Loading...
HomeMy WebLinkAbout018_Stormwater pkg 190 NORTHSTAR LANE BOZEMAN, MT 59718 406-581-5730 www.headwatersmt.net Page 1 of 8 Storm Water Management Design Report Urban Villas North 27th & Catalyst Street Lot 3A, Block 2 of Cattail Creek Subdivision, Phase 3 Bozeman, Montana April 2023 Headwaters Engineering, Inc. Project #: 1086.019 Prepared For: Flood Gates, LLC Bozeman, MT 59718 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 Storm Water Facility and Initial Abstraction…………………………………………………….. 6 4. Maintenance…………………………………………………………………………………………………………….. 7 IV. Conclusion………………………………………………………………………………………….……………………. 7 List of Tables Table 1. Estimated Pre-Development Peak Flows……………………………………………………………………….. 4 Table 2. Estimated Post-Development Peak Flows……………………………………………………………………… 5 Table 3. Required Pond Volumes ……………………………………..………………………………………………………… 6 Table 4. Proposed Drainage Conveyance Structures Capacities …………………………………………………… 6 Table 5. Initial Storm Volumes …………………………………………………………………………………………………….. 7 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 proposed Urban Villas Project consists of four residential buildings, with a total of 48 residential units. The site is on the 2.4395-acre Lot 3A, Block 2 of Plat J-415A 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. Five residential buildings currently exist on the west side of the lot, totaling 16 units, with a paved access road and concrete sidewalks. This design report outlines the storm water analysis conducted for the site and describes the storm water drainage and management facilities required 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 well nearest the subject property showed groundwater at a maximum elevation of 4.94 feet below ground surface. The bottom of the proposed onsite detention pond is proposed to be approximately 1 foot below existing ground, providing more than 3 feet of separation from high ground water. Proposed underground infiltration chambers have been designed to be installed at, or above the seasonal high groundwater. Land Use The pre-development land use on the site was a partially developed residential lot from the Cattail Creek Subdivision. The land is currently zoned R-3 and the proposed use is to remain residential. Figure 1 – Vicinity map of subject property and regional storm pond. 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 4 of 8 II. Existing Conditions The Urban Villas project lies on the south side of Catalyst Street, at its intersection with North 27th Avenue. The existing site slopes generally to the north. Slopes vary from 5% on the southern edge due to a material pile, to 1% northward across the majority of the lot. The existing high point of the property is located along the southern edge at said pile. The existing topography routed all runoff naturally to the north end of the parcel, and eventually onto Catalyst Street and N. 27th Avenue, where it entered the stormwater infrastructure of the Cattail Creek Subdivision. There are five existing residential buildings along the property’s western edge, with accompanying concrete sidewalks and a paved access. The existing developments convey runoff in a similar pattern as described above, and utilize the Cattail Creek Subdivision stormwater infrastructure. Existing stormwater infrastructure near the property is comprised of paved roadways with curb and gutter, curb inlets, and a 24” RCP pipe system under North 27th Ave. 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 recently 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 had completed work on all of the storm ponds within the Subdivision, with the exception of 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. We have also been in contact with the HOA and offered to assist with determining a solution, if necessary. Drainage Basins and Pre-development Peak Flows Headwaters identified three onsite drainage basins and one offsite basin as shown on the stormwater basin exhibit ST-1 in Appendix A. The 2.43-acre lot was divided into the three basins based on the proposed drainage patterns of the development. Estimates of runoff