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WILLOW STREET RESIDENCES - FDP - FDP180027 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT
FINAL DRAINAGE REPORT Willow Street Residences Fort Collins, Colorado October 31, 2018 Prepared for: CA Ventures 130 East Randolph St., Suite 2100 Chicago, IL 60601 Prepared by: 301 North Howes Street, Suite 100 Fort Collins, Colorado 80521 Phone: 970.221.4158 Fax: 970.221.4159 www.northernengineering.com Project Number: 1287-005 This Drainage Report is consciously provided as a PDF. Please consider the environment before printing this document in its entirety. When a hard copy is absolutely necessary, we recommend double-sided printing. October 31, 2018 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Final Drainage Report for WILLOW STREET RESIDENCES Dear Staff: Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for your review. This report accompanies the Project Development Plan submittal for the proposed Willow Street Residences development. 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 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. Aaron Cvar, PhD, PE Blaine Mathisen, EI Senior Project Engineer Project Engineer Willow Street Residences Final Drainage Report TABLE OF CONTENTS I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1 A. Location ............................................................................................................................................. 1 B. Description of Property ..................................................................................................................... 2 C. Floodplain.......................................................................................................................................... 3 II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 4 A. Major Basin Description .................................................................................................................... 4 B. Sub-Basin Description ....................................................................................................................... 5 III. DRAINAGE DESIGN CRITERIA ................................................................................... 5 C. Regulations........................................................................................................................................ 5 D. Four Step Process .............................................................................................................................. 5 E. Development Criteria Reference and Constraints ............................................................................ 6 F. Hydrological Criteria ......................................................................................................................... 6 G. Hydraulic Criteria .............................................................................................................................. 6 H. Modifications of Criteria ................................................................................................................... 7 IV. DRAINAGE FACILITY DESIGN .................................................................................... 7 I. General Concept ............................................................................................................................... 7 J. Specific Details .................................................................................................................................. 7 V. CONCLUSIONS ........................................................................................................ 8 K. Compliance with Standards .............................................................................................................. 8 L. Drainage Concept .............................................................................................................................. 8 APPENDICES: APPENDIX A – Hydrologic Computations APPENDIX B – Hydraulic Computations B.1 – Storm Sewers B.2 – Inlets B.3 – Detention Facilities APPENDIX C – Water Quality Design Computations APPENDIX D – Erosion Control Report Willow Street Residences Final Drainage Report LIST OF TABLES AND FIGURES: Figure 1 – Aerial Photograph ................................................................................................ 2 Figure 2– Proposed Site Plan ................................................................................................ 3 Figure 3 –Area Floodplain Mapping ....................................................................................... 4 MAP POCKET: Figure 1 - Existing Drainage Exhibit Figure 2 – C-500 - Drainage Exhibit Willow Street Residences Final Drainage Report 1 I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map 2. The project site is located in the northwest quarter of Section 12, 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 is located just east of the intersection of College Ave. and Willow Street. 4. The project site lies within the Poudre River Basin. Detention will be provided with an allowable release rate based on historic pervious and impervious areas. Historic developed area will be granfathered and will be allowed to release at a historic 100- year rate. Historic undeveloped area will be allowed to release at a historic 2-year rate. Please see Appendix A for computation of allowable release rate. 5. Water quality treatment for the project site will be provided in the form of LID treatment within a proposed underground chamber system, as described in further detail below. 