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HomeMy WebLinkAbout013-Stormwater pkg 190 NORTHSTAR LANE BOZEMAN, MT 59718 406-581-5730 www.headwatersmt.net Page 1 of 9 Storm Water Management Design Report Nelson Meadows Business Park TBD Prince Lane Block 3, Lot 4 of Nelson Meadows Subdivision (J-680) Bozeman, Montana April 2023 Headwaters Engineering, Inc. Project #: 1204.003 Prepared For: Summit Properties, LLC 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 2 of 9 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…………………………………………………………………………………………….. 4 2. Minor Drainage System…………………………………………………………………………………………….. 4 3. Initial Storm Water Facility and Initial Abstraction…………………………………………………….. 5 4. Maintenance…………………………………………………………………………………………………………….. 7 IV. Conclusion………………………………………………………………………………………….……………………. 8 List of Tables & Figures Table 1. Estimated Pre-Development Peak Flows……………………………………………………………………….. 5 Table 2. Estimated Post-Development Peak Flows……………………………………………………………………… 6 Figure 1. Original Regional Pond Basin………………………………………………………………………………………… 7 Table 3. Storage Facility Volumes ……………………………………..………………………………………………………… 7 Table 4. Proposed Drainage Conveyance Structures Capacities …………………………………………………… 8 Table 5. Initial Abstraction Volumes ……………………………………………………………………………………………. 8 Appendix A—Calculations Grading and Drainage Exhibit Groundwater Monitoring Data (Morrison-Maierle, 2018) 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 Comprehensive Drainage Plan, Nelson Meadows Subdivision (Morrison-Maierle, March 2019) 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 3 of 9 I. Project Background Introduction The proposed Nelson Meadows Business Park Project consists of three industrial buildings, with a total of approximately 36,098 square feet of building area. The site is located on the 2.59-acre lot that is Block 3, Lot 4 of Nelson Meadows Subdivision (J-680). The existing lot is located in the SE1/4 of Section 22, Township 1, Range 5 East, PMM, 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 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 two major soil types on the property, Blackdog Silt Loam, 0 to 4 percent slopes (50B) and Blackdog Silt Loam, 4 to 8 percent slopes (50C). The majority of the lot, roughly 80 percent, is comprised of 50B. This soil belongs to hydrologic soil group C and is comprised primarily of silts and loams with moderately high saturated conductivity. Groundwater monitoring for the subdivision was conducted by Morrison-Maierle in 2018 and the well located on the subject property showed groundwater at a maximum elevation of approximately 5.5 feet below ground surface. The bottom of the proposed retention ponds are proposed to be 18 inches, or less, below existing ground, providing roughly 4 feet of separation from high ground water. Land Use The pre-developed land use on the site was a vacant lot with surrounding infrastructure from the Nelson Meadows Subdivision. The lot is zoned M-1 and the proposed use is commercial. 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 9 II. Existing Conditions The proposed project lies on the north side of Prince Lane, approximately 500 feet west of its intersection with Nelson Road. The existing site slopes generally to the northwest. Slopes vary from 2% to 4.5% across the property. The existing high point on the property is located in the southeast corner of the lot along the southern boundary along Prince Lane. The existing topography routed all runoff naturally to the western edge of the property, where it flowed into the Cattail Creek drainage. Existing stormwater infrastructure near the property is comprised of paved roadways with curb and gutter, storm inlets, underground storm pipe, a 9’ by 5’ box culvert under Prince Lane, and a regional storm pond just north of the property. The existing infrastructure was designed to support the runoff associated with the subdivision at full build-out with the exception of a portion of some of the lots. The original design report, prepared by Morrison-Maierle, is included in the subsequent pages. Drainage Basins and Pre-development Peak Flows Headwaters identified four onsite drainage