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HomeMy WebLinkAboutCARRIAGE HOUSE APARTMENTS - FDP - FDP130024 - REPORTS - DRAINAGE REPORTJuly 24, 2013 FINAL DRAINAGE REPORT Carriage House Apartments Fort Collins, Colorado Prepared for: Catamount Properties Ltd. 7302 Rozena Drive Longmont, Colorado 80503 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: 620-002 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. July 24, 2013 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Final Drainage Report for Carriage House Apartments Dear Staff: Northern Engineering is pleased to submit this Final Drainage Report for your review. Comments from the Carriage House Apartments, FDP130024, Round Number 1 letter dated July 2, 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 with the Fort Collins Stormwater Criteria Manual (FCSCM), and serves to document the stormwater impacts associated with the proposed Carriage House Apartments student housing project. We understand that review by the City of Fort Collins 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 Andrew Reese Project Manager Project Engineer Carriage House Apartments Final Drainage 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 – Detention Facilities APPENDIX C – Water Quality Design Computations APPENDIX D – Erosion Control Report MAP POCKET: DR1 – Drainage Exhibit Carriage House Apartments Final Drainage Report 1 I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map Figure 1 – Vicinity Map 2. The Carriage House Apartments project site is located in the Southeast quarter of Section 15, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. 3. The project site (refer to Figure 1) is bordered to the north by Springfield Drive (60' Right-of-Way); to the south by Bennett Road Bungalows, a detention pond and single- family residential; to the east by South Shields Street (proposed 100' Right-of-Way); and to the west by single-family residential. Carriage House Apartments Final Drainage Report 2 4. There are no major drainageways within or adjacent to the site. B. Description of Property 1. Carriage House Apartments is comprised of ±1.45 acres. 2. The site is currently occupied by three single-family residences and associated improvements. Figure 2 – Aerial Photograph 3. The existing groundcover consists of grasses and numerous mature trees. The existing on-site runoff generally drains west-to-east across flat grades (e.g., <2.00%) into Springfield Drive and South Shields Street. 4. A soils report (Project No. 12-1-5-517 | Date: December 12, 2012) was completed by Kumar and Associates, Inc. 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 borings encountered 4 to 6 inches of topsoil overlying nil to 5 feet of man- placed fill. The fill was composed of fine to coarse-grained sandy lean clay with occasional small gravels. The natural soil underlying the fill material consisted of fine-grained sandy lean clay with occasional zones of lean clay. In the deeper foundation borings, fine to coarse-grained clayey sand was encountered below the clayey soil and continued to the overburden soil/bedrock interface. The natural overburden clay soils were slightly moist to moist, and generally very stiff to hard. The natural clayey sands were slightly moist to wet below ground water, and medium dense to dense." Project Site Carriage House Apartments Final Drainage Report 3 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 Carriage House Apartments development will consist of a student residential complex with five multi-unit buildings. Other proposed improvements include: a new asphalt and permeable Modular Block Paver (MBP) parking area and landscaping. 