The URL can be used to link to this page

Home My WebLink AboutWEST RANGE FORT COLLINS - PDP - PDP120028 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE AND EROSION CONTROL REPORT WEST RANGE FORT COLLINS Fort Collins, Colorado October 24, 2012 Prepared for: Epsilon Theta Corporation 200 South Avenue, Suite 10 Fort Collins, Colorado 80524 Prepared by: 200 South College Avenue, Suite 10 Fort Collins, Colorado 80524 Phone: 970.221.4158 Fax: 970.221.4159 www.northernengineering.com Project Number: 875-001 3This 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. October 24, 2012 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Preliminary Drainage and Erosion Control Report for West Range Fort Collins Dear Staff: Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for your review. Comments from the Conceptual Review letter dated 10.17.11 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 West RangeFort Collins student housing 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. Nicholas W. Haws, PE Herman H. Feissner, PE Project Manager Project Engineer West Range Fort Collins Preliminary Drainage and Erosion Control Report TABLE OF CONTENTS I. GENERAL LOCATION AND DESCRIPTION ......................................................... 1 II. DRAINAGE BASINS AND SUB-BASINS ............................................................. 4 III. DRAINAGE DESIGN CRITERIA ......................................................................... 5 IV. DRAINAGE FACILITY DESIGN .......................................................................... 7 V. CONCLUSIONS............................................................................................... 9 References ............................................................................................................. 10 APPENDICES: APPENDIX A – Hydrologic Computations APPENDIX B – Hydraulic Computations B.1 – Storm Sewers (reserved for future use) B.2 – Street Flow (reserved for future use) B.3 – Inlets (reserved for future use) B.4 – Detention Facilities APPENDIX C – Water Quality Design Computations (reserved for future use) APPENDIX D – Operations and Maintenance Guidelines for Rain Gardens (reserved for future use) APPENDIX E – Erosion Control Report LIST OF TABLES AND FIGURES: MAP POCKET: C4.00 – Drainage Exhibit NOTE: TABLE OF CONTENTS WILL BE UPDATED/CORRECTED WITH SUBSEQUENT REPORT ISSUANCES. West Range Fort Collins Preliminary Drainage and Erosion Control Report 1 I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map Figure 1 – Vicinity Map 2. The West Range Fort Collins project site is located in the Northeast quarter of Section 11, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. 3. West Range Fort Collins is bordered to the north by an existing alleyway and existing multi-family and single family developments; to the south by West Laurel Street and Colorado State University; to the east by Meldrum Street (100' Right-of-Way); and to the west by the Kappa Delta Sorority house. 4. There are no major drainageways within or adjacent to the site. The existing Arthurs Ditch runs parallel to the east property line. As it approaches the north property line, the enclosed concrete irrigation ditch alignment shifts to the northwest. The existing irrigation ditch receives excess developed stormwater from two existing inlets near the project site. The ditch's concrete top slab is at grade, visible and currently used for a sidewalk along the west side of Meldrum Street. West Range Fort Collins Preliminary Drainage and Erosion Control Report 2 B. Description of Property 1. West Range Fort Collins is comprised of ±0.71 acre. 2. The recent existing condition (See Figure 2 - Aerial Photograph) included two (2) fraternity houses which fronted to West Laurel Street, an associated detached garage and a duplex which fronted to Meldrum Street. The asphalt parking lot was constructed in the mid-1990s as a part of the Phase I condition described in the Final Drainage and Erosion Control Report for the Pi Kappa Alpha Fraternity Expansion (Shear Engineering or Phase I, Sheet No. 1 - Phase I Grading, Drainage and Erosion Control Plan is provided for reference in the Map Pocket of the study). The ultimate condition described in the drainage report was never constructed. Figure 2 – Aerial Photograph 3. The subject property was fully developed until the late fall of 2011. At that time, everything but the asphalt parking lot (northwest corner), concrete curb and gutter and several mature trees were removed from the property. The existing groundcover currently consists of weeds and bare soil. The existing on-site excess runoff drains across flat grades (e.g., <2.00%) into West Laurel Street, Meldrum Street and the alleyway. 