January 20, Nate Hatleback Project Manager, City of Thornton Development Engineering 9500 Civic Center Drive Thornton, CO (303)

Transcription

1 January 20, 2017 Nate Hatleback Project Manager, City of Thornton Development Engineering 9500 Civic Center Drive Thornton, CO (303) RE: Riverdale Five Retail Drainage Conformance Letter Dear Mr. Hatleback, On behalf of our Client, Best Properties, we are submitting this letter as an attachment to the Riverdale Five Retail (Project) Development Plan Permit application. The Project is situated in Lot 5 of the Riverdale Retail Filing No. 1 Subdivision, City of Thornton, County of Adams, and State of Colorado. This drainage conformance letter is intended to fulfill the City of Thornton s (City) submittal requirement for the Phase III Drainage Report. The Project consists of an 8,400 square foot retail building. Site improvements include handicap parking, compact parking, standard parking, trash enclosure, site walk, private drives, and utilities. The Project, which is approximately 1.55 acres, is bounded by E. 128 th Avenue to the south, Jasmine Street to the east, Lake View Tributary to the northeast, and an existing retail development to the west. The site slopes generally from the southwest to northeast at approximately 3.7 percent. The Project is included as a part of the approved Drainage Report for Riverdale Retail Filing No. 1, (Master Drainage Report), prepared by CLC Associates Inc., dated February 16, 2007, current revision April 24, As outlined within the Master Drainage Report, developed runoff from the project site is a part of Basin C-1 and has been accounted for within the off-site storm sewer detention facility. The Master Drainage Report designed the off-site storm sewer detention facility for the anticipated imperviousness for the Project of 95%. Water quality for the Project will be provided within a regional water quality pond as outlined in the approved Sage Creek Filing No. 1 Water Quality Pond Plans prepared by MMC Engineering, dated February 27, Excerpts of the Master Drainage Report can be seen in Appendix A for reference. Approximately 0.86 acres of the Project will be disturbed by proposed site improvements. The rational Method was used to calculate the peak flow rate of storm water runoff. The Project was delineated into three sub basins (A, B, and C). The flow from sub-basin A and B flows towards the proposed 5 type R inlet on the northwest corner of the Project. The flow from sub basin C sheet flows over land to the existing Lake View Tributary to the northeast. The 100-year flow for the Project is 8.98 cfs. Excerpts of the Master Drainage Report and rational calculations have been attached to this letter. The design storms that were analyzed for this Project are 5-year and 100-year for the minor and major storm, respectively. The drainage concept for this Project is to convey on-site flows into a proposed 5 type R inlet in the northwest corner of the Project, and connect this proposed inlet, via proposed and existing storm sewer, to 1120 Lincoln Street, Suite 1000, Denver, Colorado I P : I F : I

2 the existing off-site storm sewer detention facility outlined in the Master Drainage Report. The capacity of the storm sewer stub pipe has been analyzed and adequate capacity has been provided for the 100-year flow proposed by the Project. All on-site storm sewer facilities, including streets, storm sewer pipes, and storm sewer inlets, have been sized to convey the runoff from the major storm. Calculations and analysis are attached to this letter. The basis for design and analysis of the drainage system and drainage impacts for the Project were the City of Thornton Storm Drainage Design and Technical Criteria, (City Criteria) and Urban Drainage and Flood Control District s Urban Storm Drainage Criteria Manuals (Urban Drainage Criteria), Volumes 1, 2, and 3. As previously mentioned, the Master Drainage Report for the Project has provided anticipated site imperviousness of 95% for the Project. It was determined the Project will result in a weighted imperviousness percentage of 45%, resulting in less than the anticipated imperviousness for the Project. The Project will have no adverse impact to downstream infrastructure and is in general conformance with the Master Drainage Report. A copy of the proposed drainage calculation and the Final Drainage Plan can be seen in Appendix B for reference. The proposed 5 type R inlet in the northwest corner of the site is designed to collect within a sump condition the peak flows of 2.6 cfs and 5.3 cfs for the minor and major storm respectively. The proposed 18 reinforced concrete pipe connecting the proposed 5 type R inlet to the existing storm sewer has sufficient capacity for both the minor and major storms as it conveys the stormwater to the existing off-site storm sewer detention facility. A copy of the proposed drainage calculation can be seen in Appendix B for reference. We acknowledge that the City of Thornton s review of this study is only for general conformance with submittal requirements, current design criteria and standard engineering principles and practices. Please let me know if you have any questions or require additional information. Sincerely, HARRIS KOCHER SMITH Michael S. Moore, P.E. Project Engineer 1120 Lincoln Street, Suite 1000, Denver, Colorado I P : I F : I