7. The proposed land use is residential, multi-family dwellings. This is a permitted use in the Neighborhood Community - Buffer District (NCB). 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 08069C0978G (Effective date: May 2, 2012). Figure 4 – FEMA Firmette (Map Number 08069C0978G) Project Site Carriage House Apartments Final Drainage Report 4 II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. Carriage House Apartments is located within the City of Fort Collins Old Town major drainage basin. Specifically, the project site is situated in the southwest corner of this 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. B. Sub-Basin Description 1. The outfall for the project site is an existing curb inlet located at the southwest corner of South Shields Street and Springfield Drive. 2. The existing subject site can be defined by three (3) sub-basins (i.e., EX1 through EX3). Refer to the Existing Conditions Drainage & Erosion Control Exhibit. x Sub-basin EX1 delineates the proposed project site. Approximately twelve feet of Right-Of-Way (ROW) will be dedicated along South Shields Street with this project. This area is included in sub-basin EX1, which was used to approximate the 2- and 100-year existing runoff. x Sub-basins EX2 and EX3 delineate the existing Springfield Drive and South Shields Street right-of-way areas contiguous with the project site, respectively. The existing site runoff generally drains from west-to-east into Springfield Drive and South Shields Street. 3. The project site does not receive notable runoff from contiguous off-site properties. Carriage House Apartments Final Drainage Report 5 III. DRAINAGE DESIGN CRITERIA A. There are no optional provisions outside of the FCSCM proposed with Carriage House Apartments. B. The overall stormwater management strategy employed with Carriage House Apartments 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. Carriage House Apartments aims to reduce runoff peaks, volumes and pollutant loads from frequently occurring storm events (i.e., water quality (i.e., 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 grass-lined swales and Modular Block Pavers (MBPs). This LID practice reduces the overall amount of impervious area, while at the same time Minimizing Directly Connected Impervious Areas (MDCIA). 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 treatment will occur in the Modular Block Paver (MBP) section in sub-basin A. 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 Carriage House Apartments, the proposed project indirectly helps achieve stabilized drainageways nonetheless. Once again, site selection has a positive effect on stream stabilization. By redeveloping an existing project with existing stormwater infrastructure, combined with LID and MDCIA strategies, the likelihood of bed and bank erosion is 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 (ODP) drainage study or similar “development/project” drainage master plan. 2. The site plan is constrained on two sides by public streets, as well as by existing and fully developed sites along the remaining two sides. As previously mentioned, the drainage outfall for sub-basin A is an existing curb inlet at the southwest corner of Springfield Drive and South Shields Street. Total runoff, from the project site during Carriage House Apartments Final Drainage Report 6 the 2- and 100-year storm events, will decrease. During the 2-year storm event, runoff decreased negligibly from ±0.91 cfs to ±0.90 cfs; and during the 100-year storm event runoff decreased from ±4.01 cfs to ±2.01 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 Carriage House Apartments 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 Carriage House Apartments 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. Carriage House Apartments Final Drainage Report 7 IV. DRAINAGE FACILITY DESIGN A. General Concept 1. The main objective of the Carriage House Apartments drainage design is to maintain existing drainage patterns, while not adversely impacting adjacent properties. 