4. A soils report (Soilogic Project # 08-1051) was completed by Soilogic, Inc on September 29, 2008. The report contains the results of a complete geotechnical subsurface exploration as well as pertinent geotechnical recommendations. According to the summary of findings presented in the aforementioned report, the "subsurface materials encountered in the completed site borings consisted of a thin layer of asphaltic concrete and base course or topsoil and vegetation underlain by brown to reddish brown lean clay with varying amounts of silt and sand. A majority of the site West Range Fort Collins Preliminary Drainage and Erosion Control Report 3 lean clay tested showed low volume change potential with variation in moisture content at in situ moisture and density conditions. Lean clay with low to moderate swell potential was encountered near surface boring location B-1 completed at the south end of the development. Groundwater was not encountered in any of the completed site borings at the time of drilling." The boring logs show that USCS soil group CL is predominant on-site. These soils are inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays and lean clays. 5. There are no major drainageways within or adjacent to the project site. 6. The proposed West Range Fort Collins project site will include a single backwards L- shaped building with a plan area of approximately 8000 ft2. The completed structure will be two stories. Other proposed improvements include: a new asphalt parking area, an enhanced entryway and landscaping. The north-to-south portion of the proposed building will include an open first level (i.e., breezeway) beneath which approximately one-half of the total on-site parking will be located.. 7. The existing Arthurs Ditch runs parallel to the east property line. As it approaches the northeast corner of the subject site, the concrete box alignment shifts toward the northwest (See Figure 3 – Existing Drainage and Irrigation Infrastructure). Figure 3 – Existing Drainage and Irrigation Infrastructure 8. The proposed land use is residential, multi-family dwellings. This is a permitted use in the Neighborhood Community - Buffer District (NCB). West Range Fort Collins Preliminary Drainage and Erosion Control Report 4 C. Floodplain 1. The subject property is not located in a FEMA regulatory or City of Fort Collins designated floodplain. In particular, the project site is not located within a FEMA designated 100-year floodplain per Map Number 08069C0979H (Effective date: May 2, 2012). Figure 4 – FEMA Firmette (Map Number 08069C0979H) II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. West Range Fort Collins is located within the City of Fort Collins Old Town major drainage basin. This basin is located in north-central Fort Collins and has a drainage area of approximately 2,120 acres, including approximately 400 acres of the Colorado State University campus. The Old Town major drainage basin generally drains from west to east. It receives some runoff from the Canal Importation Basin directly west of Old Town. Most of the runoff from the Old Town major drainage basin drains into the Poudre River. Street flooding is a common occurrence in Old Town. Several capital projects such as the Howes Street, Locust Street and Oak Street Outfall projects have addressed the problem and improved drainage in the area. West Range Fort Collins Preliminary Drainage and Erosion Control Report 5 2. As previously mentioned, the Arthurs Ditch runs parallel to the east property line. This irrigation conveyance was historically influenced by excess developed runoff from the project site (Shear Engineering: sub-basins 1a and 1c). Excess developed runoff from the subject site will continue to outfall into this irrigation conveyance as described below. B. Sub-Basin Description 1. Shear Engineering, in the Final Drainage and Erosion Control Report for the Pi Kappa Alpha Fraternity Expansion, described and evaluated an existing condition, Phase I condition and Ultimate condition. The existing condition was used to establish the historic release rate. Phase I represented an interim developed condition in which the existing gravel parking lot was paved and used for on-site detention storage. The pond was designed to release at the historic 2-year rate (0.50 cfs). The pond was also designed to over detain (i.e., the total site area was used to size the pond instead of the total area tributary to the pond). The Ultimate condition was never constructed. 2. The subject site can be historically defined by three (3) sub-basins (i.e., Ia. Ib and Ic). From the center of each of the three (3) previously existing structures, runoff drained in three different directions. First, runoff from the east portion (sub-basin Ib) of the project site drained into Meldrum Street and travelled north. Second, runoff from the south portion (sub-basin 1c) of the subject site drained into West Laurel Street. From there, runoff traveled east, via curb and gutter, and into an existing combination inlet. Excess runoff from the central and northwest portion of the subject site (sub-basin Ia) currently drains across the existing asphalt parking lot and into an existing outlet structure. This structure outfalls to the storm drain system in the alleyway.The West Range Fort Collins development aims to preserve these existing drainage patterns and will utilize the historic outfall location. 