 0.24 2.85 4.87 9.95 0.0 0.1 0.19 os1 OS1 0.06 5 5 5 0.55 0.55 0.69 2.85 4.87 9.95 0.1 0.2 0.39 Intensity, i100 (in/hr) Basin(s) C. Snowdon December 20, 2013 Intensity, i10 (in/hr) Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1 C10 Area, A (acres) Intensity, i2 (in/hr) 100-yr Tc (min) Undetained release DEVELOPED RUNOFF COMPUTATIONS Undetained release Undetained release C100 Notes Design Point Flow, Q100 (cfs) Flow, Q2 (cfs) 10-yr Tc (min) 2-yr Tc (min) C2 Flow, Q10 (cfs) Q C f C i A Page 6 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Direct-Runoff Engines Energy Conversion Lab CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: Geico Office Building Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: Asphalt ……....……………...……….....…...……………….………………………………….. 0.95 100% Date: Concrete …….......……………….….……….………………..….………………………………… 0.95 90% Gravel ……….…………………….….…………………………..……………………………….. 0.50 40% Roofs …….…….………………..……………….…………………………………………….. 0.95 90% Pavers…………………………...………………..…………………………………………….. 0.40 22% Lawns and Landscaping Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0% Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf = 1.00 100-year Cf = 1.25 Design Point Basin IDs Basin Area (s.f.) Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Roofs (ac) Area of Gravel (ac) Area of Pavers (ac) Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. a1 A1-A4 17526 0.402 0.132 0.051 0.085 0.000 0.039 0.095 0.71 0.71 0.88 63% COMBINED DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS December 20, 2013 **Soil Classification of site is Sandy Loam** 10-year Cf = 1.00 Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I. Engines Energy Conversion Lab Overland Flow, Time of Concentration: Project: Geico Office Building Calculations By: Date: Gutter/Swale Flow, Time of Concentration: Tt = L / 60V Tc = T i + Tt (Equation RO-2) Velocity (Gutter Flow), V = 20·S ½ Velocity (Swale Flow), V = 15·S ½ NOTE: C-value for overland flows over grassy surfaces; C = 0.25 Is Length >500' ? C*Cf (2-yr Cf=1.00) C*Cf (10-yr Cf=1.00) C*Cf (100-yr Cf=1.25) Length, L (ft) Slope, S (%) Ti 2-yr (min) Ti 10-yr (min) Ti 100-yr (min) Length, L (ft) Slope, S (%) Velocity, V (ft/s) Tt (min) Length, L (ft) Slope, S (%) Velocity, V Engines Energy Conversion Lab Rational Method Equation: Project: Geico Office Building Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: a1 A1-A4 0.40 5 5 5 0.71 0.71 0.88 2.85 4.87 9.95 0.8 1.4 3.5 Intensity, i100 (in/hr) COMBINED DEVELOPED RUNOFF COMPUTATIONS C. Snowdon December 20, 2013 Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1 Design Point Basin(s) Area, A (acres) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) Flow, Q2 (cfs) Flow, Q10 (cfs) Flow, Q100 (cfs) C2 C10 C100 Intensity, i2 (in/hr) Intensity, i10 (in/hr) Q C f C i A Page 9 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Comb-Direct-Runoff Engines Energy Conversion Lab DESIGN POINT BASIN ID TOTAL AREA (acres) C10 C100 10-yr Tc (min) 100-yr Tc (min) Q10 (cfs) Q100 (cfs) a1 A1 0.26 0.74 0.93 5.0 5.0 0.94 2.39 a2 A2 0.02 0.83 1.00 5.0 5.0 0.10 0.24 a3 A3 0.03 0.82 1.00 