STORM DRAIN STUDY WRIGHT PROPERTY 203 CENTRAL AVENUE GAITHERSBURG, MD

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Pearl McKenzie
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1 STORM DRAIN STUDY WRIGHT PROPERTY 203 CENTRAL AVENUE GAITHERSBURG, MD PRELIMINARY PLAN OF SUBDIVISION LOTS 1-6 AND PARCEL A BEING A RESUBDIVISION OF LOTS 12, 14, & 16 AND PARTS OF LOTS 13,15, & 17 BLOCK 2, OAKMONT JUNE 03, 2016 PREPARED BY: LANDMARK ENGINEERING, INC EXECUTIVE BOULEVARD SUITE 110 ROCKVILLE, MD 20852

3 ~ Il ===A...A G, c. L ===========================================================: consi Iling engineers pi nnar s > surveyors Jun e 03, 2016 Storm Drainage Study 0 1 (30 I) Fax : ( G-S884 E-f fall. larl clma' engr@aol.c(jm RE: Wright Property - Prel iminary Plan of Subdivis ion Prop osed Lots 1-6 and Parcel A being a Resubd ivision of Lots 12,14 & 16 and Part of Lots J3, 15, & 17, Block 2, Oakmont 203 Central Ave, Gaithe rs burg, Md La ndmark Job No Narra tive Statement The prop erty is curre ntly kn own as Lots 12, 14 & 16 and Part of Lots 13, 15, & 17, Block 2, Oakmont. The total property is a 3.68 acre lot with fro ntage along Central Ave nue and is zoned R-200. The site is within the M uddy Branch water shed. The Water Catego ry is W- I and the Sewe r Category is S- I. Existing Conditions: The property is currently developed with one ex isting sing le family dwellin g. The approx imately 302 foo t lot frontage is mostly forested but is brok en by a sing le driveway and cnlvert. There is a stream between the ex isting house and the roadway. Downstream of the prop erty th ere is an ex isting storm drainage sys tem whi ch conveys dra inage across Centra l A venue to a larg e wooded o pen space and on through the resid ential neighborh ood toward Frederick Road (.MD Rou te 355). A schematic ofthe downstream storm drain system is shown on the accompanying Stormwa ter Management Concept Plan. The N atural Resourc es Co nservation Service class ifies the soils as hyd rologic group B and D. T he hydrologic gro up D.' /\V'/ / ' ~:~ "J:< ~ / \ S U BJE CT P RO P E R~/ ;:. ~/\. '"' \ / /< r-. //~/ <\'\" ~\~ l\x ~\)//'\ \ \ soils are close to the strea m. The NRJ/FSD No lo was approved for the property on Jun e 23, Thi s prop erty is su bject to the Montgomery County Fores t Conservation Regulati ons. A Final Forest Co nservation P lan will be required and will be coo rdinated with the Sed imen t Control Pl an.

4 Proposed Development: The owner wants to re-subdivide this property and develop an additional 5 single family dwellings with appurtenances. All 6 lots will be served by a private road which will cross the stream in the same location as the existing driveway. A Stormwater Management Concept has been filed to support the pending submittal of the Preliminary Plan of Subdivision. The property will be served by public water and public sewer. Drainage Area Map: Property boundaries and aerial 2 foot contour topographic information were obtained from MNCPPC GIS web page for the purpose of creating the overall drainage area map. The limits of the drainage areas were estimated from the GIS topography and field confirmed. The aerial GIS information was supplemented by a field survey which included general site improvements, topography, existing roadway features, stream centerline, top and bottom of bank. Hydrology: The contributing drainage area includes properties which are in three different regulatory jurisdictions. The percent impervious was taken from the zoning regulations for Montgomery County, City of Gaithersburg and the Town of Washington Grove and assuming ultimate conditions based on zoning code impervious areas. In addition there is a railroad right of way which was considered 100% impervious. The topography and land cover were evaluated starting from multiple points to find the time of concentration. The drainage areas and time of concentration assumptions were field checked to the ability possible without trespassing on personal property. WinTR55 was used to determine the ultimate runoff conditions for the 2-year, 10-year and 100- year storms at four different study points. Two study points model the separate drainage ways which enter from the east and join 10 feet inside the subject property. An additional study point was evaluated just above the existing driveway culvert. The contributing drainage area does not become 40 acres until below the existing culvert. The last study point is at the stream where it exits the subject property. TR-55 Summary See Appendix A, Pg 3 Tc Point Description 10-Year Discharge 100-Year Discharge A4 Junction SP1 & SP A6 SP3 at upper end of on-site driveway culvert A8 SP4 at exit of property Culvert Design: The existing driveway culvert was determined to be inadequate to pass the 10Year storm event without overtopping the driveway. A new culvert will be installed to replace the existing 18 CMP. Twin 36 inch HDPE pipes are being proposed and are modeled for these studies. A program provided by the Federal Highway Administration called HY-8 was used to evaluate the

