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Home My WebLink About011 Stormwater Design ReportSS62 STORM DRAINAGE PLAN Sundance Springs Comm Lot 2 Synergy Engineering and Konsulting, Inc 3731 Equestrian Lane, STE 102, Bozeman, MT 59718/ 406-624-6137 /marlene@seakmt.com Date: January 10, 2022 REVISED July 27, 2022 Prepared for: City of Bozeman Sundance Springs Subdivision Phase 1B Sundance Springs COMM LOT 2 July 13, 2022 1 Table of Contents 1. GENERAL LOCATION AND DESCRIPTION ........................................................................................... 2 A. LOCATION ....................................................................................................................................... 2 B. DESCRIPTION ............................................................................................................................... 3 2. DRAINAGE DESIGN ........................................................................................................................... 5 A. RUNOFF COEFFICIENTS ................................................................................................................ 5 B. TIME OF CONCENTRATION (Tc) ..................................................................................................... 6 C. STORM INTENSITY (i).................................................................................................................... 6 D. ESTIMATION OF PEAK RUNOFF RATE (RATIONAL METHOD) ......................................................... 6 E. RUNOFF VOLUME, MODIFIED RATIONAL METHOD....................................................................... 6 F. DRAINAGE FACILITIES ................................................................................................................... 7 G. INITIAL STORM WATER FACILITY CALCULATIONS .......................................................................... 7 3. FACILITY MAINTENANCE PLAN ......................................................................................................... 8 A. OWNERSHIP OF FACILITY ............................................................................................................. 8 2. SCHEULE FOR MAINTENANCE ...................................................................................................... 8 3. RESPONSIBLE PARTY .................................................................................................................... 8 4. CERTIFICATION ................................................................................................................................ 8 Sundance Springs COMM LOT 2 July 13, 2022 2 1. GENERAL LOCATION AND DESCRIPTION This Storm Drainage Plan is prepared for the 2-building commercial project proposed within the Sundance Springs Subdivision Phase 1B, Plat J-257. Total acreage is 1.31 acres. The project includes paved access and parking, gravel paths connecting to neighborhood trail systems, two buildings with patios and landscaped areas. A. LOCATION The Sundance Springs Comm Lot 2 project is on 1.31 acres in Bozeman, MT. The closest intersection to the site is South 3rd Ave and Little Horse Drive. The site is bordered on the north and east by open space, Little Horse Drive on the south and South 3rd Ave on the west. The site is currently undeveloped. 1. Owner/Developer: 406 Coal Blowers LLC 2. B-1 Zoning 3. Township 2S, Range 5E, Section 25 4. Access provided by Little Horse Drive Figure 1: Sundance Springs Comm Lot 2 Location Map Sundance Springs COMM LOT 2 July 13, 2022 3 B. DESCRIPTION In-situ Conditions: The site is mostly covered by short herbaceous grasses. The drainage in the general area flows in a north-northeasterly direction. Surveyed ground elevation at the site is between 5032’-5040’ (NAD 88 vertical datum). The site is adjacent to the Middle Creek Ditch and the topography of the site slopes gently toward the ditch in an easterly direction. Existing conditions indicate the property drains as one onsite basin. There is no indication of channelized surface flow within lot boundaries. The longest onsite flow path, based on surveyed ground contours, is shown in Figure 2 (below). Groundwater Elevation: Test pits were excavated for the purpose of geotechnical assessment of the soils pertaining to building foundation designs by Allied Engineering in 2019. A monitoring pipe was installed that is approximately nine feet deep. Groundwater depth was recorded at 6.5 feet below ground surface on August 21, 2019 and 4.7 feet below ground surface on September 24, 2019. The monitoring pipe was checked for ground water in the Spring of 2020 and again in the Spring of 2021 and Spring and Summer of 2022 after an unusually wet weather cycle. No groundwater was found in the monitoring well during any of these site visits. Depth to ground water is estimated at