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HomeMy WebLinkAboutTHE NORTHERN_DrainageReport_20250429Stormwater Drainage Report for The Northern Planning Application #24595 Bozeman, Montana April 29, 2025 Prepared For: Drake Building & Development 29785 Max Avenue, #1050 Bozeman, MT 59718 406-595-1782 Contact: Cole Nelson Prepared By: Incline Civil LLC 101 East Loucks Street, #300 Sheridan, WY 82801 970-227-0714 Contact: Ryan C. Meisel, PE Stormwater Drainage Report The Northern Bozeman, MT The Northern STORMWATER DRAINAGE REPORT Bozeman, Montana CERTIFICATION I hereby state that this Stormwater Drainage Report has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community of professional engineers. This analysis has been prepared utilizing procedures and practices specified by the City of Bozeman and within the standard accepted practices. _______________________________ _____________________________ Ryan C. Meisel, PE Date State of Montana No. PEL-PE-LIC-36846 For and on behalf of Incline Civil LLC 4/29/25 Stormwater Drainage Report The Northern Bozeman, MT TABLE OF CONTENTS DESCRIPTION PAGE A. INTRODUCTION 4 1. LOCATION 4 2. DESCRIPTION OF PROPERTY 4 3. PROPOSED PROJECT DESCRIPTION 4 B. HYDROLOGY AND HYDROGEOLOGY 5 C. EXISTING STORMWATER DRAINAGE CONDITIONS 5 1. MAJOR BASIN DESCRIPTION 5 2. SUB-BASIN DESCRIPTION 6 3. HYDROLOGIC AND HYDRAULIC CALCULATIONS OR MODELING 6 D. PROPOSED STORMWATER DRAINAGE SYSTEM 6 1. DESIGN STANDARDS 6 2. DRAINAGE SYSTEM DESIGN 6 3. HYDROLOGIC AND HYDRAULIC CALCULATIONS 7 E. EVALUATION OF MAJOR STORM FLOOD RISKS 7 F. OPERATION, INSPECTION, AND MAINTENANCE CONSIDERATIONS 8 G. LIST OF REFERENCES 9 APPENDICES: A BACKGROUND DATA - VICINITY MAP AND FLOODPLAIN MAPS B HYDROLOGIC COMPUTATIONS C HYDRAULIC COMPUTATIONS D MISCELLANEOUS INFORMATION E OPERATION, INSPECTION, AND MAINTENANCE CONSIDERATIONS F ACKNOWLEDGEMENT OF STORMWATER FACILITY MAINTENANCE REQUIREMENTS G DRAINAGE PLAN Stormwater Drainage Report The Northern Bozeman, MT 4 A. INTRODUCTION 1. Location The proposed development is located at 621 W. Mendenhall Street in Bozeman, Montana. The property is bound on the west by N. 7th Avenue, on the south by W. Mendenhall Street, on the north by an existing alley and on the east by an existing residence. The project site can also be described as situated in a portion of Lots 15-20 of Tracy’s Second Addition, City of Bozeman, Gallatin County Montana (see vicinity map Appendix A). 2. Description of Property The Northern project consists of a 0.46 acre parcel previously developed with an existing commercial building, paved parking lot and landscaping. The existing site has topography which generally slopes from the southwest to the northeast at approximately 1.0%, with varying slopes from 0.5% to 2.0%. The project is located within the Bozeman Creek Drainage Basin. The site currently conveys flows via sheet flow to the existing alley along the north side of the property and curb and gutter within N. 7th Avenue and W. Mendenhall Street. No previous drainage studies have been prepared for the property. The site is not located within a flood hazard zone and there are no significant geologic features, natural watercourses, or wetlands present at the site. 3. Proposed Project Description The Northern project will consist of a new, mixed-use 7-story multi-family apartment building with structured parking. There will be no changes to existing floodplains associated with the project. Proposed storm sewer system improvements will consist of an underground detention vault designed to capture onsite flows to be released at the historic flow rate via a sidewalk chase to existing curb and gutter in N. 7th Avenue. Stormwater Drainage Report The Northern Bozeman, MT 5 B. Hydrology and Hydrogeology Drainage analysis for the proposed development has been prepared utilizing a design storm frequency recurrence interval of 10 years for the minor storm and 100 years for the major storm in accordance with the City of Bozeman Design and Construction Standards. A design storm rainfall summary table from the City of Bozeman (Table 6.5.1) and the geotechnical analysis