5 culve rt. The attached comp utations s how the proposed c ulvert is ca pab le of passin g the 10 Year Sto rm event w itho ut topping the prop osed private street. The JOO-Year Floodplain Stu dy has bee submitted to the Departme nt of Pe rm itt ing Se rv ices for review. The attached Floodplain and Storm Drain Drain age Area Ma p sho ws the pro posed culve rt and the proposed 100-Year Water S urface Elevation. Based on the review co mments from DP S we do not antic ipate any cha nge to the pro posed floodplain. f~:~, Cha rles T. G rims ley, P.E.

7 APPENDIX A TR-55 HYDROLOGIC COMPUTATIONS

9 WIN TR-55 APPENDIX A Page 1 of 10 WinTR-55 Current Data Description --- Identification Data --- User: DVA Date: 4/20/2016 Project: Wright Property Units: English SubTitle: Areal Units: Acres State: Maryland County: Montgomery NOAA_C Filename: P:\2013\1326-Wright-Central_Ave\dwg\Exchange\Out\DPS\Floodplain\1st Sub\Parts\Ultimate.w Sub-Area Data --- Name Description Reach Area(ac) RCN Tc SP1(Upper) Upper Rch SP2(BRNCH) Upper Rch SP3(Clvrt) Lower Rch SP4(Lower) Outlet Total area: (ac) --- Storm Data -- Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) Storm Data Source: Montgomery NOAA_C County, MD (NRCS) Rainfall Distribution Type: Type II Dimensionless Unit Hydrograph: <standard> WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

10 WIN TR-55 APPENDIX A Page 2 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Storm Data Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) Storm Data Source: Montgomery NOAA_C County, MD (NRCS) Rainfall Distribution Type: Type II Dimensionless Unit Hydrograph: <standard> WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

11 WIN TR-55 APPENDIX A Page 3 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Watershed Peak Table Sub-Area Peak Flow by Rainfall Return Period or Reach 2-Yr 10-Yr 100-Yr Identifier (cfs) (cfs) (cfs) SUBAREAS SP1(Upper) SP2(BRNCH) SP3(Clvrt) SP4(Lower) REACHES Lower Rch Down Upper Rch Down OUTLET WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

12 WIN TR-55 APPENDIX A Page 4 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Hydrograph Peak/Peak Time Table Sub-Area Peak Flow and Peak Time (hr) by Rainfall Return Period or Reach 2-Yr 10-Yr 100-Yr Identifier (cfs) (cfs) (cfs) (hr) (hr) (hr) SUBAREAS SP1(Upper) SP2(BRNCH) SP3(Clvrt) SP4(Lower) REACHES Lower Rch Down Upper Rch Down OUTLET WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

13 WIN TR-55 APPENDIX A Page 5 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Sub-Area Summary Table Sub-Area Drainage Time of Curve Receiving Sub-Area Identifier Area Concentration Number Reach Description (ac) (hr) SP1(Upper) Upper Rch SP2(BRNCH) Upper Rch SP3(Clvrt) Lower Rch SP4(Lower) Outlet Total Area: (ac) WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

14 WIN TR-55 APPENDIX A Page 6 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Reach Summary Table Receiving Reach Routing Reach Reach Length Method Identifier Identifier (ft) Lower Rch Outlet 214 CHANNEL Upper Rch Lower Rch 163 CHANNEL WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