basins as shown on the Stormwater Exhibit ST-1 found in Appendix A. The 2.59-acre lot was divided into the four basins based on the proposed grading 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-developed runoff coefficients were determined based on the amount of impervious area proposed on the site. The regional storm pond, located in the lot just north of the subject property, was originally sized to accommodate the flows associated with the development of Nelson Road and downstream property using a post- development C=0.50, which included a portion of Lot 4. The allocated storage volume for Lot 4 was calculated with onsite Basin D being modified to match this volume. To account for the remainder, additional storage 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 Prince Lane, which captures and conveys runoff to the west, where it enters curb inlets and underground stormwater pipe at the low point of the roadway and is ultimately discharged into Cattail Creek. The 2-year, 10-year, and 100-year storm intervals were used in the analysis of the existing stormwater conveyance structures in or near the site. A summary of estimated pre-development peak runoff rates are shown 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 (acres) Tc (min) Q2 (cfs) Q10 (cfs) Q100 (cfs) A Onsite Basin A 0.42 18 0.1 0.2 0.3 B Onsite Basin B 0.14 17 0.03 0.06 0.1 C Onsite Basin C 1.63 44 0.3 0.7 1.1 D Onsite Basin D 0.40 58 0.09 0.17 0.27 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 5 of 9 III. Proposed Drainage Plan and Estimated Post-Development Peak Flows The proposed drainage plan builds off the existing infrastructure of the Nelson Meadows Subdivision. The difference in flows between the proposed development and those considered in the original subdivision design will be handled onsite via retention ponds, storm inlets, and underground storm pipe. The flows associated with each onsite basin are listed in Table 2. Table 2. Estimated Post-Developed Peak Flows (See Sheet ST-1) Sub Area Description C Area (acres) Tc (min) Q2 (cfs) Q10 (cfs) Q100 (cfs) A Onsite Basin A 0.58 0.42 5.5 0.3 0.5 0.8 B Onsite Basin B 0.32 0.14 6 0.05 0.1 0.15 C Onsite Basin C 0.67 1.63 11.5 1.1 2.3 3.7 D Onsite Basin D 0.7 0.40 7 0.3 0.6 0.9 Major Drainage System The major drainage system includes an existing street system with curb and gutter, storm inlets and underground storm pipe. Site grading is to be completed so that any runoff resulting from storm events greater than the 10-year, and up to the 100-year, will flow through the parking lots and conveyance swales without inundating any structures or causing significant erosion on site. Excess runoff from the site will overflow the proposed ponds and regional pond and flow into Cattail Creek as they have historically. Minor Drainage System The minor drainage system will entail onsite retention ponds, storm inlet manholes, valley gutters, curbs, and underground piping. Runoff will be conveyed in an overland fashion to the proposed curb lines and valley gutter, which will convey it to the storm inlets and ponds. The grading of the site is proposed to convey the majority of runoff away from Prince Lane, and is oriented such that the existing regional pond and three proposed storm ponds will be the main elements of the existing infrastructure utilized by the development. Below is a description of the minor drainage system features associated with each onsite basin. Basin A: Runoff from Basin A will be routed to a proposed retention pond (Pond A on sheet ST-1) that has been sized to handle the 10-year, 2-hour storm event. The majority of Basin A is runoff from the roof of proposed Building 3. The gutters from Building 3 will direct roof runoff to Pond A. Basin B: Basin B will include a 24-inch storm inlet in the proposed loading dock, that will collect and convey stormwater from the truck dock into the proposed retention Pond B through a 12-inch PVC pipe. Basin C: Basin C will utilize parking lot surface flow into the proposed valley gutter and curb, as well as underground 12- inch PVC to route runoff into the proposed retention areas. As shown on ST-1, Basin C will include a typical retention pond off the low point of the parking lot and four curb island bioretention pond areas. Runoff will enter said bioretention areas through 24-inch curb cuts. Roof drains from Proposed Building 2 will be connected to a 12-inch PVC storm pipe and routed towards Pond C, where the water will discharge into an armored outfall leading to said pond. 