3. Arthurs Ditch receives developed stormwater runoff from the subject site at two locations. First, at an existing combination inlet located on the north side of West Laurel Street (west of Meldrum Street). This inlet is connected to the ditch with a 10” diameter metal pipe. In addition to local developed runoff from West Laurel Street, the combination inlet received developed stormwater runoff from the Phase I developed condition sub-basin Ic. Developed runoff, which is similar in peak rate, will drain to this existing inlet from sub-basin C. The attenuated flows from the proposed on-site detention pond will outfall at 0.50 cfs (historic 2-year release rate) into the existing public storm sewer system in the alleyway. This system ultimately connects to the Arthurs Ditch. A more detailed description of the project’s drainage patterns follows in Section IV, below. 4. The project site does not receive any notable runoff from off-site properties. III. DRAINAGE DESIGN CRITERIA A. There are no optional provisions outside of the FCSCM proposed with West Range Fort Collins. West Range Fort Collins Preliminary Drainage and Erosion Control Report 6 B. The overall stormwater management strategy employed with West Range Fort Collins 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. The first consideration taken in trying to reduce the stormwater impacts of this development is the site selection itself. By choosing an already developed site with public storm sewer currently in place, the burden is significantly less than developing a vacant parcel absent of any infrastructure. West Range Fort Collins aims to reduce runoff peaks, volumes and pollutant loads from frequently occurring storm events (i.e., water quality (80th percentile) and 2-year storm events) by implementing Low Impact Development (LID) strategies. Wherever practical, runoff will be routed across landscaped areas or through a grass-lined swale and bio- retention area. This LID practice reduces the overall amount of impervious area, while Minimizing Directly Connected Impervious Areas (MDCIA) at the same time. The combined LID/MDCIA techniques will be implemented, where practical, throughout the development, thereby slowing runoff and increasing opportunities for infiltration. Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with Slow Release.The efforts taken in Step 1 will help to minimize excess runoff from frequently occurring storm events; however, urban development of this intensity will still have stormwater runoff leaving the site. The primary water quality will occur in a linear bio-retention area along the northwest property line (sub-basin A). The bio-retention area design will be more fully developed at Final Design. Step 3 – Stabilize Drainageways. As stated in Section I.B.4, above, there are no major drainageways in or near the subject site. While this step may not seem applicable to West Range Fort Collins, 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 and MDCIA strategies, 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. C. Development Criteria Reference and Constraints 1. The subject property is not part of any Overall Development Plan drainage study or similar “development/project” drainage master plan. 2. There are no known drainage studies for any adjacent properties that will have any effect on West Range project. The Final Drainage and Erosion Control Report for the Pi Kappa Alpha Fraternity Expansion (Shear Engineering, 1995) was referenced during the preparation of this study. The contents of the report served as a the basis for developing our existing drainage conditions, existing pervious/impervious areas/ historic release rate and the existing detention pond volume that was associated with the historic development. West Range Fort Collins Preliminary Drainage and Erosion Control Report 7 3. The site plan will be constrained on two sides by public streets and by an alleyway on the third. An existing and fully developed site constrains the site plan on the fourth. As previously mentioned, the drainage outfall for Basin A is an existing manhole that ties into an existing 12” RCP storm sewer in the alleyway. The proposed design matches the existing historic release rate (i.e., 0.50 cfs). 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 West Range Fort Collins 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 Federal Aviation Administration (FAA) procedure has utilized for detention storage calculations. 