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HomeMy WebLinkAbout022_STORM-Warbler 190 NORTHSTAR LANE BOZEMAN, MT 59718 406-581-5730 www.headwatersmt.net Page 1 of 8 Storm Water Management Design Report Catalyst by Del Park Homes TBD Catalyst Street Lot 3, Block 21 of Cattail Creek Subdivision, Phase 3 Bozeman, Montana May 2023 Headwaters Engineering, Inc. Project #: 2036.001 Prepared For: Delpark USA (Warbler), Inc. Bozeman, MT 59715 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 2 of 8 Storm Water Management Design Report Table of Contents I. Project Background……………………………………………………………………………………………….. 3 1. Introduction………………………………………………………………………………………………………………. 3 2. Soil and Groundwater……………………………………………………………………………………………….. 3 3. Land Use……………………………………………………………………………………………………………………. 3 II. Existing Conditions…………………………………………………..………………………………………………. 4 1. Drainage Basins and Pre-Development Peak Flows…………………………………………………… 4 III. Proposed Drainage Plan and Post-Development Peak Flows…………………………………. 4 1. Major Drainage System…………………………………………………………………………………………….. 5 2. Minor Drainage System…………………………………………………………………………………………….. 5 3. Initial Stormwater Facility and Initial Abstraction………………………………………………………. 6 4. Maintenance…………………………………………………………………………………………………………….. 6 IV. Conclusion………………………………………………………………………………………….……………………. 7 List of Tables Table 1. Estimated Pre-Development Peak Flows……………………………………………………………………….. 5 Table 3. Estimated Post-Development Peak Flows……………………………………………………………………… 5 Table 4. Required Pond Volumes ……………………………………..………………………………………………………… 5 Table 5. Proposed Drainage Conveyance Structures Capacities …………………………………………………… 6 Appendix A—Calculations Grading and Drainage Exhibits Pre/Post Development Drainage Basin Flows Storm Pond Calculations Conveyance Structure Modeling List of References City of Bozeman Design Standards and Specifications Policy, March 2004, and all addenda. Cattail Creek Subdivision, Phase 3 Design Report (2004 TD&H) Cattail Creek Stormwater Detention Ponds Design Report (Confluence Consulting, Inc., October 2021) 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 3 of 8 I. Project Background Introduction The Catalyst Project consists of two 4-plex residential buildings with a total of 8 residential units. The site is on the 0.555-acre Lot 3, Block 21 of Plat J-415 of the Cattail Creek Subdivision, Phase 3. The existing lot is located in the NW ¼ of Section 35, T01S, R05E, PMM in Bozeman, Gallatin County, Montana. This design report outlines the storm water analysis conducted for the site and describes the storm water drainage and management facilities required for the Catalyst project by state and local regulations. The storm water plan follows the design standards set forth by the City of Bozeman in Design Standards and Specifications Policy, March 2004 and subsequent addenda. Soil and Groundwater The NRCS Soil Survey identifies the major soil type on the site to be Blackdog silt loam (50B). This soil belongs to hydrologic soil group C as it is comprised primarily of silts and loams with moderately high saturated conductivity. Groundwater monitoring for the subdivision was conducted by TD&H Engineering in 2004 and the wells in the area showed groundwater at a maximum elevation of 4.33 feet below ground surface. The proposed onsite detention pond is elevated roughly 2 to 3 feet above existing ground, providing roughly 6 to 7 feet of separation from high groundwater. Land Use The pre-development land use on the site was a vacant lot from the Cattail Creek Subdivision. The land is currently zoned R-3 and the proposed use is for residential units. Figure 1 – Vicinity map of subject property of regional storm ponds. II. Existing Conditions The Catalyst project lies east of Warbler Way, at its intersection with Catalyst