15 WIN TR-55 APPENDIX A Page 7 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Sub-Area Time of Concentration Details Sub-Area Flow Mannings's End Wetted Travel Identifier/ Length Slope n Area Perimeter Velocity Time (ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr) SP1(Upper) SHEET SHALLOW SHALLOW CHANNEL Time of Concentration.327 ======== SP2(BRNCH) SHEET SHALLOW CHANNEL Time of Concentration.188 ======== SP3(Clvrt) SHEET SHALLOW Time of Concentration ======== SP4(Lower) SHEET SHALLOW CHANNEL Time of Concentration ======== WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

16 WIN TR-55 APPENDIX A Page 8 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Sub-Area Land Use and Curve Number Details Sub-Area Hydrologic Sub-Area Curve Identifier Land Use Soil Area Number Group (ac) SP1(Upper)CN directly entered by user Total Area / Weighted Curve Number ===== == SP2(BRNCH)Residential districts (1/2 acre) B Residential districts (1/2 acre) C Residential districts (1/2 acre) D Total Area / Weighted Curve Number ==== == SP3(Clvrt)Residential districts (1/2 acre) B Residential districts (1/2 acre) C Residential districts (1/2 acre) D Total Area / Weighted Curve Number === == SP4(Lower)Residential districts (1/2 acre) B Residential districts (1/2 acre) D Total Area / Weighted Curve Number ==== == WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

17 WIN TR-55 APPENDIX A Page 9 of 10 DVA Wright Property Montgomery NOAA_C County, Maryland Reach Channel Rating Details Reach Reach Reach Friction Bottom Side Identifier Length Manning's Slope Width Slope (ft) n (ft/ft) (ft) Lower Rch :1 Upper Rch :1 Reach End Top Friction Identifier Stage Flow Area Width Slope (ft) (cfs) (sq ft) (ft) (ft/ft) Lower Rch Upper Rch WinTR-55, Version Page 1 4/20/2016 2:38:40 PM

18 WIN TR-55 APPENDIX A Page 10 of 10

19 APPENDIX B HY-8 CULVERT CALCULATIONS

21 HY-8 Computations (Ex. 18" Culvert) Page 1 of 9 Page 1 of 28 Site Data - Existing 18 in. Site Data Option: Culvert Invert Data Inlet Station: 0.00 ft Inlet Elevation: ft Outlet Station: ft Outlet Elevation: ft Number of Barrels: 1 Culvert Data Summary - Existing 18 in. Barrel Shape: Circular Barrel Diameter: 1.50 ft Barrel Material: Corrugated Steel Embedment: 0.00 in Barrel Manning's n: Culvert Type: Straight Inlet Configuration: Thin Edge Projecting Inlet Depression: NONE HY-8 Culvert Analysis Report

22 HY-8 Computations (Ex. 18" Culvert) Page 2 of 9 Page 2 of 28 Table 1 - Culvert Summary Table: Existing 18 in. Total Discharge (cfs) Culvert Discharge (cfs) Headwater Inlet Control Elevation (ft) Depth (ft) Outlet Control Depth (ft) Flow Type Normal Depth (ft) Critical Depth (ft) Outlet Depth (ft) Tailwater Depth (ft) Outlet Velocity (ft/s) Tailwater Velocity (ft/s) FFf FFf FFf FFf FFf FFf FFf FFf FFf FFf FFf

23 HY-8 Computations (Ex. 18" Culvert) Page 3 of 9 Page 3 of 28 ******************************************************************************** Straight Culvert Inlet Elevation (invert): ft, Outlet Elevation (invert): ft Culvert Length: ft, Culvert Slope: ********************************************************************************

24 HY-8 Computations (Ex. 18" Culvert) Page 4 of 9 Page 4 of 28 Culvert Performance Curve Plot: Existing 18 in.

25 HY-8 Computations (Ex. 18" Culvert) Page 5 of 9 Page 5 of 28 Water Surface Profile Plot for Culvert: Existing 18 in.

26 HY-8 Computations (Ex. 18" Culvert) Page 6 of 9 Page 6 of 28 Table 2 - Downstream Channel Rating Curve (Crossing: Ex. Driveway Culvert) Flow (cfs) Water Surface Elev (ft) Depth (ft) Velocity (ft/s) Shear (psf) Froude Number