2. No notable off-site runoff passes directly through the project 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. 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 Sub-basin A encompasses ±85 percent of the total site area. This sub-basin is comprised of roof area, landscaping and the on-site parking area. This parking area will be a mix of asphalt and Modular Block Pavers (MBPs). Detention will be provided within in the MBPs (WSEL100-year=5030.17). This basin will release at an adjusted 2- year rate of 0.57 cfs through an orifice plate. The orifice plate will be located on the west wall of the most downstream area inlet. Sub-Basin B Sub-basin B is a relatively small basin (0.02 acre) that is comprised of asphalt (i.e., project site drive entrance) and landscaping. The excess developed runoff will drain into Springfield Drive. The 100-year developed runoff (Q100=0.18 cfs), for sub-basin B, was subtracted from the total 2-year existing release rate (Q100=2.01cfs). Sub-Basin C Sub-basin C encompasses the northeast corner of the project site. It is comprised of roof area and landscaping. The excess developed runoff will drain into Springfield Drive and South Shields Street. The 100-year developed runoff (Q100=1.27 cfs), for sub-basin C, was subtracted from the total 2-year existing release rate (Q100=2.01cfs). A full-size copy of the Drainage Exhibit (sheet DR1) can be found in the Map Pocket at the end of this report. B. Specific Details 1. 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. 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) was established by calculating the 2-year peak runoff rate for these areas. The total of these two discharges (i.e., 1.45cfs and Carriage House Apartments Final Drainage Report 8 0.56cfs) establishes the overall maximum allowable release rate, 2.01 cfs, from the project site. The allowable release rate of 0.57 cfs utilized in the FAA procedure detention storage computations (Refer to Appendix B for these calculations) and was established by subtracting the undetained release of 1.44 cfs, from the overall maximum allowable release rate. This hybrid approach ensures that all increased impervious areas, not just those greater than 5,000 sq-ft, are over-detained down to the 2-year undeveloped (existing or pre-development) rate for the 100-year developed condition. 2. The FAA method was used to size the on-site pond for quantity detention. Calculations for this area, based on the characteristics of sub-basin A and adjusted release rate, indicate a detention volume of 8114 cu. ft. This includes 711 cu. ft. of Water Quality Capture Volume (WQCV). During water quality events the water quality capture volume will release over 12-hours. There is no-infiltration section because in-situ soils are USCS Type CL. 3. The storage volume available within the reservoir area (i.e., No. 57 and No. 2 open-graded aggregate) of the MBP section is ±8114 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. 4. Several Nyloplast 12" Standard Grates are located along the north perimeter of sub-basin A between the Springfield Drive right-of-way and the front of Building 1 through Building 4. These area inlets are designed to intercept local flows. To the maximum extent feasible, roof drains will direct flows south and into the on-site detention pond. These areas will be mostly comprised of landscaping and sidewalks. The inlet grates are connected to the outfall system and located upstream from the orifice plate; therefore, some localized ponding will occur at the two easternmost inlets during more severe storm events. These two areas will pond because the grate elevations (i.e., 5029.31 and 5029.16) are lower than the proposed 100-year water surface elevation (i.e., 5030.17). 