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HomeMy WebLinkAboutTOWNHOMES AT LIBRARY PARK - FDP - FDP140014 - REPORTS - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL REPORT TOWNHOMES @ ONE LIBRARY PARK Fort Collins, Colorado July 23, 2014 Prepared for: Brad Florin Fort Equity 1603 Oakridge Drive, Suite B Fort Collins, CO 80527 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: 963-001 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. July 23, 2014 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Final Drainage and Erosion Control Report for Townhomes @ One Library Park Dear Staff: Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for your review. This report accompanies the 05.14.14 Basic Development Review submittal for the proposed Townhomes @ One Library Park. Comments from the Basic Development Review Letter dated October 22, 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 Townhomes @ One Library Park 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 Townhomes @ One Library Park Final 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 ....................................................................... 5 A. Major Basin Description ............................................................................................................... 5 B. Sub-Basin Description .................................................................................................................. 5 III. DRAINAGE DESIGN CRITERIA ................................................................................... 5 A. Regulations .................................................................................................................................. 5 B. Four Step Process ........................................................................................................................ 5 C. Development Criteria Reference and Constraints ......................................................................... 6 D. Hydrological Criteria .................................................................................................................... 6 E. Hydraulic Criteria ......................................................................................................................... 7 F. Floodplain Regulations Compliance .............................................................................................. 7 G. Modifications of Criteria .............................................................................................................. 7 IV. DRAINAGE FACILITY DESIGN .................................................................................... 7 A. General Concept .......................................................................................................................... 7 B. Specific Details ............................................................................................................................. 8 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 Modeling B.2 – Inlets and Weir Computations APPENDIX C – Water Quality Computations APPENDIX D – Erosion Control Letter Townhomes @ One Library Park Final Drainage Report LIST OF TABLES AND FIGURES: Figure 1 – Aerial Photograph ................................................................................................ 2 Figure 2 – Proposed Site Plan ............................................................................................... 3 Figure 3 – Existing City Floodplains ....................................................................................... 4 Townhomes @ One Library Park Final Drainage Report 1 I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map 2. Townhomes @ One Library Park is located in the southwest quarter of Section 12, 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 East Olive Street and Mathews Street. 4. Currently the existing lot does not have any stormwater or water quality facilities. Due to the proximity of the existing building to the property, all of the stormwater is collected on top of the roof and discharged directly into the City Stormwater Collections System via a roof drain leader. All of runoff, located within the public Right-of-Way is discharged via overland flow into the street curb and gutter and intercepted by an existing Type ‘R’ Inlet into the aforementioned system. 5. The project is currently border to the south by East Olive Street, west by a public alley, north by a multi-family complex and east by Mathews Street. Townhomes @ One Library Park Final Drainage Report 2 B. Description of Property 1. Townhomes @ One Library Park property is approximately 0.289 net acres. Figure 1 – Aerial Photograph 2. Townhomes @ One Library Park project consists of one property that is entirely consumed by an existing building. This building was owned and occupied previously by the City of Fort Collins Utilities. On the southeast corner of the lot, there is an existing Porte-cochere acting as an old drive-thru window. The existing building was constructed with a flat roof collecting all stormwater through a central rooftop drain. This drain was discharged directly into the City stormwater system through a stormwater service