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HomeMy WebLinkAboutWEST SIDE HOUSE - PDP/FDP - FDP160021 - REPORTS - DRAINAGE REPORT (3)301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com Drainage Letter and LID Report Date: June 24, 2016 Project: West Side House Project No. 970-001 Project Development Plan/Major Amendment Fort Collins, Colorado Attn: Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Dear Wes: This letter serves to address the stormwater impacts of the West Side House project. The existing building is situated towards the northern portion of the site. The site currently consists of rooftop, concrete walks, asphalt parking areas, turf, trees, and other vegetation. It presently functions similar to a ‘B’ lot, with historic drainage being split towards Plum Street to the north and towards Shields Street to the east. Calculations using the rational method to determine the proposed runoff are attached to this letter, as is a drainage exhibit. The total impervious area of the existing site is slightly reduced due to the removal of an existing concrete pad along the north face of the building. For this reason, the total runoff was assumed to also be reduced and, therefore, no stormwater detention is proposed. Although stormwater quantity detention is not required, stormwater quality will be addressed by permanent Best Management Practices (BMPs). There is one existing bio-retention pond (Rain Garden) that is located along the south face of the building. Currently, this site is deficient with the City’s Low Impact Development Standards. In order to bring the site into compliance, two Rain Gardens will be installed along the north face collecting building downspouts and one additional rain garden will be located in the southeast corner of the site to collect runoff from the parking lot. These Rain Gardens will have an engineered section designed to remove particulates and contaminants from the stormwater. While most minor events are expected to infiltrate into the ground, weep holes and subdrains will be provided to drain the Rain Gardens should they become overburdened. During major events, runoff will spill through designed depressions in the top of the concrete retaining walls. During construction, the Contractor will follow the appropriate and applicable City of Fort Collins standards for erosion and sediment control. Since the approximately 1,250 sf area of disturbance for the project is less than 10,000 sf, a comprehensive Stormwater Management Plan will not be prepared for this project. Post construction water quality and erosion control will be achieved by a fully established and stabilized site. All areas disturbed during construction will receive permanent hardscape, landscape, or building structure. There are no regulatory floodplains associated with the project. The City LID requirements specify that either 75% of all impermeable areas are provided LID treatment OR 50% LID treatment by which 25% is treated by permeable pavers. In the case of this project, we will meet or exceed the 75% treatment of impermeable areas through the use of LID. The combination of treatment provided by the 4 infiltration Rain Gardens will treat 10,987 square-feet of impervious area on the site, which is 84.7% of the total impervious areas with the project, which again far exceeds the amount required by city code. A LID Treatment Exhibit is provided with this report. To summarize, the proposed grading concept closely matches existing elevations and drainage patterns. On-site detention is proven to be unnecessary. Stormwater quality has been provided, and exceeds the city requirements for Low Impact Development treatment. Therefore, it is my professional opinion that the West Side House satisfies all applicable stormwater criteria. Please do not hesitate to contact me if you have questions or require additional information. Sincerely, Danny Weber, PE Project Engineer enc. CHARACTER OF SURFACE: Runoff Coefficient Percentage Impervious Project: West Side House Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: D. Weber 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. NW 3,180 0.07 0.02 0.01 0.02 