6. As this is an infill site, much of the area surrounding the site is fully developed. Willow Street Residences Final Drainage Report 2 B. Description of Property 1. The development area is roughly 2.0 net acres. Figure 1 – Aerial Photograph 2. The subject property is currently composed of existing buildings, gravel surfaced drive and parking areas, and landscaped areas. Existing ground slopes are mild to moderate (i.e., 1 - 3±%) through the interior of the property. General topography slopes from southwest to northeast. 3. According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey website: http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx, the site consists of Paoli Fine Sandy Loam, which falls into Hydrologic Soil Group A. 4. The proposed project site plan is composed of the development of two apartment buildings and amenities. Associated site work, water, and sewer lines will be constructed with the development. Onsite water quality treatment is proposed within an underground chamber system, as discussed in Section IV, below. PROJECT SITE Willow Street Residences Final Drainage Report 3 Figure 2– Proposed Site Plan 5. There are no known irrigation laterals crossing the site. 6. The proposed land use is residential/apartments. C. Floodplain 1. The project site is not encroached by any City designated or FEMA 100-year floodplain. Willow Street Residences Final Drainage Report 4 Figure 3 –Area Floodplain Mapping II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. The project site lies within the Poudre River Basin. Detention will be provided with an allowable release rate based on historic pervious and impervious areas. Historic developed area will be grandfathered and will be allowed to release at a historic 100- year rate. Historic undeveloped area will be allowed to release at a historic 2-year rate. Generally, historic developed areas consist of gravel surfaced drive and parking areas, which have been accounted for in the computation of the composite historic release rate from the site. An allowable release rate of 13.15 cfs has been calculated for the overall site. However, Basins OS1 and OS2 will release undetained into Willow Street, thus, allowable release rate has been reduced by 0.86 cfs, which is the peak 100-year discharge from these basins. Please see Appendix A for computation of allowable release rate. 2. The entire site area has allowance for water quality treatment in the existing Baysaver located just southeast of the site. As identified in the “Downtown River District (DTRD) Final Design Report”, by Ayres Associates, dated February 2012, the current project area was considered part of master sub-basins 210 and 213, which was accounted for in the original sizing of the existing Baysaver. Please see the DTRD Plan, “Exhibit B-Future Development Map for DTRD Area” provided in Appendix D. 3. The Downtown River District (DTRD) Final Design Report accounts for all of Willow Street Right of Way area in its fully developed condition draining into the recently completed storm main in Willow Street. Because of this, the project site does not provide Water Quality or detention for the adjacent half street (Willow Street). PROJECT SITE Willow Street Residences Final Drainage Report 5 4. Please see Appendix B for detention volume calculations. All detention is provided in underground storage chamber systems as discussed below. 5. A 24-inch diameter offsite pipe from the southwest is being routed through the site. We have estimated maximum capacity of this offsite storm line at 28.0 cfs, and have conservatively added this full flow rate to our developed onsite design flow rate. Please see Appendix B.1 for calculation of maximum pipe flow calculations for the offsite storm line. B. Sub-Basin Description 1. The subject property historically drains overland from southwest to northeast. Runoff from the majority of the site has historically been collected in the adjacent Willow Street Right of Way. There is an existing storm main and a series of inlets within Willow Street, which collected historic runoff from the existing site. The proposed outfall for the project site is this existing storm main. Please see Appendix D for information on the Willow Street storm main. 2. A more detailed description of the project drainage patterns is provided below. III. DRAINAGE DESIGN CRITERIA A. Regulations There are no optional provisions outside of the FCSCM proposed with the proposed project. B. Four Step Process The overall stormwater management strategy employed with the proposed project utilizes the “Four Step Process” to minimize adverse impacts of urbanization on receiving waters. The following is a description of how the proposed development has incorporated each step. Step 1 – Employ Runoff Reduction Practices Several techniques have been utilized with the proposed development to facilitate the reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the current use by implementing multiple Low Impact Development (LID) strategies including: Conserving existing amenities in the site. Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with Slow Release The efforts taken in Step 1 will facilitate the reduction of runoff; however, urban development of this intensity will still generate stormwater runoff that will require additional BMPs and water quality. Water quality treatment is fully provided in existing Baysaver located just southeast of the site, as identified in the “Downtown River District (DTRD) Final Design Report”, by Ayres Associates, dated February 2012. Onsite LID treatment will occur in the underground chamber systems as described below. Step 3 – Stabilize Drainageways There are no major drainageways within the subject property. While this step may not seem applicable to proposed development, the project indirectly helps achieve stabilized drainageways nonetheless. By providing water quality treatment, where none previously Willow Street Residences Final Drainage Report 6 existed, sediment with erosion potential is removed from downstream drainageway systems. Furthermore, this project will pay one-time stormwater development fees, as well as ongoing monthly stormwater utility fees, both of which help achieve City-wide drainageway stability. Step 4 – Implement Site Specific and Other Source Control BMPs. The proposed project will improve upon site specific source controls compared to historic conditions: The proposed development will provide LID treatment; thus, eliminating sources of potential pollution previously left exposed to weathering and runoff processes. C. Development Criteria Reference and Constraints The subject property is surrounded by currently developed properties. Thus, several constraints have been identified during the course of this analysis that will impact the proposed drainage system including: Existing elevations along the property lines will generally be maintained. As previously mentioned, overall drainage patterns of the existing site will be maintained. Elevations of existing downstream facilities that the subject property will release to will be maintained. D. Hydrological Criteria 1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations associated with the proposed 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. Three separate design storms have been utilized to address distinct drainage scenarios. A fourth design storm has also been computed for comparison purposes. The first design storm considered is the 80th percentile rain event, which has been employed to design the project’s water quality features. The second event analyzed is the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third event considered is the “Major Storm,” which has a 100-year recurrence interval. The fourth storm computed, for comparison purposes only, is the 10-year event. 4. No other assumptions or calculation methods have been used with this development that are not referenced by current City of Fort Collins criteria. E. Hydraulic Criteria 1. As previously noted, the subject property maintains historic drainage patterns. 2. All drainage facilities proposed with the project are designed in accordance with criteria outlined in the FCSCM and/or the Urban Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria Manual. 3. As stated above, the subject property is not located in a City designated floodplain. The proposed project does not propose to modify any natural drainageways. Willow Street Residences Final Drainage Report 7 F. Modifications of Criteria 1. The proposed development is not requesting any modifications to criteria at this time. IV. DRAINAGE FACILITY DESIGN A. General Concept 1. The main objectives of the project drainage design are to maintain existing drainage patterns, and to ensure no adverse impacts to any adjacent properties. 2. Water Quality treatment is provided in the existing Baysaver located just southeast of the site. LID treatment will be provided in the proposed underground chamber system, as discussed further below. 3. Drainage patterns anticipated for drainage basins shown in the Drainage Exhibit are described below. Drainage basins have been defined for preliminary design purposes and are subject to change at Final design; however, general drainage patterns and concepts are not expected to be significantly altered. Basins W1 – W3 Basins W1 through W3 generally consist of paved parking areas, rooftop areas, and landscaped areas. These basins will generally drain via sheet flow and proposed concrete pans to collection points and inlets, which will convey flows into the proposed west underground chamber system. Basins E1 – E3 Basins E1 through E3 generally consist of paved parking areas, rooftop areas, and landscaped areas. These basins will generally drain via sheet flow and proposed concrete pans to collection points and inlets, which will convey flows into the proposed east underground chamber system. Basins OS1, OS2 Basins OS1 and OS2 generally consist of paved drive areas, and landscaped areas. Basin OS1 will sheet flow to proposed curb and gutter which will drain to the adjacent Willow Street Right of Way. Basin OS2 will sheet flow directly into the adjacent Willow Street Right of Way. Concrete pavers are proposed in Basin OS1 to provide LID treatment of the majority of this basin. Allowable overall site release rate has been reduced to compensate for undetained runoff from Basins OS1 and OS2. A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report. B. Specific Details 1. An open bottom