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 6 of 9 Basin D: Runoff from Basin D will be conveyed to the existing regional storm pond just north of the property. Two 24- inch storm inlets are proposed to capture the flows associated with the loading ramps of Building 1 & 2, which will be piped into the regional pond. A drainage swale is also proposed along the eastern edge of the lot, behind Buildings 1 & 2 to convey surface water from the roof of proposed Building 1 to the regional pond. Our research concluded that the original subdivision design allocated 825 cft of storage volume in the regional pond to the subject property. Figure 1 below shows the originally contemplated area on Lot 4 for the regional pond. This information was gathered from the Morrison-Maierle Drainage Plan for the subdivision. Basin D is estimated to contribute 824 cft of runoff into the existing pond, and therefore additional onsite retention for Basin D is not required. Table 3 outlines the proposed components of the minor drainage system. Figure 1: Drainage Basin associated with existing storm pond (Morrison-Maierle, March 2019) Table 3. Storage Facility Volumes Pond Type Location Req'd Vol. (cft) Provided Vol. (cft) A Retention Basin A 711 713 B Retention Basin B 133 140 C Retention Basin C 3184 (Basin C) 1985 C-1 Retention Basin C-1 275 C-2 Retention Basin C-2 300 C-3 Retention Basin C-3 275 C-4 Retention Basin C-4 350 Total Basin C Ponds 3185 Ex. Regional Retention Offsite 824 825 (available) Lot 4 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 7 of 9 The values shown in Table 3 reflect the design volume in the existing regional pond and the provided volume of the onsite retention ponds. 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 Q10 PST Q100 PST Capacity Passes Design Subareas (ft) (%) (cfs) (cfs) (cfs) Storm 12" PVC Basin C 5 0.3 2.3 3.7 6.6 Y 10" PVC Basin B 3 0.5 0.1 0.15 1.7 Y Swale 1 Basin D 0.5 1 0.6 0.9 1.22 Y 24" Curb Cut Basin C 0.4 1 2.3 3.7 3.97 Y 24" Storm Grate Basin B 1 0 0.1 0.15 1.1 Y 24" Storm Grate Basin D 1 0 0.12 0.2 1.1 Y Initial Stormwater Facility and Initial Abstraction The City of Bozeman requires that the first 0.5 inches of precipitation be captured and not allowed to become direct runoff. Retention facilities for all onsite basins have been sized to store the first 0.5 inches of runoff from a 24-hour storm. Table 5 shows the required and provided initial abstraction volumes for each basin. Table 5. Onsite Basin Initial Abstraction Basin Required Vol.* Pond Vol. (cft) (cft) A 647 713 B 72 140 C 3119 3185 D 541 825 * DEQ-8, Appendix G Standard Plan Spreadsheet 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 cleaning curb cuts, curb lines, and storm inlet grates will be required to prevent standing water and clogging. Mechanical and chemical weed maintenance within the bioretention ponds will also be required monthly. More substantial maintenance, such as sediment removal with heavy equipment may be required in the coming decades to restore pond volume and swale function. Storm inlets in the proposed loading ramps shall have the sump cleaned out when the silt reaches 2” below the outlet pipe. This should be monitored at least once per year. Similar monitoring and cleaning shall occur in the 36” storm drain manholes. The 12” PVC storm pipe shall be flushed if more than 1” of sediment is visible in the bottom of the pipe. This can be inspected inside the manholes and at the pipe discharge locations. Maintenance of the regional storm pond is the responsibility of the Nelson Meadows Owners Association. Onsite retention ponds shall have sediment removed when the average pond bottom is 1.5” above design. The armored outfall channels shall be inspected annually to ensure sediment does not build up and impair flows out of the pipe and that fabric is not exposed. 