and the corresponding calculations for the basins were completed using the Modified Rational Method. The basins utilized a pre-development runoff coefficient of C=0.20. Post-development runoff coefficients for each basin were determined based on the amount of impervious area proposed, and existing, on the site. The regional storm pond, located in the subdivision’s park area to the west, was originally sized to accommodate this lot using a post-development C=0.54, which is less than that of the proposed development. To account for the difference in post-developed conditions, additional storage volume is necessary. Offsite flows were considered from the undeveloped lot to the south, as depicted by basin OSA on sheet ST-1. Flows associated with this basin were considered to be the only offsite source of runoff that could reach the subject property as a result of the grading and road network. Estimated pre-development flows for each basin are shown in Table 1. Table 1. Estimated Pre-Development Peak Flows (see sheet ST-1) Sub Area Description Area Tc Q2 Q10 Q100 (acres) (min) (cfs) (cfs) (cfs) OSA Offsite Basin A 0.60 28 0.03 0.05 0.07 A Onsite Basin A 0.27 24 0.01 0.02 0.04 B Onsite Basin B 0.31 35 0.02 0.03 0.04 C Onsite Basin C 1.84 35 0.18 0.34 0.53 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 5 of 8 III. Proposed Drainage Plan and Estimated Post-Development Peak Flows The proposed drainage plan builds off the existing infrastructure of the Cattail Creek Subdivision. The difference in flows between the proposed development and those contemplated in the original subdivision design will be handled onsite via an onsite retention pond in the southwest portion of the property, as well as an underground retention pond on the east side. Runoff produced by the development equal to those used in the original design will be conveyed across the site via surface flow, curb and gutter, curb inlets, and 12” PVC storm pipe that is proposed to connect to the existing underground stormwater system. Runoff from the site will be treated by a Contech CDS Hydrodynamic Separator prior to entering the existing stormwater infrastructure. The flows associated with each onsite basin are listed in Table 2. Table 2. Estimated Post-Development Peak Flows (see sheet ST-1) Sub Area Description Area C Tc Q2 Q10 Q100 (acres) (min) (cfs) (cfs) (cfs) OSA Offsite Basin A 0.60 0.70 6 0.13 0.22 0.33 Basin A Onsite Basin A 0.28 0.72 6 0.05 0.08 0.13 Basin B Onsite Basin B 0.31 0.59 10 0.05 0.08 0.12 Basin C Onsite Basin C 1.84 0.71 33 0.67 1.24 1.97 Flows for the Offsite Basin A (OSA) were estimated based on a C factor of 0.70 to account for future development of the vacant lot. Major Drainage System The major drainage system is comprised of an existing street system with curb and gutter, and grading of developed lots that convey runoff to said streets. Site grading 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 conveyance swales without inundating any structures or causing significant erosion onsite. Runoff from the site will then continue in an overland fashion along the curbed streets, valley gutters and storm inlets into the existing regional storm pond. Flows that surpass the capacity of the regional pond will discharge into Cattail Creek and flow north as they have historically. Minor Drainage System The minor drainage system will entail an onsite retention pond, curb inlets, valley gutters, curbs, underground piping, and an underground infiltrator system to handle the flows associated with each onsite basin. Runoff will be conveyed in an overland fashion to proposed curbs and valley gutters, which will convey it to the storm inlets and ponds. There is an existing underground RCP storm pipe system below the subdivision’s street system that routes stormwater to a large regional storm pond. Below is a description of the proposed minor drainage features associated with each onsite basin. Basin A: Runoff from Basin A will be routed to a proposed storm inlet connected to an underground infiltration system. The proposed infiltration system is comprised of a series of seven StormTech SC-740 