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HomeMy WebLinkAboutStormDrainageReport STORM WATER DESIGN REPORT FOR NWX APARTMENTS (INCLUSIVE OF MASTER SITE PLAN, PHASE 1 AND PHASE 2) BOZEMAN, MONTANA Prepared By: Morrison-Maierle, Inc. 2880 Technology Blvd. West P.O. Box 1113 Bozeman, Montana 59771-1113 Engineer: Kevin D. Jacobsen, P.E. Date: September 16, 2021 File: 5305.008 __________________________________________________________________________________ NWX APARTMENTS - STORM WATER DESIGN REPORT 2 NWX APARTMENTS STORM WATER DESIGN REPORT TABLE OF CONTENTS 1.0 Introduction ..................................................................................................... Page 3 2.0 Drainage Patterns ............................................................................................ Page 3 3.0 Hydrological Methodology and Calculations (On-Site Basin) ....................... Page 3 4.0 Retention Pond Calculations and Storm Water Treatment (On-Site Basin) ... Page 4 5.0 Storm Drain Pipe Calculations (On-Site Basin) ............................................. Page 5 6.0 Storm Water Maintenance Plan ...................................................................... Page 6 7.0 Summary ......................................................................................................... Page 6 LIST OF APPENDICES Appendix A. Overall Storm Exhibit B. City of Bozeman Intensity-Duration-Frequency Curve (IDF) C. Basin Hydrology and Calculations __________________________________________________________________________________ NWX APARTMENTS - STORM WATER DESIGN REPORT 3 NWX APARTMENTS STORM WATER DESIGN REPORT 1.0 Introduction A multi-family development is being proposed north of West Oak Street, west of Cottonwood Road, east of Rosa Way, and south of Harvest Parkway. The site plan is in the Northwest Crossing Subdivision that is nearing the final stages of final plat. Eighteen buildings are spread over 15 acres with approximately 338 residential units, a clubhouse and maintenance building. Improvements include driveway approaches off adjacent streets, parking drive aisles and associated parking infrastructure, utility infrastructure including storm drainage, water, sanitary sewer and dry utilities. Park and open spaces are included throughout this development as well. Existing infrastructure surrounding the development is being installed as part of the approved subdivision. 2.0 Drainage Patterns This project is being separated into three areas as it relates to drainage. Each area is essentially a block that will collect its own runoff. Please refer to the attached “STORM” exhibit for a depiction of each drainage area (SW, NW, and NE). The subdivision will handle all the post-development runoff from the right of way areas and pre-development flows from the site. Each individual drainage basin will attenuate the post-development flows. The existing land generally flows from the south to the north at approximately 1.25%. Baxter ditch flows along the west side of Rosa Way. Proposed grading will provide for appropriate vehicular and pedestrian access while routing runoff to the northern edges of each basin. Sheet flow will be the predominant means of conveyance on this site although a limited amount of piping will be utilized to route runoff. 