0.00 0.00 0.02 0.77 0.77 0.97 70.6 NE 3,192 0.07 0.00 0.01 0.02 0.00 0.00 0.05 0.51 0.51 0.64 33.4 S 10,777 0.25 0.15 0.02 0.04 0.00 0.00 0.04 0.85 0.85 1.00 83.3 Total 17,149 0 0 0 0 0 0 0 0.77 0.77 0.97 71.7 DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS Overland Flow, Time of Concentration: Project: West Side House 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, S (%) Velocity, Rational Method Equation: Project: West Side House Calculations By: Date: From Section 3.2.1 of the CFCSDDC Rainfall Intensity: NW NW 0.07 5.0 5.0 5.0 0.77 0.77 0.97 2.85 4.87 9.95 0.2 0.3 0.7 NE NE 0.07 5.5 5.5 5.1 0.51 0.51 0.64 2.85 4.87 9.95 0.1 0.2 0.5 S S 0.25 5.0 5.0 5.0 0.85 0.85 1.00 2.85 4.87 9.95 0.6 1.0 2.5 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) DEVELOPED RUNOFF COMPUTATIONS C100 Design Point Flow, Q100 (cfs) Flow, Q2 (cfs) 10-yr Tc (min) 2-yr Tc (min) C2 Flow, Q10 (cfs) Intensity, i100 (in/hr) Basin(s) D. Weber June 24, 2016 Q = C f ( C )( i )( A ) D:\Projects\970-001\Drainage\Hydrology\970-001_Rational-Calcs_Proposed.xlsx\Direct-Runoff Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Jun 23 2016 Northwest Driveway Chase Rectangular Bottom Width (ft) = 1.00 Total Depth (ft) = 0.24 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.013 Calculations Compute by: Known Q Known Q (cfs) = 0.20 Highlighted Depth (ft) = 0.12 Q (cfs) = 0.200 Area (sqft) = 0.12 Velocity (ft/s) = 1.67 Wetted Perim (ft) = 1.24 Crit Depth, Yc (ft) = 0.11 Top Width (ft) = 1.00 EGL (ft) = 0.16 0 .25 .5 .75 1 1.25 1.5 Elev (ft) Depth (ft) Section 99.75 -0.25 100.00 0.00 100.25 0.25 100.50 0.50 100.75 0.75 101.00 1.00 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Jun 23 2016 Southeast Driveway Chase Rectangular Bottom Width (ft) = 1.00 Total Depth (ft) = 0.41 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.013 Calculations Compute by: Known Q Known Q (cfs) = 0.60 Highlighted Depth (ft) = 0.25 Q (cfs) = 0.600 Area (sqft) = 0.25 Velocity (ft/s) = 2.40 Wetted Perim (ft) = 1.50 Crit Depth, Yc (ft) = 0.23 Top Width (ft) = 1.00 EGL (ft) = 0.34 0 .25 .5 .75 1 1.25 1.5 Elev (ft) Depth (ft) Section 99.75 -0.25 100.00 0.00 100.25 0.25 100.50 0.50 100.75 0.75 101.00 1.00 Reach (ft) T S CTV W X X X X X X G CT VAULT ELEC T C S C S ELEC ELEC RAIN GARDEN A EXISTING RAIN GARDEN RAIN GARDEN B RAIN GARDEN C D:\PROJECTS\970-001\DWG\DRNG\970-001_LID.DWG WEST SIDE HOUSE FORT COLLINS COLORADO 301 N. Howes Street, Suite 100 Fort Collins, Colorado 80521 ENGINEER ING N O R T H E RN PHONE: 970.221.4158 www.northernengineering.com DESCRIPTION LID TREATMENT EXHIBIT DRAWN BY D. WEBER DATE JUNE 24, 2016 PROJECT 970-001 LID-1 SCALE DRAWING 1"=30' ( IN FEET ) 1 inch = ft. 30 0 30 Feet 30 LEGEND RAIN GARDEN RAIN GARDEN TREATMENT AREA On-Site LID Treatment Project Area Total Impervious Area 12,972 sf Target Treatment Percentage 75% Minimum Area to be Treated by LID measures 9,729.00 sf Rain Garden Treatment Run-on area for Rain Garden 10,987 sf Total Treatment Area 10,987 sf Percent Total Project Area Treated 84.7% Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 800 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 27 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) DWQCV = 4.75 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin = 16 sq ft D) Actual Flat Surface Area AActual = 69 sq ft E) Area at Design Depth (Top Surface Area) ATop = 69 sq ft F) Rain Garden Total Volume VT= 27 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided? B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft iii) Orifice Diameter, 3/8" Minimum DO = N/A in Design Procedure Form: Rain Garden (RG) D. Weber Northern Engineering June 24, 2016 West Side House Rain Garden A Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO Rain Garden A.xlsm, RG 6/23/2016, 8:34 AM Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 800 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 27 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) DWQCV = 4.75 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin = 16 sq ft D) Actual Flat Surface Area AActual = 69 sq ft E) Area at Design Depth (Top Surface Area) ATop = 69 sq ft F) Rain Garden Total Volume VT= 27 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided? B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft iii) Orifice Diameter, 3/8" Minimum DO = N/A in Design Procedure Form: Rain Garden (RG) D. Weber Northern Engineering June 24, 2016 West Side House Rain Garden B Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO Rain Garden B.xlsm, RG 6/23/2016, 8:34 AM Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 99.