infiltration chambers installed with a gravel bed. The chamber system was designed to handle the required minimum facility volume associated with the post-developed basin characteristics. Stormwater flow which exceeds the design storm will overflow the infiltration system and flow into North 27th Avenue before inundating any parking stalls or buildings. Basin B: The proposed onsite retention pond is located on the west side of Basin B. The pond was sized to handle the post developed flows for the site that exceeded the available capacity in the existing regional pond. Runoff in 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 6 of 8 Basin B will be conveyed to the proposed retention pond by overland flow across the pavement and into the proposed curb line before discharging into the pond. Flows in excess of the design flows will be conveyed away from the site through an existing swale along the western edge of the property, and into Catalyst Street, where it will then continue along the street system and into the regional storm pond before inundating any parking areas or buildings. Basin C: The existing regional storm pond was originally designed assuming a post-developed C factor of 0.54. Since the proposed development exceeds that of the original design, runoff in excess of the available regional pond volume is to be handled on-site. Basin C was identified as the portion of the site that would produce the amount of runoff available in the existing regional pond. Flows from Basin C will be routed through the paved parking lots into a curb inlet, before being treated with a Contech CDS Hydrodynamic Separator and routed through an 12” PVC storm pipe into the existing RCP under North 27th Avenue and eventually into the regional pond. The 12” PVC will connect into an existing curb inlet in North 27th Avenue. As was discussed and approved by Lance Lehigh, even though the curb inlet connected to the 12” RCP was not sized for the additional storm flow, any flow exceeding its capacity will flow down the curb line of North 27th and to the regional storm pond, as intended. This connection was an effort to remove a sidewalk chase from the proposed site plan. As part of the site grading, Basins B and C are separated by grade breaks in the proposed parking lots. Table 3 outlines the proposed components of the minor drainage system. Table 3. Storage Facility Volumes Pond/Feature Type Location Required Vol. Provided Vol. (cft)_____________ _(cft)____________________ Ex. Regional Pond Detention Offsite 1,957 (available) Proposed Pond Retention Basin B 501 522 Infiltration System Retention Basin A 606 660 The values shown in Table 3 reflect the design volume in the existing regional pond and the provided volume in the onsite retention ponds. The flows associated with Basin C will account for 1,837 cubic feet of the available regional pond capacity, and are proposed to reach the regional pond via onsite 12” PVC that connects to the existing 12” RCP under North 27th Avenue. In addition to the storage facilities outlined above, Table 4 shows the proposed conveyance structures and their respective capacities. Table 4. Proposed Drainage Conveyance Structure Capacity Description Contributing Depth Slope Q10PST Q100PST Capacity Passes Subareas (ft) (%) (cfs) (cfs) (cfs) Design Storm Existing Swale-West OSA+B 0.7 0.5 1.31 2.10 7.63 Y 12” PVC Storm Pipe Basin C 1.0 1.0 1.24 1.97 5.8 Y Curb & Gutter Basins A, B, or C 0.5 0.5 1.24 1.97 4.2 Y 24” Storm Grate Basin A or C 0.5 0.0 1.24 1.97 2.0 Y Initial Stormwater Facility and Initial Abstraction The City of Bozeman requires that the first 0.5 inches of precipitation must be captured and not allowed to become direct runoff. Since Basins A and B are retention ponds, none of the initial storm will be discharged unless it undergoes treatment to remove a minimum of 80% of TSS first. For Basin C, the hydrodynamic separator is designed to handle the first 0.5-inch storm runoff from a 24-hour storm, by removing 80% of TSS. Table 5 shows the initial storm volumes associated with the onsite basins A and B. 