5.0 5.0 0.10 0.26 a4 A4 0.09 0.54 0.68 5.0 5.0 0.25 0.63 oe1 OE1 0.02 0.15 0.19 5.0 5.0 0.01 0.03 on1 ON1 0.08 0.19 0.24 5.0 5.0 0.07 0.19 os1 OS1 0.06 0.55 0.69 5.0 5.0 0.15 0.39 DESIGN POINT BASIN ID TOTAL AREA (acres) C10 C100 10-yr Tc (min) 100-yr Tc (min) Q10 (cfs) Q100 (cfs) h1 H1 0.56 0.59 0.73 10.6 9.8 1.2 3.22 Page 10 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\SUMMARY-TABLE APPENDIX B HYDRAULIC COMPUTATIONS B.1 – Storm Sewers B.2 – Inlets B.3 – Detention Facilities APPENDIX B.1 STORM SEWERS (RESERVED FOR FUTURE USE) APPENDIX B.2 INLETS (RESERVED FOR FUTURE USE) Worksheet Protected Project: Inlet ID: Design Flow: ONLY if already determined through other methods: Minor Storm Major Storm (local peak flow for 1/2 of street, plus flow bypassing upstream subcatchments): *Q = 0.5 2.4 cfs * If you entered a value here, skip the rest of this sheet and proceed to sheet Q-Allow) Geographic Information: (Enter data in the blue cells): Subcatchment Area = Acres Percent Imperviousness = % NRCS Soil Type = A, B, C, or D Slope (ft/ft) Length (ft) Overland Flow = Gutter Flow = Rainfall Information: Intensity I (inch/hr) = C1 * P 1 / ( C2 + Tc ) ^ C 3 Minor Storm Major Storm Design Storm Return Period, Tr = years Return Period One-Hour Precipitation, P1 = inches C1 = C2 = C3 = User-Defined Storm Runoff Coefficient (leave this blank to accept a calculated value), C = User-Defined 5-yr. Runoff Coefficient (leave this blank to accept a calculated value), C5 = Bypass (Carry-Over) Flow from upstream Subcatchments, Qb = cfs Total Design Peak Flow, Q = 0.6 1.5 cfs Site Type: <--- FILL IN THIS SECTION OR… FILL IN THE SECTIONS BELOW. <--- DESIGN PEAK FLOW FOR ONE-HALF OF STREET BY THE RATIONAL METHOD Design Flow = Gutter Flow + Carry-over Flow Geico Office Building Design Point A1 Site is Urban Site is Non-Urban Show Details Inlet DP A1.xls, Q-Peak 3/5/2014, 3:26 PM Project = Inlet ID = Design Information (Input) MINOR MAJOR Type of Inlet Inlet Type = Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') alocal = 2.00 2.00 inches Number of Unit Inlets (Grate or Curb Opening) No = 1 1 Flow Depth outside of Local Depression at Inlet Flow Depth = 6.0 12.0 inches Grate Information MINOR MAJOR Length of a Unit Grate Lo (G) = 3.00 3.00 feet Width of a Unit Grate Wo = 1.73 1.73 feet Area Opening Ratio for a Grate (typical values 0.15-0.90) Aratio = 0.43 0.43 Clogging Factor for a Single Grate (typical value 0.50 - 0.70) Cf (G) = 0.50 0.50 Grate Weir Coefficient (typical value 2.15 - 3.60) Cw (G) = 3.30 3.30 Grate Orifice Coefficient (typical value 0.60 - 0.80) Co (G) = 0.60 0.60 Curb Opening Information MINOR MAJOR Length of a Unit Curb Opening Lo (C) = 3.00 3.00 feet Height of Vertical Curb Opening in Inches Hvert = 6.50 6.50 inches Height of Curb Orifice Throat in Inches Hthroat = 5.25 5.25 inches Angle of Throat (see USDCM Figure ST-5) Theta = 0.00 0.00 degrees Side Width for Depression Pan (typically the gutter width of 2 feet) Wp = 2.00 2.00 feet Clogging Factor for a Single Curb Opening (typical value 0.10) Cf (C) = 0.10 0.10 Curb Opening Weir Coefficient (typical value 2.3-3.6) Cw (C) = 3.70 3.70 Curb Opening Orifice Coefficient (typical value 0.60 - 0.70) Co (C) = 0.66 0.66 MINOR MAJOR Total Inlet Interception Capacity (assumes clogged condition) Qa = 3.2 9.0 cfs Inlet Capacity IS GOOD for Minor and Major Storms (>Q PEAK) Q PEAK REQUIRED = 0.6 1.5 cfs INLET IN A SUMP OR SAG LOCATION Sunshine House - FC 139 Design Point A2 CDOT/Denver 13 Combination H-VertCurb H- W Lo (C) Lo (G) WP Wo Inlet DP A1.xls, Inlet In Sump 3/5/2014, 3:26 PM 3130 Verona Avenue • Buford, GA 30518 (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490 © Nyloplast Inlet Capacity Charts June 2012 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Capacity (cfs) Head (ft) Nyloplast 8" Dome Grate Inlet Capacity Chart APPENDIX B.3 DETENTION FACILITIES Project No. 959-001 Calculations By: CNS Northern Engineering Services, Inc. Geico Office Building Pond No : a1 100-yr 0.76 5.00 min 3365 ft3 0.56 acres 0.08 ac-ft Max Release Rate = 0.60 cfs Time (min) Ft Collins 100-yr Intensity (in/hr) Inflow Volume (ft3) Outflow Adjustment Factor Qav (cfs) Outflow Volume (ft3) Storage Volume (ft3) 5 9.950 1265 1.00 0.60 180 1085 10 7.720 1962 0.75 0.45 270 1692 15 6.520 2486 0.67 0.40 360 2126 20 5.600 2847 0.63 0.38 450 2397 25 4.980 3165 0.60 0.36 540 2625 30 4.520 3447 0.58 0.35 630 2817 35 4.080 3630 0.57 0.34 720 2910 40 3.740 3803 0.56 0.34 810 2993 45 3.460 3958 0.56 0.33 900 3058 50 3.230 4105 0.55 0.33 990 3115 55 3.030 4236 0.55 0.33 1080 3156 60 2.860 4362 0.54 0.33 1170 3192 65 2.720 4494 0.54 0.32 1260 3234 70 2.590 4609 0.54 0.32 1350 3259 75 2.480 4728 0.53 0.32 1440 3288 80 2.380 4840 0.53 0.32 1530 3310 85 2.290 4948 0.53 0.32 1620 3328 90 2.210 5056 0.53 0.32 1710 3346 95 2.130 5144 0.53 0.32 1800 3344 100 2.060 5237 0.53 0.32 1890 3347 105 2.000 5338 0.52 0.31 1980 3358 110 1.940 5425 0.52 0.31 2070 3355 115 1.890 5525 0.52 0.31 2160 3365 120 1.840 5613 0.52 0.31 2250 3363 *Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2. A = Tc = Project Location : Design Point C = Design Storm DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF Project Title Date: Project Number Calcs By: Client Pond Designation Invert Elevation Water Quality Volume 100-yr Detention Volume Total Pond Volume Total Adjusted Volume 4,962.40 2.31 N/A N/A 0 0 N/A N/A N/A 0 0 4,962.50 348.87 0.1 17.56 17.56 7.024 N/A N/A N/A 0 7.024 4,962.60 1,444.89 0.1 89.69 107.25 42.9 N/A N/A N/A 0 42.9 4,962.70 3,332.05 0.1 238.85 346.09 138.436 N/A N/A N/A 0 138.436 4,962.80 4,751.59 0.1 404.18 750.28 300.112 N/A N/A N/A 0 300.112 4,962.90 5,320.30 0.1 503.59 1253.87 501.548 N/A N/A N/A 0 501.548 4,963.00 5,342.91 0.1 533.16 1787.03 714.812 N/A N/A N/A 0 714.812 4,963.10 5,344.28 0.1 534.36 2321.39 928.556 N/A N/A N/A 0 928.556 4,963.20 5,345.65 0.1 534.5 2855.89 1142.356 N/A N/A N/A 0 1142.356 4,963.30 5,347.02 0.1 534.63 3390.52 1356.208 N/A N/A N/A 0 1356.208 4,963.40 5,348.39 0.1 534.77 3925.29 1570.116 N/A N/A N/A 0 1570.116 4,963.50 5,349.76 0.1 534.91 4460.2 1784.08 N/A N/A N/A 0 1784.08 4,963.60 5,351.13 0.1 535.04 4995.24 1998.096 N/A N/A N/A 0 1998.096 4,963.70 5,352.50 0.1 535.18 5530.42 2212.168 N/A N/A