5. The emergency spillway will be located on the southern side of the parking area. The spillway will be built into the curb, and will be defined by a 3” notch in the curb that will be 20’ long. The spillway has been sized to pass the entire 100-yr flow from Basin A. In the event that an emergency overflow occurs, the drainage will flow to the south, into the existing drainage facilities that were constructed with the Bennett Bungalows. The drainage will pass through the pond to the existing outlet structure, and then into the Bennet Road Right-of-Way. The weir crest elevation is set at 5030.84, which is approximately 8” above the 100-yr WSEL. The elevation is more than 1’ below the lowest finished floor elevation. Carriage House Apartments Final Drainage Report 9 V. CONCLUSIONS A. Compliance with Standards 1. The design elements comply without variation. 2. The drainage design proposed with Carriage House Apartments complies with the City of Fort Collins Master Drainage Plan for the Old Town Basin. 3. There are no regulatory floodplains associated with the Carriage House Apartments development. 4. The drainage plan and stormwater management measures proposed with the Carriage House Apartments 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. Carriage House Apartments will detain for the pervious area converted to impervious areas to release at the 2-year existing rate during the 100-year storm. 2. The proposed Carriage House Apartments development will not impact the Master Drainage Plan recommendations for the Old Town major drainage basin. Carriage House Apartments 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. Geotechnical Engineering Study and Pavement Thickness Design Proposed Student Apartment Development 1305 and 1319 South Shields Avenue Fort Collins, Colorado, December 13, 2012, Kumar and Associates, Inc. (Project No. 12-1-517). 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 Carriage House Apartments Project: Carriage House Apartments Project Site Area 62991 Calculations By: EX1 62991 Date: A 54170 B 1439 C 7382 Basin Area, sq. ft. Surface Description % Impervious Area, sq. ft. Notes EX1 0 Asphalt 100% 0 EX1 2864 Concrete (e.g., walks & parking) 90% 2578 EX1 1773 Gravel 40% 709 EX1 4893 Roofs 90% 4404 Impervious Area 7691 % Impervious 12% Total Impervious Area 7691 % Impervious 12% Basin Area, sq. ft. Surface Description % Impervious Area, sq. ft. Notes A 6941 Asphalt 100% 6941 A 9142 Pavers 22% 2011 A 5046 Concrete (e.g., walks & parking) 90% 4541 A 13725 Roofs 90% 12353 Impervious Area 25846 % Impervious 48% B 492 Asphalt 100% 492 B 59 Concrete (e.g., walks & parking) 90% 53 SUMMARY OF EXISTING AND PROPOSED IMPERVIOUS AREA A. Reese July 24, 2013 EXISTING CONDITION PROPOSED CONDITION Areas, sq. ft. B 59 Concrete (e.g., walks & parking) 90% 53 Impervious Area 545 % Impervious 38% C 566 Concrete (e.g., walks & parking) 90% 509 C 3106 Roofs 90% 2795 Impervious Area 3305 % Impervious 45% Impervious Area 26391 % Impervious 42% Area, sq. ft. Area, acre Total Impervious Area Increase 18701 0.429 SUMMARY 7/24/2013 12:38 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs.xlsx\Impervious Area Carriage House Apartment Homes CHARACTER OF SURFACE1: Runoff Coefficient Percentage Impervious Project: Carriage House Apartments Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Reese 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) Area