Street. The existing site slopes generally to the north. Slopes on the site vary from 10% near the southern edge to 1.5% moving north. The existing high point of the property is located along the southern edge at the existing sidewalk with the low 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 4 of 8 point occurring in the northeast corner of the parcel. The existing topography routed all runoff naturally to the northeast portion of the lot, and eventually into the stormwater infrastructure of the Cattail Creek Subdivision. Existing stormwater infrastructure near the site is composed of 15” RCP pipe under Warbler Way, standard curb inlets, and regional storm ponds on the west side of Warbler Way in the Subdivision’s park area. Existing infrastructure was designed to accommodate the runoff associated with the subdivision at full build-out. The original design report, prepared by TD&H Engineering, is included in the subsequent pages. The aforementioned regional storm ponds were later analyzed by Confluence Consulting, where it was determined that the existing conditions of the regional ponds had significantly reduced the available capacity. Their report, completed in October 2020, recommended that action be taken to clear sediment build-up, vegetation, and further update the ponds to restore their volume. Conversations were had with the Cattail Creek HOA, and they stated that they were working on updating all of the storm ponds within the Subdivision, but had not yet gotten to the regional pond of interest. The Cattail Creek HOA was going to reach back out to the City to help determine the best path forward. Drainage Basins and Pre-development Peak Flows Headwaters has identified the onsite drainage basin as shown on the Stormwater Exhibit ST-1 found in Appendix A. The 0.56-acre basin encompasses the full area of the subject lot. Estimates of runoff and the corresponding calculations for the basin were completed using the Modified Rational Method. The basin uses a pre-development runoff coefficient of C = 0.20. The post-developed coefficient of C = 0.63 was determined as a result of the proposed site developments and increase to the impervious area. The regional storm pond was designed with a C factor of 0.45 for this lot and therefore additional pond volume is necessary. Offsite flows have been accounted for with the original design of the subdivision and its stormwater infrastructure. The site does not experience offsite flows as a result of the high side of the lot being Catalyst Street which captures and conveys all upgradient stormwater flows. The west side of the property is Warbler Way which also captures and conveys any stormwater flows. The stormwater from the property to the east flows north, not entering the subject property. The 10-year, 25-year, and 100-yr storm intervals were used in the analysis of the existing storm water conveyance structures in or near the site. A summary of estimated pre-development peak runoff rates can be found in Table 1. Detailed calculations are available in Appendix A. Table 1. Estimated Pre-Development Peak Flows (see sheet ST-1) Sub Area Description Area Tc Q10 Q25 Q100 (acres) (min) (cfs) (cfs) (cfs) A Onsite Basin - Rational 0.56 30 0.11 0.14 0.18 III. Proposed Drainage Plan and Estimated Post-Development Peak Flows The proposed drainage plan will build off the existing drainage system in place. The plan consists of two separate drainage systems. First, the major drainage system is designed to provide much higher conveyance capacity and shall convey excess runoff from the 100-year storm without inundating any structures. Secondly, the minor drainage system fits within the major drainage system and feeds into it. The minor drainage system(s) are designed to accommodate moderate and relatively frequent storm events without inconveniencing the public. The minor system is comprised of the pavements, curb and gutter, culverts, and swales designed to convey runoff from the 10-year and 25-year events, and retention or detention ponds designed to attenuate the 10-year storm event. Table 2 presents a summary of the expected post- development peak flow rates passing through the proposed project. Appendix E of the attached Cattail Creek Subdivision’s Design Report also addresses storm water. 