3.0 Hydrological Methodology and Calculations (On-Site Basin) Below is a table that lists each drainage basin, along with the corresponding values necessary for utilizing the Rational Method. The resultant runoff rates and pond sizing can be seen in table as well. The City of Bozeman IDF curves were utilized for the calculations. The C-values used were 0.20 for the pre-development rate which is reasonable for the open land that currently exists. The post-development C-value was generated utilizing a composite calculation based on the percentage of impervious and pervious land. Areas of pervious were given a C-value of 0.20 and pervious areas a value of 0.85. In general, this dense multi-family development has approximately 75% impervious area and we feel that the calculated composite C-value of 0.70 used is appropriate, if not conservative. __________________________________________________________________________________ NWX APARTMENTS - STORM WATER DESIGN REPORT 4 Condition Area (ac) Composite C-Value Tc (min) Q10 (cfs) Q25 (cfs) Detention Size (cu.ft.) First ½” (cu.ft.) Retention Size (cu.ft.) Basin SW Pre-Dev. 6.74 0.20 35 1.22 Basin SW Post-Dev. 6.74 0.70 20 6.17 7.43 5,940 9,800 13,930 Basin NW Pre-Dev. 4.90 0.20 32 0.94 Basin NW Post-Dev. 4.90 0.70 13 5.93 7.12 3,900 7,200 10,130 Basin NE Pre-Dev. 2.47 0.20 36 0.44 Basin NE Post-Dev. 2.47 0.70 16 2.61 3.14 2,090 3,370 5,100 4.0 Storage Pond Calculations and Storm Water Treatment The calculations shown above in the table depict the storage volumes for both detention and retention ponds, as well as the volume associated with the first 0.5-inch of rain. This site is being designed to provide retention for all drainage basins and storage ponds. All ponds will be underground within parking areas around the site. Each retention pond is sized based on a 10-year, 2-hour storm intensity per City of Bozeman requirements. The formula for calculating the retention volume is listed below. V = 7200(C)(I)(A) C = 0.70 I = 0.41 in/hr A = varies per basin The City’s design standards also require Low Impact Development (LID) practices that infiltrate, evapotranspire or capture runoff, to the extent feasible, for a specified design runoff event as noted above with the first 0.5-inch of rainfall. The proposed underground systems will combine both runoff capture and infiltration. Underground systems are __________________________________________________________________________________ NWX APARTMENTS - STORM WATER DESIGN REPORT 5 widely accepted LID systems found to remove 80 percent of total suspended solids from municipal storm runoff, and in the case of retention there will be no discharge from the site for the 10-year storm event. It meets LEED criteria for storm water treatment (SS6.2 water quality credit). The facilities proposed for this project provide for infiltration. Runoff from the first 0.5-inch of rainfall will percolate through a gravel filter layer before infiltrating into the native soil beneath. The native soil underneath the gravel filter layer is a well-draining gravel, cobble and sand mix (based on geotechnical report). This sandy gravel layer exists at various elevations and (~3-feet to 5-feet below existing grade) throughout the site. The bottom of the chambers will be set to ensure that groundwater does not impact the storage volume. Groundwater monitoring has occurred on the site to measure the high groundwater and a groundwater lowering system is being installed to lower the groundwater approximately two feet below the high groundwater level. The system will be installed above the high groundwater and will ensure connection to the underlying gravel strata. In order to provide pretreatment for the underground systems, a combination of pervious pavers and isolator rows will contribute to reducing the amount of debris and sediment that enters the infiltration media. Both the isolator rows and pervious pavers can be periodically cleaned when necessary. Several small underground drywells are proposed to the south of buildings 13 and 14 in basin NW. These drywells will retain small localized low spots due to building finished floor being set below the adjacent roadway. This is the only area where this circumstance