pipe. Al stormwater surrounding the building was routed via overland flow into the surrounding streets and public alleyway. No off-site stormwater was routed on-site. 3. According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey, 79 percent of the site consists of Fort Collins loam, which falls into Hydrologic Soil Groups B, while the remaining site consists of Satanta loam, which falls into Hydrologic Soil Groups B. 4. The proposed development will include the deconstruction of the old City building along with all associated utility services. The proposed site will include two large building, each being divided into five single family attached units, and a central access drive composed of both permeable and inpermeable pavers. The site is located in the Old Town master drainage basin, and therefore, on-site detention is not required so long as the increase in impervious area is less than 5,000 square-feet. The proposed development will be decreasing the amount of imperviousness by approximately 2,746 square-feet (16,927-14,181). A detailed breakdown of the existing and proposed impervious area is attached to this report. Although the project site is located within the Uhdal Basin and water quality is not required, the center section of drive constructed of permeable pavers will act as the projects water quality facility. Townhomes @ One Library Park Final Drainage Report 3 Figure 2– Proposed Site Plan 5. No irrigation facilities are known to be within the property limits. 6. The project site is within the Neighborhood Conservation Buffer (N-C-B) 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. The FEMA Panel 08069C0979H, shown below, illustrates the proximity of the project site to the nearest FEAM delineated regulatory floodplain. It is noted that the vertical datum utilized for site survey work is the City of Fort Collins Benchmark #1- 13 (Elevation = 4976.58, Fort Collins NVGD 29 – Unadjusted) Townhomes @ One Library Park Final Drainage Report 4 Figure 3 – Existing FEMA Floodplains Figure 4 – Existing City Floodplains Townhomes @ One Library Park Final Drainage Report 5 II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. Townhomes @ One Library Park is located within the Old Town Basin, which is located primarily in Old Town Fort Collins. B. Sub-Basin Description 1. The subject property primarily consists of a commercial building. This area routes stormwater through a roof drain and directly into the City’s Stormwater system. The areas surrounding the building to the north, south and east route stormwater away from the building and into the streets. Both streets discharge directly into the City’s Stormwater system via a curb inlet located at the southeast corner of the project site. 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, north or south. III. DRAINAGE DESIGN CRITERIA A. Regulations There are no optional provisions outside of the FCSCM proposed with Townhomes @ One Library Park. B. Four Step Process The overall stormwater management strategy employed with Townhomes @ One Library Park 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 trees along Mathews Street and Olive Street. 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. Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with Slow Release Although this project site is located within the Udall Natural Area and Water Quality is not required, approximately 70 percent of the building and the entire central drive aisle will drain across or into the permeable paver section located within the drive. In addition, the northern half of the northern building will drain into a grass lines swale achieving further water quality. Townhomes @ One Library Park Final Drainage Report 6 Step 3 – Stabilize Drainageways As stated in Section I.B.5, above, there are no major drainageways in or near the subject site. While this step may not seem applicable to Townhomes @ One Library Park, the proposed project indirectly helps achieve stabilized drainageways nonetheless. Once again, site selection has a positive effect on stream stabilization. By repurposing an already developed, under-utilized site with existing stormwater infrastructure, combined with LID, the likelihood of bed and bank erosion is greatly reduced. Furthermore, this project will pay one-time stormwater development fees, as well as ongoing monthly stormwater utility fees, both of which help achieve Citywide drainageway stability. Step 4 – Implement Site Specific and Other Source Control BMPs. This step typically applies to industrial and commercial developments and is not applicable for this project. 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 Townhomes @ One Library Park 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, east and west property lines adjacent to Olive Street, Mathews Street and the Public Alley will be maintained. Existing trees along Mathews Street and Olive Street will be preserved. As previously mentioned, overall drainage patterns of the existing site will be maintained. 