3 Appendix A Existing Reports and Data 1120 Lincoln Street, Suite 1000, Denver, Colorado I P : I F : I

4

5

6

7

8

9

10

11

12 Appendix B Proposed Calculations and Drainage Plan 1120 Lincoln Street, Suite 1000, Denver, Colorado I P : I F : I

13 Project Name: Riverdale Five Retail Soil Type C Project No: Date: 12/21/16 Revised: Design by: TJS Checked by: MSM Zone : 1 BASIN TOTAL AREA (ACRES) BUILDING COVERAGE (90%) DRIVES &SIDEWALKS (90)% STREETS (PAVED) (100%) LANDSCAPE AREA (2%) PERCENT IMPERVIOUS C 5 = C 100 = A % B % C % Correction Factors C/D A 2 YR - K CD = YR - K CD = -0.10i i YR - K CD = -0.39i i+0.32 Weighted Imperviousness 44.60% Runoff Coefficient C A =K A +(1.31i i i-0.12) for CA 0, otherwise CA=0 C CD =K CD +(0.858i i i+0.04) C B =(C A +C CD )/2

14 CALCULATED BY: TJS STANDARD FORM SF-2 JOB NO: DATE: 12/21/16 TIME OF CONCENTRATION PROJECT: Riverdale Five Retail CHECKED BY: MSM DESIGN STORM: 5-YR REVISION DATE: SUB-BASIN INITIAL/OVERLAND TRAVEL TIME Tc CHECK FINAL DATA TIME (Ti) (Tt) (URBANIZED BASINS) BASIN AREA C 5 LENGTH SLOPE Ti LENGTH SLOPE C v VELOCITY Tt COMPOSITE TOTAL Tc = (L/180) + 10 Tc (AC) (FT) FT/FT (MIN) (FT) FT/FT (FPS) (MIN) Tc (MIN) LENGTH (MIN) (MIN) A By Inspection B By Inspection C By Inspection REMARKS

15 CALCULATED BY: TJS STANDARD FORM SF-2 JOB NO: DATE: 12/21/16 TIME OF CONCENTRATION PROJECT: Riverdale Five Retail CHECKED BY: MSM DESIGN STORM: 100-YR REVISION DATE: SUB-BASIN INITIAL/OVERLAND TRAVEL TIME Tc CHECK FINAL DATA TIME (Ti) (Tt) (URBANIZED BASINS) BASIN AREA C 100 LENGTH SLOPE Ti LENGTH SLOPE C v VELOCITY Tt COMPOSITE TOTAL Tc = (L/180) + 10 Tc (AC) (FT) FT/FT (MIN) (FT) FT/FT (FPS) (MIN) Tc (MIN) LENGTH (MIN) (MIN) A By Inspection B By Inspection C By Inspection REMARKS

16 *BASED ON ONE-HOUR POINT RAINFALL DEPTHS FROM ADAMS COUNTY STORM DRAIANGE DESIGN AND TECHNICAL CRITERIA Zone 1 Return Interval (YR) 1-hour Rainfall

17 CALCULATED BY: TJS STANDARD FORM SF-3 JOB NO: DATE: 12/21/16 PROJECT: Riverdale Five Retail CHECKED BY: MSM STORM DRAINAGE SYSTEM DESIGN DESIGN STORM: 5 YR REVISED DATE: (RATIONAL METHOD PROCEDURE) DIRECT RUNOFF TOTAL RUNOFF STREET/INLET STORM SEWER PIPE TRAVEL TIME DESIGN POINT AREA (AC) RUNOFF COEFF Tc (min) C x A (AC) BASIN (s) A B C I (IN/HR) DIRECT RUNOFF, Q (CFS) Tc (MIN) S(C x A) (AC) I (IN/HR) TOTAL RUNOFF, Q (CFS) SLOPE (%) STREET FLOW (CFS) INLET DESIGN FLOW (CFS) STREET OR INLET INTERCEPTION (CFS) CARRYOVER (CFS) DESIGN FLOW (CFS) PIPE SLOPE (%) PIPE SIZE (IN) QFULL (CFS) LENGTH (FT) VELOCITY (FPS) Tt (min) REMARKS