occurs. Calculations were completed for these small areas, although not included at this time. Refined calculations will be completed and made available once the site is finalized and the roof drainage lines are confirmed. An area in the NW basin will require a small underground system and outlet pipe connection to the storm drain line in Rosa Way (see “STORM” Exhibit). Calculations have been completed for this small internal basin (475 cu. ft.) and can be made available as necessary. The underground stormwater systems, as described above, along with the gravel strata below the chambers, will provide for runoff capture, TSS removal and infiltration necessary to not only meet, but exceed, the City’s current design standards. 5.0 Storm Drain Pipe Calculations Piping will be utilized only where required for collection and convenance, as the majority of runoff will be via surface flow. The piping, in accordance with City Standards shall be designed to accommodate the 25-year storm event. The SW basin includes most of the piping due the size and complexity of the basin. This basin also includes the clubhouse and pool, which will require area drains in coordination __________________________________________________________________________________ NWX APARTMENTS - STORM WATER DESIGN REPORT 6 with the pool consultant. The overflow for this SW basin, during events larger than 10 years, will surcharge the inlet at the far northwest corner of the site and flow to Wellspring Drive. The NW and NE basins have nearby storm drain infrastructure within the adjacent roadways and will therefore have connections to for storm events exceeding 10 years. Piping throughout the entire site will generally be 15 inches in size, with a larger 18-inch outlet pipe in the NW basin and smaller piping as needed around the pool area. The locations of the outlet pipes and overflows is such that a very large storm event has a route to flow away from structures. Runoff will flow to adjacent roadways and flow down the streets, ultimately making its way to Baxter Ditch. See piping chart below. Basin Interior Pipe (in.) Outlet Pipe (in.) SW 15 N/A NW N/A 18 NE N/A 15 6.0 Storm Water Maintenance Plan The maintenance of on-site storm water collection, retention, and overflow facilities will be integrated as part of the maintenance of the site per the Storm Water Management System Operation and Maintenance Manual submitted with the site plan. Duties shall include routine inspection to ensure that sediment, debris, yard waste, and seasonal ice does not impede operation of the storm drain facilities. It is recommended that these inspections occur after major runoff events and monthly throughout the year. Maintenance of the pervious pavers and underground systems shall be per manufacture recommendations. 7.0 Summary The storm water analysis for the proposed site was completed using applicable state and local regulations/standards as well as sound engineering practices. The result is a storm water plan that provides for the conveyance, storage and treatment of storm water runoff while protecting private property and promoting public safety. APPENDIX A LOT 4 1.62 acs. LOT 2 0.75 acs. LOT 1 2.62 acs. D DSDSDSD DDSDSDSDSDD SD SD D D SDSDSDD 4745.67 D D D SDSDSDSDSDSDDD D D D D D D SD SDSD II ESD BLDG 1 BLDG 2 BLDG 3 BLDG 4 BLDG 7 BLDG 8 BLDG 9 BLDG 13 BLDG 14 BLDG 15 BLDG 17 BLDG 18 BLDG 12 BLDG 11 BLDG 10 BLDG 5 BLDG 6 BLDG 16 8W8S8S8W8W8W 8S8W8W 8WPPPPPPPPPP PPP P P P P P P P PPPPP P D D D SDSDDD DD D D D D SDSDD D D D D D D PPPD P P P P DSD FIGURE NUMBER © PROJECT NO.DRAWN BY: DSGN. BY: APPR. BY: DATE: COPYRIGHT MORRISON-MAIERLE, INC.,2021 N:\5305\008 - NW Crossing Multi Family\ACAD\Exhibits\Storm Drainage Exhibit.dwg Plotted by kevin d. jacobsen on Sep/16/2021 