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HomeMy WebLinkAboutOLD TOWN FLATS - PDP - PDP130022 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTJuly 31, 2013 PRELIMINARY DRAINAGE REPORT OLD TOWN FLATS Fort Collins, Colorado Prepared for: Brinkman Development, LLC 3003 East Harmony Road, Suite 300 Fort Collins, Colorado 80528 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: 379-039 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 31, 2013 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Preliminary Drainage Report for Old Town Flats Dear Staff: Northern Engineering is pleased to submit this Preliminary Drainage Report for your review. Comments from the Block 23 – Preliminary Design Review, PDR130002, Round Number 1 letter dated March 15, 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 Old Town Flats 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 Old Town Flats Preliminary Drainage Report TABLE OF CONTENTS I. GENERAL LOCATION AND DESCRIPTION ......................................................... 1 II. DRAINAGE BASINS AND SUB-BASINS ............................................................. 5 III. DRAINAGE DESIGN CRITERIA ......................................................................... 6 IV. DRAINAGE FACILITY DESIGN .......................................................................... 8 V. CONCLUSIONS............................................................................................. 10 References ............................................................................................................. 11 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 EX1 – Existing Drainage Exhibit Old Town Flats Preliminary Drainage Report 1 I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map Figure 1 – Vicinity Map 2. The Old Town Flats 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. The project site (refer to Figure 1) is bordered to the north by vacant property; to the south by Maple Street (100’ ROW); to the east by an existing public alley (20' Right- of-Way); and to the west by Mason Street (100’ ROW). 4. There are no major drainageways within or adjacent to the site. Old Town Flats Preliminary Drainage Report 2 B. Description of Property 1. Old Town Flats is comprised of ±0.87 acres. 2. The site is currently unoccupied, vacant land. Figure 2 – Aerial Photograph 3. The existing groundcover consists of grasses and gravel. The existing on-site runoff generally drains from the southwest-to-northeast east across flat grades (e.g., <2.00%) into the existing alley. From there it is directed to an existing inlet via a concrete pan, at which point the drainage continues through an existing storm system down College Avenue to Willow Street, and on to the Cache La Poudre River. The existing concrete pan and area inlet are encompassed by an existing 10’ drainage easement (Rec. #2004-0002334) on Lot 10, Block 23. 4. A soils report (Project No. 1132055 | Date: July 30, 2013) was completed by Earth Engineering Consultants, LLC. The report contains the results of a complete geotechnical subsurface exploration as well as pertinent geotechnical Project Site Old Town Flats Preliminary Drainage Report 3 recommendations. According to the summary of findings presented in the aforementioned report, "…a surficial layer of gravel, asphaltic concrete, topsoil/landscape material or concrete was observed through the site at the boring location. An approximate 1-1/2 to 4-foot layout of fill material was encountered immediately beneath the surface materials. Native cohesive to slightly cohesive sandy lean clay and/or clayey sand subsoils were encountered at approximate depths of 2 ½ to 4 feet below site grades.” 5. There are no major drainageways within or adjacent to the project site. 6. The proposed Old Town Flats development will consist of a single residential building. Other proposed improvements include: a new concrete and permeable Modular Block Paver (MBP) parking area and landscaping. 