chamber system is proposed as the primary LID treatment method for the site. The system will provide standard 12-hour holding time per UDFCD criteria (please see computations provided in Appendix C). The chamber system will provide treatment of a minimum of 75% of the proposed site. 2. The entire site area has allowance for water quality treatment in the existing Baysaver located just southeast of the site. As identified in the “Downtown River District (DTRD) Final Design Report”, by Ayres Associates, dated February 2012, the current Willow Street Residences Final Drainage Report 8 project area was considered part of master sub-basins 210 and 213, which was accounted for in the original sizing of the existing Baysaver. Please see the DTRD Plan, “Exhibit B-Future Development Map for DTRD Area” provided in Appendix F. 3. Final design details, and construction documentation shall be provided to the City of Fort Collins for review prior to Final Development Plan approval. 4. Stormwater facility Standard Operating Procedures (SOP) will be provided by the City of Fort Collins in the Development Agreement. V. CONCLUSIONS C. Compliance with Standards 4. The drainage design proposed with the proposed project complies with the City of Fort Collins’ Stormwater Criteria Manual. 5. The drainage design proposed with this project complies with requirements for the Poudre River Basin. 6. The drainage plan and stormwater management measures proposed with the proposed development are compliant with all applicable State and Federal regulations governing stormwater discharge. D. Drainage Concept 7. The drainage design proposed with this project will effectively limit any potential damage associated with its stormwater runoff by providing detention and water quality mitigation features. 8. The drainage concept for the proposed development is consistent with requirements for the Poudre River Basin. Willow Street Residences Final Drainage Report 9 References 1. 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. 2. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007. 3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service, United States Department of Agriculture. 4. Downtown River District (DTRD) Final Design Report, Ayres Associates, February 2012. 5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District, Wright-McLaughlin Engineers, Denver, Colorado. APPENDIX A HYDROLOGIC COMPUTATIONS CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: Willow Street Apartments Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: B. Mathisen Asphalt ……....……………...……….....…...……………….………………………………….. 0.95 100% Date: Concrete …….......……………….….……….………………..….………………………………… 0.95 90% Gravel ……….…………………….….…………………………..……………………………….. 0.50 40% Roofs …….…….………………..……………….…………………………………………….. 0.95 90% Pavers…………………………...………………..…………………………………………….. 0.40 22% Lawns and Landscaping Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0% Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year C f = 1.00 100-year C f = 1.25 Basin ID Basin Area (s.f.) Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Roofs (ac) Area of Gravel (ac) Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. HN1 15608 0.358 0.261 0.003 0.061 0.022 0.010 0.90 0.90 1.00 92% HS1 73243 1.681 0.000 0.044 0.097 1.541 0.000 0.54 0.54 0.67 44% Total 88851 2.040 0.261 0.047 0.158 1.563 0.010 0.60 0.60 0.75 53% H1 (Impervious) 88396 2.03 0.26 0.05 0.16 1.56 0.00 0.60 0.60 0.75 53% H1 (Pervious) 455 0.01 0.00 0.00 0.00 0.00 0.01 0.15 0.15 0.19 0% Existing Impervious Area Breakdown HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Notes April 5, 2018 Overland Flow, Time of Concentration: Project: Willow Street Apartments 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 Tc Rational Method Equation: Project: Willow Street Apartments Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: hn1 HN1 0.36 5 5 5 0.90 0.90 1.00 2.85 4.87 9.95 0.92 1.57 3.57 hs1 HS1 1.68 12 12 9 0.54 0.54 0.67 2.05 3.50 8.03 1.85 3.16 9.07 n/a H1 (Impervious) 2.03 11 11 8 0.60 0.60 0.75 2.17 3.71 8.59 2.66 4.54 13.15 n/a H1 (Pervious) 0.01 5 5 5 0.15 0.15 0.19 2.85 4.87 9.95 0.00 0.01 0.02 HISTORIC RUNOFF COMPUTATIONS Intensity, i2 (in/hr) Intensity, i10 (in/hr) Intensity, i100 (in/hr) Notes B. Mathisen April 5, 2018 Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1 Design Point Basin(s) Area, A (acres) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) Flow, Q2 (cfs) C2 Total allowable release from Basin H1 = 13.15 Existing Impervious Area Breakdown C10 C100 Flow, Q10 (cfs) Flow, Q100 (cfs) Q = C f ( C )( i )( A ) Page 3 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Hist-Direct-Runoff W ST ST X X X X X X X X X X D M W MW ELEC BRKR CONTROL IRR MW MW MW MW D ELEC MW C.O. C.O. CONTROL IRR MW C S E G CONTROL IRR CONTROL IRR ELEC BRKR D ST ST ST ELEC VAULT ELEC CONTROL IRR X MW MW WILLOW STREET HN1 HS1 hs1 hn1 EXISTING INLET (TO BE REMOVED) CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: Willow Street Apartments Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: Asphalt ……....……………...……….....…...……………….………………………………….0.. 95 100% Date: Concrete …….......……………….….……….………………..….………………………………… 0.95 90% Gravel ……….…………………….….…………………………..……………………………….0.. 50 40% Roofs …….…….………………..……………….…………………………………………….. 0.95 90% Pavers…………………………...………………..…………………………………………….. 