N/A 0 2212.168 4,963.80 5,353.87 0.1 535.32 6065.74 2426.296 N/A N/A N/A 0 2426.296 4,963.90 5,355.25 0.1 535.46 6601.2 2640.48 N/A N/A N/A 0 2640.48 4,964.00 5,356.62 0.1 535.59 7136.79 2854.716 N/A N/A N/A 0 2854.716 4,964.10 5,357.99 0.1 535.73 7672.52 3069.008 N/A N/A N/A 0 3069.008 4,964.20 5,359.36 0.1 535.87 8208.39 3283.356 N/A N/A N/A 0 3283.356 4,964.30 5,360.73 0.1 536 8744.39 3497.756 N/A N/A N/A 0 3497.756 Surface Volume Incremental Depth (ft) Incremental Vol. (ft 3 ) 959-001 Steve Allen 3401 cu. ft. Total Volume (ft 3 ) Total Vol. (ft 3 ) Permeable Paver Detention Area 406 cu. ft. 4964.39 ft Geico Office Building Elevation (ft) Surface Area (ft 2 ) Incremental Depth (ft) Project Title Date: Project Number Calcs By: Client Pond Designation Q = 0.60 cfs C = 0.609 Q = Release Rate (cfs) Eh = 66.25 ft C = Discharge Coefficients (unitless) Ei = 63.06 ft Aa = Area Allowed of Opening (ft2) g = Gravity (32.2 ft/s2) 0.068738 ft2 Eh = High Water Surface Elevation (ft) 9.898244 in2 Ei = Elevation of Outlet Invert (ft) H = Height of Opening (in.) Steve Allen 959-001 Geico Office Building Permeable Paver Detention Area C. Snowdon December 23, 2013 Aa = > @ 2 2 R Sin S R R S K Q CA 2 g E h E i S R T Cos R Cos R ' o ' 2 2 1 T T Ac S R 2 K H = Height of Opening (in.) R = Inner Radius of Outfall Pipe (in.) ȴ = Top of Plate to Center of Pipe (in.) S = Arc Length of Open Area (in.) Ac = Area of Opening (in2) ɽ = Angle of Plate on Pipe to Center Pipe (radians) 1-5/8 in 12 in Calculated Area of Opening (Ac) Design Height of Opening (H) Proposed Outfall Pipe Diameter 9.17 sq. in. Project Title Date: Project Number Calcs By: Client Pond Designation Q = 0.60 cfs C = 0.65 Q = Release Rate (cfs) Eh = 66.25 ft C = Discharge Coefficients (unitless) Ei = 63.06 ft Aa = Area Allowed of Opening (ft 2 ) Ec = 63.20 ft Circular g = Gravity (32.2 ft/s 2 ) Ec = 63.19 ft Rectangular Eh = High Water Surface Elevation (ft) Ei = Elevation of Outlet Invert (ft) 0.064402 ft 2 Ec = Elevation of Outlet Centroid (ft) 9.273894 in 2 Orifice Size (in.) 3 - 3/8 in. Area (in 2 ) 9.12 sq-in Q 0.58 cfs Orifice Height (in.) 3 - 1/16 in. Aa = Circular Orifice 10-Year Orifice Rectangular Orifice 10-Year Orifice Geico Office Building December 23, 2013 959-001 C. Snowdon Steve Allen Permeable Paver Detention Area Orifice Height (in.) 3 - 1/16 in. Orifice Width (in.) 3 in. Area (in 2 ) 9.12 sq-in Q 0.58 cfs B 405.663 0.009 4965.00 3401.00 Basin ID Pond Volume (cu. ft.) Pond Spillway Elevation (ft) Provided Water Quality (ac-ft) Required Water Quality Storage (ac-ft) APPENDIX C WATER QUALITY DESIGN COMPUTATIONS Project Title Date: Project Number Calcs By: Client Pond Designation 0.8 WQCV = Watershed inches of Runoff (inches) 51.00% a = Runoff Volume Reduction (constant) i = Total imperviousness Ratio (i = Iwq/100) 0.167 in Drain Time a = i = WQCV = Geico Office Building December 23, 2013 959-001 C. Snowdon Steve Allen Permeable Paver Detention Area 0.167 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 WQCV (watershed inches) Water Quality Capture Volume 6 hr 12 hr 24 hr 40 hr WQCV a 0.91 i 3 1 . 19 i 2 0 . 