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 8 of 9 All maintenance and repairs should be prioritized and scheduled in advance. Structures and pipes should be inspected yearly, at a minimum. Typical routine maintenance items include removing obstructions, cleaning and flushing pipes, mowing grass and weeds, tree and shrub maintenance to prevent limbs from blocking swales, and establishing (and maintaining) groundcover on bare ground. See the Stormwater Maintenance Manual for additional information. IV. Conclusion Storm water analyses and calculations indicate that the proposed storm water management plan for Nelson Meadows Business Park is adequate to safely handle the 10-year, 25-year, and 100-year storm events while satisfying state and local regulations for peak attenuation and storage. All proposed buildings on the site are to be set with first floor elevations above the estimated water level during a 100-year storm determined by Headwaters Engineering. H:\1204\003\DOCS\DESIGN\STORM\01_StormwaterDR_NelsonMeadows.doc 190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 9 of 9 Appendix A Exhibits & Calculations & O&M FDC FDCFDCSD SD SD SD SD11"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:\1204\003\ACAD\SHEETS\ONSITE BASINS.dwg Plot Date: 4/7/2023 9:30 AM© HEADWATERS ENGINEERING, INC.REVISION DATE:190 NORTHSTAR LANE, BOZEMAN, MT 59718HEADWATERSMT.NET406-581-5730PROJECT LOCATIONMONTANABOZEMAN04/06/2023RESTORM BASINSBLOCK 3, LOT 4, NELSON MEADOWS SUB.NELSON MEADOWS BUSINESS PARK1204.003ST-1PROPOSEDBUILDING 2PROPOSEDBUILDING 1PROPOSEDBUILDING 3LEGEND:EXISTING FLOW DIRECTIONPROPOSED FLOW DIRECTIONEXIST ING REG IONALSTORM PONDPRINCE LANECATTAIL CREEKEXISTING CURB INLET & 15" HP STORM PIPEEXISTING CURB INLET & 15" HP STORM PIPEEXISTING 9' x 5' RCB BOX CULVERTBASIN C1.61 ACRESC=0.67BASIN A0.42 ACRESC=0.58BASIN B0.14 ACRESC=0.32BASIN D0.40 ACRESC=0.70PROPOSED POND AREQ. CAPACITY = 711 CFPROVIDED CAPACITY = 713 CFDEPTH = 1.5'PROPOSED POND BREQUIRED CAPACITY = 133 CFPROVIDED CAPACITY = 140 CFDEPTH = 0.9'PROPOSED POND CPROVIDED CAPACITY = 1,985 CFDEPTH = 1.5'SEE BASIN C NOTESPROPOSED POND C-1PROPOSED POND C-3PROPOSED POND C-4PROPOSED POND C-2PROPOSED ROCK ARMORED OUTFALL #2PROPOSED 12" PVC STORM DRAINPIPE TO EXISTING REGIONAL POND12" PVC OUTLETPOND C-1275 CFPOND C-2300 CFPOND C-3275 CFPOND C-4350 CFN24" CURB CUTBBBASIN C NOTES:1.BASIN C RETENTION AREAS ARE DIVIDED AMONGSTPOND C AND CURB ISLAND PONDS C-1 THROUGH C-4,AS SHOWN.2.CURB ISLAND PONDS UTILIZE 30% VOIDS IN SAND AND40% VOIDS IN GRAVEL, AS SHOWN ON BIORETENTIONSECTION DETAIL.3.TOTAL PROVIDED POND CAPACITY = 3,185 CF4.TOTAL REQUIRED CAPACITY = 3,184 CFBIO-RETENTION POND DETAIL(SECTION B-B)6"STANDING WATER6" DIRTY SANDW/30% VOIDS12" OF WASHED ROCK W/40% VOIDS6 OZ FELT SEPARATION FABRIC3:1 MAX SLOPEPLANTS ABLE TO WITHSTANDOCCASIONAL FLOODINGAPPROX. EXISTING GROUNDFINISHED GRADESTORMWATER RETENTION POND A1.5' DEPTH4:14:17.5'STORMWATER RETENTION POND B0.9' DEPTH4:14:14.5'STORMWATER RETENTION POND C1.5' DEPTH4:14:1STORM POND CROSS SECTIONS4'TRUCK LOADING RAMPTRUCK LOADING RAMPTRUCK LOADING RAMP STORM PIPE NOTES:1.THE FLOWS ASSOCIATED WITH LOADING RAMPFLOOR DRAINS ARE ACCOUNTED FOR IN THEIRRESPECTIVE BASIN RUNOFF VOLUMES.2.ROOF DRAIN CONNECTIONS FROM BUILDING 2 AREPROPOSED TO BE PIPED TO POND C, AS SHOWNPROPOSED 24" STORM INLETS24" STORM INLET &10" PVC OUTLETPIPEPROPOSED 36" STORM MANHOLEPROPOSED 36" STORM MANHOLEPROPOSED ARMOREDOUTFALL #1S=0.90%12" PVC STORM PIPE FROM BUILDING 2PROPOSED 36"STORM MANHOLEEXISTING REGIONAL STORM PONDPLANNED CAPACITY FOR LOT 4 = 825 CFCAPACITY USED FOR LOT 4 (BASIN D) = 824 CF24" CURB CUT24" CURB CUT24" CURB CUT12" PVC STORM PIPE TO POND CSWALE 1S=0.50% MIN.DEPTH=0.5' MIN.CURB CUT DETAILCURB FLOW LINETBC24"SWALE 1 DETAIL3:16" MIN.ARMORED OUTFALL #1 DETAIL9" MIN.3:16" OF 3" ROCK ONGEOTEX 315ST WOVENGEOTEXTILES=0.90%FIN ISHED GROUNDARMORED OUTFALL #2 DETAIL12" MIN.3:16" OF 3" ROCK ONGEOTEX 315ST WOVENGEOTEXTILES=0.50% MIN.CAPACITY = 6.85 CFSS=0.50% MIN.CAPACITY = 1.22 CFSCAPACITY = 2.91 CFSBASIN D 100-YR = 0.9 CFSAASECTION A-A: 100-YR BASIN CCURB CUTLOADING RAMPSIDEWALKNOT TO SCALE100-YR BASIN C (3.7 CFS) Post Development C Factor BASIN A BASIN B Weighted C 0.417815 Weighted C 