0.40 22% Lawns and Landscaping Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0% Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year C f = 1.00 100-year C f = 1.25 Basin ID Basin Area (s.f.) Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Roofs (ac) Area of Gravel (ac) Area of Pavers (ac) Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. W1 14482 0.332 0.239 0.000 0.000 0.000 0.000 0.093 0.73 0.73 0.91 72% W2 8828 0.203 0.158 0.000 0.000 0.000 0.000 0.045 0.77 0.77 0.97 78% W3 29479 0.677 0.000 0.000 0.677 0.000 0.000 0.000 0.95 0.95 1.00 90% E1 10430 0.239 0.184 0.020 0.000 0.000 0.000 0.036 0.83 0.83 1.00 84% E2 4791 0.110 0.042 0.000 0.000 0.000 0.000 0.068 0.45 0.45 0.57 38% E3 16674 0.383 0.000 0.000 0.383 0.000 0.000 0.000 0.95 0.95 1.00 90% Overland Flow, Time of Concentration: Project: Willow Street Apartments 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) Slope, Rational Method Equation: Project: Willow Street Apartments Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: w1 W1 0.33 5 5 5 0.73 0.73 0.91 2.85 4.87 9.95 0.69 1.17 3.00 w2 W2 0.20 5 5 5 0.77 0.77 0.97 2.85 4.87 9.95 0.45 0.76 1.95 w3 W3 0.68 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.83 3.13 6.73 e1 E1 0.24 5 5 5 0.83 0.83 1.00 2.85 4.87 9.95 0.57 0.97 2.38 e2 E2 0.11 8 8 7 0.45 0.45 0.57 2.46 4.21 9.06 0.12 0.21 0.56 e3 E3 0.38 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.04 1.77 3.81 os1 OS1 0.07 5 5 5 0.79 0.79 0.98 2.85 4.87 9.95 0.16 0.27 0.68 0.68 n/a os2 OS2 0.03 5 5 5 0.65 0.65 0.81 2.85 4.87 9.95 0.05 0.08 0.21 0.21 n/a Total 13.15 DEVELOPED RUNOFF COMPUTATIONS C10 Area, A (acres) Intensity, i2 (in/hr) 100-yr Tc (min) 100-year Release Rate C100 Design Point Flow, Q100 (cfs) Flow, Q2 (cfs) 10-yr Tc (min) 2-yr Tc (min) Basin(s) 8.41 B. Mathisen April 13, 2018 Intensity, i10 (in/hr) Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1 3.85 West POND ID East C2 Flow, Q10 (cfs) Intensity, i100 (in/hr) APPENDIX B HYDRAULIC COMPUTATIONS B.1 – Storm Sewers B.2 – Inlets B.3 – Detention Facilities APPENDIX B.1 STORM SEWERS APPENDIX B.2 INLETS 3130 Verona Avenue • Buford, GA 30518 (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490 © Nyloplast Inlet Capacity Charts June 2012 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Capacity (cfs) Head (ft) Nyloplast 2' x 2' Road & Highway Grate Inlet Capacity Chart INLET A4.2-1 Qact = 8.30 cfs Qreq = 2.38 cfs Qact > Qreq (Based on Basin E1) 3130 Verona Avenue • Buford, GA 30518 (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490 © Nyloplast Inlet Capacity Charts June 2012 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Capacity (cfs) Head (ft) Nyloplast 2' x 2' Curb Inlet Diagonal Grate Inlet Capacity Chart High Hood Setting (8.47" Curb Setting) Mid Hood Setting (6.47" Curb Setting) Low Hood Setting (4.47" Curb Setting) INLET A4.2-4 Qact = 5.00 cfs Qreq = 0.62 cfs Qact > Qreq (Based on Basin E2 + 10% of Basin E2 to account for nuisance flows generated within the parking lot) 3130 Verona Avenue • Buford, GA 30518 (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490 © Nyloplast Inlet Capacity Charts June 2012 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Capacity (cfs) Head (ft) Nyloplast 2' x 2' Curb Inlet Diagonal Grate Inlet Capacity Chart High Hood Setting (8.47" Curb Setting) Mid Hood Setting (6.47" Curb Setting) Low Hood Setting (4.47" Curb Setting) INLET A5.3-2 Qact = 5.00 cfs Qreq = 3.00 cfs Qact > Qreq (Based on Basin W1) 3130 Verona Avenue • Buford, GA 30518 (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490 © Nyloplast Inlet Capacity Charts June 2012 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Capacity (cfs) Head (ft) Nyloplast 2' x 2' Road & Highway Grate Inlet Capacity Chart INLET A5.4 Qact = 4.25 cfs Qreq = 1.95 cfs Qact > Qreq (Based on Basin W2) APPENDIX B.3 DETENTION FACILITIES Pond No : East Pond 100-yr 0.87 5.00 min 1419 ft3 0.73 acres 0.033 ac-ft Max Release Rate = 3.85 cfs Time (min) Ft Collins 100-yr Intensity (in/hr) Inflow Volume (ft3) Outflow Adjustment Factor Qav (cfs) Outflow Volume (ft3) Storage Volume (ft3) 5 9.950 1896 1.00 3.85 1154 742 10 7.720 2942 0.75 2.88 1731 1211 15 6.520 3727 0.67 2.56 2308 1419 20 5.600 4268 0.63 2.40 2885 1383 25 4.980 4744 0.60 2.31 3462 1283 30 4.520 5167 0.58 2.24 4039 1129 35 4.080 5442 0.57 2.20 4616 826 40 3.740 5701 0.56 2.16 5192 508 45 3.460 5933 0.56 2.14 5769 164 50 3.230 6154 0.55 2.12 6346 -192 55 3.030 6350 0.55 2.10 6923 -573 60 2.860 6539 0.54 2.08 7500 -961 65 2.720 6737 0.54 2.07 8077 -1340 70 2.590 6909 0.54 2.06 8654 -1746 75 2.480 7088 0.53 2.05 9231 -2143 80 2.380 7255 0.53 2.04 9808 -2553 85 2.290 7417 0.53 2.04 10385 -2968 90 2.210 7579 0.53 2.03 10962 -3383 95 2.130 7711 0.53 2.02 11539 -3828 100 2.060 7850 0.53 2.02 12116 -4266 105 2.000 8002 0.52 2.01 12693 -4690 110 1.940 8132 0.52 2.01 13270 -5138 115 1.890 8282 0.52 2.01 13847 -5564 120 1.840 8414 0.52 2.00 14424 -6010 *Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2. A = Tc = Project Location : Design Point C = Design Storm DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF Input Variables Results Required Detention Volume Fort Collins, Colorado %2#:@: +! +&AB!'($;;- 4$ 4$ $ ) % * < F++'(!4'$$ ++ ,B+- - 3$! #4$# !"5 CDE .= G.#$ > 678 /01 H.9 ? 7/IE J :*O P#3$3$3$ + ' #+++!!!; 4$ : U+ W)B , ( K'$+# + 3$+! !X % B$,+'$$ 'A Q+ LM"M B+&'(! K ") -#$(& V V 1T N H 8R E S WX 'A %K BA!K BA! % %+++!!X 2X % $ $ 'B! 