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 7 of 8 Table 5. Initial Storm Volumes Description Area Required Min. Facility Vol. Provided Facility Vol. (Acres) (cft) (cft) Basin A 0.28 396 660 Basin B 0.31 347 520 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 retention pond shall have sediment removed when the average pond bottom is 1.5” above design. The 12” PVC storm pipe shall be flushed if more than 1” of sediment is visible in the bottom of the pipe. The storm inlet for the underground storage shall have sediment cleaned out when the sediment reaches 6” below the outlet pipe invert. 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 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. The StormTech Infiltration System shall be inspected every 6 months for the first year of operation, then annually every year thereafter at a minimum. The Isolator Row, as it is referred to in the StormTech O&M manual, incorporates inspection ports for visual inspections to be made. Sediment depth shall be measured during inspections and when the average depth of sediment exceeds 3 inches throughout the length of the Isolator Row, the sediment shall be removed by jetting out the system. 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 The analysis and calculations for the stormwater indicate that the proposed stormwater management plan for the Urban Villas project is adequate to safely convey the 10-year, 25-year, and 100-year storm events while satisfying state and local regulations for attenuation and stormwater storage. The proposed first floor elevations for the structures are all above the estimated 100-year base flood elevation determined by Headwaters Engineering. H:\1086\019\DOCS\DESIGN\Storm\1_StormwaterDR_Urban Villas.doc 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 8 of 8 Appendix A Exhibits & Calculations & O&M 12 SD 12 SD SD SDSDSDSDSDU11"X17": 1"= 160 ftNGRAPHIC SCALE1 inch = ft.0( IN FEET )40808080HEADWATERSPROJECT NUMBERDRAWING NUMBERDRAWN BY:DATE:2023VERIFY SCALETHESE PRINTS MAY BEREDUCED. LINE BELOWMEASURES ONE INCH ONORIGINAL DRAWING. MODIFY SCALE ACCORDINGLYH:\1086\019\ACAD\SHEETS\BASINS.dwg Plot Date: 2/15/2023 7:32 AM© HEADWATERS ENGINEERING, INC.REVISION DATE:190 NORTHSTAR LANE, BOZEMAN, MT 59718HEADWATERSMT.NET406-581-5730PROJECT LOCATIONMONTANABOZEMAN02/15/2023JRM/RESTORM BASINSN. 27TH & CATALYST STREETURBAN VILLAS1086.019ST-1BASIN A0.28 ACRESC=0.72BASIN B0.31 ACRESC=0.59BASIN C1.84 ACRESC=0.71EXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGPROPOSEDBUILDING 1PROPOSEDBUILDING 2PROPOSEDBUILDING 3PROPOSEDBUILDING 4CATALYST STREETN. 27TH AVE.CATAMOUNT STREETEXISTINGREGIONALSTORM PONDWARBLER WAY11"X17": 1"= 80 ftNGRAPHIC SCALE1 inch = ft.0( IN FEET )20404040N. 27TH AVE.CATALYST STREETBASIN OSA0.60 ACRESCATRON STREETCATRON STREETLEGEND:PROPOSED SURFACEFLOW DIRECTIONEXISTING 30" RCPEXISTING 12" RCPEXISTING FLOW DIRECTIONEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGEXISTINGBUILDINGPROPOSED RETENTION PONDREQUIRED CAPACITY = 501 CFPROVIDED CAPACITY = 522 CFDEPTH = 1.5'PROPOSED CONTECHHYDRODYNAMIC SEPARATORPROPOSED CURB INLETPROPOSED 12" PVC STORM PIPEPROPOSED CONNECTIONTO EXISTING CURB INLETEXISTING 12" RCPPROPOSED STORMTECH SC-740UNDERGROUND CHAMBERS.REQUIRED CAPACITY = 606 CFPROVIDED CAPACITY = 660 CFCATTAIL CREEK BBAASECTION A-A RETENTION PONDSECTION B-B EXISTING SWALE-WESTNOT TO SCALENOT TO SCALE10'0.7'1.5'10'7.63 CFSPOST-DEVELOPED 100-YEAR FLOWS:BASIN OSA = 1.98 CFSBASIN B = 0.12 CFSTOTAL = 2.10 CFS1.5'4:1 4:1WSE=4670.50BTM=4669.0PROPOSED 36"STORM INLETEXISTINGSWALE-WESTEXISTING PAVEMENT EXISTINGGRAVELEXISTING 18" RCP Urban Villas 2/2/2023 BASIN A BASIN B POST POST Weighted C Weighted C Area (sf) 12292 Area (sf) 13594 Area (Acres) 0.28 Area (Acres) 0.31 Area Impervious (0.9) 9514 Area Impervious (0.9) 8325 Area Gravel (0.8) 0 Area Gravel (0.8) 0 Area Unimproved (0.2) Area Unimproved (0.2) Area Landscaped (0.1) 2778 Area Landscaped (0.1) 5269 Weighted C= 0.72 Weighted C= 0.59 BASIN C TOTAL LOT 3A POST POST Weighted C Weighted C Area (sf) 80118 Area (sf) 106004 Area (Acres) 1.84 Area (Acres) 2.43 Area Impervious (0.9) 61272 Area Impervious (0.9) 79111 Area Gravel (0.8) 