18 CALCULATED BY: TJS STANDARD FORM SF-3 JOB NO: DATE: 12/21/16 PROJECT: Riverdale Five Retail CHECKED BY: MSM STORM DRAINAGE SYSTEM DESIGN DESIGN STORM: 100 YR REVISED DATE: (RATIONAL METHOD PROCEDURE) DIRECT RUNOFF TOTAL RUNOFF STREET/INLET STORM SEWER PIPE TRAVEL TIME DESIGN POINT AREA (AC) RUNOFF COEFF Tc (min) C x A (AC) BASIN (s) A B C I (IN/HR) DIRECT RUNOFF, Q (CFS) Tc (MIN) S(C x A) (AC) I (IN/HR) TOTAL RUNOFF, Q (CFS) SLOPE (%) STREET FLOW (CFS) INLET DESIGN FLOW (CFS) STREET OR INLET INTERCEPTION (CFS) CARRYOVER (CFS) DESIGN FLOW (CFS) PIPE SLOPE (%) PIPE SIZE (IN) QFULL (CFS) LENGTH (FT) VELOCITY (FPS) Tt (min) REMARKS

19 Version 4.04 Released November 2016 DESIGN PEAK FLOW FOR SWALE OR ONE-HALF OF STREET BY THE RATIONAL METHOD Worksheet Protected Project: Riverdale Five Retail Show Details Design Flow: ONLY if already determined through other methods: Minor Storm Major Storm (local peak flow for 1/2 of street OR grass-lined channel): *Q Known = cfs * If you enter flows in Row 14, select "Street Inlet" or "Area Inlet" button and then skip the rest of this sheet and click "Add New Inlet" at bottom of sheet. Geographic Information: (Enter data in the blue cells): Site Type: Site is Urban Site is Rural Flows Developed For: Street Inlet Area Inlet in a Swale Subcatchment Area = Acres Percent Imperviousness = % NRCS Soil Type = A, B, C, or D Overland Flow = Gutter Flow = Slope (ft/ft) Length (ft) <--- FILL IN THIS SECTION OR FILL IN THE SECTIONS BELOW. <--- Rainfall Information: Intensity I (inch/hr) = C 1 * P 1 / ( C 2 + T c ) ^ C 3 Minor Storm Major Storm Design Storm Return Period, T r = Return Period One-Hour Precipitation, P 1 = C 1 = C 2 = C 3 = User-Defined Storm Runoff Coefficient (leave this blank to accept a calculated value), C = User-Defined 5-yr. Runoff Coefficient (leave this blank to accept a calculated value), C 5 = Bypass (Carry-Over) Flow from upstream Subcatchments, Q b = cfs years inches Total Design Peak Flow, Q = cfs UD-Inlet_v4.04.xlsm, Q-Peak 1/18/2017, 5:51 PM

20 Version 4.04 Released November 2016 ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm) Project: Inlet ID: (Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread) Riverdale Five Retail A1 Gutter Geometry (Enter data in the blue cells) Maximum Allowable Width for Spread Behind Curb T BACK = 11.5 ft Side Slope Behind Curb (leave blank for no conveyance credit behind curb) S BACK = ft/ft Manning's Roughness Behind Curb (typically between and 0.020) n BACK = Height of Curb at Gutter Flow Line H CURB = 6.00 inches Distance from Curb Face to Street Crown T CROWN = 30.0 ft Gutter Width W = 2.00 ft Street Transverse Slope S X = ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or ft/ft) S W = ft/ft Street Longitudinal Slope - Enter 0 for sump condition S O = ft/ft Manning's Roughness for Street Section (typically between and 0.020) n STREET = Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm T MAX = ft Max. Allowable Depth at Gutter Flowline for Minor & Major Storm d MAX = inches Allow Flow Depth at Street Crown (leave blank for no) check = yes MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm MAJOR STORM Allowable Capacity is based on Depth Criterion Q allow = SUMP SUMP cfs UD-Inlet_v4.04.xlsm, A1 1/18/2017, 5:51 PM