'B!$ $ KB(& !'( B+) ! 0ZS Y Project Title Date: Project Number Calcs By: Client Pond Designation Q = 3.85 cfs C = 0.65 Q = Release Rate (cfs) Eh = 4969.23 ft C = Discharge Coefficients (unitless) Ei = 4965.91 ft Aa = Area Allowed of Opening (ft2) Ec = 4966.27 ft Circular g = Gravity (32.2 ft/s2) Ec = 4966.20 ft Rectangular Eh = High Water Surface Elevation (ft) Ei = Elevation of Outlet Invert (ft) 0.40507496 ft2 Ec = Elevation of Outlet Centroid (ft) 58.330794 in2 Orifice Size (in.) 8 - 1/2 in. Area (in2) 58.33 sq-in Q 3.64 cfs Orifice Height (in.) 7 in. Orifice Width (in.) 8 - 1/2 in. Area (in2) 58.33 sq-in Q 3.68 cfs Aa = Circular Orifice 100-Year Orifice Rectangular Orifice 100-Year Orifice Willow Street Residences October 30, 2018 1287-005 B. Mathisen Richmark East Pond Pond No : n1 100-yr 0.96 5.00 min 1746 ft3 1.21 acres 0.040 ac-ft Max Release Rate = 8.45 cfs Time (min) Ft Collins 100-yr Intensity (in/hr) Inflow Volume (ft3) Outflow Adjustment Factor Qav (cfs) Outflow Volume (ft3) Storage Volume (ft3) 5 9.950 3467 1.00 8.45 2535 932 10 7.720 5381 0.75 6.34 3803 1578 15 6.520 6816 0.67 5.63 5070 1746 20 5.600 7806 0.63 5.28 6338 1468 25 4.980 8677 0.60 5.07 7605 1072 30 4.520 9451 0.58 4.93 8873 578 35 4.080 9953 0.57 4.83 10140 -187 40 3.740 10427 0.56 4.75 11408 -981 45 3.460 10852 0.56 4.69 12675 -1823 50 3.230 11256 0.55 4.65 13943 -2687 55 3.030 11615 0.55 4.61 15210 -3595 60 2.860 11960 0.54 4.58 16478 -4518 65 2.720 12322 0.54 4.55 17745 -5423 70 2.590 12636 0.54 4.53 19013 -6377 75 2.480 12963 0.53 4.51 20280 -7317 80 2.380 13270 0.53 4.49 21548 -8277 85 2.290 13566 0.53 4.47 22815 -9249 90 2.210 13863 0.53 4.46 24083 -10220 95 2.130 14103 0.53 4.45 25350 -11247 100 2.060 14357 0.53 4.44 26618 -12260 105 2.000 14636 0.52 4.43 27885 -13249 110 1.940 14873 0.52 4.42 29153 -14279 115 1.890 15148 0.52 4.41 30420 -15272 120 1.840 15389 0.52 4.40 31688 -16299 *Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2. DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF Input Variables Results Required Detention Volume Fort Collins, Colorado 1287-005 Willow Street Residences Project Number : Project Name : West Pond A = Project Title Date: Project Number Calcs By: Client Pond Designation Q = 8.45 cfs C = 0.65 Q = Release Rate (cfs) Eh = 4970.33 ft C = Discharge Coefficients (unitless) Ei = 4967.33 ft Aa = Area Allowed of Opening (ft2) Ec = 4967.88 ft Circular g = Gravity (32.2 ft/s2) Ec = 4967.71 ft Rectangular Eh = High Water Surface Elevation (ft) Ei = Elevation of Outlet Invert (ft) 0.935276002 ft2 Ec = Elevation of Outlet Centroid (ft) 134.679744 in2 Orifice Size (in.) 13 in. Area (in2) 134.68 sq-in Q 7.64 cfs Orifice Height (in.) 9 in. Orifice Width (in.) 15 in. Area (in2) 134.68 sq-in Q 7.90 cfs October 30, 2018 1287-005 B. Mathisen Richmark West Pond Aa = Circular Orifice 100-Year Orifice Rectangular Orifice 100-Year Orifice Willow Street Residences APPENDIX C WATER QUALITY DESIGN COMPUTATIONS Design Point Basin ID Basin Area Treatment Type LID System Area Treated by LID System Percent of Site Treated by LID System w1 W1 0.332 ac. StormTech Chambers Yes 0.332 ac. 16% w2 W2 0.203 ac. StormTech Chambers Yes 0.203 ac. 10% w3 W3 0.677 ac. StormTech Chambers Yes 0.677 ac. 33% e1 E1 0.239 ac. StormTech Chambers Yes 0.239 ac. 12% e2 E2 0.110 ac. StormTech Chambers Yes 0.110 ac. 5% e3 E3 0.383 ac. StormTech Chambers Yes 0.383 ac. 19% ose1 OSE1 0.070 ac. Concrete Pavers Yes 0.011 ac. 1% osw1 OSW1 0.026 ac. None No N/A 0% Total 2.04 ac. 1.955 ac. 96% LID SUMMARY TABLE Project Title Date: Project Number Calcs By: Client Basin 0.8 WQCV = Watershed inches of Runoff (inches) 80.24% a = Runoff Volume Reduction (constant) i = Total imperviousness Ratio (i = Iwq /100) 0.264 in A = 0.73 ac V = 0.0161 ac-ft V = Water Quality Design Volume (ac-ft) WQCV = Water Quality Capture Volume (inches) A = Watershed Area (acres) 699 cu. ft. Drain Time a = i = WQCV = Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event Willow Street Residences April 5, 2018 1287-005 B. Mathisen Richmark East Pond 0.231 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 WQCV (watershed inches) Total Imperviousness Ratio (i = Iwq /100) 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 ) V * A 12 WQCV Pond No : east pond WQ 0.87 5.00 min 471 ft3 0.73 acres 0.01 ac-ft Max Release Rate = 0.26 cfs Time (min) Ft Collins WQ Intensity (in/hr) Inflow Volume (ft3) Outflow Adjustmen t Factor Qav (cfs) Outflow Volume (ft3) Storage Volume (ft3) 5 1.425 272 1.00 0.26 78 194 10 1.105 421 1.00 0.26 156 265 15 0.935 534 0.67 0.17 156 379 20 0.805 614 0.63 0.16 195 419 25 0.715 681 0.60 0.16 233 448 30 0.650 743 0.58 0.15 272 471 35 0.585 780 0.57 0.15 311 469 40 0.535 815 0.56 0.15 350 465 45 0.495 849 0.56 0.14 389 460 50 0.460 876 0.55 0.14 428 448 55 0.435 912 0.55 0.14 467 445 60 0.410 937 0.54 0.14 506 431 65 0.385 954 0.54 0.14 545 409 70 0.365 974 0.54 0.14 584 390 75 0.345 986 0.53 0.14 623 363 80 0.330 1006 0.53 0.14 662 344 85 0.315 1020 0.53 0.14 700 320 90 0.305 1046 0.53 0.14 739 307 95 0.290 1050 0.53 0.14 778 271 100 0.280 1067 0.53 0.14 817 250 105 0.270 1080 0.52 0.14 856 224 110 0.260 1090 0.52 0.14 895 195 115 0.255 1117 0.52 0.14 934 183 120 0.245 1120 0.52 0.14 973 147 *Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2. A = Tc = Client : Design Point C = Design