engineers surveyors planners scientists MorrisonMaierle 2880 Technology Blvd West Bozeman, MT 59718 406.587.0721 www.m-m.net 5305.008 STORM KDJ BOZEMAN MONTANA STORM DRAINAGE PLAN KDJ NWX APARTMENTS 09/2021 W. OAK STREET HARVEST P A R K W A Y ROSA WAYWELLSPRING DRIVE DAYSPRING AVENUE COTTONWOOD ROAD80 1600 SCALE IN FEET TWIN LAKES AVEPHASE 1 BOUNDARY: BUILDINGS 1-12 PHASE 2 BOUNDARY: BUILDINGS 13-18 NOTES: 1. STORAGE AND INFILTRATION SYSTEMS WILL INCLUDE A COMBINATION OF UNDERGROUND CHAMBERS (I.E. STORMTECH) AS WELL AS PERVIOUS PAVERS WITHIN DRIVE/PARKING SURFACES TO AID IN PRE-TREATMENT AND INFILTRATION. 2. RUNOFF CONVEYANCE IS PRIMARILY VIA SURFACE RUNOFF ALTHOUGH PIPING IS UTILIZED IN SPECIFIC AREAS THROUGHOUT THE SITE AS NECESSARY. POOL AREA DRAIN PIPING LAYOUT AND SIZING WILL BE FINALIZED IN COORDINATION WITH THE POOL CONSULTANT. 3. ALL STORAGE VOLUMES ARE SIZED FOR RETENTION. THE NW AND NE QUADRANTS HAVE OUTLET PIPING TO ACCOMMODATE LARGER STORM EVENTS. THE SW QUADRANT IS DESIGNED TO OVERFLOW TO WELLSPRING DRIVE DURING LARGER EVENTS. NW NE SW NE DRAINAGE BASIN DESCRIPTOR STORM PIPING STORAGE / INFILTRATION FACILITY UNDERGROUND INFILTRATION CHAMBER RETENTION V=5,100 CU.FT. LINEAR SLOTTED COLLECTION DRAIN 15" OUTLET PIPEUNDERGROUND INFILTRATION CHAMBER RETENTION V=10,130 CU.FT. 18" OUTLET PIPE INLET DRAIN 15" OUTLET PIPE CURB INLET DRAIN UNDERGROUND INFILTRATION CHAMBER RETENTION V=475 CU.FT. UNDERGROUND INFILTRATION DRYWELL RETENTION V=300 CU.FT.UNDERGROUND INFILTRATION DRYWELL RETENTION V=300 CU.FT. UNDERGROUND INFILTRATION CHAMBER RETENTION V=13,930 CU.FT. INLET DRAIN CURB INLET DRAIN 15" PIPE (TYP. THROUGHOUT QUADRANT)BAXTER DITCH APPENDIX B 0 5 10 15 20 25 30 35 40 45 50 55 60 Int. (in/hr) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 10.00 10.00 12.00 12.00 14.00 14.00 Time (min) 100-Yr 50-Yr 25-Yr 10-Yr 5-Yr 2-Yr IDF file: COB IDF.IDF Express Hydraflow IDF Curves Hydraflow IDF Report Page 1 of 1 Return Equation Coefficients (FHA) Period (Yrs) B D E (N/A) 1 0.0000 0.0000 0.0000 -------- 2 4.1995 0.0000 0.6000 -------- 3 0.0000 0.0000 0.0000 -------- 5 7.1453 0.0000 0.6400 -------- 10 9.1617 0.0000 0.6500 -------- 25 10.7179 0.0000 0.6400 -------- 50 13.7204 0.0000 0.6600 -------- 100 15.6922 0.0000 0.6700 -------- N:\2605\027\Design Docs\Reports\Storm Drainage\COB IDF.IDF Intensity = B / (Tc + D)^E Return Intensity Values (in/hr) Period (Yrs) 5 min 10 15 20 25 30 35 40 45 50 55 60 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2 1.60 1.05 0.83 0.70 0.61 0.55 0.50 0.46 0.43 0.40 0.38 0.36 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5 2.55 1.64 1.26 1.05 0.91 0.81 0.73 0.67 0.63 0.58 0.55 0.52 10 3.22 2.05 1.58 1.31 1.13 1.00 0.91 0.83 0.77 0.72 0.68 0.64 25 3.83 2.46 1.89 1.58 1.37 1.22 1.10 1.01 0.94 0.88 0.82 0.78 50 4.74 3.00 2.30 1.90 1.64 1.45 1.31 1.20 1.11 1.04 0.97 0.92 100 5.34 3.35 2.56 2.11 1.82 1.61 1.45 1.33 1.22 1.14 1.07 1.01 Tc = time in minutes. Min Tc = 0 APPENDIX C Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Pre Basin Hydrology (10-yr) Basin SW Hydrograph type = Rational Peak discharge (cfs) = 1.225 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 6.740 Runoff coeff. (C) = 0.2 Rainfall Inten (in/hr) = 0.909 Tc by FAA (min) = 35 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 2,572 (cuft); 0.059 (acft) 0 10 20 30 40 50 60 70 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 1.22 (cfs) FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Pre Basin Hydrology (10-yr) Basin SW Description Flow length (ft) = 610.00 Watercourse slope (%) = 1.56 Runoff coefficient (C) = 0.20 Time of Conc. (min) = 35 Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Post Basin Hydrology (10-yr) Basin SW Hydrograph type = Rational Peak discharge (cfs) = 6.167 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 6.740 Runoff coeff. (C) = 0.7 Rainfall Inten (in/hr) = 1.307 Tc by FAA (min) = 20 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 7,400 (cuft); 0.170 (acft) 0 5 10 15 20 25 30 35 40 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 4.00 4.00 5.00 5.00 6.00 6.00 7.00 7.