4. Two separate design storms have been utilized to address distinct drainage scenarios. The first event analyzed is the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The second event considered is the “Major Storm,” which has a 100-year recurrence interval. E. Hydraulic Criteria 1. The drainage facilities proposed with the West Range Fort Collins 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. 2. As stated in Section I.C.1, above, the subject property is not located in a FEMA regulatory or a City of Fort Collins designated floodplain. F. Floodplain Regulations Compliance 1. As previously mentioned, this project is not subject to any floodplain regulations. G. Modifications of Criteria 1. No modifications are requested at this time. IV. DRAINAGE FACILITY DESIGN A. General Concept 1. The main objective of the West Range Fort Collins drainage design is to maintain existing drainage patterns, while not adversely impacting any adjacent properties. 2. No notable off-site runoff flows directly through the project site. West Range Fort Collins Preliminary Drainage and Erosion Control Report 8 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 project site has been divided into three (3) drainage sub-basins, designated as sub-basins A, B, and C. The drainage patterns anticipated for each basin are further described below. Sub-Basin A Basin A encompasses a little over of one-half of the total project site area. It is comprised of roof area, concrete walks and asphalt parking. A large part of the parking area in this basin will comprise the on-site detention pond (Pond 1). D.P. A is situated at the proposed outfall. A short section of pipe will connect to an existing manhole in the alleyway. This basin releases at a 2-year historic rate of 0.50 cfs. Sub-Basin B Basin B encompasses the eastern third of the project site. It is comprised of roof area, a concrete patio and landscaping. The downspouts will direct developed runoff from the roof into the landscaping. The excess developed runoff will primarily drain into Meldrum Street as sheet flow (i.e., non-concentrated). The developed flows in this basin are similar to the existing (i.e., Phase I) condition. During the 2-year and 100- year storm events, the proposed condition increases runoff into Meldrum Street by ±0.11cfs and ±0.51cfs, respectively. Sub-Basin C Basin C is very similar in composition to Basin B. It is situated along the south portion of the subject site. The excess developed runoff will primarily drain into West Laurel Street as sheet flow. In West Laurel Street, the runoff drains into an existing combination inlet which is connected to the Arthurs Ditch. During the 2-year and 100-year storm events, the proposed condition increases runoff into Meldrum Street by ±0.08cfs and ±0.34cfs, respectively. A full-size copy of the Drainage Exhibit (sheet C4.00) can be found in the Map Pocket at the end of this report. B. Specific Details 1. According to the Old Town Master Drainage Plan, Section R3, Redevelopment Criteria and with respect to the required storage volume, the proposed redevelopment can take credit for the existing on-site impervious area. The required storage volume was estimated with the FAA method using the procedure outlined below. We took credit for the existing Phase I (Shear Engineering) impervious area, ±0.28 acre. The proposed development will add ±0.24 acre of impervious area. This includes the entire site and not just the increase in sub-basin A, which is tributary to the on-site detention pond. An FAA method computation has been performed to determine the additional storage volume required for the pervious area converted into impervious area, by this development. The Phase I (computed by Shear Engineering - 1995) volume requirement was 2756 ft3. The original storage volume calculation is West Range Fort Collins Preliminary Drainage and Erosion Control Report 9 based on the total site area (i.e., 0.71 acre) and the historic release rate (0.50 cfs). Therefore, the pond was originally designed to overdetain. To the Phase I volume requirement, we added the volume required to detain the total additional impervious area releasing at the historic rate of 0.50 cfs (i.e., 1053 ft3). Therefore, the total required storage volume is 3809 ft3 (0.0874 ac-ft). 2. During Final Design, water quality computations will be performed for the proposed bio-retention area in sub-basin A by utilizing the UDFCD’s UD-BMP Version 3.01 “Rain Garden (RG)” Design Procedure Form. 3. The detention storage information for Pond 1 is contained in Appendix B.4. The drainage features associated with West Range Fort Collins project are private facilities and located on private property. 4. As previously mentioned, the outfall for the West Range Fort Collins project is the public storm sewer in the neighboring alleyway. This storm sewer flows northwest to an existing area inlet before heading north towards Myrtle Street. As shown above in Figure 3, this storm drain outfalls into the Arthurs Ditch due south of Myrtle Street. There are no additional facilities or upgrades needed off-site in order to accommodate the developed runoff from West Range Fort Collins. V. CONCLUSIONS A. Compliance with Standards 1. The design elements comply without variation. 