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. Townhomes @ One Library Park Final Drainage Report 7 E. Hydraulic Criteria 1. As previously noted, the subject property historically drains directly into the City’s Stormwater system. The majority of the site drains stormwater via overland and pipe flow. 2. All drainage facilities proposed with Townhomes @ One Library Park 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. Townhomes @ One Library Park 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 Townhomes @ One Library Park development is not requesting any modifications to criteria at this time. IV. DRAINAGE FACILITY DESIGN A. General Concept 1. The main objectives of Townhomes @ One Library Park drainage design are to maintain existing drainage patterns and ensure no adverse impacts to any adjacent properties. 2. The existing site does not have off-site flows entering the site. 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. Townhomes @ One Library Park project divided the site into four (4) major drainage basins, designated as Basins A, B, C and OS. The project was not further subdivided. The drainage patterns anticipated for each basin is further described below. Basin A Basin A consists of the northern half of the northern building and the landscape/walk north of the building. Runoff from this basin is routed through a combination of overland and swale flow. The runoff from the roof is collected through a central drain and discharged directly into the grass lined swale running along the north from west to east. This runoff is discharged directly into the street section and finally intercepted by the existing storm inlet located at the northwest corner of Mathews and Olive Street. Basin B Basin B consists of the 70 percent of both building and the entire central drive aisle. Runoff from this basin is routed through a combination of overland and gutter flow. Townhomes @ One Library Park Final Drainage Report 8 The runoff from the roof is collected through a central drain and discharged directly into the paver section located in the center of the private drive. All runoff from the private drive is routed across the pavers and intercepted by a combination inlet located at the east end of the drive aisle. This private storm system is connected directly to the City’s Stormwater system. In the case that the inlet is clogged, the runoff will spill over the curb and gutter. The inlet/ will then act like a weir and is able to handle 133 percent of the 100-year event. Basin C Basin C consists of the southern half of the southern building and the landscape between the building and the public walk. Runoff from this basin is routed through a combination of overland and pipe flow. The runoff from the roof is collected through a central drain and discharged directly into the private storm sewer running along the south from west to east. This runoff is discharged directly into the City’s Stormwater system. Basin OS Basin OS consist entirely of the public sidewalk and landscape buffer. Runoff from this basin is routed overland and discharged directly into the street section and finally intercepted by the existing storm inlet located at the northwest corner of Mathews and Olive Street. A Drainage Exhibit can be found at the end of this report. B. Specific Details 1. Although this located within the Udall Natural Area, water quality is always a concern. Additional treatment will include the proposed paver section within the central drive aisle, which will treat 48 percent of the project site and a grass lined swale located to the north of the property, which will treat and additional 17 percent of the site. 2. The project is located within the Old Town Master Drainage Basin, which does not require detention as long as the addition imperviousness proposed is less than 500 square feet. Townhomes @ One Library Park will actually be reducing the overall imperviousness of the site by 2,746 square-feet (14,181-16,927), therefore no detention is required. 3. There are Nyloplast Drain Basins located along the southern and eastern sides of the building. 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 City’s Stormwater system. 4. The emergency spillway will be located at the low point on the eastern side of the drive aisle. In the event that an emergency overflow occurs, the drainage will flow to the east, into the existing street. Weir calculations are attached and only account for the area directly above the inlet. More capacity is available along the entire section of the curb and gutter. Townhomes @ One Library Park Final Drainage Report 9 V. CONCLUSIONS A. Compliance with Standards 1. The drainage design proposed with Townhomes @ One Library Park project complies with the City of Fort Collins’ Stormwater Criteria Manual. 2. The drainage design proposed with Townhomes @ One Library Park project complies with the City of Fort Collins’ Master Drainage Plan for Old Town. 3. There are no regulatory floodplains associated with Townhomes @ One Library Park development. 4. The drainage plan and stormwater management measures proposed with Townhomes @ One Library Park 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. Townhomes @ One Library Park has decreased the amount of impervious area, therefore reducing the overall amount of runoff generated from the site. 2. The proposed Townhomes @ One Library Park development will not have any impact on the Master Drainage Plan recommendations for Old Town. Townhomes @ One Library Park Final 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. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007. 4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service, United States Department of Agriculture. 5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008. APPENDIX A HYDROLOGIC COMPUTATIONS Townhomes @ One Library Park CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: One Library Park 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. H1 12937 0.30 0.00 0.00 0.30 0.00 0.00 0.95 0.95 1.00 90% H2 6946 0.16 0.00 0.09 0.00 0.00 0.07 0.61 0.61 0.76 52% HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Notes July 17, 2014 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. Page 1 of 7 D:\Projects\963-001\Drainage\Hydrology\963-001_Rational-Calcs.xlsx\Hist-C-Values Townhomes @ One Library Park Overland Flow, Time of Concentration: Project: One Library Park 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 Townhomes @ One Library Park Rational Method Equation: Project: One Library Park Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: h1 H1 0.30 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.80 1.37 2.96 h2 H2 0.16 6 6 5 0.61 0.61 0.76 2.76 4.72 9.95 0.27 0.46 1.21 HISTORIC RUNOFF COMPUTATIONS Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) C. Snowdon July 17, 2014 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 Q C f C i A Page 3 of 7 D:\Projects\963-001\Drainage\Hydrology\963-001_Rational-Calcs.xlsx\Hist-Direct-Runoff Townhomes @ One Library Park CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: One Library Park 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. A 3461 0.079 0.000 0.016 0.028 0.000 0.000 0.035 0.60 0.60 0.75 50% B 9514 0.218 0.000 0.058 0.127 0.000 0.025 0.009 0.86 0.86 1.00 76% C 2001 0.046 0.000 0.002 0.029 0.000 0.000 0.015 0.69 0.69 0.86 60% OS 4907 0.113 0.000 0.055 0.000 0.000 0.000 0.057 0.54 0.54 0.68 44% TOTAL 19883 0.456 0.000 0.132 0.184 0.000 0.025 0.141 0.72 0.72 0.91 62% DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Townhomes @ One Library Park Overland Flow, Time of Concentration: Project: One Library Park 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 Townhomes @ One Library Park Rational Method Equation: Project: One Library Park Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: a A 0.08 5 5 5 0.60 0.60 0.75 2.85 4.87 9.95 0.1 0.2 0.6 b B 0.22 5 5 5 0.86 0.86 1.00 2.85 4.87 9.95 0.5 0.9 2.2 c C 0.05 5 5 5 0.69 0.69 0.86 2.85 4.87 9.95 0.1 0.2 0.4 os OS 0.11 5 5 5 0.54 0.54 0.68 2.85 4.87 9.95 0.2 0.3 0.8 DEVELOPED RUNOFF COMPUTATIONS C100 Design Point Flow, Q100 (cfs) Flow, Q2 (cfs) 10-yr Tc (min) 2-yr Tc (min) C2 Flow, Q10 (cfs) Intensity, i100 (in/hr) Basin(s) C. Snowdon July 17, 2014 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) Q C f C i A Page 6 of 7 D:\Projects\963-001\Drainage\Hydrology\963-001_Rational-Calcs.xlsx\Direct-Runoff Townhomes @ One Library Park DESIGN POINT BASIN ID TOTAL AREA (acres) C10 C100 10-yr Tc (min) 100-yr Tc (min) Q10 (cfs) Q100 (cfs) a A 0.079 0.60 0.75 5.0 5.0 0.23 0.59 b B 0.218 0.86 1.00 5.0 5.0 0.91 2.17 c C 0.046 0.69 0.86 5.0 5.0 0.15 0.39 os OS 0.113 0.54 0.68 5.2 5.0 0.30 0.76 DESIGN POINT BASIN ID TOTAL AREA (acres) C10 C100 10-yr Tc (min) 100-yr Tc (min) Q10 (cfs) Q100 (cfs) h1 H1 0.30 0.95 1.00 5.0 5.0 1.4 2.96 h2 H2 0.16 0.61 0.76 5.8 5.4 0.5 1.21 Page 7 of 7 D:\Projects\963-001\Drainage\Hydrology\963-001_Rational-Calcs.xlsx\SUMMARY-TABLE APPENDIX B HYDRAULIC COMPUTATIONS B.1 – Storm Sewers Modeling B.2 – Inlets and Weir Computations APPENDIX B.1 STORM SEWERS MODELING APPENDIX B.2 INLETS AND WEIR COMPUTATION 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 2.2 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 = 0.5 2.2 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 Townhomes at One Library Park Design Point b Site is Urban Site is Non-Urban Show Details Combination Inlet.xls, Q-Peak 7/17/2014, 9:25 AM 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 6.0 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 3.2 cfs Inlet Capacity IS GOOD for Minor and Major Storms (>Q PEAK) Q PEAK REQUIRED = 0.5 2.2 cfs INLET IN A SUMP OR SAG LOCATION Townhomes at One Library Park Design Point b CDOT/Denver 13 Combination H-VertCurb H- W Lo (C) Lo (G) WP Wo Combination Inlet.xls, Inlet In Sump 7/17/2014, 9:25 AM 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 Weir Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Jul 17 2014 Emergency Overflow (section above inlet) Rectangular Weir Crest = Broad Bottom Length (ft) = 5.00 Total Depth (ft) = 0.50 Calculations Weir Coeff. Cw = 2.60 Compute by: Known Q Known Q (cfs) = 2.89 Highlighted Depth (ft) = 0.37 Q (cfs) = 2.890 Area (sqft) = 1.83 Velocity (ft/s) = 1.58 Top Width (ft) = 5.00 0 1 2 3 4 5 6 7 Depth (ft) Emergency Overflow (section above inlet) Depth (ft) -0.50 -0.50 0.00 0.00 0.50 0.50 1.00 1.00 Weir W.S. Length (ft) APPENDIX C WATER QUALITY COMPUTATIONS Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Type of Permeable Pavement Section A) What type of section of permeable pavement is used? (Based on the land use and activities, proximity to adjacent structures and soil characteristics.) B) What type of wearing course? 