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 6.17 (cfs)Outflow Hyd *Req. Stor = 5,935 (cuft) * * Estimated FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Post Basin Hydrology (10-yr) Basin SW Description Flow length (ft) = 860.00 Watercourse slope (%) = 1.15 Runoff coefficient (C) = 0.70 Time of Conc. (min) = 20 Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Post Basin Hydrology (25-yr) Basin SW Hydrograph type = Rational Peak discharge (cfs) = 7.434 Storm frequency (yrs) = 25 Time interval (min) = 1 Drainage area (ac) = 6.740 Runoff coeff. (C) = 0.7 Rainfall Inten (in/hr) = 1.576 Tc by FAA (min) = 20 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 8,921 (cuft); 0.205 (acft) 0 5 10 15 20 25 30 35 40 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 Q (cfs) Time (min) Runoff Hydrograph 25-yr frequency Runoff Hyd - Qp = 7.43 (cfs) FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Post Basin Hydrology (25-yr) Basin SW Description Flow length (ft) = 860.00 Watercourse slope (%) = 1.15 Runoff coefficient (C) = 0.70 Time of Conc. (min) = 20 Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 SW Pipe Flow (25-yr Storm) / Piping splits basin so 15-inch appropriate Circular Diameter (ft) = 1.50 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.013 Calculations Compute by: Known Q Known Q (cfs) = 7.43 Highlighted Depth (ft) = 1.23 Q (cfs) = 7.430 Area (sqft) = 1.55 Velocity (ft/s) = 4.78 Wetted Perim (ft) = 3.41 Crit Depth, Yc (ft) = 1.06 Top Width (ft) = 1.15 EGL (ft) = 1.59 0 1 2 3 Elev (ft)Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft) Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Pre Basin Hydrology (10-yr) Basin NW Hydrograph type = Rational Peak discharge (cfs) = 0.944 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 4.900 Runoff coeff. (C) = 0.2 Rainfall Inten (in/hr) = 0.963 Tc by FAA (min) = 32 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 1,812 (cuft); 0.042 (acft) 0 10 20 30 40 50 60 70 Q (cfs) 0.00 0.00 0.10 0.10 0.20 0.20 0.30 0.30 0.40 0.40 0.50 0.50 0.60 0.60 0.70 0.70 0.80 0.80 0.90 0.90 1.00 1.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 0.94 (cfs) FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Pre Basin Hydrology (10-yr) Basin NW Description Flow length (ft) = 490.00 Watercourse slope (%) = 1.43 Runoff coefficient (C) = 0.20 Time of Conc. (min) = 32 Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Post Basin Hydrology (10-yr) Basin NW Hydrograph type = Rational Peak discharge (cfs) = 5.932 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 4.900 Runoff coeff. (C) = 0.7 Rainfall Inten (in/hr) = 1.729 Tc by FAA (min) = 13 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 4,627 (cuft); 0.106 (acft) 0 5 10 15 20 25 30 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 4.00 4.00 5.00 5.00 6.00 6.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 5.93 (cfs)Outflow Hyd *Req. Stor = 3,896 (cuft) * * Estimated FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Post Basin Hydrology (10-yr) Basin NW Description Flow length (ft) = 520.00 Watercourse slope (%) = 1.85 Runoff coefficient (C) = 0.70 Time of Conc. (min) = 13 Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Post Basin Hydrology (25-yr) Basin NW Hydrograph type = Rational Peak discharge (cfs) = 7.120 Storm frequency (yrs) = 25 Time interval (min) = 1 Drainage area (ac) = 4.900 Runoff coeff. (C) = 0.7 Rainfall Inten (in/hr) = 