2. The drainage design proposed with West Range Fort Collins complies with the City of Fort Collins Master Drainage Plan for the Old Town Basin. 3. There are no regulatory floodplains associated with the West Range Fort Collins development. 4. The drainage plan and stormwater management measures proposed with the West Range Fort Collins student housing project 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 potential damage associated with its stormwater runoff. West Range Fort Collins will detain for the pervious area converted to impervious areas to release at the 2-year historic rate during the 100-year storm. 2. The proposed West Range Fort Collins development will not impact the Master Drainage Plan recommendations for the Old Town Basin. West Range Fort Collins Preliminary Drainage and Erosion Control 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. Final Drainage and Erosion Control Report for Pi Kappa Alpha Fraternity Expansion, October 1995, Shear Engineering Corporation (Project No. 1060-02-95). 3. 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. 4. Geotechnical Exploration Report, Pike Redevelopment, 406 West Laurel Street, Fort Collins, Colorado, September 29, 2008, Soilogic, Inc. (Soilogic # 08-1051). 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. APPENDIX A HYDROLOGIC COMPUTATIONS West Range Fort Collins CHARACTER OF SURFACE1: Runoff Coefficient Percentage Impervious Project: West Range Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: H. Feissner 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 Flat <2% ……………………………………………………………………………………………………………… 0.10 0% Average 2% to 7% ………………………………………………………………………………………………….0.15 0% . Steep >7% …………………………………………………………………………………………………………… 0.20 0% Clayey Soil Flat <2% ……………………………………………………………………………………………………………… 0.20 0% Average 2% to 7% ………………………………………………………………………………………………….0.25 0% . Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25 Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11 Basin ID Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Gravel (ac) Area of Roofs (ac) Soil Type and Average Slope Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. Ia 0.34 0.00 0.00 0.16 0.05 Clayey | Flat <2% 0.13 0.45 0.45 0.56 32% Ib 0.24 0.00 0.02 0.00 0.05 Clayey | Flat <2% 0.17 0.42 0.42 0.52 26% Ic 0.13 0.00 0.01 0.00 0.03 Clayey | Flat <2% 0.09 0.43 0.43 0.54 28% Irowb 0.34 0.26 0.02 0.00 0.00 Clayey | Flat <2% 0.06 0.82 0.82 1.00 82% Irowc 0.13 0.08 0.02 0.00 0.00 Clayey | Flat <2% 0.03 0.78 0.78 0.97 75% West Range Fort Collins Overland Flow, Time of Concentration: Project: West Range 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 West Range Fort Collins Rational Method Equation: Project: West Range Calculations By: Date: Rainfall Intensity: Ia Ia 0.34 5 5 5 0.45 0.45 0.56 3.29 5.64 9.30 0.51 0.87 1.78 To on-site detention pond Ib Ib 0.24 5 5 5 0.42 0.42 0.52 3.29 5.64 9.30 0.33 0.57 1.17 To Meldrum Street Ic Ic 0.13 5 5 5 0.43 0.43 0.54 3.29 5.64 9.30 0.18 0.32 0.65 To West Laurel Street Irowb Irowb 0.34 5 5 5 0.82 0.82 1.00 3.29 5.64 9.30 0.91 1.57 3.16 Meldrum Street Irowc Irowc 0.13 5 5 5 0.78 0.78 0.97 3.29 5.64 9.30 0.33 0.57 1.17 West Laurel Street C100 Notes Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) EXISTING CONDITIONS RUNOFF COMPUTATIONS H. Feissner October 24, 2012 Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8 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 Q C f C i A 10/24/201212:25 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Historic_Rational_Calcs\Runoff_Exist_OLD idf West Range Fort Collins CHARACTER OF SURFACE1: Runoff Coefficient Percentage Impervious Project: West Range Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: H. Feissner Asphalt ……....……………...……….....…...……………….………………………………………………………….0.95 100% . Date: Concrete …….......……………….….……….………………..….…………………………………………………….0.95 90% . Gravel (packed) ……….…………………….….…………………………..………………………………………….0.50 40% . Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90% Pavers…………………………...………………..……………………………………………………………………… 0.40 22% Lawns and Landscaping Sandy Soil Flat <2% ……………………………………………………………………………………………………………… 0.10 0% Average 2% to 7% ………………………………………………………………………………………………….0.15 0% . Steep >7% …………………………………………………………………………………………………………… 0.20 0% Clayey Soil Flat <2% ……………………………………………………………………………………………………………… 0.20 0% Average 2% to 7% ………………………………………………………………………………………………….0.25 0% . Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25 Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11 Basin ID Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Gravel (ac) Area of Roofs (ac) Soil Type and Average Slope Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. Ia 0.340 0.16 0.00 0.00 0.050 Clayey | Flat <2% 0.13 0.66 0.66 0.83 60% Ib 0.240 0.00 0.02 0.00 0.050 Clayey | Flat <2% 0.17 0.42 0.42 0.52 26% Ic 0.130 0.00 0.01 0.00 0.030 Clayey | Flat <2% 0.09 0.43 0.43 0.54 28% Irowb 0.340 0.26 0.02 0.00 0.000 Clayey | Flat <2% 0.06 0.82 0.82 1.00 82% Irowc 0.130 0.08 0.02 0.00 0.000 Clayey | Flat <2% 0.03 0.78 0.78 0.97 75% West Range Fort Collins Overland Flow, Time of Concentration: Project: West Range 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 West Range Fort Collins Rational Method Equation: Project: West Range Calculations By: Date: Rainfall Intensity: Ia Ia 0.34 5 5 5 0.66 0.66 0.83 3.29 5.64 9.30 0.74 1.27 2.62 Modified w/Phase I Ib Ib 0.24 5 5 5 0.42 0.42 0.52 3.29 5.64 9.30 0.33 0.57 1.17 No change w/Phase I Ic Ic 0.13 5 5 5 0.43 0.43 0.54 3.29 5.64 9.30 0.18 0.32 0.65 No change w/Phase I Irowb Irowb 0.34 5 5 5 0.82 0.82 1.00 3.29 5.64 9.30 0.91 1.57 3.16 No change w/Phase I Irowc Irowc 0.13 5 5 5 0.78 0.78 0.97 3.29 5.64 9.30 0.33 0.57 1.17 No change w/Phase I * Pond Release Rates for each basin include the 100-year flow rate from the historic impervious area plus the 2-year release rate from the historic pervious area. Notes PHASE I 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) H. Feissner October 24, 2012 Intensity, i10 (in/hr) Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8 C10 Area, A (acres) Intensity, i2 (in/hr) 100-yr Tc (min) Q C f C i A 10/24/201212:25 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Historic_Rational_Calcs\Runoff_Phase I_OLD idf West Range Fort Collins CHARACTER OF SURFACE 1 : Runoff Coefficient Percentage Impervious Project: West Range Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: H. Feissner Asphalt ……....……………...……….....…...……………….………………………………………………………….0.95 100% . Date: October 24, 2012 Concrete …….......……………….….……….………………..….…………………………………………………….0.95 90% . Gravel (packed) ……….…………………….….…………………………..………………………………………….0.50 40% . Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90% Pavers…………………………...………………..……………………………………………………………………… 0.40 22% Lawns and Landscaping Sandy Soil Flat <2% ……………………………………………………………………………………………………………… 0.10 0% Average 2% to 7% ………………………………………………………………………………………………….0.15 0% . Steep >7% …………………………………………………………………………………………………………… 0.20 0% Clayey Soil Flat <2% ……………………………………………………………………………………………………………… 0.20 0% Average 2% to 7% ………………………………………………………………………………………………….0.25 0% . Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25 Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11 Basin ID Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Gravel (ac) Area of Roofs (ac) Soil Type and Average Slope Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. Basin A 0.39 0.21 0.00 0.00 0.13 Clayey | Average 2% to 7% 0.05 0.87 0.87 1.00 85% Basin B 0.20 0.03 0.00 0.00 0.10 Clayey | Average 2% to 7% 0.07 0.69 0.69 0.87 58% Basin C 0.12 0.02 0.00 0.00 0.05 Clayey | Average 2% to 7% 0.04 0.72 0.72 0.90 62% West Range Fort Collins Overland Flow, Time of Concentration: Project: West Range Calculations By: Date: Gutter/Swale Flow, Time of Concentration: Tt = L / 60V Tc = Ti + 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) West Range Fort Collins Rational Method Equation: Project: West Range Calculations By: Date: Rainfall Intensity: A Basin A 0.39 5 5 5 0.87 0.87 1.00 2.85 4.87 9.95 0.96 1.63 3.85 B Basin B 0.20 5 5 5 0.69 0.69 0.87 2.85 4.87 9.95 0.40 0.69 1.76 C Basin C 0.12 5 5 5 0.72 0.72 0.90 2.85 4.87 9.95 0.24 0.41 1.04 PROPOSED 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) H. Feissner Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8 October 24, 2012 Intensity, i10 (in/hr) C10 Area, A (acres) Intensity, i2 (in/hr) 100-yr Tc (min) Q C f C i A 10/24/201212:35 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Proposed_Rational_Calcs\Runoff West Range Fort Collins Surface Area % Impervious Surface Area (sq. ft.) Impervious Area (sq. ft.) Surface Area (sq. ft.) Impervious Area (sq. ft.) Surface Area (sq. ft.) Impervious Area (sq. ft.) Asphalt 100% 6970 6970 0 0 0 0 Concrete 90% 0 0 871 784 436 392 Gravel 40% 0 0 0 0 0 0 Roofs 90% 2178 1960 2178 1960 0 0 Pavers 22% 0 0 0 0 1307 287 Lawns and Landscaping 0% 5663 0 7405 0 3920 0 (sq. ft.) (acre) 8930 2744 680 12354 0.28 Surface Area % Impervious Surface Area (sq. ft.) Impervious Area (sq. ft.) Surface Area (sq. ft.) Impervious Area (sq. ft.) Surface Area (sq. ft.) Impervious Area (sq. ft.) Asphalt 100% 9819 9819 623 623 1032 1032 Concrete 90% 0 0 0 0 0 0 Gravel 40% 0 0 0 0 0 0 Roofs 90% 5687 5118 4361 3925 2354 2119 Pavers 22% 0 0 0 0 0 0 Lawns and Landscaping 0% 1976 0 3256 0 1690 0 (sq. ft.) (acre) 17482 14937 8239 4547 5076 3151 22635 0.52 6008 1803 2471 10282 0.24 Exhibit XX. Existing Pervious Area Converted to Impervious Area with Proposed West Range Development Increase/Decrease w/Proposed Condition: Phase I (Existing Condition) Proposed Conditions (i.e., West Range) Totals Totals Basin A Basin B Basin C Ia Ib Ic 10/24/201212:35 