27 HY-8 Computations (Ex. 18" Culvert) Page 7 of 9 Page 7 of 28 Tailwater Channel Data - Ex. Driveway Culvert Tailwater Channel Option: Trapezoidal Channel Bottom Width: 1.50 ft Side Slope (H:V): 2.00 (_:1) Channel Slope: Channel Manning's n: Channel Invert Elevation: ft Roadway Data for Crossing: Ex. Driveway Culvert Roadway Profile Shape: Irregular Roadway Shape (coordinates) Roadway Surface: Paved Roadway Top Width: ft Crossing Discharge Data Discharge Selection Method: Specify Minimum, Design, and Maximum Flow Minimum Flow: 80 cfs Design Flow: 95 cfs Maximum Flow: 225 cfs

28 HY-8 Computations (Ex. 18" Culvert) Page 8 of 9 Page 8 of 28 Table 3 - Summary of Culvert Flows at Crossing: Ex. Driveway Culvert Headwater Elevation (ft) Total Discharge (cfs) Existing 18 in. Discharge (cfs) Roadway Discharge (cfs) Iterations Overtopping

29 HY-8 Computations (Ex. 18" Culvert) Page 9 of 9 Page 9 of 28 Rating Curve Plot for Crossing: Ex. Driveway Culvert

30 HY-8 Computations (Prop. 2 x 36") Page 1 of 9 Page 10 of 28 HY-8 Culvert Analysis Report Site Data - Proposed Culvert (2 X 36) Site Data Option: Culvert Invert Data Inlet Station: 0.00 ft Inlet Elevation: ft Outlet Station: ft Outlet Elevation: ft Number of Barrels: 2 Culvert Data Summary - Proposed Culvert (2 X 36) Barrel Shape: Circular Barrel Diameter: 3.00 ft Barrel Material: Smooth HDPE Embedment: 0.00 in Barrel Manning's n: Culvert Type: Straight Inlet Configuration: Square Edge with Headwall Inlet Depression: NONE

31 HY-8 Computations (Prop. 2 x 36") Page 2 of 9 Page 11 of 28 Table 1 - Culvert Summary Table: Proposed Culvert (2 X 36) Total Discharge (cfs) Culvert Discharge (cfs) Headwater Inlet Control Elevation (ft) Depth (ft) Outlet Control Depth (ft) Flow Type Normal Depth (ft) Critical Depth (ft) Outlet Depth (ft) Tailwater Depth (ft) Outlet Velocity (ft/s) Tailwater Velocity (ft/s) S2n S2n S2n S2n S2n S2n S2n S2n S2n S2n S2n

32 HY-8 Computations (Prop. 2 x 36") Page 3 of 9 Page 12 of 28 ******************************************************************************** Straight Culvert Inlet Elevation (invert): ft, Outlet Elevation (invert): ft Culvert Length: ft, Culvert Slope: ********************************************************************************

33 HY-8 Computations (Prop. 2 x 36") Page 4 of 9 Page 13 of 28 Culvert Performance Curve Plot: Proposed Culvert (2 X 36)

34 HY-8 Computations (Prop. 2 x 36") Page 5 of 9 Page 14 of 28 Water Surface Profile Plot for Culvert: Proposed Culvert (2 X 36)

35 HY-8 Computations (Prop. 2 x 36") Page 6 of 9 Page 15 of 28 Table 2 - Downstream Channel Rating Curve (Crossing: Proposed Culvert (2x36)) Flow (cfs) Water Surface Elev (ft) Depth (ft) Velocity (ft/s) Shear (psf) Froude Number

36 HY-8 Computations (Prop. 2 x 36") Page 7 of 9 Page 16 of 28 Tailwater Channel Data - Proposed Culvert (2x36) Tailwater Channel Option: Trapezoidal Channel Bottom Width: 8.00 ft Side Slope (H:V): 2.00 (_:1) Channel Slope: Channel Manning's n: Channel Invert Elevation: ft Roadway Data for Crossing: Proposed Culvert (2x36) Roadway Profile Shape: Irregular Roadway Shape (coordinates) Roadway Surface: Paved Roadway Top Width: ft Crossing Discharge Data Discharge Selection Method: Specify Minimum, Design, and Maximum Flow Minimum Flow: 80 cfs Design Flow: 95 cfs Maximum Flow: 225 cfs

37 HY-8 Computations (Prop. 2 x 36") Page 8 of 9 Page 17 of 28 Table 3 - Summary of Culvert Flows at Crossing: Proposed Culvert (2x36) Headwater Elevation (ft) Total Discharge (cfs) Proposed Culvert (2 X 36) Discharge (cfs) Roadway Discharge (cfs) Iterations Overtopping