21 INLET IN A SUMP OR SAG LOCATION Version 4.04 Released November 2016 H-Curb W W P H-Vert Lo (C) Wo Lo (G) Design Information (Input) MINOR MAJOR CDOT Type R Curb Opening Type of Inlet Type = CDOT Type R Curb Opening Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') a local = inches Number of Unit Inlets (Grate or Curb Opening) No = 1 1 Water Depth at Flowline (outside of local depression) Ponding Depth = inches Grate Information MINOR MAJOR Override Depths Length of a Unit Grate L o (G) = N/A N/A feet Width of a Unit Grate W o = N/A N/A feet Area Opening Ratio for a Grate (typical values ) A ratio = N/A N/A Clogging Factor for a Single Grate (typical value ) C f (G) = N/A N/A Grate Weir Coefficient (typical value ) C w (G) = N/A N/A Grate Orifice Coefficient (typical value ) C o (G) = N/A N/A Curb Opening Information MINOR MAJOR Length of a Unit Curb Opening L o (C) = feet Height of Vertical Curb Opening in Inches H vert = inches Height of Curb Orifice Throat in Inches H throat = inches Angle of Throat (see USDCM Figure ST-5) Theta = degrees Side Width for Depression Pan (typically the gutter width of 2 feet) W p = feet Clogging Factor for a Single Curb Opening (typical value 0.10) C f (C) = Curb Opening Weir Coefficient (typical value ) C w (C) = Curb Opening Orifice Coefficient (typical value ) C o (C) = Low Head Performance Reduction (Calculated) MINOR MAJOR Depth for Grate Midwidth d Grate = N/A N/A ft Depth for Curb Opening Weir Equation d Curb = ft Combination Inlet Performance Reduction Factor for Long Inlets RF Combination = Curb Opening Performance Reduction Factor for Long Inlets RF Curb = Grated Inlet Performance Reduction Factor for Long Inlets RF Grate = N/A N/A MINOR MAJOR Total Inlet Interception Capacity (assumes clogged condition) Q a = cfs Inlet Capacity IS GOOD for Minor and Major Storms(>Q PEAK) Q PEAK REQUIRED = cfs UD-Inlet_v4.04.xlsm, A1 1/18/2017, 5:51 PM

22 Channel Report Hydraflow Express Extension for Autodesk AutoCAD Civil 3D by Autodesk, Inc. Wednesday, Jan Riverdale Five Retail Circular Diameter (ft) = 1.50 Invert Elev (ft) = 1.00 Slope (%) = 0.50 N-Value = Calculations Compute by: Known Q Known Q (cfs) = 5.48 Highlighted Depth (ft) = 0.96 Q (cfs) = Area (sqft) = 1.19 Velocity (ft/s) = 4.59 Wetted Perim (ft) = 2.78 Crit Depth, Yc (ft) = 0.91 Top Width (ft) = 1.44 EGL (ft) = 1.29 Elev (ft) 3.00 Section Reach (ft)

23 Profile Report Engineering Profile - Riverdale Five Retail (Model.stsw) O-1 Rim: 5, ft Invert: 5, ft A5 (p-storm) Rim: 5, ft Invert: 5, ft A1 (p-storm) Rim: 5, ft Invert: 5, ft 5, , Station (ft) Model.stsw 1/6/2017 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 4) [ ] Page 1 of 1

24 Profile Report Engineering Profile - Riverdale Five Retail (Model.stsw) Elevation (ft) Model.stsw 1/6/2017 Bentley Systems, Inc. Haestad Methods Solution Center 27 Siemon Company Drive Suite 200 W Watertown, CT USA Bentley StormCAD V8i (SELECTseries 4) [ ] Page 1 of 1

25 NO CHANGES ARE TO BE MADE TO THIS DRAWING WITHOUT WRITTEN PERMISSION OF HARRIS KOCHER SMITH. PROPOSED DRAINAGE CALCULATONS DRAINAGE BASIN A B C AREA 0.73 AC 0.13 AC 0.69 AC C TC 5.00 MIN 5.00 MIN 5.00 MIN Q CFS 0.64 CFS 3.08 CFS HISTORIC DRAINAGE CALCULATONS DRAINAGE BASIN A B C AREA 0.93 AC 0.14 AC 0.48 AC C TC 5.00 MIN 5.00 MIN 5.00 MIN Q CFS 0.70 CFS 2.14 CFS BASIN AREA C CMAJOR MINOR AC 0.51 BASIN AREA A CMAJOR MINOR AC 0.82 FILEPATH: P:\160910\ENGINEERING\DRAINAGE\CD - DRAINAGE PLAN.DWG LAYOUT: FINAL DRAINAGE PLAN 7 XREFs: cd - stamp, e-base, e-legal, e-util, p-base, p-legal, p-util PLOTTED: THU 01/19/17 5:13:49P BY: TIM SAYLER BASIN AREA B CMAJOR MINOR AC SCALE: 1" = 20' DESIGNED BY: TJS CHECKED BY: MSM DRAWN BY: TJS Lincoln Street, Suite 1000 Denver, Colorado P: F: HarrisKocherSmith.com BEST PROPERTIES RIVERDALE FIVE RETAIL ISSUE DATE: PROJECT #: DATE REVISION COMMENTS SHEET NO. 12 FINAL DRAINAGE PLAN 12 OF 19