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Proposed_Rational_Calcs\Impervious Area Added APPENDIX B HYDRAULIC COMPUTATIONS B.1 – Storm Sewers (reserved for future use) B.2 – Street Flow (reserved for future use) B.3 – Inlets (reserved for future use) B.4 – Detention Facilities APPENDIX B.1 STORM SEWERS (reserved for future use) APPENDIX B.2 STREET FLOW (reserved for future use) APPENDIX B.3 INLETS (reserved for future use) APPENDIX B.4 DETENTION FACILITIES West Range Fort Collins DETENTION POND CALCULATION | FAA METHOD w/Fort Collins IDF Project Number: 875-001 HHF Date: 10/24/2012 Project Number: 875-001 Project Location: Fort Collins, Colorado Calculations By: HHF Date: 10/24/2012 Pond No.: Pond 1 Calculations By: A Input Variables Results Design Point A 100-yr Design Point Design Storm Required Detention Volume 1.00 Phase I 2756 ft2 Area (A)= 0.24 acres +New Imp. Area 1053 ft3 Developed "C" = Area (A)= 0.24 acres +New Imp. Area 1053 ft Max Release Rate = 0.50 cfs Total Volume 3809 ft4 0.0874 ac-ft Time Time Ft.Collins 100-yr Q100 Inflow (Runoff) Outflow (Release) Volume Storage Time Time 100-yr Detention Intensity Q100 (Runoff) Volume (Release) Volume Detention Volume (ft 3 ) (ft 3 ) (ft 3 (mins) (secs) (in/hr) (cfs) (ft ) 3 ) (ft 3 ) (ft 3 ) 5 300 9.95 2.39 716 150 566 10 600 7.72 1.85 1112 300 812 15 900 6.52 1.56 1408 450 958 20 1200 5.60 1.34 1613 600 1013 25 1500 4.98 1.20 1793 750 1043 30 1800 4.52 1.08 1953 900 1053 35 2100 4.08 0.98 2056 1050 1006 40 2400 3.74 0.90 2154 1200 954 45 2700 3.46 0.83 2242 1350 892 50 3000 3.23 0.78 2326 1500 826 West Range Fort Collins Stage - Storage Calculation Project Number: 875-001 HHF Date: 10/24/2012 Project Number: 875-001 Project Location: Fort Collins, Colorado Calculations By: HHF Date: 10/24/2012 Pond No.: Pond 1 Calculations By: A Required Volume Water Surface Elevation (WSE) Design Point A 10-yr At Final ft. 1.00 ft 3 Design Point Design Storm Require Volume= 1.00 ft 3 Design Storm 100-yr Required Volume= 3809 ft 3 5001.52 ft. Require Volume= Required Volume= 3809 ft 3 5001.52 ft. Contour Elevation Contour Area Depth Incremental Area Avg. End Cumulative Volume Avg. End Incremental Volume Conic Cummulative Elevation Area Avg. End Avg. End Conic Volume Conic ft 3 ft. ft 3 ft 3 ft 3 ft 3 ft ft. ft ft ft ft 4999.60 53 0.00 0 0 0 0 4999.80 127 0.20 18 18 17 17 5000.00 201 0.20 33 51 33 50 5000.20 253 0.20 45 96 45 95 5000.40 316 0.20 57 153 57 152 5000.60 817 0.20 113 266 109 261 5000.80 1776 0.20 259 526 253 515 5001.00 3180 0.20 496 1021 489 1003 5001.20 4807 0.20 799 1820 793 1796 APPENDIX C WATER QUALITY DESIGN COMPUTATIONS (reserved for future use) APPENDIX D OPERATIONS AND MAINTENANCE GUIDELINES FOR RAIN GARDENS(reserved for future use) APPENDIX E EROSION CONTROL REPORT West Range Fort Collins Preliminary Erosion Control Report 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 Best Management Practices (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 C.?? of the Utility Plans. The Final Plans will contain a full-size Erosion Controlsheet 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 the Development Agreement for West Range Fort Collins. 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, prior to any earth disturbance 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. West Range Fort Collins Preliminary Erosion Control Report MAP POCKET C4.00 – DRAINAGE EXHIBIT X D acres D A 0.87 0.40 1.00 acres B 0.67 0.19 0.84 acres C 0.72 0.12 0.90 B C ROOF ROOF ROOF ROOF ROOF ROOF ROOF ROOF ROOF ROOF ROOF W. LAUREL STREET S. MELDRUM STREET PROPOSED MULTIFAMILY BUILDING LOT 1 BLOCK 1 A POND 1 No. Revisions: By: Date: REVIEWED BY: N. Haws DESIGNED BY: DRAWN BY: SCALE: DATE: 10.24.12 PROJECT: 875-001 Sheet Of 6 Sheets WEST RANGE FORT COLLINS T�� N�� E�� S��, I��. �� P�� E�� N�� E�� S��, I��. NOT FOR CONSTRUCTION REVIEW SET 10.24.12 200 S�� C�� A��, S�� 010 F�� C��, C�� 80524 E N G I N E E R I N G � � � � � � �� PHONE: 970.221.4158 FAX: 970.221.4159 ��.��.�� C4.00 DRAINAGE EXHIBIT H. Feissner H. Feissner 1" = 20' NORTH ( IN FEET ) 1 inch = ft. 20 0 20 Feet 20 40 60 GRAPHIC SCALE: CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE, OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. CALL UTILITY NOTIFICATION CENTER OF COLORADO K�� '� ��. C�� . R BENCHMARK/BASIS OF BEARING Date Date Date Date Date Date APPROVED: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: City Engineer Water & Wastewater Utility Stormwater Utility Parks & Recreation Traffic Engineer Environmental Planner City of Fort Collins, Colorado UTILITY PLAN APPROVAL BENCHMARK #1: City of Fort Collins Benchmark 6-00 Located on a catch basin at the northwest corner of Mulberry Street and College Avenue. Elevation = 4990.68 (NGVD 29 - Unadjusted) BENCHMARK #2: City of Fort Collins Benchmark CSU 2 Standard brass Larimer County Geodetic Control Disk located in the campus of Colorado State University approzimately 240.8 feet south from the