7. The proposed land use is residential, multi-family dwelling. This is a permitted use in the Downtown District (D). Old Town Flats Preliminary Drainage 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) Project Site Old Town Flats Preliminary Drainage Report 5 II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. Old Town Flats is located within the City of Fort Collins Old Town major drainage basin. Specifically, the project site is situated in the north-central portion 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 area inlet located just west of College Avenue between Cherry Street and Maple Street. The existing area inlet is encompassed by an existing 10’ drainage easement (Rec. #2004-0002334) on Lot 10, Block 23. 2. The existing subject site can be defined with one (1) sub-basin. Refer to the Existing Drainage Exhibit for additional information. x Sub-basin EX1 delineates the proposed project site, which was used to approximate the 2- and 100-year existing runoff. The existing site runoff generally drains from southwest-to-northeast into the existing alley along the eastern boundary of the site. 3. The project site does not receive notable runoff from contiguous off-site properties. Old Town Flats Preliminary Drainage Report 6 III. DRAINAGE DESIGN CRITERIA A. There are no optional provisions outside of the FCSCM proposed with Old Town Flats. B. The overall stormwater management strategy employed with Old Town Flats 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. Old Town Flats 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 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 Old Town Flats, the proposed project indirectly helps achieve stabilized drainageways nonetheless. Once again, site selection has a positive effect on stream stabilization. By developing an infill site 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 undeveloped and developed sites along the remaining two sides. As previously mentioned, the drainage outfall for sub-basin A is an existing area inlet located just west of College Avenue between Cherry Street and Maple Street on Lot 10. 3. Peak runoff from the project site during the 2-year event will remain unchanged and will decrease during the 100-year storm event. During the 2-year storm event, runoff Old Town Flats Preliminary Drainage Report 7 will remain at ±0.82 cfs; and during the 100-year storm event runoff will decrease from ±3.91 cfs to ±0.54 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 Old Town Flats 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 Old Town Flats 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. H. Conformance with Low Impact Development (LID) 1. 15,941 sf of paving is proposed with this project, and of the total, 4912 sf is proposed to be Modular Block Pavers (MBPs). This means that ± 31% of the paved areas in the project are pervious, exceeding the minimum requirement of 25%. 2. The total project area is 38,050 sf. Of that area, 34,473 sf will be treated by LID techniques, primarily Modular Block Pavers (MBPs). This means that ± 91% of the site will be treated by LID-type technology, exceeding the minimum requirement of 50%. Old Town Flats Preliminary Drainage Report 8 IV. DRAINAGE FACILITY DESIGN A. General Concept 1. The main objective of the Old Town Flats 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 four (4) drainage sub-basins, designated as sub- basins A, B, C and D. The drainage patterns anticipated for each basin are further described below. Sub-Basin A Sub-basin A encompasses ±90 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 concrete and Modular Block Pavers (MBPs). Detention will be provided within in the MBPs (WSEL100-year=4976.0±). This basin will release at an adjusted 2-year rate of 0.54 cfs through an orifice plate. An orifice plate located on the east wall of the proposed area inlet will be used to control the flow rate. Sub-Basin B Sub-basin B is a relatively small basin (0.02 acre) that is comprised of landscaping. The developed runoff will follow the historic drainage path north and then east at rates significantly less than the existing condition. The 100-year developed runoff (Q100=0.04 cfs), for sub-basin B, was subtracted from the total 2-year existing release rate (Q100=0.82 cfs). Sub-Basin C Sub-basin C encompasses the western edge of the project site along the Mason Street frontage. It is comprised of public sidewalks and landscaping. The developed runoff will drain into Mason Street and flow north. The 