0 Area Gravel (0.8) Area Unimproved (0.2) Area Unimproved (0.2) Area Landscaped (0.1) 18846 Area Landscaped (0.1) 26893 Weighted C= 0.71 Weighted C= 0.70 PRE DevelopmentURBAN VILLASFINAL TCOSA150 4673.4 4671.9 0.01 1.13 0.13 26.84 50 4671.9 4671.5 0.008 1 0.8328BASIN A150 4670.7 4668.5 0.015 1.13 0.13 22.82 42 4668.5 4667.8 0.017 1 0.7024BASIN B200 4671 4669 0.01 1.13 0.13 33.78 50 4669 4668.5 0.01 1 0.8335BASIN C300 4669 4667 0.007 1.13 0.015 9.58 65 4665 4661 0.062 1.5 0.72 1412 4661 4654 0.005 0.031944 0.011 24.4135POST DevelopmentURBAN VILLASFINAL TCOSA100 4673.4 4671.9 0.015 1.13 0.011 5.00 75 4671.9 4671.5 0.005 1.8 0.69 25 4671.5 4671 0.02 0.031944 0.011 0.226BASIN A150 4671 4670.5 0.003 1.13 0.011 6.02 25 4670.5 4670 0.02 2.6 0.16 25 4670 4668.45 0.062 0.031944 0.011 0.126BASIN B150 4672 4671.8 0.001 1.13 0.011 9.35 50 4671.8 4670.8 0.02 2.6 0.32 25 4670.8 4670 0.032 0.031944 0.011 0.1710BASIN C300 4669 4667 0.007 1.13 0.011 7.47 65 4667 4661 0.092 1.5 0.72 1412 4661 4654 0.005 0.031944 0.011 24.4133ELEV. END (ft)S (ft/ft)r5 (ft)n6TtcTcELEV. END (ft)S (ft/ft)V4        (ft/s)TtL3ELEV. START (ft)S (ft/ft)P2 (in)n6Tt‐ Sheet FlowL2ELEV. START (ft)n6TtcTcBASIN IDInitial / Sheet Flow1Shallow Concentrated Flow2Concentrated Flow2,3L1ELEV START (ft)ELEV END (ft)TtL3ELEV. START (ft)ELEV. END (ft)S (ft/ft)r5 (ft)Tt‐ Sheet FlowL2ELEV. START (ft)ELEV. END (ft)S (ft/ft)V4        (ft/s)BASIN IDInitial / Sheet Flow1Shallow Concentrated Flow2Concentrated Flow2,3L1ELEV 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 Flow4Velocity vs. Slope for Shallow Concentrated Flows5Geometric Elements of Channel Sections6ze HW#: DATE: ENGINEER: OSA 2 YEAR OSA 10 YEAR OSA 100 YEAR MODIFIED RATIONAL METHOD MODIFIED RATIONAL METHOD PRE-DEVELOPMENT PRE-DEVELOPMENT RAINFALL FREQ = 2 YR (DURATION = 1) RAINFALL FREQ = 10 YR (DURATION = 1 RAINFALL FREQ = 100 YR (DURATION = 1) BASIN AREA PRE = 0.6 AC BASIN AREA PRE = 0.60 AC BASIN AREA PRE = 0.60 AC PRE-DEV Tc = 28.0 MIN 0.47 PRE-DEV Tc = 28.00 MIN PRE-DEV Tc = MIN 0.00 PRE-DEV C = 0.20 PRE-DEV C = 0.20 PRE-DEV C = 0.2 STORM A = 0.36 STORM A = 0.64 STORM A = 1.01 B = 0.6 B = 0.66 B = 0.67 STORM INTENSITY = 0.57 IN/HR STORM INTENSITY = 1.06 IN/HR STORM INTENSITY = 1.68 IN/HR PRE-DEV Qp = 0.07 CFS PRE-DEV Qp = 0.13 CFS PRE-DEV Qp = 0.20 CFS POST-DEVELOPMENT POST-DEVELOPMENT BASIN AREA POST = 0.6 AC BASIN AREA POST = 0.60 AC BASIN AREA POST = 0.60 AC POST-DEV Tc = 6.0 MIN POST-DEV Tc = 6.00 MIN POST-DEV Tc = 6.00 MIN POST-DEV C = 0.7 POST-DEV C = 0.70 POST-DEV C = 0.70 STORM INTENSITY = 1.43 IN/HR STORM INTENSITY = 2.93 IN/HR STORM INTENSITY = 4.72 IN/HR POST-DEV Qp = 0.60 CFS POST-DEV Qp = 1.23 CFS POST-DEV Qp = 1.98 CFS STORM EVENT INTENSITY (YR) A B (IN/HR) 2 0.36 0.6 0.59 5 0.52 0.64 0.89 10 0.64 0.66 1.1125 0.78 0.64 1.33 50 0.92 0.66 1.60 100 1.01 0.67 1.77 STORM i COEFF (BOZEMAN AREA)i = A * (Tc/60) -B Qp = C i A Qp = C i A 1086.019 2/6/2023 Ryan Estep MODIFIED RATIONAL METHOD Qp = C i A PRE-DEVELOPMENT POST-DEVELOPMENT H:\1086\019\DOCS\DESIGN\Storm\CALCS\BASIN OSA.xls 1 OF 1 PRINTED: 2/6/2023 Sudivision NameEQ#CountyGallatin 0.9LocationCatamount 0.8Lot/Area No.Basin A 0.10.2Intensity ValuesQ=C*i*A2‐year, Tc0.24 inches/hour2‐year, 24‐hour1.13 inches10‐year, Tc0.41 inches/hour100‐year, Tc0.63 inches/hour100‐year, 24‐hour3.71 inchesTotal Area/Lot Size0.28 acres  = 12196.8ft2Initial Stormwater Facility Volume (0.5" x Impervious Area) =396.42ft3Paved/House Area0 acres 0ft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secGravel Area0 acresft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secLawn/Landscaping0 acres 0ft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secUnimproved Area0.28 acres 12196.8ft2Q= 0.014ft3/secV= 229.706ft3Q= 0.023ft3/secQ= 0.036ft3/secTotal0.28 acres 12196.8ft2QTotal=0.014ft3/secVTotal=229.706ft3QTotal=0.023ft3/secQTotal=0.036ft3/secPaved/House Area0.218411387 acres 9514ft2Q= 0.048ft3/secV= 806.312ft3Q= 0.081ft3/secQ= 0.125ft3/secGravel Area0 acresft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secLawn/Landscaping0.051538108 acres 2245ft2Q= 0.001ft3/secV= 21.140ft3Q= 0.002ft3/secQ= 0.003ft3/secUnimproved