center line of North Drive, 46.6 feet south from the center of the delivery road to the University Club and 1.1 feet southwest from the edge of the sidewalk. Elevation = 5003.12 (NGVD 29 - Unadjusted) Basis of Bearings Considering the west property line of Lot 6, Block 87 of the Plat of the Town of Fort Collins which bears North 00�19'39' East. LEGEND: 4953 PROPOSED CONTOUR 93 PROPOSED STORM SEWER PROPOSED SWALE EXISTING CONTOUR PROPOSED CURB & GUTTER PROPERTY BOUNDARY PROPOSED INLET A DESIGN POINT FLOW ARROW DRAINAGE BASIN LABEL BASIN DESIGNATION BASIN AREA (AC) DRAINAGE BASIN BOUNDARY PROPOSED SWALE SECTION 1 1 B2 1.45 ac PROPOSED 100-YEAR WATER SURFACE ELEVATION NOTES: 1.REFER TO THE "PRELIMINARY DRAINAGE AND EROSION CONTROL REPORT FOR WEST RANGE FORT COLLINS" BY NORTHERN ENGINEERING, DATED {OCTOBER 24, 2012} FOR ADDITIONAL INFORMATION.{ } PROPOSED BIO-RETENTION 5001.40 6448 0.20 1125 2945 1121 2918 5001.60 8089 0.20 1454 4399 1451 4369 Stage-Storage Curve 5002.00 Stage-Storage Curve 5002.00 5001.50 5001.00 Contour Elevation 5000.50 Contour Elevation 5000.00 4999.50 0 500 1000 1500 2000 2500 3000 3500 4000 4500 Cummulative Volume, cu. ft. 10/24/20121:45 PM D:\Projects\875-001\Drainage\Detention\875-001__Detention Pond.xls\Stage_Storage 55 3300 3.03 0.73 2400 1650 750 60 3600 2.86 0.69 2471 1800 671 65 3900 2.72 0.65 2546 1950 596 10/24/20121:29 PM D:\Projects\875-001\Drainage\Detention\875-001__Detention Pond.xls\FAA_Current idf_Add Vol Slope, S (%) Velocity, V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) A Basin A No 0.87 0.87 1.00 1 2.00% 0.3 0.3 0.1 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 B Basin B No 0.69 0.69 0.87 1 2.00% 0.6 0.6 0.3 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 C Basin C No 0.72 0.72 0.90 1 2.00% 0.6 0.6 0.3 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. PROPOSED TIME OF CONCENTRATION COMPUTATIONS H. Feissner October 24, 2012 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 10/24/201212:35 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Proposed_Rational_Calcs\Tc TOTAL (Site ONLY ) 0.71 0.26 0.00 0.00 0.28 Clayey | Average 2% to 7% 0.16 0.79 0.79 0.99 73% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Composite Runoff Coefficient with Adjustment 10/24/201212:35 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Proposed_Rational_Calcs\Composite Runoff Coeff Tc (min) 10-yr Tc (min) 100-yr Tc (min) Ia Ia No 0.66 0.66 0.83 1 2.00% 0.6 0.6 0.4 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Ib Ib No 0.42 0.42 0.52 1 2.00% 1.0 1.0 0.9 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Ic Ic No 0.43 0.43 0.54 1 2.00% 1.0 1.0 0.8 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Irowb Irowb No 0.82 0.82 1.00 1 2.00% 0.4 0.4 0.1 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Irowc Irowc No 0.78 0.78 0.97 1 2.00% 0.5 0.5 0.2 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. PHASE I TIME OF CONCENTRATION COMPUTATIONS H. Feissner October 24, 2012 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 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. 10/24/201212:25 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Historic_Rational_Calcs\Tc_Phase 1 TOTAL (Site ONLY ) 0.710 0.16 0.03 0.00 0.130 Clayey | Flat <2% 0.39 0.54 0.54 0.67 43% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis PHASE I COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS October 24, 2012 Composite Runoff Coefficient with Adjustment 10/24/201212:25 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Historic_Rational_Calcs\Composite Runoff Coeff_Phase I (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) Ia Ia No 0.45 0.45 0.56 1 2.00% 1.0 1.0 0.8 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Ib Ib No 0.42 0.42 0.52 1 2.00% 1.0 1.0 0.9 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Ic Ic No 0.43 0.43 0.54 1 2.00% 1.0 1.0 0.8 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Irowb Irowb No 0.82 0.82 1.00 1 2.00% 0.4 0.4 0.1 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 Irowc Irowc No 0.78 0.78 0.97 1 2.00% 0.5 0.5 0.2 1 0.50% 1.41 0.0 1 0.50% 1.06 0.0 5 5 5 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. EXISTING CONDITIONS TIME OF CONCENTRATION COMPUTATIONS Gutter Flow Swale Flow Design Point Basin Overland Flow H. Feissner October 24, 2012 Time of Concentration (Equation RO-4) 3 1 1 . 87 1 . 1 * S Ti C Cf L * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. 10/24/201212:25 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Historic_Rational_Calcs\Tc_Exist TOTAL (Site ONLY ) 0.71 0.00 0.03 0.16 0.13 Clayey | Flat <2% 0.39 0.44 0.44 0.55 29% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis EXISTING CONDITIONS COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS October 24, 2012 Composite Runoff Coefficient with Adjustment 10/24/201212:25 PM D:\Projects\875-001\Drainage\Hydrology\875-001_Historic_Rational_Calcs\Composite Runoff Coeff_Exist