between 6 and greater than 9 feet. Seasonal high groundwater between 4.5-6 feet is possible and most likely due to localized irrigation effects. Interpolated groundwater elevation at the site is approximately 5020’ (Slagle Contours, Gallatin County GIS). Because high groundwater conditions are common throughout the Gallatin Valley, precautions will be taken to ensure ductile iron water mains are protected against corrosion effects. Stormwater retention ponds have been designed to a depth of 2 feet below ground surface to ensure that groundwater is not encountered in those ponds. Sundance Springs COMM LOT 2 July 13, 2022 4 Figure 2: Sundance Springs Comm Lot 2 existing conditions. Proposed Conditions: • Asphalt access drive and parking 0.46 acres • Two commercial buildings, sidewalks, paths, and patios 0.31 acres • Landscape and natural scape areas 0.54 acres • Two retention ponds to capture, infiltrate, and/or evapotranspire runoff. Sundance Springs COMM LOT 2 July 13, 2022 5 Figure 3: Sundance Springs Comm Lot 2 proposed conditions. Proposed grading contours and retention ponds are shown in figure 3. The four proposed onsite drainage sub-basins are outlined in red and the longest flow paths through each sub-basin are shown in blue. 2. DRAINAGE DESIGN Drainage design is based on the requirements in the City of Bozeman Design Standards and Specifications Policy March 2004 (DSSP). DSSP requires that retention ponds be sized based on a 10- year, 2-hour storm intensity. Pre-development, the entire site drains as one basin. Proposed grading and development break the lot into four separate drainage basins. The parking lot and building areas are divided into two basins that terminate in proposed retention basins. Basins 3 and 4 are undeveloped and/or landscaped areas that drain office. Basin 3 is entirely within the watercourse setback and will be undeveloped. Basin 4 is separated from the rest of the site by a proposed berm and will be landscaped. See Figure 3. A. RUNOFF COEFFICIENTS USDA Hydrology Module 206D, Table 1 Value of Runoff Coefficients. a. Pre-Development: Flat Clay and Silt Loam Pasture = 0.36 b. Developed: Asphalt Drive and Parking = 0.70 Commercial Buildings (Roofs, Walkways) = 0.75 Lawn, Landscape = 0.15 c. Developed condition weighted C-coefficient: Sundance Springs COMM LOT 2 July 13, 2022 6 a. Asphalt drive and parking, 0.46 acres, C = 0.70 b. Commercial buildings roofs, walkways, 0.31 acres, C = 0.75 c. Lawn, landscape, and natural areas, 0.54 acres, C = 0.15 B. TIME OF CONCENTRATION (Tc) Peak runoff occurs when the duration of the storm equals the time of concentration (calculations attached). a. Pre-development Tc: 15.2 minutes b. Developed Conditions Basin 1 Tc: 14.2 minutes c. Developed Conditions Basin 2 Tc: 10.6 minutes d. Developed Conditions Basin 3 Tc: 8.1 minutes e. Developed Conditions Basin 4 Tc: 2.5 minutes C. STORM INTENSITY (i) Duration is assumed to be equal to the time of concentration. Bozeman DSSP Figures 1-2, 1-3 were used to determine rainfall intensity for the design storm. As storm duration increases, intensity decreases. a. Pre-development design storm intensity: 1.56 in/hr b. Developed Conditions Basin 1 design storm intensity: 1.63 in/hr c. Developed Conditions Basin 2 design storm intensity: 1.97 in/hr d. Developed Conditions Basin 3 design storm intensity: 2.36 in/hr e. Developed Conditions Basin 4 design storm intensity: 5 in/hr D. ESTIMATION OF PEAK RUNOFF RATE (RATIONAL METHOD) Rational Formula, Q = CIA (Calculations attached). a. Pre-development peak runoff rate: 0.74 cfs b. Developed Conditions Basin 1 peak runoff rate: 0.51 cfs c. Developed Conditions Basin 2 peak runoff rate: 0.63 cfs d. Developed Conditions Basin peak runoff rate: 0.12 cfs e. Developed Conditions Basin 4 peak runoff rate: 0.06 cfs E. RUNOFF VOLUME, MODIFIED RATIONAL METHOD Autodesk Storm and Sanitary Analysis (SSA) was used to compute modified rational method outputs for the pre- and post-development drainage conditions. SSA output reports are attached. 1. Bozeman DSSP requires that the modified rational method approach be used to compute runoff volume for storm durations equal to or greater than the time of concentration. 