100-year developed runoff (Q100=0.17 cfs), for sub-basin C, was subtracted from the total 2-year existing release rate (Q100=0.82 cfs). Sub-Basin D Sub-basin D encompasses the southern edge of the project site along the Maple Street frontage. It is comprised of public sidewalks and landscaping. The developed runoff will drain into Maple Street and flow east. The 100-year developed runoff (Q100=0.12 cfs), for sub-basin D, was subtracted from the total 2-year existing release rate (Q100=0.82 cfs). A full-size copy of the Drainage Exhibit (sheet C500) can be found in the Map Pocket at the end of this report. B. Specific Details Old Town Flats Preliminary Drainage Report 9 1. The release rate for the undeveloped land (pre-development) was established by calculating the 2-year peak runoff rate for the entire project area. The total establishes the overall maximum allowable release rate, 0.82 cfs, from the project site. The allowable release rate of 0.49 cfs utilized in the FAA procedure detention storage computations (Refer to Appendix B for these calculations) and was established by subtracting the total undetained release of 0.33 cfs (0.04 cfs +0.17 cfs+0.12 cfs) from the overall maximum allowable release rate. 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 6978 cu. ft. This includes 855 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 accounted for with this design. 3. The storage volume available within the reservoir area (i.e., No. 57 and No. 2 open-graded aggregate) of the MBP section is ±7682 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. An area inlet is located at the downstream end of the landscape island. This inlet will have an orifice installed on the east wall that will limit the release from the site to the maximum allowable release rate (0.49 cfs). 5. All roof drain downspouts will discharge into landscaped areas or the MBP section. 6. The emergency spill path will be from the landscaping island into the existing alley, where flows will proceed along the historic path north along the alley and east to the existing area inlet. Old Town Flats Preliminary Drainage Report 10 V. CONCLUSIONS A. Compliance with Standards 1. The design elements comply without variation, and meet all LID requirements. 2. The drainage design proposed with Old Town Flats complies with the City of Fort Collins Master Drainage Plan for the Old Town Basin. 3. There are no regulatory floodplains associated with the Old Town Flats development. 4. The drainage plan and stormwater management measures proposed with the Old Town Flats 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. Old Town Flats 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 Old Town Flats development will not impact the Master Drainage Plan recommendations for the Old Town major drainage basin. Old Town Flats Preliminary Drainage Report 11 References 1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities, November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services. 2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No. 174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code. 3. Subsurface Exploration Report Block 23 – Phase I, July 30, 2013, Earth Engineering Consultants, LLC (Project No. 1132055). 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 CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: Old Town Flats 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 Concrete 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 Concrete 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. EX1 38,050 0.87 0.00 0.00 0.00 0.87 0.00 0.00 0.50 0.50 0.63 40.0 EXISTING COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I. 10-year Cf = 1.00 July 31, 2013 D:\Projects\379-039\Drainage\Hydrology\379-039_Rational Calcs_Existing.xlsx\C-Values Overland Flow, Time of Concentration: Project: Old Town Flats Calculations By: Date: Gutter/Swale Flow, Time of Concentration: Tt = L / 60V T = T + T (Equation RO-2) EXISTING TIME OF CONCENTRATION COMPUTATIONS A. Reese July 31, 2013 3 1 1 . 87 1 . 