0.144628 Area (sf)18200 Area (sf)6300 Area (Acres)0.42 Area (Acres)0.14 Area Impervious (0.9)10076 Area Impervious (0.9)1088 Area Unimproved (0.2)6350 Area Gravel (0.8)0 Area Unimproved (0.1)1774 Area Unimproved (0.2)5212 Weighted C=0.58 Weighted C=0.32 BASIN C BASIN D Weighted C 1.61 Weighted C 0.399449 Area (sf)70132 Area (sf)17400 Area (Acres)1.61 Area (Acres)0.40 Area Impervious (0.9)50277 Area Impervious (0.9)12984 Area Gravel (0.8)0 Area Gravel (0.8)0 Area Landscaped (0.1)19854.6 Area Landscaped (0.1)4416 Weighted C=0.67 Weighted C=0.70 FINAL TC BASIN A 115 4589.5 4587.25 0.02 1.13 0.15 18.44 0 0 0 #DIV/0!0.7 0.00 0 0 0 0.000 0.031944 0.04 0.00 18.44BASIN B 132 4594 4589.5 0.034 1.13 0.15 16.65 0 0 0 #DIV/0!0.7 0.00 0 0 0 0.000 0.031944 0.04 0.00 16.65BASIN C 300 4595.25 4590 0.018 1.13 0.15 41.42 150 4590 4586 0.027 1.2 2.08 0 0 0 0.000 0.031944 0.04 0.00 43.5 BASIN D 300 4595.25 4592.9 0.008 1.13 0.15 57.29 50 4592.9 4590 0.058 1.5 0.56 0 0 0 0.000 0.031944 0.04 0.00 57.85 POST Development FINAL TC BASIN A 50 4595.1 4594.1 0.02 1.13 0.011 5.00 50 4594.1 4589.85 0.085 3 0.28 15 4589.85 4589 0.057 0.031944 0.04 0.28 5.56BASIN B 20 4594 4593.5 0.025 1.13 0.011 5.00 80 4593.5 4590 0.044 3.5 0.38 32 4590 4589 0.031 0.031944 0.04 0.80 6.18BASIN C 150 4595 4593 0.013 1.13 0.011 5.00 150 4593 4588.5 0.03 4 0.63 150 4588.5 4588 0.003 0.031944 0.04 11.55 17.18 BASIN D 150 4596.1 4595 0.007 1.13 0.011 5.00 150 4595 4592.5 0.017 2.5 1.00 150 4592.5 4591 0.010 0.031944 0.04 6.67 12.67 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 ze Tc P2 (in)n6 Initial / Sheet Flow1 Shallow Concentrated Flow2 Concentrated Flow2,3 ELEV. START (ft)ELEV. END (ft)S (ft/ft)r5 (ft)n6 Ttc ELEV. START (ft)ELEV. END (ft)S (ft/ft)V4 (ft/s)Tt L3L2BASIN ID L1 ELEV START (ft)ELEV END (ft)S (ft/ft)Tt- Sheet Flow BASIN ID Initial / Sheet Flow1 Shallow Concentrated Flow2 Concentrated Flow2,3 L1 ELEV START (ft)ELEV END (ft)S (ft/ft)P2 (in)n6 Tt- Sheet Flow L2 ELEV. START (ft)ELEV. END (ft)S (ft/ft)V4 (ft/s)r5 (ft)n6 Ttc TcTtL3 ELEV. START (ft)ELEV. END (ft)S (ft/ft) City of Bozeman Retention Pond Sizing Date 3/29/2023 Project Nelson Meadows Project #1204.003 Engineer Jeremy May Pond Pond A Q=C x i x A V=7200 x Q C 0.58 intensity (i)0.41 in/hr (COB 10yr 2hr Design Storm) Storm Basin Area 0.415 acres Peak Runoff (Q)0.10 cfs Req. Pond Volume (V)711 cf City of Bozeman Retention Pond Sizing Date 3/29/2023 Project Nelson Meadows Project #1204.003 Engineer Jeremy May Pond Pond B Q=C x i x A V=7200 x Q C 0.32 intensity (i)0.41 in/hr (COB 10yr 2hr Design Storm) Storm Basin Area 0.141 acres Peak Runoff (Q)0.02 cfs Req. Pond Volume (V)133 cf City of Bozeman Retention Pond Sizing Date 3/29/2023 Project Nelson Meadows Project #1204.003 Engineer Jeremy May Pond Pond C Q=C x i x A V=7200 x Q C 0.67 intensity (i)0.41 in/hr (COB 10yr 2hr Design Storm) Storm Basin Area 1.61 acres Peak Runoff (Q)0.44 cfs Req. Pond Volume (V)3184 cf City of Bozeman Retention Pond Sizing Date 3/29/2023 Project Nelson Meadows Project #1204.003 Engineer Jeremy May Pond Pond D Q=C x i x A V=7200 x Q C 0.70 intensity (i)0.41 in/hr (COB 10yr 2hr Design Storm) Storm Basin Area 0.399 acres Peak Runoff (Q)0.11 cfs Req. Pond Volume (V)824 cf Sudivision Name EQ# County Gallatin 0.9 Location Prince Lane 0.8 Lot/Area No.A 0.1 0.2 Intensity Values Q=C*i*A 2-year, Tc 1.05 inches/hour 2-year, 24-hour 1.13 inches 10-year, Tc 2.09 inches/hour 100-year, Tc 3.35 inches/hour 100-year, 24-hour 3.71 inches Total Area/Lot Size 0.42 acres =18295.2 ft2 Initial Stormwater Facility Volume (0.5" x Impervious Area) =419.83 ft3 Paved/House Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Unimproved Area 0.42 acres 18295.2 ft2 Q=0.089 ft3/sec V=344.560 ft3 Q=0.177 ft3/sec Q=0.284 ft3/sec V=1131.253 ft3 Total 0.42 acres 18295.2 ft2 QTotal=0.089 ft3/sec VTotal=344.560 ft3 QTotal=0.177 ft3/sec QTotal=0.284 ft3/sec VTotal=1131.253 ft3 Paved/House Area 0.231313131 acres 10076 ft2 Q=0.220 ft3/sec V=853.941 ft3 Q=0.439 ft3/sec Q=0.703 ft3/sec V=2803.647 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0.040725436 acres 1774 ft2 Q=0.004 ft3/sec V=16.705 ft3 Q=0.009 ft3/sec Q=0.014 ft3/sec V=54.846 ft3 Unimproved Area 0.147961433 acres 6445.2 