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 5 of 8 Table 2. Estimated Post-Development Peak Flows (see sheet ST-1) Sub Area Description Area C Tc Q10 Q25 Q100 (acres) (min) (cfs) (cfs) (cfs) A Onsite Basin A - Rational 0.56 0.67 25 0.40 0.48 0.64 Major Drainage System The major drainage system in the area is comprised of a paved street network with curb and gutter that are graded in a manner to convey runoff through and out of the subdivision to Catamount Street. Developed sites within the area are graded to promote surface flow onto said streets, with building elevations set above the back of curb heights. Site grading onsite shall be completed so that any runoff resulting from storm events greater than the 10-year and less than the 100-year will flow through the parking lots and down conveyance swales without inundating any structures or causing significant erosion onsite. Runoff from the site will then continue along the existing subdivision grading features, being asphalt roadways with curb and gutter, storm inlets, and overland flow into the existing regional storm ponds. Any flows which over inundate the regional storm ponds will discharge into Cattail Creek as they have historically. The stormwater from the site which exceeds the capacity of the storm infrastructure will flow in a shallow swale on the north side of Building 1. Section A-A, shown on sheet ST-1 was modeled with the 100-year discharge to confirm that the water level in the swale north of building 1 will not exceed the edges of the swale, and therefore not overtop the retaining wall or inundate the buildings. Calculations and a section-view are attached in Appendix A. Minor Drainage System There is existing storm infrastructure in Warbler Way and Catamount Street which capture and convey 25-year flows to a large regional pond via curb inlets and RCP pipe. The large regional storm pond discharges to the north into Cattail Creek. The existing infrastructure will be utilized for the site through a new curb inlet structure on the existing 15” RCP in Warbler Way. The onsite storm pipe will connect to the new curb inlet to convey onsite water to the existing regional pond. The minor drainage system also includes the proposed detention pond on the north edge of the lot. The proposed detention pond is designed to have an 8” PVC outlet pipe equipped with an outlet weir to control the pond’s outflow. The outlet control was designed in accordance with the requirements set forth by the City of Bozeman Design Standards, and was sized for a release rate equal to that of the pre-development runoff rate. The outlet pipe is also proposed to have a vertical tee installed to allow for a free-flowing overflow for runoff rates exceeding the design storm events. The proposed 8” PVC is capable of conveying more than the runoff associated with the 25-year event. Stormwater from the site will be treated via an inline Contech Hydrodynamic Separator prior to discharging into the existing 15” RCP storm system under Warbler Way and eventually into the regional storm pond. In the event of runoff that surpass the capacity of the existing RCP storm system, excess stormwater will rise to levels above the existing curb inlets be able to flow down the existing streets without causing failure of the underground facilities. As mentioned above, the existing