2. Maximum Runoff Rates (SSA outputs, modified rational method) a. Pre-development: 0.19 cfs b. Developed Conditions Basin 1: 0.13 cfs c. Developed Conditions Basin 2: 0.13 cfs Sundance Springs COMM LOT 2 July 13, 2022 7 d. Developed Conditions Basin 3: 0.02 cfs e. Developed Conditions Basin 4: 0.01 cfs 3. Total runoff volume is computed by multiplying the duration of the storm by the runoff rate. Bozeman DSSP specifies a 2-hour design storm with a return interval of 10 years for commercial development. a. Pre-development Runoff Volume: 1368 cf b. Developed Conditions Basin 1 Runoff Volume: 936 cf c. Developed Conditions Basin 2 Runoff Volume: 936 cf d. Developed Conditions Basin 3 Runoff Volume: 144 cf e. Developed Conditions Basin 4 Runoff Volume: 72 cf : f. Entire Developed Site Runoff Volume: 2088 cf g. Increase in Runoff Volume Post-Development: 2088 – 1368 = 720 cf F. DRAINAGE FACILITIES 1. The existing site slopes to the northeast. Finished grading shall direct drainage to the east. Two retention basins are proposed adjacent to the parking lot as shown in Figure 3. While Basins 3 and 4 do not have retention facilities, these portions of the site will remain undeveloped and will experience no increase in runoff. The west retention pond shall be 44 feet wide and 63 feet in length. It will be south of the West Building entrance. Side slopes shall be 4:1 to a maximum basin depth of 2 feet. West retention pond capacity calculated by average end area area is 2,469 cf. The east retention pond shall be 25 feet wide and 47 feet in length. Side slopes shall be 4:1 to a maximum basin depth of 2 feet. Pond capacity calculated by average end area is 1,045 cf. Both retention ponds are large enough to retain the entirety of the estimated runoff from a 10-year storm event for their catchment subbasins. Overall retention volume is 3,514 cubic feet. Any overflow during large storms will exit the retention ponds through a riprap channel into landscaped areas following historic flow patterns to Middle Creek Ditch. Runoff is not expected to negatively impact surface water quality of Middle Creek Ditch, which already serves as a receiving water for outfall from the storm sewer infrastructure in the adjacent neighborhood. The basins shall be grass lined and complement landscaping of the site. G. INITIAL STORM WATER FACILITY CALCULATIONS Bozeman DSSP and DEQ-8 require any project greater or equal to one acre to provide facilities to retain and/or infiltrate the first 0.5 inches of rainfall from a 24-hour storm event preceded by 48 hours of no measurable precipitation. Calculations below follow guidance in DEQ-8 Appendix C. 1. Lot size = 1.31 acres 2. Post-Development Impervious area = 35283.6 SQFT (buildings, concrete, and asphalt) 3. V = (0.5 in * 35,283.6 SQFT) / 12 in/ft = 1470.15 cubic feet of volume Sundance Springs COMM LOT 2 July 13, 2022 8 The initial storm water facility must provide a minimum volume of 1,470 ft3 of storage to retain or infiltrate the first 0.5 inches from a storm event. The two proposed retention ponds provide 3,514 ft3 of storage capacity meeting this requirement. 3. FACILITY MAINTENANCE PLAN A. OWNERSHIP OF FACILITY 1. Sundance Springs Commercial HOA. 2. SCHEULE FOR MAINTENANCE 1. The retention area should be regularly inspected for signs of erosion, seepage, and structural damage. Sediment should be removed and the basin restored to its original dimensions when the sediment has accumulated to one-half the design depth of the basin or 50% of the design capacity. Andy signs of erosion and/or structural damage to the detention basin noted during an inspection should be repaired immediately. Basin should be inspected once every 14 calendar days and within 24 hours of the end of a storm event of 0.5 inches or greater. 3. RESPONSIBLE PARTY 1. Sundance Springs Commercial HOA. 4. CERTIFICATION This report and drainage plan for the Sundance Springs Commercial Lot 2 was prepared by me (or under my direct supervision) in accordance with the provisions of the City of Bozeman “Design Standards and Specifications Policy”. Signature: State of Montana No. 20459 7-27-22 Time of Concentration Equation: 1.87(1.1-C*Cf)D0.5 / S0.33 Rational Method, 10-year storm Modified Rational Method Flat Clay/Silt Loam Pasture 0.36 10-year storm 10-year storm, D=Tc Asphalt Drive/Parking 0.7 D=Tc RUNOFF RATES FROM SSA Commercial Buildings 0.75 Lawn, Landscape 0.15 Predevelopment: 1 Basin Predevelopment: 1 Basin AC C C*SF C = 0.36 C = 0.36 Total Area 1.31 i = 1.562428 in/hr Q = 0.19 cfs Area Undeveloped 1.31 0.36 0.47 A = 1.31 ac V = 1368 CF Area Building 0.00 0.75 0.00 Q = 0.736841 cfs Area Asphalt 0.00 0.7 0.00 V = 5305.257 CF Area Lawn 0.00 0.15 0.00 Weighted C, Developed 0.36 Drainage Path Length 319.00 ft Drainage Path Slope 4.30 % Frequency Adjustment Factor 1.00 Time of Concentration, Tc 15.20 min Developed Basin 1 Developed Basin 1 AC C C*SF C = 0.55 C = 0.55 Total Area 0.57 i = 1.632096 in/hr Q = 0.13 cfs Area Undeveloped 0.00 0.36 0.00 A = 0.57 ac V = 936 CF Area Building 0.20 0.75 0.15 Q = 0.506564 cfs Area Asphalt 0.19 0.7 0.14 V = 3647.26 CF Area Lawn 0.18 0.15 0.03 Weighted C, Developed 0.55 Drainage Path Length 247.00 ft Drainage Path Slope 1.50 % Frequency Adjustment Factor 1.00 Time of Concentration, Tc 14.21 min Developed Basin 2 Developed Basin 2 AC C C*SF C = 0.61 C = 0.61 Total Area 0.52 i = 1.974182 in/hr Q = 0.13 cfs Area Undeveloped 0.00 0.36 0.00 A = 0.52 ac V = 936 CF Area Building 0.17 0.75 0.13 Q = 0.629125 cfs Area Asphalt 0.25 0.7 