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.990 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.39 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 7,449 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 243 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) DWQCV = 6.50 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin = 147 sq ft D) Actual Flat Surface Area AActual = 455 sq ft E) Area at Design Depth (Top Surface Area) ATop = 455 sq ft F) Rain Garden Total Volume VT= 246 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided? B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft iii) Orifice Diameter, 3/8" Minimum DO = N/A in Design Procedure Form: Rain Garden (RG) D. Weber Northern Engineering June 24, 2016 West Side House Rain Garden C Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO Rain Garden C.xlsm, RG 6/23/2016, 8:35 AM UD CTV CTV CTV X X X X X X X X X X X X X X X util DS DS NW S NW 0.07 ac S 0.25 ac NE NE 0.07 ac RAIN GARDEN A RAIN GARDEN B EXISTING RAIN GARDEN RAIN GARDEN C NORTH ( IN FEET ) 1 inch = ft. 10 0 10 Feet 10 20 30 C500 DRAINAGE EXHIBIT D. Weber D. Weber 1"=10' No. Revisions: By: Date: REVIEWED BY: A. Reese DESIGNED BY: DRAWN BY: SCALE: DATE: JUNE 24, 2016 PROJECT: 970-001 Sheet Of 9 Sheets WEST SIDE HOUSE E N G I N E E R I N G N O R T H E RN 301 North Howes Street, Suite 010 Fort Collins, Colorado 80521 www.northernengineering.com Phone: 970.221.4158 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 04/27/16 CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE, OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. CALL UTILITY NOTIFICATION CENTER OF COLORADO Know what'sbelow. Call before you dig. R LEGEND: 4953 PROPOSED CONTOUR 93 PROPOSED STORM SEWER PROPOSED SWALE EXISTING CONTOUR PROPOSED PROPERTY BOUNDARY CURB & GUTTER PROPOSED INLET A DESIGN POINT FLOW ARROW DRAINAGE BASIN LABEL DRAINAGE BASIN BOUNDARY PROPOSED SWALE SECTION 1 1 NOTES: 1.REFER TO THE "DRAINAGE LETTER REPORT FOR WEST SIDE HOUSE PROJECT #970-001" DATED JUNE 24, 2016 BY NORTHERN ENGINEERING FOR ADDITIONAL INFORMATION.{ } BASIN DESIGNATION BASIN AREA (AC) PROPOSED MODULAR BLOCK PAVERS FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION UD PROPOSED UNDERDRAIN A 0.67 DEVELOPED RUNOFF SUMMARY TABLE DESIGN POINT BASIN ID TOTAL AREA (acres) C2 C10 C100 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) Q2 (cfs) Q10 (cfs) Q100 (cfs) NW NW 0.07 0.77 0.77 0.97 5.0 5.0 5.0 0.2 0.3 0.7 NE NE 0.07 0.51 0.51 0.64 5.5 5.5 5.1 0.1 0.2 0.5 S S 0.25 0.85 0.85 1.00 5.0 5.0 5.0 0.6 1.0 2.5 City Engineer Date Date Date Date Date Stormwater Utility Parks & Recreation Traffic Engineer Date APPROVED: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: Water & Wastewater Utility City of Fort Collins, Colorado UTILITY PLAN APPROVAL Environmental Planner On-Site LID Treatment Project Area Total Impervious Area 12,972 sf Target Treatment Percentage 75% Minimum Area to be Treated by LID measures 9,729.00 sf Rain Garden Treatment Run-on area for Rain Garden 10,987 sf Total Treatment Area 10,987 sf Percent Total Project Area Treated 84.7% V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) NW NW No 0.95 0.95 1.00 30 2.8 2.0 1.1 0.7 47 0.5 1.41 0.6 41 0.5 1.06 0.6 5.0 5.0 5.0 NE NE No 0.25 0.25 0.31 35 5.0 5.5 5.5 5.1 0 0.0 0.00 N/A 0 0.0 0.00 N/A 5.5 5.5 5.1 DEVELOPED TIME OF CONCENTRATION COMPUTATIONS Gutter Flow Swale Flow Design Point Basin Overland Flow D. Weber June 24, 2016 Time of Concentration (Equation RO-4) ( ) 3 1 1 . 87 1 . 1 * S C Cf L Ti − = D:\Projects\970-001\Drainage\Hydrology\970-001_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 June 24, 2016 D:\Projects\970-001\Drainage\Hydrology\970-001_Rational-Calcs_Proposed.xlsx\C-Values