regional storm pond, Pond G as shown on ST-1, is in need of maintenance due to sediment build-up and vegetation growth to restore its design capacity. Headwaters has been in contact with the Cattail Creek Community Association, which is responsible for the maintenance of the pond, and is working to remedy the known capacity issues. The City of Bozeman Design Standards and Specifications Policy requires that detention pond volume be adequate to accommodate the difference in peak runoff between the pre-development and post-development 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 6 of 8 design storm of 10 years, while retention ponds must contain the entire 10-year 2-hour design storm volume. Table 3 shows the calculated pond volume. The required detention volume for Basin A was determined from the difference in the onsite runoff accounted for with the original subdivision design (C=0.45) and the proposed development (C=0.65) which is accounted for in the detention pond, as outlined in Table 3. Table 3. Pond Volumes Pond Type Location Volume (cft)__________________________________ A Detention Basin A (C = 0.63 @ 0.56 acres) 437 cf A Detention Designed w/ subdivision (C=0.45 @ 0.56 acres) 226 cf Minimum Required Capacity 211 cf A Detention Proposed Detention 307 cf At Drainage Basin A, the curb and gutter in the parking lot will direct the runoff to the curb cut which empties the storm infrastructure including a detention pond and a Contech stormwater separator. The proposed curb cut has a capacity of 2.6 cfs which passes the 100-year onsite storm event without overtopping the curb. The remainder of the storm infrastructure is also designed to pass the 100-year event as shown in Table 4. All stormwater will pass through the storm separator before leaving the site. The discharge will be connected to the existing 15” RCP in Warbler Way with a curb inlet. As was approved by Lance Lehigh for Urban Villas, the curb inlet will act as an overflow for storms that overfill the 15” RCP. Should this occur, the water will bubble up through the curb inlet and flow down Warbler Way. The curb network will then carry stormwater to the regional storm pond. Table 4. Proposed Drainage Conveyance Structure Capacity Description Contributing Depth Slope Q10PST Q100PST Capacity Passes Subareas (ft) (%) (cfs) (cfs) (cfs) Design Storm Curb & Gutter A 0.50 0.5 0.40 0.64 4.2 Y 24” Curb Cut A 0.40 0.5 0.40 0.64 2.7 Y 8” PVC A 0.5 0.5 0.40 0.64 2.4 Y 24” Storm Grate A 0.5 0.0 0.40 0.64 2.0 Y Initial Stormwater Facility and Initial Abstraction The City of Bozeman requires that the first 0.5 inch of precipitation must be captured and not be allowed to become direct runoff. For Basin A, the proposed Contech CDS hydrodynamic separator is designed to treat the first 0.5-inch storm runoff from a 24-hour storm. The CDS separator is designed to remove 80% of TSS. Maintenance Regular maintenance of storm water facilities is necessary for proper functioning of the drainage system. In general, regular mowing of any grass swales and unclogging of curb cuts and curb lines be required to prevent standing water and clogging. More substantial maintenance, such as sediment removal with heavy equipment, may be required in coming decades to restore pond volume and swale function. Sediment removal from the regional storm pond is the responsibility of the Cattail Creek Subdivision Owners Association. The onsite curb inlet shall have the sump cleaned out when the silt reaches 2” below the outlet pipe. This should be monitored yearly. The onsite detention pond shall have sediment removed when the average pond bottom is 1.5” above design. The 8” PVC storm pipe shall be flushed if more than 1” of sediment is visible in the bottom of the pipe. The Hydrodynamic Separator is to be visually inspected every 6 months