1 * S Ti C Cf L  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) Rational Method Equation: Project: Old Town Flats Calculations By: Date: From Section 3.2.1 of the CFCSDDC EXISTING RUNOFF COMPUTATIONS A. Reese July 31, 2013 Q C f C i A From Section 3.2.1 of the CFCSDDC Rainfall Intensity: EX1 EX1 0.87 15.4 15.4 12.2 0.50 0.50 0.63 1.87 3.19 7.16 0.82 1.39 3.91 Area, A (acres) Intensity, i2 (in/hr) 100-yr Tc (min) 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) Intensity, i10 (in/hr) Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1 C10 D:\Projects\379-039\Drainage\Hydrology\379-039_Rational Calcs_Existing.xlsx\Direct-Runoff CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: Old Town Flats 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 Concrete 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 Concrete 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 34,473 0.79 0.00 0.24 0.41 0.00 0.11 0.03 0.84 0.84 1.00 77.0 B 943 0.02 0.00 0.00 0.00 0.00 0.00 0.02 0.15 0.15 0.19 0.0 C 1,742 0.04 0.00 0.01 0.00 0.00 0.00 0.03 0.34 0.34 0.42 21.1 D 892 0.02 0.00 0.01 0.00 0.00 0.00 0.01 0.47 0.47 0.59 36.1 TOTAL ONSITE 38,050 0.87 0.00 0.25 0.41 0.00 0.11 0.09 0.79 0.79 0.99 71.6 DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Overland Flow, Time of Concentration: Project: Old Town Flats Calculations By: Date: Gutter/Swale Flow, Time of Concentration: Tt = L / 60V T = T + T (Equation RO-2) DEVELOPED TIME OF CONCENTRATION COMPUTATIONS A. Reese July 31, 2013 3 1 1 . 87 1 . 1 * S Ti C Cf L  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) Rational Method Equation: Project: Old Town Flats Calculations By: Date: From Section 3.2.1 of the CFCSDDC DEVELOPED RUNOFF COMPUTATIONS A. Reese July 31, 2013 Q C f C i A Rainfall Intensity: A A 0.79 5.1 5.1 5.0 0.84 0.84 1.00 2.85 4.87 9.95 1.90 3.25 7.87 B B 0.02 5.0 5.0 5.0 0.15 0.15 0.19 2.85 4.87 9.95 0.01 0.02 0.04 C C 0.04 5.0 5.0 5.0 0.34 0.34 0.42 2.85 4.87 9.95 0.04 0.07 0.17 D D 0.02 5.0 5.0 5.0 0.47 0.47 0.59 2.85 4.87 9.95 0.03 0.05 0.12 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) 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) D:\Projects\379-039\Drainage\Hydrology\379-039_Rational-Calcs_Proposed.xlsx\Direct-Runoff APPENDIX B DETENTION FACILITIES Old Town Flats Old Town Flats Fort Collins, Colorado Detention Pond Calculation | FAA Method Project: Project Location: Fort Collins, Colorado A. Reese Date: July 31, 2013 Pond No.: Paver Parking Project Location: Calculations By: Pond No.: Paver Parking A Input Variables Results Design Point A 100-yr 1.00 WQCV 855 ft 3 Design Point Design Storm Required Detention Volume Developed "C" = 1.00 WQCV 855 ft 3 Area (A)= 0.79 acres Quantity Detention 6978 ft 3 Max Release Rate = 0.49 cfs Total Volume 6978 ft 3 Developed "C" = Max Release Rate = 0.49 cfs Total Volume 6978 ft Total Volume 0.160 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 7.9 2358 147 2211 10 600 7.72 6.1 3659 294 3365 15 900 6.52 5.2 4636 441 4195 20 1200 5.60 4.4 5309 588 4721 25 1500 4.98 3.9 5901 735 5166 30 1800 4.52 3.6 6427 882 5545 35 2100 4.08 3.2 6769 1029 5740 40 2400 3.74 3.0 7091 1176 5915 45 2700 3.46 2.7 7380 1323 6057 50 3000 3.23 2.6 7655 1470 6185 Carriage House Apartments Old Town Flats Stage - Storage Calculation Project Number: Old Town Flats Fort Collins, Colorado A. Reese Date: July 31, 2013 Project Number: Project Location: Calculations By: A. Reese Date: July 31, 2013 Pond No.: Paver Parking 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% 855 ft3 Required Material Volume 17444 Design Storm Require Volume= 855 ft Volume 17444 Design Storm 100-yr Required Volume= 6978 ft3 WSEL 4975.80 ft. Require Volume= Required Volume= 6978 ft3 WSEL 4975.80 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 4,972.20 2 N/A N/A 0 N/A 0 4,972.40 725.91 0.2 72.79 72.79 51.07 51.07 4,972.60 2,264.76 0.2 299.07 371.86 284.86 335.92 4,972.80 3,545.05 0.2 580.98 952.84 576.22 912.15 4,973.00 4,704.70 0.2 824.97 1777.81 822.24 1734.39 4,973.20 5,469.86 0.2 1017.46 2795.27 1016.5 2750.88 4,973.40 5,826.77 0.2 1129.66 3924.93 1129.48 3880.36 4,973.60 5,859.75 0.2 1168.65 5093.58 1168.65 5049.01 4,973.80 5,863.21 0.2 1172.3 6265.88 1172.3 6221.31 4,974.00 5,866.68 0.2 1172.99 7438.87 1172.99 7394.3 4,974.20 5,870.15 0.2 1173.68 8612.55 1173.68 8567.98 4,974.40 5,873.62 0.2 1174.38 9786.93 1174.38 9742.35 4,974.60 5,877.09 0.2 1175.07 10962 1175.07 10917.42 4,974.80 5,880.56 0.2 1175.76 12137.76 1175.76 12093.19 APPENDIX C WATER QUALITY DESIGN COMPUTATIONS Project Title Date: Project Number Calcs By: Client Pond Designation 0.8 WQCV = Watershed inches of Runoff (inches) 77.00% a = Runoff Volume Reduction (constant) i = Total imperviousness Ratio (i = Iwq/100) 0.248 in Old Town Flats July 31, 2013 379-039 A. Reese Brinkman Partners Parking Lot Drain Time a = i = WQCV = 0.248 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 WQCV (watershed inches) Water Quality Capture Volume 6 hr 12 hr 24 hr 40 hr WQCV a 0.91 i 3  1 . 