ft2 Q=0.031 ft3/sec V=121.385 ft3 Q=0.062 ft3/sec Q=0.100 ft3/sec V=398.528 ft3 Total 0.42 acres 18295.2 ft2 QTotal=0.256 ft3/sec VTotal=992.031 ft3 QTotal=0.510 ft3/sec QTotal=0.817 ft3/sec VTotal=3257.021 ft3 ΔQ=0.167 ft3/sec ΔV=647.471 ft3 ΔQ=0.333 ft3/sec ΔQ=0.533 ft3/sec ΔV=2125.768 ft3 647.47 ft3 = input field (volume) Runoff Flow/Volume Change Required Minimum Facility Volume: 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Post-Development Characteristics (flow rate)volume)(flow rate)(flow rate) Pre-Development Characteristics (flow rate)(volume)(flow rate)(flow rate)(volume) Unimproved areas 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Appendix G: Standard Storm Drainage Plan Nelson Meadows - Lot 4 Rational Method Co-Efficients (C) Paved/hard surfaces Gravel surfaces Lawn/landscaping Sudivision Name EQ# County Gallatin 0.9 Location Prince Lane 0.8 Lot/Area No.B 0.1 0.2 Intensity Values Q=C*i*A 2-year, Tc 1.05 inches/hour 2-year, 24-hour 1.13 inches 10-year, Tc 2.09 inches/hour 100-year, Tc 3.35 inches/hour 100-year, 24-hour 3.71 inches Total Area/Lot Size 0.14 acres =6098.4 ft2 Initial Stormwater Facility Volume (0.5" x Impervious Area) =45.333 ft3 Paved/House Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Unimproved Area 0.14 acres 6098.4 ft2 Q=0.030 ft3/sec V=114.853 ft3 Q=0.059 ft3/sec Q=0.095 ft3/sec V=377.084 ft3 Total 0.14 acres 6098.4 ft2 QTotal=0.030 ft3/sec VTotal=114.853 ft3 QTotal=0.059 ft3/sec QTotal=0.095 ft3/sec VTotal=377.084 ft3 Paved/House Area 0.024977043 acres 1088 ft2 Q=0.024 ft3/sec V=92.208 ft3 Q=0.047 ft3/sec Q=0.076 ft3/sec V=302.736 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Unimproved Area 0.115022957 acres 5010.4 ft2 Q=0.024 ft3/sec V=94.363 ft3 Q=0.048 ft3/sec Q=0.078 ft3/sec V=309.810 ft3 Total 0.14 acres 6098.4 ft2 QTotal=0.048 ft3/sec VTotal=186.571 ft3 QTotal=0.096 ft3/sec QTotal=0.154 ft3/sec VTotal=612.546 ft3 ΔQ=0.019 ft3/sec ΔV=71.717 ft3 ΔQ=0.037 ft3/sec ΔQ=0.059 ft3/sec ΔV=235.461 ft3 71.717 ft3 = input field Appendix G: Standard Storm Drainage Plan Nelson Meadows - Lot 4 Rational Method Co-Efficients (C) Paved/hard surfaces Gravel surfaces Lawn/landscaping (volume) Unimproved areas 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Post-Development Characteristics (flow rate)volume)(flow rate)(flow rate) Pre-Development Characteristics (flow rate)(volume)(flow rate)(flow rate) (volume) Runoff Flow/Volume Change Required Minimum Facility Volume: 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Sudivision Name EQ# County Gallatin 0.9 Location Prince Lane 0.8 Lot/Area No.C 0.1 0.2 Intensity Values Q=C*i*A 2-year, Tc 1.05 inches/hour 2-year, 24-hour 1.13 inches 10-year, Tc 2.09 inches/hour 100-year, Tc 3.35 inches/hour 100-year, 24-hour 3.71 inches Total Area/Lot Size 1.61 acres =70131.6 ft2 Initial Stormwater Facility Volume (0.5" x Impervious Area) =2094.9 ft3 Paved/House Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Unimproved Area 1.61 acres 70131.6 ft2 Q=0.341 ft3/sec V=1320.812 ft3 Q=0.679 ft3/sec Q=1.088 ft3/sec V=4336.471 ft3 Total 1.61 acres 70131.6 ft2 QTotal=0.341 ft3/sec VTotal=1320.812 ft3 QTotal=0.679 ft3/sec QTotal=1.088 ft3/sec VTotal=4336.471 ft3 Paved/House Area 1.154201102 acres 50277 ft2 Q=1.100 ft3/sec V=4260.976 ft3 Q=2.189 ft3/sec Q=3.509 ft3/sec V=13989.575 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0.475734619 acres 20723 ft2 Q=0.050 ft3/sec V=195.142 ft3 Q=0.100 ft3/sec Q=0.161 ft3/sec V=640.686 ft3 Unimproved Area -0.019935721 acres -868.4 ft2 Q=-0.004 ft3/sec V=-16.355 ft3 Q=-0.008 ft3/sec Q=-0.013 ft3/sec V=-53.696 ft3 Total 1.61 acres 70131.6 ft2 QTotal=1.146 ft3/sec VTotal=4439.762 ft3 QTotal=2.281 ft3/sec QTotal=3.656 ft3/sec VTotal=14576.565 ft3 ΔQ=0.805 ft3/sec ΔV=3118.951 ft3 ΔQ=1.602 ft3/sec ΔQ=2.568 ft3/sec ΔV=10240.095 ft3 3119 ft3 = input field Appendix G: Standard Storm Drainage Plan Nelson Meadows - Lot 4 Rational Method Co-Efficients (C) Paved/hard surfaces Gravel surfaces Lawn/landscaping (volume) Unimproved areas 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Post-Development Characteristics (flow rate)volume)(flow rate)(flow rate) Pre-Development Characteristics (flow rate)(volume)(flow rate)(flow