Storm DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF Input Variables Results Required Detention Volume Project Title Date: Project Number Calcs By: Client Basin 0.8 WQCV = Watershed inches of Runoff (inches) 83.08% a = Runoff Volume Reduction (constant) i = Total imperviousness Ratio (i = Iwq /100) 0.279 in A = 1.21 ac V = 0.0282 ac-ft V = Water Quality Design Volume (ac-ft) WQCV = Water Quality Capture Volume (inches) A = Watershed Area (acres) 1227 cu. ft. Drain Time a = i = WQCV = Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event Willow Street Residences April 5, 2018 1287-005 B. Mathisen Richmark West Pond 0.231 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 WQCV (watershed inches) Total Imperviousness Ratio (i = Iwq /100) 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 ) V * A 12 WQCV Pond No : west pond WQ 0.96 5.00 min 866 ft3 1.21 acres 0.02 ac-ft Max Release Rate = 0.47 cfs Time (min) Ft Collins WQ Intensity (in/hr) Inflow Volume (ft3) Outflow Adjustmen t Factor Qav (cfs) Outflow Volume (ft3) Storage Volume (ft3) 5 1.425 497 1.00 0.47 142 356 10 1.105 771 1.00 0.47 283 488 15 0.935 979 0.67 0.31 283 696 20 0.805 1124 0.63 0.29 354 770 25 0.715 1248 0.60 0.28 425 823 30 0.650 1361 0.58 0.28 495 866 35 0.585 1429 0.57 0.27 566 863 40 0.535 1494 0.56 0.27 637 857 45 0.495 1555 0.56 0.26 708 847 50 0.460 1606 0.55 0.26 778 827 55 0.435 1670 0.55 0.26 849 821 60 0.410 1717 0.54 0.26 920 798 65 0.385 1747 0.54 0.25 991 756 70 0.365 1784 0.54 0.25 1061 722 75 0.345 1806 0.53 0.25 1132 674 80 0.330 1843 0.53 0.25 1203 640 85 0.315 1869 0.53 0.25 1274 596 90 0.305 1916 0.53 0.25 1344 572 95 0.290 1923 0.53 0.25 1415 508 100 0.280 1955 0.53 0.25 1486 469 105 0.270 1979 0.52 0.25 1557 422 110 0.260 1997 0.52 0.25 1627 369 115 0.255 2047 0.52 0.25 1698 349 120 0.245 2052 0.52 0.25 1769 284 *Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2. C = Tc = A = West Pond Input Variables Results Design Point Design Storm Required Detention Volume Client : Richmark DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF Vault ID Total Required WQ Volume (cf) Flow, WQ (cfs) Chamber Type Chamber Release Ratea (cfs) Chamber Volumeb (cf) Installed Camber w/ Aggregatec (cf) Mimimum No. of Chambersd Total Release Ratee (cfs) Required Storage Volume by FAA Method (cf) Mimimum No. of Chambersf Storage Provided within the Chambersg (cf) Total Installed System Volumeh (cf) East Pond 699 0.87 SC-740 0.024 45.90 74.90 10 0.24 471 11 505 824 West Pond 1227 1.49 SC-740 0.024 45.90 74.90 17 0.40 866 19 872 1423 a. Release rate per chamber, limited by flow through geotextile with accumulated sediment. b. Volume within chamber only, not accounting for void spaces in surrounding aggregate. c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit. d. Number of chambers required to provide full WQCV within total installed system, including aggregate. e. Release rate per chamber times number of chambers. f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage). g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume. e. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV. Chamber Configuration Summary D:\Projects\1287-005\Drainage\WatQual\1287-005 Chamber Summary.xlsx Chamber Dimensions SC-160 SC-310 SC-740 Width (in) 25.0 34.0 51.0 Length (in) 84.4 85.4 85.4 Height (in) 12.0 16.0 30.0 Floor Area (sf) 14.7 20.2 30.2 Chamber Volume (cf) 6.9 14.7 45.9 Chamber/Aggregate Volume (cf) 16.0 29.3 74.9 Flow Rate* 0.35 gpm/sf 1 cf = 7.48052 gal 1 gallon = 0.133681 cf 1 GPM = 0.002228 cfs *Flow rate based on 1/2 of Nov 07 QMAX in Figure 17 of UNH Testing Report SC-160 SC-310 SC-740 Flow Rate/chamber (cfs) 0.011426 0.015724 0.023586 StormTech Chamber Data Chamber Flow Rate Chamber Flow Rate Conversion (gpm/sf to cfs) D:\Projects\1287-005\Drainage\WatQual\1287-005 Chamber Summary.xlsx APPENDIX D EROSION CONTROL REPORT Willow Street Residences Final 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 the Utility Plans. The Final Plans will contain a full-size Erosion Control sheet 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 the development. 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. APPENDIX E EXCERPTS – DTRD WATER QUALITY; WILLOW STREET STORM E E E E B M E E F E S AC E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E B M E E F E S AC E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E MAP POCKET SS SS SS SS SS X X X X X X X X X X X X X X X X X X X X X X D ST ST D ST ST ST ST CONTROL IRR T ST ST ST S NYLOPLAST DO NOT POLLUTE DRAINS TO WATERWAYS NYLOPLAST DO NOT POLLUTE DRAINS TO WATERWAYS NYLOPLAST DO NOT POLLUTE DRAINS TO WATERWAYS NYLOPLAST DO NOT POLLUTE DRAINS TO WATERWAYS NYLOPLAST DO NOT POLLUTE DRAINS TO WATERWAYS DO NOT POLLUTE DRAINS TO WATERWAYS NYLOPLAST DUCTILE IRON NYLOPLAST DO NOT POLLUTE DRAINS TO WATERWAYS DO NOT POLLUTE DRAINS TO WATERWAYS NYLOPLAST DUCTILE IRON UD UD UD UD UD UD UD UD UD UD UD M ONITORING WELL TRAFFIC RATED MONITORING WELL TRAFFIC RATED S w1 w2 e1 e2 WILLOW STREET w3 e3 W3 OS1 E3 E1 W2 E2 W1 OS2 "WEST POND" 34 SC-740 STORMTECH CHAMBERS 23 SC-740 ISOLATOR CHAMBERS "EAST POND" 21 SC-740 STORMTECH CHAMBERS 21 SC-740 ISOLATOR CHAMBERS SEE SHEET C-300 FOR STORM SEWER INFORMATION ± 732 SQ. FT. OF RUNOFF FLOWING OVER THE PUBLIC SIDEWALK INLET INLET INLET INLET INLET INLET 2' CONCRETE PAN 2' CONCRETE PAN os2 os1 ± 597 SQ. FT. OF RUNOFF FLOWING OVER