report can be found in Appendix D. Hydrologic analysis has been performed for the proposed development utilizing the Rational Method in accordance with the City of Bozeman Design and Construction Standards. This analysis was performed using rainfall precipitation depths, intensities and runoff coefficients provided in the criteria. Hydrologic calculations can be found in Appendix B. Hydraulic analysis has been performed for the proposed development utilizing the Modified Rational Method (also known as the Rational Method Triangular Hydrograph Method) in accordance with the City of Bozeman Design and Construction Standards as presented in Chapter 10 of the HEC- 22, 4th Edition. Hydraulic calculations can be found in Appendix C. C. EXISTING STORMWATER DRAINAGE CONDITIONS 1. Major Basin Description The Bozeman Creek Drainage Basin generally flows from the south to north where flows are ultimately conveyed into the East Gallatin River. Bozeman Creek is classified as a Special Flood Hazard Area according to FEMA Flood Insurance Rate Map number 30031C0816E (Panel 816) dated April 21, 2021. The proposed development is located within areas determined to be outside the 0.2% annual chance floodplain per map number 30031C0816E (see FIRM Map located in Appendix A). In the existing condition, the site conveys flows via sheet flow to the existing alley along the north side of the property and curb and gutter within N. 7th Avenue and W. Mendenhall Street. Flows are ultimately conveyed via curb and gutter and municipal storm sewer networks to Bozeman Creek and the East Gallatin River. There are no offsite flows within the major basin upstream of the property that are conveyed into the site. Stormwater Drainage Report The Northern Bozeman, MT 6 2. Sub-Basin Description Due to the small area of the site and the proposed building layout which encompasses the entire parcel, a single drainage basin (Basin 1) has been analyzed to compare pre-developed flows with the proposed flows generated onsite. The pre-developed peak discharge flow for the 10-year and 100-year storms was determined to be 0.1 cfs and 0.2 cfs, respectively. Rational Method hydrologic calculations can be found in Appendix B. A Grading and Drainage Plan depicting the site layout can be found in Appendix G. 3. Hydrologic and Hydraulic Calculations or Modeling Hydrologic and hydraulic methods are described in Section B above and hydraulic capacity for the adjacent curb and gutter in N. 7th Avenue can be found in Appendix C. An offsite tributary basin analysis has also been prepared for the site by Incline Civil LLC and is dated April 11, 2025. D. PROPOSED STORMWATER DRAINAGE SYSTEM 1. Design Standards Refer to Section B above for all design standards used in accordance with the City of Bozeman Design and Construction Standards. 2. Drainage System Design Runoff generated on the proposed development will be collected in roof drains which will convey flows via internal piping to a proprietary system for providing water quality below grade. After treatment, the flows will be conveyed to an underground stormwater detention vault sized to detain the difference between the 100-year proposed peak inflow rate (2.3 cfs) and the pre-developed 100-year flow rate (0.2 cfs). Rational Method calculations for these flow rates can be found in Appendix B. An internal pump will be used to release controlled flows from the vault at the allowable pre-developed 100- year flow rate of 0.2 cfs. These flows will be discharged via a sidewalk chase located near the northwest corner of the proposed building to the curb and gutter in N. 7th Avenue. Stormwater Drainage Report The Northern Bozeman, MT 7 3. Hydrologic and Hydraulic Calculations Due to the small area of the proposed site, a single drainage basin (Basin 1) has been delineated for the purpose of calculating the pre-developed and proposed runoff for the site. To calculate the pre-developed flows a runoff coefficient of 0.10 was used for unimproved areas. In the proposed condition Basin 1 consists entirely of impervious drives, walks and roofs resulting in a runoff coefficient of 0.95. These runoff coefficients