rate) (volume) Runoff Flow/Volume Change Required Minimum Facility Volume: 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Sudivision Name EQ# County Gallatin 0.9 Location Prince Lane 0.8 Lot/Area No.D 0.1 0.2 Intensity Values Q=C*i*A 2-year, Tc 1.05 inches/hour 2-year, 24-hour 1.13 inches 10-year, Tc 2.09 inches/hour 100-year, Tc 3.35 inches/hour 100-year, 24-hour 3.71 inches Total Area/Lot Size 0.40 acres =17424 ft2 Initial Stormwater Facility Volume (0.5" x Impervious Area) =541 ft3 Paved/House Area 0.199724518 acres 8700 ft2 Q=0.190 ft3/sec V=737.325 ft3 Q=0.379 ft3/sec Q=0.607 ft3/sec V=2420.775 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Unimproved Area 0.200275482 acres 8724 ft2 Q=0.042 ft3/sec V=164.302 ft3 Q=0.084 ft3/sec Q=0.135 ft3/sec V=539.434 ft3 Total 0.4 acres 17424 ft2 QTotal=0.233 ft3/sec VTotal=901.627 ft3 QTotal=0.463 ft3/sec QTotal=0.742 ft3/sec VTotal=2960.209 ft3 Paved/House Area 0.298071625 acres 12984 ft2 Q=0.284 ft3/sec V=1100.394 ft3 Q=0.565 ft3/sec Q=0.906 ft3/sec V=3612.798 ft3 Gravel Area 0 acres ft2 Q=0.000 ft3/sec V=0.000 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=0.000 ft3 Lawn/Landscaping 0.10137741 acres 4416 ft2 Q=0.011 ft3/sec V=41.584 ft3 Q=0.021 ft3/sec Q=0.034 ft3/sec V=136.528 ft3 Unimproved Area 0.000550964 acres 24 ft2 Q=0.000 ft3/sec V=0.452 ft3 Q=0.000 ft3/sec Q=0.000 ft3/sec V=1.484 ft3 Total 0.4 acres 17424 ft2 QTotal=0.295 ft3/sec VTotal=1142.430 ft3 QTotal=0.587 ft3/sec QTotal=0.941 ft3/sec VTotal=3750.810 ft3 ΔQ=0.062 ft3/sec ΔV=240.803 ft3 ΔQ=0.124 ft3/sec ΔQ=0.198 ft3/sec ΔV=790.601 ft3 541 ft3 = input field (volume) Runoff Flow/Volume Change Required Minimum Facility Volume: 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Post-Development Characteristics (flow rate)volume)(flow rate)(flow rate) Pre-Development Characteristics (flow rate)(volume)(flow rate)(flow rate)(volume) Unimproved areas 2-year, Tc 2-year, 24-hour 10-year, Tc 100-year, Tc 100-year, 24-hour Appendix G: Standard Storm Drainage Plan Nelson Meadows - Lot 4 Rational Method Co-Efficients (C) Paved/hard surfaces Gravel surfaces Lawn/landscaping Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.035 Channel Slope 0.01000 ft/ft Normal Depth 0.50 ft Left Side Slope 3.00 ft/ft (H:V) Right Side Slope 3.00 ft/ft (H:V) Results Discharge 1.22 ft³/s Flow Area 0.75 ft² Wetted Perimeter 3.16 ft Hydraulic Radius 0.24 ft Top Width 3.00 ft Critical Depth 0.40 ft Critical Slope 0.03274 ft/ft Velocity 1.63 ft/s Velocity Head 0.04 ft Specific Energy 0.54 ft Froude Number 0.57 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 0.50 ft Critical Depth 0.40 ft Channel Slope 0.01000 ft/ft Critical Slope 0.03274 ft/ft Swale 1 4/6/2023 8:17:45 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 Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.035 Channel Slope 0.01000 ft/ft Normal Depth 0.50 ft Left Side Slope 3.00 ft/ft (H:V) Right Side Slope 3.00 ft/ft (H:V) Discharge 1.22 ft³/s Cross Section Image Swale 1 4/6/2023 8:18:14 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 Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.013 Channel Slope 0.01000 ft/ft Normal Depth 0.40 ft Bottom Width 2.00 ft Results Discharge 3.97 ft³/s Flow Area 0.80 ft² Wetted Perimeter 2.80 ft Hydraulic Radius 0.29 ft Top Width 2.00 ft Critical Depth 0.50 ft Critical Slope 0.00532 ft/ft Velocity 4.96 ft/s Velocity Head 0.38 ft Specific Energy 0.78 ft Froude Number 1.38 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 0.50 ft Channel Slope 0.01000 ft/ft Critical Slope 0.00532 ft/ft Worksheet for 24" Curb Cut 4/6/2023 8:24:30 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 Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.041 Channel Slope 0.00900 ft/ft Normal Depth 0.75 ft Left Side Slope 3.00 ft/ft (H:V) Right Side Slope 3.00 ft/ft (H:V) Discharge 2.91 ft³/s Cross Section Image Cross Section for Outfall 1 4/7/2023 7:32:29 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 Project Description Friction Method Manning Formula Solve For Discharge Input Data Channel Slope 0.00500 ft/ft Normal Depth 1.00 ft Discharge 6.85 ft³/s Cross Section Image Cross Section for Outfall 2 4/7/2023 6:39:01 