to check for build-up of sediment in the bottom of the unit. If the sediment depth exceeds 75% of the sump depth or 18 inches deep, the sediment is to be removed using a vac-truck to suck out the sediment and dispose of it at a disposal site. The sediment 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 7 of 8 depth can also be measured from the top of the unit. If the sediment is measured to be 5.7’ or less below the top of the separator unit, then the sediment needs to be removed. Floatables (trash) are to be netted out and disposed of prior to removing sediment with the vac-truck. Any oils or hydrocarbons are to be removed using absorbent pads prior to vac-trucking out the sediment. Reference the Contech CDS Inspection and Maintenance Guide for additional details. All maintenance and repairs should be prioritized and scheduled in advance. Structures and pipes should be visually inspected yearly. Typical maintenance items include removing obstructions, cleaning and flushing pipes, mowing grass and weeds, tree maintenance to prevent limbs from falling and blocking swales, and establishing groundcover on bare ground. See the Stormwater Maintenance Manual for additional information. IV. Conclusion Storm water analysis and calculations indicate that the proposed storm water management plan for the Catalyst project is adequate to safely convey the 10-year, 25-year, and 100-year storm events while satisfying state and local regulations for peak attenuation and stormwater storage. Furthermore, the proposed first floor elevations for the structures are all above the estimated 100-yr Base flood Elevation as determined by Headwaters Engineering. H:\2036\001\DOCS\DESIGN\STORM\1_StormwaterDR_warbler.doc 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 8 of 8 Appendix A Exhibits & Calculations & O&M SDSDSDSDSDLOT 3 BLOCK 2 1 R-3 LOT 2 BLOCK 2 1 R-3 LOT 1A BLOCK 2 1 R-3 LOT 4 BLOCK 2 1 R-3 LOT 6 BLOCK 2 R-3 LOT 5 BLOCK 2 R-3 LOT 3 BLOCK 1 R-3 LOT 4 BLOCK 1 R-3 LOT 5 BLOCK 1 R-3 11"X17": 1"= 100 ft N GRAPHIC SCALE 1 inch = ft. 0 ( IN FEET ) 2550 50 50 HEADWATERS PROJECT NUMBER DRAWING NUMBER DRAWN BY: DATE: 2023 VERIFY SCALE THESE PRINTS MAY BE REDUCED. LINE BELOW MEASURES ONE INCH ON ORIGINAL DRAWING. MODIFY SCALE ACCORDINGLY H:\2036\001\ACAD\SHEETS\STORM BASIN.dwg Plot Date: 5/2/2023 8:06 AM © HEADWATERS ENGINEERING, INC. REVISION DATE: 190 NORTHSTAR LANE, BOZEMAN, MT 59718 HEADWATERSMT.NET 406-581-5730 PROJECT LOCATION MONTANA BOZEMAN 05/02/2023 RE STORMWATER SITE MAP TBD CATALYST STREET CATALYST BY DEL PARK HOMES 2036.001 ST-1WARBLER WAYCATALYST STREET CATA M O U N T S T R E E T EXISTING REGIONAL STORM POND (POND G)BLACKBIRD DRIVEBASIN A 0.56 ACRES C=0.63 EXISTING 15" RCP STORM PIPE PROPOSED 8" PVC SEE SHEET C-4 FOR DETAILS PROPOSED DETENTION POND DEPTH = 8" REQUIRED CAPACITY = 211 CF PROVIDED CAPACITY = 307 CF SEE SHEET C-4 FOR DETAILS APPROXIMATE BASIN J-2 FROM TD&H DESIGN REPORT2.87 ACRES C=0.45 N 27TH AVE.SURFACE FLOW DIRECTION LEGEND: PROPOSED CURB INLET STRUCTURE PROPOSED CONTECH CDSHYDRODYNAMIC SEPARATOR PIPE FLOW DIRECTIONCATTAIL CREEKA A SECTION A-A NOT TO SCALE 100-YR WSE (0.64 CFS) BUILDING FLOOR ELEVATION PROPOSED RETAINING WALL FINISHED GROUND Catalyst by Del Park Homes 1/22/2023POST DEVELOPMENT Basin A Weighted C Basin Area (sf)24176 Area (Acres)0.56 Area Impervious (0.9)15520 Area Gravel (0.8)645 Area Unimproved (0.2)0 Area Landscaped (0.1)8011 Weighted C=0.63 PRE Development Lot 3, Block 21, Cattail Creek Sub. Phs. III FINAL TC BASIN A 80 4667.42 4663 0.055 1.01 0.24 14.18 30 4663 4662.8 0.007 0.45 1.11 30 4662.8 4662.7 0.003 0.031944 0.24 14.61 30 POST Development Lot 3, Block 21, Cattail Creek Sub. Phs. III FINAL TC BASIN A 120 4667.18 4667 0.002 1.14 0.011 5.90 150 4667 4666.5 0.003 1.5 1.67 140 4666.5 4666.25 0.002 0.031944 0.05 17.39 25 