38 HY-8 Computations (Prop. 2 x 36") Page 9 of 9 Page 18 of 28 Rating Curve Plot for Crossing: Proposed Culvert (2x36)

39 HY-8 computations (Existing 42 in. System) Page 1 of 10 Page 19 of 28 Site Data - Ex. 42 in. system Site Data Option: Culvert Invert Data Inlet Station: 0.00 ft Inlet Elevation: ft Upper Break Station: ft Upper Break Elevation: ft Lower Break Station: ft Lower Break Elevation: ft Outlet Station: ft Outlet Elevation: ft Number of Barrels: 1 HY-8 Culvert Analysis Report

40 HY-8 computations (Existing 42 in. System) Page 2 of 10 Page 20 of 28 ******************************************************************************** Double Broken-back Culvert Inlet Elevation (invert): ft Upper Break Elevation (invert): ft Lower Break Elevation (invert): ft Culvert Length: ft Upper Culvert Section Slope: Steep Culvert Section Slope: Runout Culvert Section Slope: ********************************************************************************

41 HY-8 computations (Existing 42 in. System) Page 3 of 10 Page 21 of 28 Culvert Data Summary - Ex. 42 in. system Barrel Shape: Circular Barrel Diameter: 3.50 ft Upper & Middle Section Material: Concrete Lower Section Material: Concrete Embedment: 0.00 in Upper & Middle Section Manning's n: Lower Section Manning's n: Culvert Type: Double Broken-back Inlet Configuration: Square Edge with Headwall Inlet Depression: NONE

42 HY-8 computations (Existing 42 in. System) Page 4 of 10 Page 22 of 28 Table 1 - Culvert Summary Table: Ex. 42 in. system Total Discharge (cfs) Culvert Discharge (cfs) Headwater Inlet Control Elevation (ft) Depth (ft) Outlet Control Depth (ft) Flow Type Normal Depth (ft) Critical Depth (ft) Outlet Depth (ft) Tailwater Depth (ft) Outlet Velocity (ft/s) Tailwater Velocity (ft/s) S1f S1f S1f S1f S1f S1f S1f S1f S1f S1f S1f

43 HY-8 computations (Existing 42 in. System) Page 5 of 10 Page 23 of 28 Culvert Performance Curve Plot: Ex. 42 in. system

44 HY-8 computations (Existing 42 in. System) Page 6 of 10 Page 24 of 28 Water Surface Profile Plot for Culvert: Ex. 42 in. system

45 HY-8 computations (Existing 42 in. System) Page 7 of 10 Page 25 of 28 Table 2 - Downstream Channel Rating Curve (Crossing: Downstream Storm Drain) Flow (cfs) Water Surface Elev (ft) Depth (ft)

46 HY-8 computations (Existing 42 in. System) Page 8 of 10 Page 26 of 28 Tailwater Channel Data - Downstream Storm Drain Tailwater Channel Option: Enter Constant Tailwater Elevation Constant Tailwater Elevation: ft Roadway Data for Crossing: Downstream Storm Drain Roadway Profile Shape: Irregular Roadway Shape (coordinates) Roadway Surface: Paved Roadway Top Width: ft Crossing Discharge Data Discharge Selection Method: Specify Minimum, Design, and Maximum Flow Minimum Flow: 80 cfs Design Flow: 95 cfs Maximum Flow: 240 cfs

47 HY-8 computations (Existing 42 in. System) Page 9 of 10 Page 27 of 28 Table 3 - Summary of Culvert Flows at Crossing: Downstream Storm Drain Headwater Elevation (ft) Total Discharge (cfs) Ex. 42 in. system Discharge (cfs) Roadway Discharge (cfs) Iterations Overtopping

48 HY-8 computations (Existing 42 in. System) Page 10 of 10 Page 28 of 28 Rating Curve Plot for Crossing: Downstream Storm Drain

HY-8 Version 7.2 Build Date January 17, Federal Highway Administration.

HY-8 Version 7.2 Build Date January 17, 2012 Federal Highway Administration http://www.fhwa.dot.gov/engineering/hydraulics/software/hy8/index.cfm SIMPLE Simple to use Use for simple culverts and bridges