of Pavers (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. Carriage House Apartments Overland Flow, Time of Concentration: Project: Carriage House Apartments 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 Carriage House Apartments Rational Method Equation: Project: Carriage House Apartments Calculations By: Date: Rainfall Intensity: n/a EX1Impervious 0.22 15.8 15.8 14.8 0.87 0.87 1.00 1.84 3.14 6.62 0.35 0.59 1.45 n/a EX1Pervious 1.23 15.8 15.8 14.8 0.25 0.25 0.31 1.84 3.14 6.62 0.56 0.96 2.54 EX1 EX1 1.45 15.83 15.83 14.82 0.34 0.34 0.43 1.84 3.14 6.62 0.91 1.56 4.10 EX2 EX2 0.34 5.00 5.00 5.00 0.82 0.82 1.00 2.85 4.87 9.95 0.80 1.36 3.39 EX3 EX3 0.17 5.00 5.00 5.00 0.80 0.80 1.00 2.85 4.87 9.95 0.39 0.66 1.69 Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) Allowable release rate: 1.45 + 0.56 = 2.01 cfs Notes EXISTING RUNOFF COMPUTATIONS A. Reese July 24, 2013 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 C100 Q C f C i A 7/24/2013 12:38 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs.xlsx\Runoff Carriage House Apartments CHARACTER OF SURFACE1: Runoff Coefficient Percentage Impervious Project: Carriage House Apartments Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Reese 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) Area of Pavers (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. A 1.25 0.16 0.12 0.00 0.32 0.21 Clayey | Average 2% to 7% 0.45 0.60 0.60 0.76 47% B 0.02 0.01 0.00 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.01 0.66 0.66 0.82 58% Carriage House Apartments Overland Flow, Time of Concentration: Project: Carriage House Apartments 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 Carriage House Apartments Rational Method Equation: Project: Carriage House Apartments Calculations By: Date: Rainfall Intensity: A A 1.25 5.00 5.00 5.00 0.60 0.60 0.76 2.85 4.87 9.95 2.16 3.69 9.43 Q100 = 0.57 cfs B B 0.02 5.00 5.00 5.00 0.66 0.66 0.82 2.85 4.87 9.95 0.04 0.07 0.18 Undetained release C C 0.17 5.00 5.00 5.00 0.59 0.59 0.74 2.85 4.87 9.95 0.29 0.50 1.27 Undetained release OS1 OS1 0.34 5.00 5.00 5.00 0.87 0.87 1.00 2.85 4.87 9.95 0.85 1.45 3.39 OS2 OS2 0.17 5.00 5.00 5.00 0.82 0.82 1.00 2.85 4.87 9.95 0.40 0.68 1.69 Flow, Q100 (cfs) C2 C10 C100 Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) Notes RUNOFF COMPUTATIONS A. Reese July 24, 2013 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) Q C f C i A 7/24/2013 12:37 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs.xlsx\Runoff APPENDIX B DETENTION FACILITIES Carriage House Apartment Homes 620-002 Fort Collins, Colorado Detention Pond Calculation | FAA Method Project Number: Project Location: Fort Collins, Colorado A. Reese Date: July 24, 2013 Pond No.: Pond A Project Location: Calculations By: Pond No.: Pond A A Input Variables Results Design Point A 100-yr 0.74 WQCV 711 ft 3 Design Point Design Storm Required Detention Volume Developed "C" = 0.74 WQCV 711 ft 3 Area (A)= 1.25 acres Quantity Detention 8114 ft 3 Max Release Rate = 0.57 cfs Total Volume 8114 ft 3 Developed "C" = Max Release Rate = 0.57 cfs Total Volume 8114 ft Total Volume 0.186 ac-ft Time Time Ft.Collins 100-yr Intensity Q100 Inflow (Runoff) Volume Outflow (Release) Volume Storage Detention Intensity Volume Volume (Release) Volume Volume (mins) (secs) (in/hr) (cfs) (ft 3 ) (ft 3 ) (ft 3 ) 5 300 9.95 9.1 2742 171 2571 10 600 7.72 7.1 4256 342 3914 15 900 6.52 6.0 5391 513 4878 20 1200 5.60 5.1 6174 684 5490 25 1500 4.98 4.6 6863 855 6008 30 1800 4.52 4.2 7475 1026 6449 35 2100 4.08 3.7 7872 1197 6675 40 2400 3.74 3.4 8247 1368 6879 45 2700 3.46 3.2 8583 1539 7044 50 3000 3.23 3.0 8903 1710 7193 Carriage House Apartments 620-002 Stage - Storage