n6 Ttc TcTtL3 ELEV. START (ft)ELEV. END (ft)S (ft/ft)r5 (ft)Tt- Sheet Flow L2 ELEV. START (ft)ELEV. END (ft)S (ft/ft) V4 (ft/s)BASIN ID Initial / Sheet Flow1 Shallow Concentrated Flow2 Concentrated Flow2,3 L1 ELEV START (ft)ELEV END (ft)S (ft/ft)P2 (in)n6 n6 Ttc TcTtL3 ELEV. START (ft)ELEV. END (ft)S (ft/ft)r5 (ft)Tt- Sheet Flow L2 ELEV. START (ft)ELEV. END (ft)S (ft/ft) V4 (ft/s)BASIN ID Initial / Sheet Flow1 Shallow Concentrated Flow2 Concentrated Flow2,3 L1 ELEV START (ft)ELEV END (ft)S (ft/ft)P2 (in)n6 1 Manning's Kinematic Solution 2 Shallow Concentrated Flow Equation 3 Manning's Equation for Concentrated Flow 4 Velocity vs. Slope for Shallow Concentrated Flows 5 Geometric Elements of Channel Sections 6 z e HW#: DATE: ENGINEER: RAINFALL FREQ =10 YR (DURATION = 1) BASIN AREA PRE =0.56 AC STORM EVENT INTENSITY (YR)A B (IN/HR) PRE-DEV Tc =30.0 MIN 0.50 2 0.36 0.6 0.55 5 0.52 0.64 0.81 PRE-DEV C =0.20 10 0.64 0.66 1.01 25 0.78 0.64 1.22 STORM A =0.64 50 0.92 0.66 1.45 B =0.66 100 1.01 0.67 1.61 STORM INTENSITY =1.01 IN/HR PRE-DEV Qp =0.11 CFS BASIN AREA PRE =0.56 AC POST-DEV Tc =25.0 MIN POST-DEV C =0.63 STORM INTENSITY =1.14 IN/HR POST-DEV Qp =0.40 CFS PRE-DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) -B STORM i COEFF 2036.001 JRM 5/2/2023 POST-DEVELOPMENT Qp = C i A Basin A H:\2036\001\DOCS\DESIGN\STORM\calcs\basin A.xls 1 OF 1 PRINTED: 5/2/2023 HW#: DATE: ENGINEER: RAINFALL FREQ =25 YR (DURATION = 1) BASIN AREA PRE =0.56 AC STORM EVENT INTENSITY (YR)A B (IN/HR) PRE-DEV Tc =30.0 MIN 0.50 2 0.36 0.6 0.55 5 0.52 0.64 0.81 PRE-DEV C =0.20 10 0.64 0.66 1.01 25 0.78 0.64 1.22 STORM A =0.78 50 0.92 0.66 1.45 B =0.64 100 1.01 0.67 1.61 STORM INTENSITY =1.22 IN/HR PRE-DEV Qp =0.14 CFS BASIN AREA PRE =0.56 AC POST-DEV Tc =25.0 MIN POST-DEV C =0.63 STORM INTENSITY =1.37 IN/HR POST-DEV Qp =0.48 CFS 2036.001 JRM 5/2/2023 POST-DEVELOPMENT Qp = C i A Basin A i = A * (Tc/60) -B STORM i COEFF PRE-DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN) H:\2036\001\DOCS\DESIGN\STORM\calcs\basin A.xls 1 OF 1 PRINTED: 5/2/2023 HW#: DATE: ENGINEER: RAINFALL FREQ =100 YR (DURATION = 1) BASIN AREA PRE =0.56 AC STORM EVENT INTENSITY (YR)A B (IN/HR) PRE-DEV Tc =30.0 MIN 0.50 2 0.36 0.6 0.55 5 0.52 0.64 0.81 PRE-DEV C =0.20 10 0.64 0.66 1.01 25 0.78 0.64 1.22 STORM A =1.01 50 0.92 0.66 1.45 B =0.67 100 1.01 0.67 1.61 STORM INTENSITY =1.61 IN/HR PRE-DEV Qp =0.18 CFS BASIN AREA PRE =0.56 AC POST-DEV Tc =25.0 MIN POST-DEV C =0.63 STORM INTENSITY =1.82 IN/HR POST-DEV Qp =0.64 CFS PRE-DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) -B STORM i COEFF 2036.001 JRM 5/2/2023 POST-DEVELOPMENT Qp = C i A Basin A H:\2036\001\DOCS\DESIGN\STORM\calcs\basin A.xls 1 OF 1 PRINTED: 5/2/2023 HW#: DATE: ENGINEER: RAINFALL FREQ =10 YR (DURATION = 1) BASIN AREA PRE =0.56 AC STORM EVENT INTENSITY (YR)A B (IN/HR) PRE-DEV Tc =30.0 MIN 0.50 2 0.36 0.6 0.55 5 0.52 0.64 0.81 PRE-DEV C =0.20 10 0.64 0.66 1.01 25 0.78 0.64 1.22 STORM A =0.64 50 0.92 0.66 1.45 B =0.66 100 1.01 0.67 1.61 STORM INTENSITY =1.01 IN/HR PRE-DEV Qp =0.11 CFS BASIN AREA PRE =0.56 AC POST-DEV Tc =25.0 MIN POST-DEV C =0.63 STORM INTENSITY =1.14 IN/HR POST-DEV Qp =0.40 CFS PRE-DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) -B STORM i COEFF 2036.001 JRM 5/2/2023 POST-DEVELOPMENT Qp = C i A TOTAL DETENTION POND - LOT 3 H:\2036\001\DOCS\DESIGN\STORM\calcs\DETENTION POND.xls 1 OF 1 PRINTED: 5/2/2023 HW#: DATE: ENGINEER: RAINFALL FREQ =10 YR (DURATION = 1) BASIN AREA PRE =0.56 AC STORM EVENT INTENSITY(YR)A B (IN/HR) PRE-DEV Tc =30.0 MIN 0.50 2 0.36 0.6 0.55 5 0.52 0.64 0.81PRE-DEV C =0.20 10 0.64 0.66 1.01250.78 0.64 1.22 STORM A =0.64 50 0.92 0.66 1.45 B =0.66 100 1.01 0.67 1.61 STORM INTENSITY =1.01 IN/HR PRE-DEV Qp =0.11 CFS BASIN AREA PRE =0.56 AC POST-DEV Tc =25.0 MIN POST-DEV C =0.45 STORM INTENSITY =1.14 IN/HR POST-DEV