78 i WQCV a 0.91 i 3 1 . 19 i 2 0 . 78 i 12 hr A = 0.56 ac V = 0.0093 ac-ft V = Water Quality Design Volume (ac-ft) WQCV = Water Quality Capture Volume (inches) A = Watershed Area (acres) 1.2 = 20% Additional Volume (Sediment Accumulation) Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event 0 0.05 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 WQCV (watershed inches) Total Imperviousness Ratio (i = Iwq/100) * * 1 . 2 12 APPENDIX D EROSION CONTROL REPORT Geico Office Building Preliminary Erosion Control Report A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included with the final construction drawings. It should be noted, however, that any such Erosion and Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of the BMPs depicted, and additional or different BMPs from those included may be necessary during construction, or as required by the authorities having jurisdiction. It shall be the responsibility of the Contractor to ensure erosion control measures are properly maintained and followed. The Erosion and Sediment Control Plan is intended to be a living document, constantly adapting to site conditions and needs. The Contractor shall update the location of BMPs as they are installed, removed or modified in conjunction with construction activities. It is imperative to appropriately reflect the current site conditions at all times. The Erosion and Sediment Control Plan shall address both temporary measures to be implemented during construction, as well as permanent erosion control protection. Best Management Practices from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways and inlet protection at existing and proposed storm inlets. Vehicle tracking control pads, spill containment and clean-up procedures, designated concrete washout areas, dumpsters, and job site restrooms shall also be provided by the Contractor. Grading and Erosion Control Notes can be found on Sheet CS2 of the Utility Plans. The Utility Plans at final design will also contain a full-size Erosion Control Plan as well as a separate sheet dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets, the Contractor shall be aware of, and adhere to, the applicable requirements outlined in any existing Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior to issuance of the Development Construction Permit. Also, the Site Contractor for this project will be required to secure a Stormwater Construction General Permit from the Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division – Stormwater Program, before commencing any earth disturbing activities. Prior to securing said permit, the Site Contractor shall develop a comprehensive StormWater Management Plan (SWMP) pursuant to CDPHE requirements and guidelines. The SWMP will further describe and document the ongoing activities, inspections, and maintenance of construction BMPs. Geico Office Building Preliminary Erosion Control Report MAP POCKET DR1 – OVERALL DRAINAGE EXHIBIT V WQCV A ¸ ¹ · ¨ © § Incremental Vol. (ft 3 ) Total Vol. 100% Capacity(ft 3 ) Total Vol. 40% Capacity(ft 3 ) Paver Volume 3401 cu. ft. Surface Area (ft 2 ) 4,964.30 5,360.73 0.1 