Calculation Project Number: 620-002 Fort Collins, Colorado A. Reese Date: July 24, 2013 Project Number: Project Location: Calculations By: A. Reese Date: July 24, 2013 Pond No.: Pond A Calculations By: Required Volume Water Surface Elevation (WSE) A WQCV Void Ratio 40% Design Point Design Storm Required Volume Water Surface Elevation (WSE) WQCV Void Ratio 40% 722 ft3 Required Material Volume 20301.00 Design Storm Require Volume= 722 ft Volume 20301.00 Design Storm 100-yr Required Volume= 8114 ft3 WSEL 5030.17 ft. Require Volume= Required Volume= 8114 ft3 WSEL 5030.17 ft. Contour Contour Incremental Incremental Area Cumulative Volume Incremental Volume Contour Cummulative Elevation (Y- values) Contour Area Incremental Depth Incremental Area Avg. End Cumulative Volume Avg. End Incremental Volume Conic Cummulative Volume Conic (X- values) values) ft2 ft. ft3 ft3 ft3 ft3 5,027.80 1,856.25 n/a n/a 0 N/A 0 5,028.00 6,192.23 0.20 804.85 805 763 763 5,028.20 8,756.80 0.20 1494.90 2300 1488 2250 5,028.40 9,033.52 0.20 1779.03 4079 1779 4029 5,028.60 9,041.24 0.20 1807.48 5886 1807 5837 5,028.80 9,048.95 0.20 1809.02 7695 1809 7646 5,029.00 9,056.68 0.20 1810.56 9506 1811 9456 5,029.20 9,064.40 0.20 1812.11 11318 1812 11268 5,029.40 9,072.12 0.20 1813.65 13132 1814 13082 5,029.60 9,079.85 0.20 1815.20 14947 1815 14897 5,029.80 9,087.58 0.20 1816.74 16764 1817 16714 5,030.00 9,095.31 0.20 1818.29 18582 1818 18532 5,030.20 9,103.04 0.20 1819.83 20402 1820 20352 5,030.40 9,110.75 0.20 1821.38 22223 1821 22173 ORIFICE RATING CURVE Area Inlet 2 100-yr Orifice PROJECT: Carriage House DATE: July 24, 2013 BY: A. Reese ORIFICE RATING Orifice Dia (in) 3.50 Orifice Area (sf) 0.0668 Orifice invert (ft) 5026.52 Orifice Coefficient 0.65 Outlet Stage release (FT) (CFS) 5026.52 0.00 5026.62 0.00 5026.72 0.08 5026.82 0.14 5026.92 0.18 5027.02 0.21 5027.12 0.23 5027.22 0.26 5027.32 0.28 5027.42 0.30 5027.52 0.32 5027.62 0.34 5027.72 0.36 5027.82 0.37 5027.92 0.39 5028.02 0.41 5028.12 0.42 5028.22 0.43 5028.32 0.45 5028.42 0.46 5028.52 0.47 5028.62 0.49 5028.72 0.50 5028.82 0.51 5028.92 0.52 5029.02 0.53 5029.12 0.55 5029.22 0.56 5029.32 0.57 APPENDIX C WATER QUALITY DESIGN COMPUTATIONS Project Title Date: Project Number Calcs By: Client Pond Designation 0.8 WQCV = Watershed inches of Runoff (inches) 47.00% a = Runoff Volume Reduction (constant) i = Total imperviousness Ratio (i = Iwq/100) 0.159 in Carriage House July 24, 2013 620-002 A. Reese Catamount Properties Parking Lot Drain Time a = i = WQCV = 0.159 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 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 = 1.03 ac V = 0.0163 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 0.1 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) 40 hr * * 1 . 2 APPENDIX D EROSION CONTROL REPORT 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 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, 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. MAP POCKET DR1 –DRAINAGE EXHIBIT 12 V WQCV A ¸ ¹ · ¨ © § 5,031.00 5,030.50 5,031.00 5,030.50 5,030.00 Contour Elevation 5,029.50 Contour Elevation 5,029.00 Contour Elevation 5,028.50 Contour Elevation 5,028.00 5,028.50 5,028.00 5,027.50 0 5000 10000 15000 20000 25000 Cummulative Volume, cu. ft. 7/24/20131:26 PM D:\Projects\620-002\Drainage\Detention\620-002__Detention Pond.xlsm\Stage_Storage_MBP 55 3300 3.03 2.8 9187 1881 7306 60 3600 2.86 2.6 9459 2052 7407 65 3900 2.72 2.5 9746 2223 7523 70 4200 2.59 2.4 9994 2394 7600 75 4500 2.48 2.3 10253 2565 7688 80 4800 2.38 2.2 10496 2736 7760 85 5100 2.29 2.1 10730 2907 7823 90 5400 2.21 2.0 10964 3078 7886 95 5700 2.13 2.0 11155 3249 7906 100 6000 2.06 1.9 11356 3420 7936 105 6300 2.00 1.8 11576 3591 