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 Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 0.00500 ft/ft Normal Depth 0.83 ft Diameter 0.83 ft Discharge 1.66 ft³/s Cross Section Image Cross Section for 10" PVC 4/7/2023 9:15:04 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 Culvert Calculator Report 12" PVC untitled.cvm 04/06/23 08:05:10 AM Project Engineer: headw CulvertMaster v3.3 [03.03.00.04] © Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666 Page 1 of 1 Solve For: Discharge Culvert Summary Allowable HW Elevation 93.23 ft Headwater Depth/Height 7.17 Computed Headwater Elevation 93.23 ft Discharge 6.59 cfs Inlet Control HW Elev.88.60 ft Tailwater Elevation 86.17 ft Outlet Control HW Elev. 93.23 ft Control Type Outlet Control Grades Upstream Invert 86.06 ft Downstream Invert 85.50 ft Length 186.00 ft Constructed Slope 0.003011 ft/ft Hydraulic Profile Profile CompositeM2PressureProfile Depth, Downstream 0.97 ft Slope Type Mild Normal Depth N/A ft Flow Regime Subcritical Critical Depth 0.97 ft Velocity Downstream 8.47 ft/s Critical Slope 0.025643 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. 93.23 ft Upstream Velocity Head 1.10 ft Ke 0.20 Entrance Loss 0.22 ft Inlet Control Properties Inlet Control HW Elev.88.60 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 Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Channel Slope 0.00500 ft/ft Discharge 3.70 ft³/s Section Definitions Station (ft)Elevation (ft) 0+00 94.30 0+00 93.80 0+36 94.13 Roughness Segment Definitions Start Station Ending Station Roughness Coefficient (0+00, 94.30) (0+36, 94.13) 0.013 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 0.20 ft Elevation Range 93.80 to 94.30 ft Flow Area 2.14 ft² Wetted Perimeter 21.64 ft Hydraulic Radius 0.10 ft Top Width 21.44 ft Normal Depth 0.20 ft Critical Depth 0.20 ft Critical Slope 0.00540 ft/ft Velocity 1.73 ft/s Worksheet for Basin C 100-yr 4/7/2023 9:10:37 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 Results Velocity Head 0.05 ft Specific Energy 0.25 ft Froude Number 0.97 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 0.20 ft Critical Depth 0.20 ft Channel Slope 0.00500 ft/ft Critical Slope 0.00540 ft/ft Worksheet for Basin C 100-yr 4/7/2023 9:10:37 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 Normal Depth Input Data Channel Slope 0.00500 ft/ft Normal Depth 0.20 ft Discharge 3.70 ft³/s Cross Section Image Cross Section for Basin C 100-yr 4/7/2023 9:11:34 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 Nelson Meadows Business Park TBD Prince Lane 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. Mechanical and chemical weed maintenance within the bioretention ponds will also be required monthly. 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 Nelson Meadows Subdivision Owners Association. The lot Owner is responsible for maintenance of all onsite storm water facilities. Such facilities include, but are not limited to, onsite swales, retention ponds, bioretention ponds, storm structures, storm piping, inlet controls, 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 onsite retention ponds 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 sand layer within the bioretention ponds should be inspected every other year. If they are found to have build-up which allows for pooling within the ponds for more than 24 hours following a storm, the sand layers shall be removed and replaced. Armored outlet channels are to be monitored yearly to ensure sediment build up does not block or impair flows from the outlet pipes. Both the outfall channel and the areas immediately following the pipe outlet are to be inspected. Any visible sediment shall be removed and disposed of off-site. Armored channels should also be inspected for visible fabric. If fabric is exposed, adjust the rock or add more as needed. The sump of the onsite storm inlets and manholes shall be inspected yearly. Sediment removal shall occur when sediment build-up reaches 2” below the outlet pipe. The PVC storm pipes 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 2023 value. This amount includes some contingency to rollover into a fund to allow for larger scale maintenance in future years, if necessary.