536 8744.39 3497.756 N/A N/A N/A 0 3497.756 4,964.40 5,362.11 0.1 536.14 9280.54 3712.216 4,964.40 0.95 N/A 0 3712.216 4,964.50 5,327.06 0.1 534.46 9815 3926 4,964.50 76.24 0.1 3.86 3929.86 4,964.60 5,144.37 0.1 523.57 10338.57 4135.428 4,964.60 303.69 0.1 19 4154.428 4,964.70 4,802.07 0.1 497.32 10835.89 4334.356 4,964.70 687.66 0.1 49.57 4383.926 4,964.80 4,376.91 0.1 458.95 11294.84 4517.936 4,964.80 1,158.82 0.1 92.32 4610.256 4,964.90 3,937.13 0.1 415.7 11710.54 4684.216 4,964.90 1,717.68 0.1 143.83 4828.046 4,965.00 3,487.33 0.1 371.22 12081.76 4832.704 4,965.00 2,355.38 0.1 203.65 5036.354 Input Variables Results Required Detention Volume Fort Collins, Colorado 959-001 Geico Office Building Project Number : Project Name : Permeable Paver Detention Page 1 of 1 959-001_DetentionVolume_FAAModified Method.xls (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) a1 A1-A4 No 0.54 0.54 0.68 18.00 0.06 2.4 2.4 1.8 111 0.50% 1.41 1.3 N/A N/A N/A 5 5 5 COMBINED DEVELOPED TIME OF CONCENTRATION COMPUTATIONS C. Snowdon December 20, 2013 Design Point Basin IDs Overland Flow Pipe Flow Swale Flow Time of Concentration (Equation RO-4) 3 1 1 . 87 1 . 1 * S Ti C Cf L Page 8 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Comb-Tc-10-yr_&_100-yr C. Snowdon Page 7 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Comb-C-Values Tc (min) 10-yr Tc (min) 100-yr Tc (min) a1 A1 No 0.74 0.74 0.93 43 3.07% 3.0 3.0 1.4 95 0.53% 1.45 1.1 0 N/A N/A N/A 5 5 5 a2 A2 No 0.83 0.83 1.00 20 8.33% 1.1 1.1 0.4 0 N/A N/A N/A 0 N/A N/A N/A 5 5 5 a3 A3 No 0.82 0.82 1.00 20 8.33% 1.2 1.2 0.4 0 N/A N/A N/A 0 N/A N/A N/A 5 5 5 a4 A4 No 0.54 0.54 0.68 18 6.37% 2.4 2.4 1.8 0 N/A N/A N/A 32 0.59% 1.16 0.5 5 5 5 oe1 OE1 No 0.15 0.15 0.19 15 9.87% 3.2 3.2 3.1 0 N/A N/A N/A 0 N/A N/A N/A 5 5 5 on1 ON1 No 0.19 0.19 0.24 11 24.36% 1.9 1.9 1.8 0 N/A N/A N/A 0 N/A N/A N/A 5 5 5 os1 OS1 No 0.55 0.55 0.69 20 6.70% 2.4 2.4 1.8 0 N/A N/A N/A 0 N/A N/A N/A 5 5 5 DEVELOPED TIME OF CONCENTRATION COMPUTATIONS Gutter Flow Swale Flow Design Point Basin Overland Flow C. Snowdon December 20, 2013 Time of Concentration (Equation RO-4) 3 1 1 . 87 1 . 1 * S Ti C Cf L Page 5 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr OS1 2464 0.057 0.000 0.028 0.000 0.000 0.000 0.028 0.55 0.55 0.69 45% TOTAL 24283 0.557 0.132 0.083 0.085 0.000 0.039 0.257 0.61 0.61 0.76 51% DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I. 10-year Cf = 1.00 December 20, 2013 **Soil Classification of site is Sandy Loam** C. Snowdon Page 4 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\C-Values Tc (min) 10-yr Tc (min) 100-yr Tc (min) h1 H1 No 0.25 0.25 0.31 116 4.25% 10.6 10.6 9.8 N/A N/A N/A N/A N/A N/A 11 11 10 HISTORIC TIME OF CONCENTRATION COMPUTATIONS C. Snowdon December 20, 2013 Design Point Basin Overland Flow Gutter Flow Swale Flow Time of Concentration (Equation RO-4) 3 1 1 . 87 1 . 1 * S Ti C Cf L Page 2 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Hist-Tc-10-yr_&_100-yr Notes Imperviousness Area 'Gradnfathered' from 2024 Lot only Page 1 of 10 D:\Projects\959-001\Drainage\Hydrology\959-001_Rational-Calcs.xlsx\Hist-C-Values