2. Required Storage Volume A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia I a = 100.0 % B) Tributary Area's Imperviousness Ratio (I = Ia / 100) i = 1.000 C) Tributary Watershed Area ATotal = 3,187 sq ft (including area of permeable pavement system) D) Area of Permeable Pavement System APPS = 1,126 sq ft (Minimum recommended permeable pavement area = 1062 sq ft) E) Impervious Tributary Ratio RT = 1.8 (Contributing Imperviuos Area / Permeable Pavement Ratio) F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 106 cu ft (WQCV = (0.8 * (0.91 * i 3 - 1.19 * i 2 + 0.78 * i) / 12) * Area) G) Is flood control volume being added? H) Total Volume Needed VTotal = cu ft One Library Park Design Procedure Form: Permeable Pavement Systems (PPS) Cody Snowdon Northern Engineering July 17, 2014 Choose One No Infiltration Partial Infiltration Section Full Infiltration Section Choose One YES NO Choose One PICP Concrete Grid Pavement Pervious Concrete Porous Gravel 3. Depth of Reservoir A) Minimum Depth of Reservoir Dmin = 12.0 inches (Minimum recommended depth is 6 inches) B) Is the slope of the reservoir/subgrade interface equal to 0%? C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.40 D) Slope of the Base Course/Subgrade Interface S = 0.005 ft / ft E) Length Between Lateral Flow Barriers (max = 94.35 ft.) L = 81.0 ft F) Volume Provided Based on Depth of Base Course V = 322 cu ft Flat or Stepped: V = P * ((Dmin-1)/12) * Area Sheet 2 of 2 Designer: Company: Date: Project: Location: 6. Filter Material and Underdrain System A) Is the underdrain placed below a 6-inch thick layer of CDOT Class C filter material? CDOT CLASS C FILTER MATERIAL RECOMMENDED B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2) C) Distance from the Lowest Elevation of the Storage Volume y = 0.3 ft (i.e. the bottom of the base course to the center of the orifice) 7. Impermeable Geomembrane Liner and Geotextile Separator Fabric A) Is there a minimum 30 mil thick impermeable PVC geomembrane liner on the bottom and sides of the basin, extending up to the top of the base course? B) CDOT Class B Separator Fabric 8. Outlet (Assumes each cell has similar area, subgrade slope, and length between lateral barriers (unless subgrade is flat). Calculate cells individually where this varies.) A) Depth of WQCV in the Reservoir DWQCV = 5.26 inches (Elevation of the Flood Control Outlet) B) Diameter of Orifice for 12-hour Drain Time DOrifice = 0.36 inches MINIMUM ORIFICE SIZE IS 3/8-INCHES (Use a minimum orifice diameter of 3/8-inches) One Library Park Design Procedure Form: Permeable Pavement Systems (PPS) Cody Snowdon Northern Engineering July 17, 2014 Choose One YES NO Choose One 4-inch 6-inch Choose One Choose One YES NO Placed above the liner Placed above and below the liner N/A (Use a minimum orifice diameter of 3/8-inches) Notes: UD-BMP_v3.02.xls, PPS 7/17/2014, 9:04 AM APPENDIX D EROSION CONTROL LETTER 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 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, a final Storm Water Management Report has been created and is included within this submittal. The Contractor shall also 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 Sloped: V = P * [(Dmin - (D min - 6*SL-1)) / 12] * Area Volume assumes uniform slope & lateral flow barrier spacing. Calculate the volume of each cell individually when this varies. 4. Lateral Flow Barriers A) Type of Lateral Flow Barriers B) Number of Permeable Pavement Cells Cells = 1 5. Perimeter Barrier A) Is a perimeter barrier provided on all sides of the pavement system? (Recommeded for PICP, concrete grid pavement, or for any no-infiltration section.) Choose One YES- Flat or Stepped Installation NO- Sloped Installation Choose One Concrete Walls PVC geomembrane installed normal to flow N/A- Flat installation Other (Describe): Choose One YES NO UD-BMP_v3.02.xls, PPS 7/17/2014, 9:04 AM Tc (min) 10-yr Tc (min) 100-yr Tc (min) a A No 0.60 0.60 0.75 20 2.00% 3.3 3.3 2.3 130 2.00% 2.83 0.8 0 N/A N/A N/A 5 5 5 b B No 0.86 0.86 1.00 40 2.00% 2.3 2.3 0.9 130 2.00% 2.83 0.8 0 N/A N/A N/A 5 5 5 c C No 0.69 0.69 0.86 11 5.00% 1.5 1.5 0.9 77 0.50% 1.41 0.9 0 N/A N/A N/A 5 5 5 os OS No 0.54 0.54 0.68 20 2.00% 3.7 3.7 2.8 130 0.50% 1.41 1.5 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 July 17, 2014 Time of Concentration (Equation RO-4) 3 1 1 . 87 1 . 1 * S Ti C Cf L  Page 5 of 7 D:\Projects\963-001\Drainage\Hydrology\963-001_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr 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 July 17, 2014 **Soil Classification of site is Sandy Loam** C. Snowdon Page 4 of 7 D:\Projects\963-001\Drainage\Hydrology\963-001_Rational-Calcs.xlsx\C-Values Tc (min) 10-yr Tc (min) 100-yr Tc (min) h1 H1 No 0.25 0.25 0.31 20 3.00% 4.9 4.9 4.6 125 1.50% 2.45 0.9 N/A N/A N/A 6 6 5 h2 H2 No 0.25 0.25 0.31 20 3.00% 4.9 4.9 4.6 125 1.50% 2.45 0.9 N/A N/A N/A 6 6 5 HISTORIC TIME OF CONCENTRATION COMPUTATIONS C. Snowdon July 17, 2014 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 7 D:\Projects\963-001\Drainage\Hydrology\963-001_Rational-Calcs.xlsx\Hist-Tc-10-yr_&_100-yr