Area0.010050505 acres 437.8ft2Q= 0.000ft3/secV= 8.245ft3Q= 0.001ft3/secQ= 0.001ft3/secTotal0.28 acres 12196.8ft2QTotal=0.049ft3/secVTotal=835.697ft3QTotal=0.084ft3/secQTotal=0.129ft3/secΔQ=0.036ft3/secΔV=605.991ft3ΔQ=0.061ft3/secΔQ=0.094ft3/sec605.99ft3 = input fieldRunoff Flow/Volume Change2‐year, 24‐hour 100‐year, Tc(flow rate) volume) (flow rate)10‐year, Tc(flow rate)Appendix G: Standard Storm Drainage Plan100‐year, Tc(flow rate)(volume)2‐year, 24‐hour 10‐year, Tc(flow rate)Urban VillasRational Method Co‐Efficients (C) Paved/hard surfacesGravel surfacesLawn/landscapingUnimproved areasPre‐Development CharacteristicsPost‐Development Characteristics2‐year, Tc(flow rate)2‐year, TcRequired Minimum Facility Volume: Sudivision NameEQ#CountyGallatin 0.9LocationCatamount 0.8Lot/Area No.Basin B 0.10.2Intensity ValuesQ=C*i*A2‐year, Tc0.24 inches/hour2‐year, 24‐hour1.13 inches10‐year, Tc0.41 inches/hour100‐year, Tc0.63 inches/hour100‐year, 24‐hour3.71 inchesTotal Area/Lot Size0.31 acres  = 13503.6ft2Initial Stormwater Facility Volume (0.5" x Impervious Area) =346.88ft3Paved/House Area0 acres 0ft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secGravel Area0 acresft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secLawn/Landscaping0 acres 0ft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secUnimproved Area0.31 acres 13504ft2Q= 0.015ft3/secV= 254.318ft3Q= 0.026ft3/secQ= 0.039ft3/secTotal0.31 acres 13504ft2QTotal=0.015ft3/secVTotal=254.318ft3QTotal=0.026ft3/secQTotal=0.039ft3/secPaved/House Area0.19 acres 8325ft2Q= 0.042ft3/secV= 705.544ft3Q= 0.071ft3/secQ= 0.109ft3/secGravel Area0.00 acresft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secLawn/Landscaping0.12 acres 5179ft2Q= 0.003ft3/secV= 48.769ft3Q= 0.005ft3/secQ= 0.008ft3/secUnimproved Area0.00 acres 0ft2Q= 0.000ft3/secV= 0.000ft3Q= 0.000ft3/secQ= 0.000ft3/secTotal0.31 acres 13504ft2QTotal=0.045ft3/secVTotal=754.313ft3QTotal=0.076ft3/secQTotal=0.117ft3/secΔQ=0.029ft3/secΔV=499.995ft3ΔQ=0.050ft3/secΔQ=0.077ft3/sec499.99ft3 = input fieldRunoff Flow/Volume ChangeRequired Minimum Facility Volume:2‐year, Tc2‐year, 24‐hour 10‐year, Tc100‐year, TcPost‐Development Characteristics (flow rate) volume) (flow rate) (flow rate)Pre‐Development Characteristics (flow rate) (volume) (flow rate) (flow rate)Unimproved areas2‐year, Tc2‐year, 24‐hour 10‐year, Tc100‐year, TcAppendix G: Standard Storm Drainage PlanUrban VillasRational Method Co‐Efficients (C) Paved/hard surfacesGravel surfacesLawn/landscaping HW#: DATE: ENGINEER: BASIN C 2 YEAR BASIN C 10 YEAR BASIN C 100 YEAR MODIFIED RATIONAL METHOD MODIFIED RATIONAL METHOD PRE-DEVELOPMENT PRE-DEVELOPMENT RAINFALL FREQ = 2 YR (DURATION = 1) RAINFALL FREQ = 10 YR (DURATION = 1 RAINFALL FREQ = 100 YR (DURATION = 1) BASIN AREA PRE = 1.84 AC BASIN AREA PRE = 1.84 AC BASIN AREA PRE = 1.84 AC PRE-DEV Tc = 35.0 MIN 0.58 PRE-DEV Tc = 35.00 MIN PRE-DEV Tc = MIN 0.00 PRE-DEV C = 0.20 PRE-DEV C = 0.20 PRE-DEV C = 0.2 STORM A = 0.36 STORM A = 0.64 STORM A = 1.01 B = 0.6 B = 0.66 B = 0.67 STORM INTENSITY = 0.50 IN/HR STORM INTENSITY = 0.91 IN/HR STORM INTENSITY = 1.45 IN/HR PRE-DEV Qp = 0.18 CFS PRE-DEV Qp = 0.34 CFS PRE-DEV Qp = 0.53 CFS POST-DEVELOPMENT POST-DEVELOPMENT BASIN AREA POST = 1.84 AC BASIN AREA POST = 1.84 AC BASIN AREA POST = 1.84 AC POST-DEV Tc = 33.0 MIN POST-DEV Tc = 33.00 MIN POST-DEV Tc = 33.00 MIN POST-DEV C = 0.71 POST-DEV C = 0.71 POST-DEV C = 0.71 STORM INTENSITY = 0.52 IN/HR STORM INTENSITY = 0.95 IN/HR STORM INTENSITY = 1.51 IN/HR POST-DEV Qp = 0.67 CFS POST-DEV Qp = 1.24 CFS POST-DEV Qp = 1.97 CFS STORM EVENT INTENSITY (YR) A B (IN/HR) 2 0.36 0.6 0.59 5 0.52 0.64 0.89 10 0.64 0.66 1.1125 0.78 0.64 1.33 50 0.92 0.66 1.60 100 1.01 0.67 1.77 POST-DEVELOPMENT Qp = C i A Qp = C i A 1086.019 2/2/2023 Ryan Estep MODIFIED RATIONAL METHOD Qp = C i A PRE-DEVELOPMENT STORM i COEFF (BOZEMAN AREA)i = A * (Tc/60) -B H:\1086\019\DOCS\DESIGN\Storm\CALCS\BASIN C.xls 1 OF 1 PRINTED: 2/2/2023 HW#: DATE: ENGINEER: 10 YEAR RAINFALL FREQ = 10 YR (DURATION = 1) BASIN AREA PRE = 1.84 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE-DEV Tc = 35.0 MIN 0.58 2 0.36 0.6 0.59 5 0.52 