were obtained from Table 6.6.4 in the City of Bozeman Design and Construction Standards. The Rational Method was utilized to calculate a pre-developed 100-year peak flow of 0.2 cfs and a proposed 100-year peak flow of 2.3 cfs Please refer to the hydrology calculations in Appendix B. These peak flows were then used to calculate the proposed stormwater detention volume using the Rational Method Triangular Hydrograph Method as presented in Chapter 10 of the HEC-22 Manual. The resulting required detention vault volume is 623.10 ft3. The capacity of the proposed 6” sidewalk chase was analyzed to determine a flow depth of 0.15 ft required to convey the pre-developed peak flow rate. Please refer to the hydraulic calculations in Appendix C. Water quality will be provided by utilizing a proprietary treatment device such as a hydrodynamic separator or filtering system installed in the rooftop drainage network prior to the stormwater detention vault. This system will be specified to treat the first 0.5 inches of rainfall to remove 80% of total suspended solids (TSS). E. EVALUATION OF MAJOR STORM FLOOD RISKS There are no flood hazards associated with the proposed development as the site is located within areas determined to be outside the 0.2% annual chance floodplain. Furthermore the proposed drainage design and stormwater detention vault will ensure that any potential flood hazards will be mitigated. A finished floor elevation analysis including tributary basin delineation and tributary flow calculations for the 100-year storm has been performed to determine the pedestrian and vehicular ingress/egress location minimum elevations. The finished floor analysis was prepared by Incline Civil LLC and is dated April 11, 2025. Stormwater Drainage Report The Northern Bozeman, MT 8 F. OPERATION, INSPECTION, AND MAINTENANCE CONSIDERATIONS Please find the Operation, Inspection, and Maintenance Plan along with the stormwater facility inspection form in Appendix E. The acknowledgement of stormwater facility maintenance requirements statement can be found in Appendix F. Stormwater Drainage Report The Northern Bozeman, MT 9 G. LIST OF REFERENCES 1. City of Bozeman Design and Construction Standards, Bozeman, Montana, effective October, 2024. 2. USDA Natural Resource Conservation Service: Web Soil Survey; USDA, websoilsurvey.sc.egov.usda.gov/App/HomePage.htm, September, 2020. 3. Hydraulic Engineering Circular No. 22, Third Edition. US Department of Transportation, Federal Highway Administration. Revised February 2024. 4. Montana Post-Construction Storm Water BMP Design Guidance Manual. Prepared by HDR. First Edition September 2017. 5. The Northern – Finish Floor Elevation Analysis. Prepared by Incline Civil LLC. April 11, 2025. Stormwater Drainage Report The Northern Bozeman, MT 10 APPENDIX A BACKGROUND DATA - VICINITY MAP AND FLOODPLAIN MAPS N VICINITY MAP VICINITY MAP SCALE: 1" = 150' PROJECT LOCATION EX-1SHEET NUMBER: PROJECT 2024017 DATE: 3/27/25 101 E. Loucks Street, #300 Sheridan, WY 82801 PHONE: 970-227-0714 THE NORTHERN BOZEMAN, MONTANA DRAWING NAME: PROJECT NAME & LOCATION: W. MENDENHALL STREET N. 7TH AVENUE Stormwater Drainage Report The Northern Bozeman, MT 11 APPENDIX B HYDROLOGIC COMPUTATIONS Final Tc Design Pt.Basin IDAreaCfCCfCACfCCfCALength (300' max)Slopeti3 LengthSlopeVelocity4tt5 tc=ti+tt2-year10-year100-year2-year10-year100-yearacres ft % min. ft % fps min min in/hr in/hr in/hr cfs cfs cfs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 1 0.46 1.00 0.95 0.44 1.25 0.95 0.55 50 1.0%1.7 20 1.0%2.0 0.2 5.0 2.68 4.21 1.2 2.3 Pre-developed 0.46 1.00 0.10 0.05 1.25 0.10 0.06 100 2.0%2.3 20 2.0%2.9 0.1 5.0 2.68 4.21 0.1 0.2 Notes: 2. I = 28.5P1/(10+Tc)0.786 3. ti = (0.42/(P20.5))*((0.013*L)/S0.5)0.8 4. Velocity = KukSp0.5 5. tt = L/60*V 6. Minimun tc is 5.0 minutes for urban areas. Table A-1 Rational Method Hydrologic Calculations The Northern Bozeman, Montana Intensity2, I Peak Discharge1, QSubbasin Data Time of Concentration, Tc 1. Flows calculated using the rational method, based on the methods provided in Section 4.2.2 of the HEC-22 Manual, 4th Edition. Overland Time (ti) Travel