0.18 V = 4529.7 CF Area Lawn 0.10 0.15 0.01 Weighted C, Developed 0.61 Drainage Path Length 255.00 ft Drainage Path Slope 2.60 % Frequency Adjustment Factor 1.00 Time of Concentration, Tc 10.61 min Developed Basin 3 Developed Basin 3 AC C C*SF C = 0.36 C = 0.36 Total Area 0.14 i = 2.356453 in/hr Q = 0.02 cfs Area Undeveloped 0.14 0.36 0.05 A = 0.14 ac V = 144 CF Area Building 0.00 0.75 0.00 Q = 0.118647 cfs Area Asphalt 0.00 0.7 0.00 V = 854.2598 CF Area Lawn 0.00 0.15 0.00 Weighted C, Developed 0.36 Drainage Path Length 134.00 ft Drainage Path Slope 7.80 % Frequency Adjustment Factor 1.00 Time of Concentration, Tc 8.08 min Developed Basin 4 Developed Basin 4 AC C C*SF C = 0.15 C = 0.15 Total Area 0.08 i = 4.999821 in/hr Q = 0.01 cfs Area Undeveloped 0.36 0.00 A = 0.08 ac V = 72 SF Area Building 0.00 0.75 0.00 Q = 0.059998 cfs Area Asphalt 0.00 0.7 0.00 V = 431.9845 SF Area Lawn 0.08 0.15 0.01 Weighted C, Developed 0.15 TOTAL POST DEV RUNOFF VOLUME Drainage Path Length 15.00 ft 2088 SF Drainage Path Slope 20.00 %DIFFERENCE IN VOLUME Frequency Adjustment Factor 1.00 720 SF Time of Concentration, Tc 2.54 min Onsite Basin 3 Onsite Basin 4 Predevelopment: 1 Basin Runoff Coefficients C Onsite Basin 1 Onsite Basin 2 Project Description Post Mod Rational 10yr.SPF Project Options CFS Elevation Modified Rational User-Defined Hydrodynamic YES NO Analysis Options Mar 23, 2022 01:00:00 Mar 24, 2022 01:00:00 Mar 23, 2022 01:00:00 0 days 0 01:00:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 30 seconds Number of Elements Qty 0 4 4 0 4 0 0 0 0 0 0 0 0 0 0 0 0 Rainfall Details 10 year(s) Outlets .......................................................................... Pollutants .............................................................................. Land Uses ............................................................................ Return Period........................................................................ Links...................................................................................... Channels ...................................................................... Pipes ............................................................................ Pumps .......................................................................... Orifices ......................................................................... Weirs ............................................................................ Nodes.................................................................................... Junctions ...................................................................... Outfalls ......................................................................... Flow Diversions ........................................................... Inlets ............................................................................ Storage Nodes ............................................................. Runoff (Dry Weather) Time Step .......................................... Runoff (Wet Weather) Time Step ........................................ Reporting Time Step ............................................................ Routing Time Step ................................................................ Rain Gages ........................................................................... Subbasins.............................................................................. Enable Overflow Ponding at Nodes ...................................... Skip Steady State Analysis Time Periods ............................ Start Analysis On .................................................................. End Analysis On ................................................................... Start Reporting On ................................................................ Antecedent Dry Days ............................................................ File Name ............................................................................. Flow Units ............................................................................. Elevation Type ...................................................................... Hydrology Method ................................................................. Time of Concentration (TOC) Method .................................. Link Routing Method ............................................................. Subbasin Summary SN Subbasin Area Weighted Total Total Total Peak Time of ID Runoff Rainfall Runoff Runoff Runoff Concentration Coefficient Volume (ac)(in)(in)(ac-in)(cfs)(days hh:mm:ss) 1 OnsiteSub1 0.57 0.5500 0.82 0.45 0.26 0.13 0 00:14:12 2 OnsiteSub2 0.52 0.6100 0.82 0.50 0.26 0.13 0 00:10:36 3 OnsiteSub3 0.14 0.3600 0.82 0.29 0.04 0.02 0 00:08:04 4 OnsiteSub4 0.08 0.1500 0.82 0.12 0.01 0.01 0 00:02:32 Subbasin Hydrology Subbasin : Onsite Basin 1 Input Data Area (ac) .......................................................0.57 Weighted Runoff Coefficient ........................0.5500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Developed 0.57 B 0.55 Composite Area & Weighted Runoff Coeff.0.57 0.55 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.45 Peak Runoff (cfs) .........................................0.13 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.5500 Time of Concentration (days hh:mm:ss) ......0 00:14:13 Subbasin : Onsite Basin 1 Subbasin : Onsite Basin 2 Input Data Area (ac) .......................................................0.52 Weighted Runoff Coefficient ........................0.6100 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Developed 0.52 -0.61 Composite Area & Weighted Runoff Coeff.0.52 0.61 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.50 Peak Runoff (cfs) .........................................0.13 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.6100 Time of Concentration (days hh:mm:ss) ......0 00:10:37 Subbasin : Onsite Basin 2 Subbasin : Onsite Basin 3 Input Data Area (ac) .......................................................0.14 Weighted Runoff Coefficient ........................0.3600 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Undeveloped 0.14 -0.36 Composite Area & Weighted Runoff Coeff.0.14 0.36 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.29 Peak Runoff (cfs) .........................................0.02 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.3600 Time of Concentration (days hh:mm:ss) ......0 00:08:05 Subbasin : Onsite Basin 3 Subbasin : Onsite Basin 4 Input Data Area (ac) .......................................................0.08 Weighted Runoff Coefficient ........................0.1500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Landscaped 0.08 -0.15 Composite Area & Weighted Runoff Coeff.0.08 0.15 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.12 Peak Runoff (cfs) .........................................0.01 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.1500 Time of Concentration (days hh:mm:ss) ......0 00:02:32 Subbasin : Onsite Basin 4 Project Description Post Mod Rational 2yr.SPF Project Options CFS Elevation Modified Rational User-Defined Hydrodynamic YES NO Analysis Options Mar 23, 2022 01:00:00 Mar 24, 2022 01:00:00 Mar 23, 2022 01:00:00 0 days 0 01:00:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 30 seconds Number of Elements Qty 0 4 4 0 4 0 0 0 0 0 0 0 0 0 0 0 0 Rainfall Details 2 year(s) Outlets .......................................................................... Pollutants .............................................................................. Land Uses ............................................................................ Return Period........................................................................ Links...................................................................................... Channels ...................................................................... Pipes ............................................................................ Pumps .......................................................................... Orifices ......................................................................... Weirs ............................................................................ Nodes.................................................................................... Junctions ...................................................................... Outfalls ......................................................................... Flow Diversions ........................................................... Inlets ............................................................................ Storage Nodes ............................................................. Runoff (Dry Weather) Time Step .......................................... Runoff (Wet Weather) Time Step ........................................ Reporting Time Step ............................................................ Routing Time Step ................................................................ Rain Gages ........................................................................... Subbasins.............................................................................. Enable Overflow Ponding at Nodes ...................................... Skip Steady State Analysis Time Periods ............................ Start Analysis On .................................................................. End Analysis On ................................................................... Start Reporting On ................................................................ Antecedent Dry Days ............................................................ File Name ............................................................................. Flow Units ............................................................................. Elevation Type ...................................................................... Hydrology Method ................................................................. Time of Concentration (TOC) Method .................................. Link Routing Method ............................................................. Subbasin Summary SN Subbasin Area Weighted Total Total Total Peak Time of ID Runoff Rainfall Runoff Runoff Runoff Concentration Coefficient Volume (ac)(in)(in)(ac-in)(cfs)(days hh:mm:ss) 1 OnsiteSub1 0.57 0.5500 0.48 0.26 0.15 0.08 0 00:14:12 2 OnsiteSub2 0.52 0.6100 0.48 0.29 0.15 0.08 0 00:10:36 3 OnsiteSub3 0.14 0.3600 0.48 0.17 0.02 0.01 0 00:08:04 4 OnsiteSub4 0.08 0.1500 0.48 0.07 0.01 0.00 0 00:02:32 Subbasin Hydrology Subbasin : Onsite Basin 1 Input Data Area (ac) .......................................................0.57 Weighted Runoff Coefficient ........................0.5500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Developed 0.57 B 0.55 Composite Area & Weighted Runoff Coeff.0.57 0.55 Subbasin Runoff Results Total Rainfall (in) ..........................................0.48 Total Runoff (in) ............................................0.26 Peak Runoff (cfs) .........................................0.08 Rainfall Intensity ...........................................0.238 Weighted Runoff Coefficient ........................0.5500 Time of Concentration (days hh:mm:ss) ......0 00:14:13 Subbasin : Onsite Basin 1 Subbasin : Onsite Basin 2 Input Data Area (ac) .......................................................0.52 Weighted Runoff Coefficient ........................0.6100 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Developed 0.52 -0.61 Composite Area & Weighted Runoff Coeff.0.52 0.61 Subbasin Runoff Results Total Rainfall (in) ..........................................0.48 Total Runoff (in) ............................................0.29 Peak Runoff (cfs) .........................................0.08 Rainfall Intensity ...........................................0.238 Weighted Runoff Coefficient ........................0.6100 Time of Concentration (days hh:mm:ss) ......0 00:10:37 Subbasin : Onsite Basin 2 Subbasin : Onsite Basin 3 Input Data Area (ac) .......................................................0.14 Weighted Runoff Coefficient ........................0.3600 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Undeveloped 0.14 -0.36 Composite Area & Weighted Runoff Coeff.0.14 0.36 Subbasin Runoff Results Total Rainfall (in) ..........................................0.48 Total Runoff (in) ............................................0.17 Peak Runoff (cfs) .........................................0.01 Rainfall Intensity ...........................................0.238 Weighted Runoff Coefficient ........................0.3600 Time of Concentration (days hh:mm:ss) ......0 00:08:05 Subbasin : Onsite Basin 3 Subbasin : Onsite Basin 4 Input Data Area (ac) .......................................................0.08 Weighted Runoff Coefficient ........................0.1500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Landscaped 0.08 -0.15 Composite Area & Weighted Runoff Coeff.0.08 0.15 Subbasin Runoff Results Total Rainfall (in) ..........................................0.48 Total Runoff (in) ............................................0.07 Peak Runoff (cfs) .........................................0.00 Rainfall Intensity ...........................................0.238 Weighted Runoff Coefficient ........................0.1500 Time of Concentration (days hh:mm:ss) ......0 00:02:32 Subbasin : Onsite Basin 4 Project Description Post Mod Rational 100yr.SPF Project Options CFS Elevation Modified Rational User-Defined Hydrodynamic YES NO Analysis Options Mar 23, 2022 01:00:00 Mar 24, 2022 01:00:00 Mar 23, 2022 01:00:00 0 days 0 01:00:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 30 seconds Number of Elements Qty 0 4 4 0 4 0 0 0 0 0 0 0 0 0 0 0 0 Rainfall Details 10 year(s) Outlets .......................................................................... Pollutants .............................................................................. Land Uses ............................................................................ Return Period........................................................................ Links...................................................................................... Channels ...................................................................... Pipes ............................................................................ Pumps .......................................................................... Orifices ......................................................................... Weirs ............................................................................ Nodes.................................................................................... Junctions ...................................................................... Outfalls ......................................................................... Flow Diversions ........................................................... Inlets ............................................................................ Storage Nodes ............................................................. Runoff (Dry Weather) Time Step .......................................... Runoff (Wet Weather) Time Step ........................................ Reporting Time Step ............................................................ Routing Time Step ................................................................ Rain Gages ........................................................................... Subbasins.............................................................................. Enable Overflow Ponding at Nodes ...................................... Skip Steady State Analysis Time Periods ............................ Start Analysis On .................................................................. End Analysis On ................................................................... Start Reporting On ................................................................ Antecedent Dry Days ............................................................ File Name ............................................................................. Flow Units ............................................................................. Elevation Type ...................................................................... Hydrology Method ................................................................. Time of Concentration (TOC) Method .................................. Link Routing Method ............................................................. Subbasin Summary SN Subbasin Area Weighted Total Total Total Peak Time of ID Runoff Rainfall Runoff Runoff Runoff Concentration Coefficient Volume (ac)(in)(in)(ac-in)(cfs)(days hh:mm:ss) 1 OnsiteSub1 0.57 0.5500 0.82 0.45 0.26 0.13 0 00:14:12 2 OnsiteSub2 0.52 0.6100 0.82 0.50 0.26 0.13 0 00:10:36 3 OnsiteSub3 0.14 0.3600 0.82 0.29 0.04 0.02 0 00:08:04 4 OnsiteSub4 0.08 0.1500 0.82 0.12 0.01 0.01 0 00:02:32 Subbasin Hydrology Subbasin : Onsite Basin 1 Input Data Area (ac) .......................................................0.57 Weighted Runoff Coefficient ........................0.5500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Developed 0.57 B 0.55 Composite Area & Weighted Runoff Coeff.0.57 0.55 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.45 Peak Runoff (cfs) .........................................0.13 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.5500 Time of Concentration (days hh:mm:ss) ......0 00:14:13 Subbasin : Onsite Basin 1 Subbasin : Onsite Basin 2 Input Data Area (ac) .......................................................0.52 Weighted Runoff Coefficient ........................0.6100 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Developed 0.52 -0.61 Composite Area & Weighted Runoff Coeff.0.52 0.61 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.50 Peak Runoff (cfs) .........................................0.13 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.6100 Time of Concentration (days hh:mm:ss) ......0 00:10:37 Subbasin : Onsite Basin 2 Subbasin : Onsite Basin 3 Input Data Area (ac) .......................................................0.14 Weighted Runoff Coefficient ........................0.3600 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Undeveloped 0.14 -0.36 Composite Area & Weighted Runoff Coeff.0.14 0.36 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.29 Peak Runoff (cfs) .........................................0.02 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.3600 Time of Concentration (days hh:mm:ss) ......0 00:08:05 Subbasin : Onsite Basin 3 Subbasin : Onsite Basin 4 Input Data Area (ac) .......................................................0.08 Weighted Runoff Coefficient ........................0.1500 Runoff Coefficient Area Soil Runoff Soil/Surface Description (acres)Group Coeff. Landscaped 0.08 -0.15 Composite Area & Weighted Runoff Coeff.0.08 0.15 Subbasin Runoff Results Total Rainfall (in) ..........................................0.82 Total Runoff (in) ............................................0.12 Peak Runoff (cfs) .........................................0.01 Rainfall Intensity ...........................................0.408 Weighted Runoff Coefficient ........................0.1500 Time of Concentration (days hh:mm:ss) ......0 00:02:32 Subbasin : Onsite Basin 4