0.64 0.89 PRE-DEV C = 0.20 10 0.64 0.66 1.11 25 0.78 0.64 1.33 STORM A = 0.64 50 0.92 0.66 1.60 B = 0.66 100 1.01 0.67 1.77 STORM INTENSITY = 0.50 IN/HR PRE-DEV Qp = 0.34 CFS POND VOLUME: BASIN AREA PRE = 1.84 AC POST-DEV Tc = 33.0 MIN POST-DEV Tc = DETENTION POST-DEV C = 0.71 STORM INTENSITY = 0.95 IN/HR POST-DEV Qp = 1.24 CFS (CFT) 2336.5 10YR 2HR RETENTION VOL 2755.7 (CFT) INITIAL STORM VOL BASIN C i = A * (Tc/60) -B STORM i COEFF (CF) 826.41 TRIANGLE RELEASE AVERAGE VOLUME (CF) PRE-DEVELOPMENT CONST.RELEASE (BOZEMAN AREA) (CF) 1086.019 Jeremy May 2/2/2023 1836.69 2271.46 MODIFIED RATIONAL METHOD POST-DEVELOPMENT Qp = C i A H:\1086\019\DOCS\DESIGN\Storm\CALCS\BASIN C.xls 1 OF 1 PRINTED: 2/2/2023 HW#: DATE: ENGINEER: 10 YEAR RAINFALL FREQ = 10 YR (DURATION = 1) BASIN AREA PRE = 2.44 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE-DEV Tc = 60.0 MIN 1.00 2 0.36 0.6 0.59 5 0.52 0.64 0.89 PRE-DEV C = 0.20 10 0.64 0.66 1.11 25 0.78 0.64 1.33 STORM A = 0.64 50 0.92 0.66 1.60 B = 0.66 100 1.01 0.67 1.77 STORM INTENSITY = 0.64 IN/HR PRE-DEV Qp = 0.31 CFS POND VOLUME: BASIN AREA PRE = 2.44 AC POST-DEV Tc = 35.0 MIN POST-DEV Tc = DETENTION POST-DEV C = 0.54 STORM INTENSITY = 0.91 IN/HR POST-DEV Qp = 1.20 CFS (CFT) 0.0 10YR 2HR RETENTION VOL 2436.2 (CFT) INITIAL STORM VOL EXISTING POND - SITE i = A * (Tc/60) -B STORM i COEFF (CF) 866.48 TRIANGLE RELEASE AVERAGE VOLUME (CF) PRE-DEVELOPMENT CONST.RELEASE (BOZEMAN AREA) (CF) 1086.019 Jeremy May 2/2/2023 1956.89 2412.02 MODIFIED RATIONAL METHOD POST-DEVELOPMENT Qp = C i A H:\1086\019\DOCS\DESIGN\Storm\CALCS\EXISTING BASIN.xls 1 OF 1 PRINTED: 2/2/2023 Project Description Friction Method Manning Formula Solve For Discharge Input Data Channel Slope 0.00500 ft/ft Normal Depth 0.70 ft Section Definitions Station (ft)Elevation (ft) 0+00 0.70 0+10 0.00 0+20 1.50 Roughness Segment Definitions Start Station Ending Station Roughness Coefficient (0+00, 0.70) (0+20, 1.50) 0.035 Options Current Roughness Weighted Method Pavlovskii's Method Open Channel Weighting Method Pavlovskii's Method Closed Channel Weighting Method Pavlovskii's Method Results Discharge 7.63 ft³/s Elevation Range 0.00 to 1.50 ft Flow Area 5.13 ft² Wetted Perimeter 14.74 ft Hydraulic Radius 0.35 ft Top Width 14.67 ft Normal Depth 0.70 ft Critical Depth 0.51 ft Critical Slope 0.02843 ft/ft Velocity 1.49 ft/s Worksheet for Ex. Swale-West 2/2/2023 9:02:12 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 Project Description Friction Method Manning Formula Solve For Discharge Input Data Channel Slope 0.00500 ft/ft Normal Depth 0.70 ft Discharge 7.63 ft³/s Cross Section Image Cross Section for Ex. Swale-West 2/2/2023 9:02:47 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 1of1Page User Inputs Chamber Model: SC-740 Outlet Control Structure: No Project Name: Urban Villas Engineer: N/A Project Location: Montana Measurement Type: Imperial Required Storage Volume: 606 cubic ft. Stone Porosity: 40% Stone Foundation Depth: 6 in. Stone Above Chambers: 6 in. Average Cover Over Chambers: 18 in. Design Constraint Dimensions:(8 ft. x 70 ft.) Results System Volume and Bed Size Installed Storage Volume: 660.18 cubic ft. Storage Volume Per Chamber: 45.90 cubic ft. Number Of Chambers Required: 7 Number Of End Caps Required: 2 Chamber Rows: 1 Maximum Length:53.42 ft. Maximum Width: 6.25 ft. Approx. Bed Size Required: 333.85 square ft. System Components Amount Of Stone Required: 32 cubic yards Volume Of Excavation (Not Including Fill): 44 cubic yards Total Non-woven Geotextile Required:145 square yards Woven Geotextile Required (excluding Isolator Row): 0 square yards Woven Geotextile Required (Isolator Row): 35 square yards Total Woven Geotextile Required:35 square yards Impervious Liner Required:0 square yards Culvert Calculator Report 12" PVC h:\...