19 i 2  0 . 78 i WQCV a 0.91 i 3  1 . 19 i 2  0 . 78 i 12 hr A = 0.79 ac V = 0.0196 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 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 and/or wattles 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 C001 of the Utility Plans. The Final Utility Plans will also contain a full-size Erosion Control Plan as well as a separate sheet dedicated to Erosion Control Details. In addition to this report and the referenced plan sheets, the Contractor shall be aware of, and adhere to, the applicable requirements outlined in any existing Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior to issuance of the Development Construction Permit. Also, the Site Contractor for this project may 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 * * 1 . 2 12 V WQCV A ¸ ¹ · ¨ © § 4,975.00 5,884.03 0.2 1176.46 13314.22 1176.46 13269.65 4,975.20 5,887.50 0.2 1177.15 14491.37 1177.15 14446.8 4,975.40 5,890.98 0.2 1177.85 15669.22 1177.85 15624.65 4,975.60 5,894.45 0.2 1178.54 16847.76 1178.54 16803.19 4,975.80 5,897.93 0.2 1179.24 18027 1179.24 17982.43 4,976.00 5,901.40 0.2 1179.93 19206.93 1179.93 19162.36 4,976.00 4,975.50 4,976.00 4,975.00 4,975.50 4,974.50 4,975.00 Contour Elevation 4,974.00 Contour Elevation 4,973.50 Contour Elevation 4,973.00 Contour Elevation 4,972.50 4,972.00 0 2000 4000 6000 8000 10000 12000 14000 Cummulative Volume, cu. ft. 7/31/201310:15 AM D:\Projects\379-039\Drainage\Detention\379-039__Detention Pond.xlsm\Stage_Storage_MBP 55 3300 3.03 2.4 7899 1617 6282 60 3600 2.86 2.3 8134 1764 6370 65 3900 2.72 2.1 8380 1911 6469 70 4200 2.59 2.0 8594 2058 6536 75 4500 2.48 2.0 8816 2205 6611 80 4800 2.38 1.9 9025 2352 6673 85 5100 2.29 1.8 9226 2499 6727 90 5400 2.21 1.7 9428 2646 6782 95 5700 2.13 1.7 9591 2793 6798 100 6000 2.06 1.6 9764 2940 6824 105 6300 2.00 1.6 9954 3087 6867 110 6600 1.94 1.5 10115 3234 6881 115 6900 1.89 1.5 10302 3381 6921 120 7200 1.84 1.5 10466 3528 6938 125 7500 1.79 1.4 10606 3675 6931 130 7800 1.75 1.4 10784 3822 6962 135 8100 1.71 1.4 10942 3969 6973 140 8400 1.67 1.3 11082 4116 6966 145 8700 1.63 1.3 11203 4263 6940 150 9000 1.60 1.3 11376 4410 6966 155 9300 1.57 1.2 11535 4557 6978 160 9600 1.54 1.2 11679 4704 6975 165 9900 1.51 1.2 11810 4851 6959 170 10200 1.48 1.2 11926 4998 6928 175 10500 1.45 1.1 12028 5145 6883 180 10800 1.42 1.1 12115 5292 6823 185 11100 1.40 1.1 12277 5439 6838 190 11400 1.38 1.1 12428 5586 6842 195 11700 1.36 1.1 12570 5733 6837 200 12000 1.34 1.1 12703 5880 6823 205 12300 1.32 1.0 12826 6027 6799 210 12600 1.30 1.0 12940 6174 6766 215 12900 1.28 1.0 13044 6321 6723 220 13200 1.26 1.0 13139 6468 6671 225 13500 1.24 1.0 13225 6615 6610 230 13800 1.22 1.0 13300 6762 6538 235 14100 1.21 1.0 13478 6909 6569 240 14400 1.20 0.9 13651 7056 6595 7/31/2013 9:59 AM D:\Projects\379-039\Drainage\Detention\379-039__Detention Pond.xlsm\FAA_CoFC idf_A Slope, S (%) Velocity, V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) A A No 0.95 0.95 1.00 79 25.0 0.9 0.9 0.6 255 0.5 1.41 3.0 113 1.0 1.50 1.3 5.1 5.1 5.0 Gutter Flow Swale Flow Design Point Basin Overland Flow Time of Concentration (Equation RO-4) D:\Projects\379-039\Drainage\Hydrology\379-039_Rational-Calcs_Proposed.xlsx\Tc-2-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 31, 2013 D:\Projects\379-039\Drainage\Hydrology\379-039_Rational-Calcs_Proposed.xlsx\C-Values Slope, S (%) Velocity, V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) EX1 EX1 No 0.50 0.50 0.63 287 1.9 15.4 15.4 12.2 0 0.5 1.41 0.0 0 1.0 1.50 0.0 15.4 15.4 12.2 Gutter Flow Swale Flow Design Point Basin Overland Flow Time of Concentration (Equation RO-4) D:\Projects\379-039\Drainage\Hydrology\379-039_Rational Calcs_Existing.xlsx\Tc-2-yr_&_100-yr