2.076 Tc by FAA (min) = 13 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 5,554 (cuft); 0.127 (acft) 0 5 10 15 20 25 30 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 Q (cfs) Time (min) Runoff Hydrograph 25-yr frequency Runoff Hyd - Qp = 7.12 (cfs) FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Post Basin Hydrology (25-yr) Basin NW Description Flow length (ft) = 520.00 Watercourse slope (%) = 1.85 Runoff coefficient (C) = 0.70 Time of Conc. (min) = 13 Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 NW Pipe Flow (25-yr Storm) Circular Diameter (ft) = 1.50 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.013 Calculations Compute by: Known Q Known Q (cfs) = 7.12 Highlighted Depth (ft) = 1.18 Q (cfs) = 7.120 Area (sqft) = 1.49 Velocity (ft/s) = 4.77 Wetted Perim (ft) = 3.28 Crit Depth, Yc (ft) = 1.04 Top Width (ft) = 1.23 EGL (ft) = 1.53 0 1 2 3 Elev (ft)Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft) Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Pre Basin Hydrology (10-yr) Basin NE Hydrograph type = Rational Peak discharge (cfs) = 0.441 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 2.470 Runoff coeff. (C) = 0.2 Rainfall Inten (in/hr) = 0.892 Tc by FAA (min) = 36 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 952 (cuft); 0.022 (acft) 0 10 20 30 40 50 60 70 80 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 0.44 (cfs) FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Pre Basin Hydrology (10-yr) Basin NE Description Flow length (ft) = 520.00 Watercourse slope (%) = 1.06 Runoff coefficient (C) = 0.20 Time of Conc. (min) = 36 Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Post Basin Hydrology (10-yr) Basin NE Hydrograph type = Rational Peak discharge (cfs) = 2.613 Storm frequency (yrs) = 10 Time interval (min) = 1 Drainage area (ac) = 2.470 Runoff coeff. (C) = 0.7 Rainfall Inten (in/hr) = 1.511 Tc by FAA (min) = 16 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 2,508 (cuft); 0.058 (acft) 0 5 10 15 20 25 30 35 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 Q (cfs) Time (min) Runoff Hydrograph 10-yr frequency Runoff Hyd - Qp = 2.61 (cfs)Outflow Hyd *Req. Stor = 2,083 (cuft) * * Estimated FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Post Basin Hydrology (10-yr) Basin NE Description Flow length (ft) = 630.00 Watercourse slope (%) = 1.35 Runoff coefficient (C) = 0.70 Time of Conc. (min) = 16 Hydrology Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 Post Basin Hydrology (25-yr) Basin NE Hydrograph type = Rational Peak discharge (cfs) = 3.142 Storm frequency (yrs) = 25 Time interval (min) = 1 Drainage area (ac) = 2.470 Runoff coeff. (C) = 0.7 Rainfall Inten (in/hr) = 1.817 Tc by FAA (min) = 16 IDF Curve = COB IDF.IDF Rec limb factor = 1.00 Hydrograph Volume = 3,017 (cuft); 0.069 (acft) 0 5 10 15 20 25 30 35 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 3.00 3.00 4.00 4.00 Q (cfs) Time (min) Runoff Hydrograph 25-yr frequency Runoff Hyd - Qp = 3.14 (cfs) FAA Formula Tc Worksheet Tc = 1.8(1.1 - C) x Flow length^0.5 / Watercourse slope^0.333 Hydraflow Express by Intelisolve Rational Post Basin Hydrology (25-yr) Basin NE Description Flow length (ft) = 630.00 Watercourse slope (%) = 1.35 Runoff coefficient (C) = 0.70 Time of Conc. (min) = 16 Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Sep 15 2021 NE Pipe Flow (25-yr Storm) Circular Diameter (ft) = 1.25 Invert Elev (ft) = 100.00 Slope (%) = 0.50 N-Value = 0.013 Calculations Compute by: Known Q Known Q (cfs) = 3.14 Highlighted Depth (ft) = 0.77 Q (cfs) = 3.140 Area (sqft) = 0.79 Velocity (ft/s) = 3.96 Wetted Perim (ft) = 2.26 Crit Depth, Yc (ft) = 0.72 Top Width (ft) = 1.22 EGL (ft) = 1.01 0 1 2 3 Elev (ft)Section 99.50 100.00 100.50 101.00 101.50 102.00 Reach (ft)