\docs\design\storm\calcs\urban villas.cvm 02/15/23 07:27:59 AM© Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666 Project Engineer: headw CulvertMaster v3.3 [03.03.00.04] Page 1 of 1 Solve For: Discharge Culvert Summary Allowable HW Elevation 68.80 ft Headwater Depth/Height 4.10 Computed Headwater Elevation 68.80 ft Discharge 5.77 cfs Inlet Control HW Elev.66.84 ft Tailwater Elevation 63.48 ft Outlet Control HW Elev. 68.80 ft Control Type Outlet Control Grades Upstream Invert 64.70 ft Downstream Invert 62.81 ft Length 179.00 ft Constructed Slope 0.010559 ft/ft Hydraulic Profile Profile CompositeM2PressureProfile Depth, Downstream 0.95 ft Slope Type Mild Normal Depth N/A ft Flow Regime Subcritical Critical Depth 0.95 ft Velocity Downstream 7.49 ft/s Critical Slope 0.019363 ft/ft Section Section Shape Circular Mannings Coefficient 0.012 Section MaterialCorrugated HDPE (Smooth Interior) Span 1.00 ft Section Size 12 inch Rise 1.00 ft Number Sections 1 Outlet Control Properties Outlet Control HW Elev. 68.80 ft Upstream Velocity Head 0.84 ft Ke 0.20 Entrance Loss 0.17 ft Inlet Control Properties Inlet Control HW Elev.66.84 ft Flow Control Submerged Inlet Type Beveled ring, 33.7° bevels Area Full 0.8 ft² K 0.00180 HDS 5 Chart 3 M 2.50000 HDS 5 Scale B C 0.02430 Equation Form 1 Y 0.83000 Urban Villas Catalyst Street & N. 27th Avenue Storm Water Facilities Operation & Maintenance Manual Overview 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 Owners Association is responsible for maintenance of all onsite storm water facilities. Such facilities include, but are not limited to, onsite swales, retention ponds, storm structures, storm piping, inlet controls, storm separators, underground storage and curb cuts per the schedule below. Maintenance Curb lines and gutters are to have sediment removed on a yearly basis, or on an updated maintenance schedule as determined by monitoring the sediment build-up, quarterly. Any removed sediment shall be removed from the site and disposed of properly, as to not discharge into state waters. Areas behind curb cuts shall be inspected regularly and kept free of obstructions from ice, vegetation, etc. The Hydrodynamic Separator is to be visually inspected every 6 months to check for build-up of sediment in the bottom of the structure. If sediment depth exceeds 75% of the sump depth, or 18 inches deep, the sediment shall be removed using a vac truck and disposed of at a proper disposal site. The sediment depth can also be measured from the top of the structure. If the sediment is measured to be 6 feet or less below the rim elevation, sediment shall be removed. Floatables (trash) are to be netted out and disposed of prior to removing sediment with a vac truck. Any oils or hydrocarbons are to be removed using absorbent pads prior to vacuuming out the sediment. Reference the Contech CDS Inspection and Maintenance Guide for additional details. The StormTech Infiltration System shall be inspected every 6 months for the first year of operation, then annually every year thereafter at a minimum. The Isolator Row, as it is referred to in the StormTech O&M manual, incorporates inspection ports for visual inspections to be made. Sediment depth shall be measured during inspections and when the average depth of sediment exceeds 3 inches throughout the length of the Isolator Row, the sediment shall be removed by jetting out the system. The inlet manhole shall have sediment removed when it reaches a point of 6” below the pipe invert out of the manhole. The onsite detention pond and storm water swales shall be monitored every five years for sediment build-up. When sediment build-up raises the bottom of the pond to 1.5” above design elevation, sediment shall be removed mechanically and hauled off-site. If sediment extraction causes removal of vegetation from the bottom of the pond, the area shall be reseeded or re-sodded and appropriate storm water BMPs are to be installed until vegetation stabilization. The sump of the onsite curb inlet shall be inspected yearly. Sediment removal shall occur when sediment build-up reaches 2” below the outlet pipe. The 12” PVC storm pipe shall be flushed if more than 1” of sediment is visible in the bottom of the pipe. Budget It is estimated that the yearly budget to complete the above items is approximately $1,000 in 2022 value. This amount includes some contingency to rollover into a fund to allow for larger scale maintenance in future years, if necessary.