Qp =0.29 CFS PRE-DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) -B STORM i COEFF 2036.001 JRM 1/26/2023 POST-DEVELOPMENT Qp = C i A ORIGINAL DETENTION POND - LOT 3 H:\2036\001\DOCS\DESIGN\STORM\calcs\DETENTION POND-orig design.xls1 OF 1 PRINTED: 1/26/2023 Warbler Condos City of Bozeman Outlet Structure Weir Calculation Q=CLH^(3/2) Q=Discharge (cfs) C=Weir Coefficient = 3.33 L=Horizontal weir length (ft) H=Head (ft) Q=0.11 cfs C=3.33 L=0.060686 ft 0.728227 inches wide H=0.666667 ft Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.010 Channel Slope 0.04000 ft/ft Normal Depth 0.44 ft Diameter 0.67 ft Results Discharge 2.44 ft³/s Flow Area 0.25 ft² Wetted Perimeter 1.27 ft Hydraulic Radius 0.19 ft Top Width 0.64 ft Critical Depth 0.65 ft Percent Full 65.7 % Critical Slope 0.02073 ft/ft Velocity 9.96 ft/s Velocity Head 1.54 ft Specific Energy 1.98 ft Froude Number 2.83 Maximum Discharge 3.42 ft³/s Discharge Full 3.18 ft³/s Slope Full 0.02356 ft/ft Flow Type SuperCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % Normal Depth Over Rise 65.67 % Downstream Velocity Infinity ft/s 8in PVC 1/26/2023 8:53:17 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page GVF Output Data Upstream Velocity Infinity ft/s Normal Depth 0.44 ft Critical Depth 0.65 ft Channel Slope 0.04000 ft/ft Critical Slope 0.02073 ft/ft 8in PVC 1/26/2023 8:53:17 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of2Page Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.013 Channel Slope 0.00500 ft/ft Normal Depth 0.40 ft Left Side Slope 1.00 ft/ft (H:V) Right Side Slope 1.00 ft/ft (H:V) Bottom Width 1.50 ft Results Discharge 2.68 ft³/s Flow Area 0.76 ft² Wetted Perimeter 2.63 ft Hydraulic Radius 0.29 ft Top Width 2.30 ft Critical Depth 0.42 ft Critical Slope 0.00423 ft/ft Velocity 3.53 ft/s Velocity Head 0.19 ft Specific Energy 0.59 ft Froude Number 1.08 Flow Type Supercritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Downstream Velocity Infinity ft/s Upstream Velocity Infinity ft/s Normal Depth 0.40 ft Critical Depth 0.42 ft Channel Slope 0.00500 ft/ft 2' Curb Cut 3/16/2021 5:03:13 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page 2' Curb Cut GVF Output Data Critical Slope 0.00423 ft/ft 3/16/2021 5:03:13 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of2Page Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Channel Slope 0.02000 ft/ft Normal Depth 0.13 ft Discharge 0.68 ft³/s Cross Section Image Cross Section for Storm section AA 1/27/2023 12:50:54 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 1of1Page Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Channel Slope 0.02000 ft/ft Discharge 0.68 ft³/s Section Definitions Station (ft)Elevation (ft) 0+00 67.40 0+02 67.40 0+04 66.52 0+14 66.32 0+21 66.46 0+21 68.00 Roughness Segment Definitions Start Station Ending Station Roughness Coefficient (0+00, 67.40) (0+21, 68.00) 0.040 Options Current Roughness Weighted Method Pavlovskii's Method Open Channel Weighting Method Pavlovskii's Method Closed Channel Weighting Method Pavlovskii's Method Results Normal Depth 0.13 ft Elevation Range 66.32 to 68.00 ft Flow Area 0.81 ft² Wetted Perimeter 12.73 ft Hydraulic Radius 0.06 ft Top Width 12.73 ft Normal Depth 0.13 ft Worksheet for Storm section AA 1/27/2023 12:50:39 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page Results Critical Depth 0.10 ft Critical Slope 0.06273 ft/ft Velocity 0.84 ft/s Velocity Head 0.01 ft Specific Energy 0.14 ft Froude Number 0.59 Flow Type Subcritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Downstream Velocity Infinity ft/s Upstream Velocity Infinity ft/s Normal Depth 0.13 ft Critical Depth 0.10 ft Channel Slope 0.02000 ft/ft Critical Slope 0.06273 ft/ft Worksheet for Storm section AA 1/27/2023 12:50:39 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of2Page