7985 110 6600 1.94 1.8 11764 3762 8002 115 6900 1.89 1.7 11981 3933 8048 120 7200 1.84 1.7 12172 4104 8068 125 7500 1.79 1.6 12334 4275 8059 130 7800 1.75 1.6 12541 4446 8095 135 8100 1.71 1.6 12726 4617 8109 140 8400 1.67 1.5 12888 4788 8100 145 8700 1.63 1.5 13029 4959 8070 150 9000 1.60 1.5 13230 5130 8100 155 9300 1.57 1.4 13415 5301 8114 160 9600 1.54 1.4 13583 5472 8111 165 9900 1.51 1.4 13734 5643 8091 170 10200 1.48 1.4 13869 5814 8055 175 10500 1.45 1.3 13988 5985 8003 180 10800 1.42 1.3 14090 6156 7934 185 11100 1.40 1.3 14277 6327 7950 190 11400 1.38 1.3 14454 6498 7956 195 11700 1.36 1.2 14619 6669 7950 200 12000 1.34 1.2 14774 6840 7934 205 12300 1.32 1.2 14917 7011 7906 210 12600 1.30 1.2 15049 7182 7867 215 12900 1.28 1.2 15170 7353 7817 220 13200 1.26 1.2 15281 7524 7757 225 13500 1.24 1.1 15380 7695 7685 230 13800 1.22 1.1 15468 7866 7602 235 14100 1.21 1.1 15675 8037 7638 240 14400 1.20 1.1 15876 8208 7668 7/24/2013 1:26 PM D:\Projects\620-002\Drainage\Detention\620-002__Detention Pond.xlsm\FAA_CoFC idf_A (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) A A No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00 B B No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00 C C No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00 OS1 OS1 No 0.95 0.95 1.00 20 3.10% 0.9 0.9 0.6 429 0.90% 1.90 3.8 0 0.00% N/A N/A 5.00 5.00 5.00 OS2 OS2 No 0.95 0.95 1.00 34 1.90% 1.3 1.3 0.9 144 1.00% 2.00 1.2 0 0.00% N/A N/A 5.00 5.00 5.00 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. TIME OF CONCENTRATION COMPUTATIONS Gutter Flow Swale Flow Design Point Basin Overland Flow A. Reese July 24, 2013 Time of Concentration (Equation RO-4) 3 1 1 . 87 1 . 1 * S Ti C Cf L  7/24/2013 12:37 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs.xlsx\Tc C 0.17 0.00 0.01 0.00 0.07 0.00 Clayey | Average 2% to 7% 0.09 0.59 0.59 0.74 44% OS1 0.34 0.21 0.09 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.04 0.87 0.87 1.00 86% OS2 0.17 0.09 0.05 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.03 0.82 0.82 1.00 79% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS July 24, 2013 Composite Runoff Coefficient with Adjustment 7/24/2013 12:37 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Proposed_Rational_Calcs.xlsx\Composite Runoff Coefficient (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) EX1 EX1 No 0.25 0.25 0.31 142 2.60% 13.8 13.8 12.8 282 1.30% 2.28 2.1 0 0.00% N/A N/A 15.83 15.83 14.82 EX2 EX2 No 0.95 0.95 1.00 20 3.10% 0.9 0.9 0.6 429 0.90% 1.90 3.8 0 0.00% N/A N/A 5.00 5.00 5.00 EX3 EX3 No 0.95 0.95 1.00 34 2.80% 1.2 1.2 0.8 144 0.80% 1.79 1.3 0 0.00% N/A N/A 5.00 5.00 5.00 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. EXISTING TIME OF CONCENTRATION COMPUTATIONS Gutter Flow Swale Flow Design Point Basin Overland Flow A. Reese July 24, 2013 Time of Concentration (Equation RO-4) 3 1 1 . 87 1 . 1 * S Ti C Cf L  7/24/2013 12:38 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs.xlsx\Tc EX1Impervious 0.22 0.00 0.07 0.04 0.11 0.000 Clayey | Average 2% to 7% 0.00 0.87 0.87 1.00 81% EX1Pervious 1.23 0.00 0.00 0.00 0.00 0.000 Clayey | Average 2% to 7% 1.23 0.25 0.25 0.31 0% EX1 1.45 0.00 0.07 0.04 0.11 0.000 Clayey | Average 2% to 7% 1.23 0.34 0.34 0.43 12% EX2 0.34 0.22 0.06 0.00 0.00 0.000 Clayey | Average 2% to 7% 0.06 0.82 0.82 1.00 80% EX3 0.17 0.09 0.04 0.00 0.00 0.000 Clayey | Average 2% to 7% 0.04 0.80 0.80 1.00 76% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis EXISTING COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS July 24, 2013 Composite Runoff Coefficient with Adjustment 7/24/2013 12:38 PM D:\Projects\620-002\Drainage\Hydrology\620-002_Historic_Rational_Calcs.xlsx\Composite Runoff Coefficient