THE PUBLIC SIDEWALK Sheet WILLOW STREET RESIDENCES These drawings are instruments of service provided by Northern Engineering Services, Inc. and are not to be used for any type of construction unless signed and sealed by a Professional Engineer in the employ of Northern Engineering Services, Inc. NOT FOR CONSTRUCTION REVIEW SET E NGINEER ING N O R T H E RN FORT COLLINS: 301 North Howes Street, Suite 100, 80521 GREELEY: 820 8th Street, 80631 970.221.4158 northernengineering.com of 20 NORTH C-500 DRAINAGE EXHIBIT 13 ( IN FEET ) 0 1 INCH = 20 FEET 20 20 40 60 GRAPHIC SCALE: LEGEND: PROPOSED STORM SEWER PROPOSED CURB & GUTTER PROPERTY BOUNDARY PROPOSED STORM INLET EXISTING CURB & GUTTER PROPOSED OVERLAND FLOW EXISTING MAJOR CONTOUR PROPOSED MAJOR CONTOUR RUNOFF SUMMARY: A2 a3 DRAINAGE BASIN AREA DRAINAGE BASIN ID DRAINAGE BASIN MINOR/MAJOR COEFF. EXISTING STORM SEWER ST PROPOSED DIRECT FLOW BASIN DELINEATION 1. REFER TO "FINAL DRAINAGE REPORT FOR WILLOW STREET RESIDENCES" PREPARED BY NORTHERN ENGINEERING ON 10/31/2018 FOR ADDITIONAL INFORMATION. NOTES: BASIN ID TOTAL AREA (acres) C2 C100 Q2 (cfs) Q100 (cfs) W1 0.332 0.73 0.91 0.69 3.00 W2 0.203 0.77 0.97 0.45 1.95 W3 0.677 0.95 1.00 1.83 6.73 E1 0.239 0.83 1.00 0.57 2.38 E2 0.110 0.45 0.57 0.12 0.56 E3 0.383 0.95 1.00 1.04 3.81 OS1 0.070 0.79 0.98 0.16 0.68 OS2 0.026 0.65 0.81 0.05 0.21 City Engineer Date Date Date Date Date Stormwater Utility Parks & Recreation Traffic Engineer Date Water & Wastewater Utility City of Fort Collins, Colorado UTILITY PLAN APPROVAL Environmental Planner CALL UTILITY NOTIFICATION CENTER OF COLORADO Know what'sbelow. Call before you dig. R E E E E E E E E E E E E E E E E E E E E IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR IRR CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV B M S S S D S D D D S S S T VAULT F.O. 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O P#B+3M $! f<B , + ($ ! %4-#+,(B!A "+! ! 08R 1h8R $ eE eE <F !<b+ ++!!X !A$i_ib+&+ 2^X ! +X ! -'$ + UB- ++-'$ O+$ U')-'$+ O++_ O+ U') B4 O P#_ _ B4 U') B4 B , Z VS hV hh VV d8E d8E d8E eE eE eE j V 1287-005 Willow Street Residences Project Number : Project Name : East Pond Page 1 of 1 1287-005_FAA East Pond.xls Q = C f ( C )( i )( A ) Page 6 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Direct-Runoff S (%) Velocity, V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) w1 W1 No 0.73 0.73 0.91 15 3.21% 1.8 1.8 0.9 160 1.10% 2.10 1.3 0.5 N/A N/A 5 5 5 w2 W2 No 0.77 0.77 0.97 N/A N/A N/A 82 1.25% 2.24 0.6 1.5 N/A N/A 5 5 5 w3 W3 No 0.95 0.95 1.00 N/A N/A N/A N/A N/A N/A N/A N/A N/A 5 5 5 e1 E1 No 0.83 0.83 1.00 N/A N/A N/A N/A 2.00% N/A N/A 1.5 N/A N/A 5 5 5 e2 E2 No 0.45 0.45 0.57 46 2.00% 6.5 6.5 5.4 193 2.00% 2.83 1.1 2.5 N/A N/A 8 8 7 e3 E3 No 0.95 0.95 1.00 N/A N/A N/A N/A N/A N/A N/A N/A N/A 5 5 5 os1 OS1 No 0.79 0.79 0.98 53 1.90% 3.4 3.4 1.3 N/A N/A N/A N/A N/A 5 5 5 DEVELOPED TIME OF CONCENTRATION COMPUTATIONS Gutter/Internal Building Flow Swale Flow Design Point Basin Overland Flow B. Mathisen April 13, 2018 Time of Concentration (Equation RO-4) ( ) 3 1 1 . 87 1 . 1 * S C Cf L Ti = − Page 5 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Tc-10-yr_&_100-yr OS1 3031 0.070 0.050 0.002 0.000 0.000 0.011 0.006 0.79 0.79 0.98 74% OS2 1136 0.026 0.016 0.000 0.000 0.000 0.000 0.010 0.65 0.65 0.81 62% TOTAL 88851 2.040 0.689 0.022 1.060 0.000 0.011 0.281 0.85 0.85 1.00 81% DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I. 10-year Cf = 1.00 April 13, 2018 **Soil Classification of site is Sandy Loam** B. Mathisen Page 4 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\C-Values NORTH ( IN FEET ) 0 1 INCH = 60 FEET 60 60 120 180 GRAPHIC SCALE: LEGEND: PROPERTY BOUNDARY EXISTING STORM INLET EXISTING CURB & GUTTER EXISTING OVERLAND FLOW EXISTING MAJOR CONTOUR RUNOFF SUMMARY: A2 a3 DRAINAGE BASIN AREA DRAINAGE BASIN ID DRAINAGE BASIN MINOR/MAJOR COEFF. EXISTING STORM SEWER ST BASIN DELINEATION 1. REFER TO "PRELIMINARY DRAINAGE REPORT FOR WILLOW STREET RESIDENCES" PREPARED BY NORTHERN ENGINEERING ON 04/10/2018 FOR ADDITIONAL INFORMATION. NOTES: BASIN ID TOTAL AREA (acres) C2 C100 Q2 (cfs) Q100 (cfs) HN1 0.358 0.90 1.00 0.92 3.57 HS1 1.681 0.54 0.67 1.85 9.07 H1 (Impervious) 0.000 0.00 0.00 2.66 13.15 H1 (Pervious) 0.000 0.00 0.00 0.00 0.02 HISTORIC DRAINAGE EXHIBIT APPENDIX FORT COLLINS, CO WILLOW STREET RESIDENCES ENGINEER ING N O R T H E RN 04.11.2018 D:\PROJECTS\1287-005\DWG\DRNG\1287-005_HIST_DRNG.DWG ROOF GRAVEL CONCRETE ASPHALT (min) 10-yr Tc (min) 100-yr Tc (min) hn1 HN1 No 0.90 0.90 1.00 93 2.68% 2.6 2.6 1.3 N/A N/A N/A N/A N/A N/A 5 5 5 hs1 HS1 No 0.54 0.54 0.67 275 2.84% 12.3 12.3 9.4 N/A N/A N/A N/A N/A N/A 12 12 9 n/a H1 (Impervious) No 0.60 0.60 0.75 275 2.84% 10.9 10.9 7.6 N/A N/A N/A N/A N/A N/A 11 11 8 n/a H1 (Pervious) No 0.15 0.15 0.19 20 4.65% 4.8 4.8 4.6 N/A N/A N/A N/A N/A N/A 5 5 5 Existing Impervious Area Breakdown HISTORIC TIME OF CONCENTRATION COMPUTATIONS B. Mathisen Design Point Basin Overland Flow Gutter Flow Swale Flow Time of Concentration April 5, 2018 (Equation RO-4) ( ) 3 1 1 . 87 1 . 1 * S C Cf L Ti = − Page 2 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Hist-Tc-10-yr_&_100-yr 10-year Cf = 1.00 **Soil Classification of site is Sandy Loam** Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I. Page 1 of 24 D:\Projects\1287-005\Drainage\Hydrology\1287-005_Rational-Calcs.xlsx\Hist-C-Values