Time (tt)100-year10-year C Values 1 of 1Hydrology Calcs.xls Q Peak Recurrence Interval (yrs)1-hr Rainfall Depth (in) 2 0.42 5 0.64 10 0.79 25 0.97 50 1.10 100 1.24 Values obtained from City of Bozeman Design and Construction Standards Table 6.5.2 Table A-3 Rainfall Data - City of Bozeman The Northern Note: Hydrology Calcs_THE NORTHERN_offsite basins.xls Rainfall Stormwater Drainage Report The Northern Bozeman, MT 12 APPENDIX C HYDRAULIC COMPUTATIONS Project: The Northern Project #: 2024017 Date: 2/18/2025 Calculated By: RCM Rational Method Triangular Hydrograph Method Equation 10.4 from HEC-22, 4th Edition: Vs = 0.5ti (qi - qo) Where: Vs =Storage volume estimate, ft3 qi =Peak inflow rate into the basin, ft3/s = 2.3 cfs (from Table A-1, Basin 1 Peak Discharge) qo =Peak outflow rate out of the basin, ft3/s = 0.2 cfs (from Table A-1, Pre-developed Peak Discharge) ti = Duration of the basin inflow, s Note: ti = 2*tc = 2*5.0 min = 10.0 min = 600 s Vs = 0.5ti (qi - qo) = 0.5*600*(2.3-0.2) =623.10 ft3 Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Thursday, Mar 27 2025 <Name> Rectangular Bottom Width (ft) = 0.50 Total Depth (ft) = 0.50 Invert Elev (ft) = 4819.77 Slope (%) = 1.50 N-Value = 0.013 Calculations Compute by: Known Q Known Q (cfs) = 0.20 Highlighted Depth (ft) = 0.15 Q (cfs) = 0.200 Area (sqft) = 0.08 Velocity (ft/s) = 2.67 Wetted Perim (ft) = 0.80 Crit Depth, Yc (ft) = 0.18 Top Width (ft) = 0.50 EGL (ft) = 0.26 0 .1 .2 .3 .4 .5 .6 .7 Elev (ft) Depth (ft)Section 4819.00 -0.77 4819.50 -0.27 4820.00 0.23 4820.50 0.73 4821.00 1.23 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Wednesday, Apr 9 2025 <Name> Gutter Cross Sl, Sx (ft/ft) = 0.040 Cross Sl, Sw (ft/ft) = 0.040 Gutter Width (ft) = 1.21 Invert Elev (ft) = 4819.67 Slope (%) = 1.10 N-Value = 0.013 Calculations Compute by: Known Depth Known Depth (ft) = 0.50 Highlighted Depth (ft) = 0.50 Q (cfs) = 17.75 Area (sqft) = 3.13 Velocity (ft/s) = 5.68 Wetted Perim (ft) = 13.01 Crit Depth, Yc (ft) = 0.67 Spread Width (ft) = 12.50 EGL (ft) = 1.00 0 2 4 6 8 10 12 14 16 18 Elev (ft) Depth (ft)Section 4819.00 -0.67 4819.50 -0.17 4820.00 0.33 4820.50 0.83 4821.00 1.33 Reach (ft) Stormwater Drainage Report The Northern Bozeman, MT 13 APPENDIX D MISCELLANEOUS INFORMATION Chapter 6 - Storm Drainage Design 6-6 City of Bozeman Design and Construction Standards 6.5.2 Minor and Major Drainage Systems Every community has two distinct drainage systems, whether or not they are actually planned or designed: 1) the Minor Drainage System and; 2) the Major Drainage System. In combination, the two form the Total Drainage System. The Minor Drainage System is designed to transport the runoff from more frequent storm events with a minimum of disruption to the urban environment. For the City of Bozeman, the Minor Storm has a 10-year recurrence interval and shall be used for the design of stormwater interception and conveyance facilities. Drainage systems shall also be evaluated for the Major (100-year) storm to minimize public health and life hazards, damage to structures, and interruption to traffic and services. Drainage interception and conveyance systems may need to be designed to convey a portion, or all, of the Major storm runoff if Major storm runoff cannot be safely conveyed to a suitable receiving system through natural or constructed drainageways, or if allowable flow depths in streets cannot be achieved (see Section 6.7.2). Stormwater drainage planning and design shall address both the Minor and Major Drainage Systems. Detention storage to control the rate of runoff to pre-developed levels shall be designed for the full range of storm events (2-year through 100-year). 6.5.3 Design Storm Depth and Intensity Rainfall depths and intensities for durations from 5 minutes to 24 hours and recurrence intervals from 2 year to 100 years are provided in Table 6.5.1 and Table 6.5.2 respectively. Table 6.5.1 – Precipitation Depth – Duration (Depth In Inches) Duration 2-year 5-year 10-year 25-year 50-year 100-year 5-min 0.17 0.26 0.32 0.40 0.45 0.51 10-min 0.25 0.38 0.47 0.58 0.66 0.74 15-min 0.31 0.47 0.57 0.71 0.81 0.90 20-min 0.33 0.50 0.61 0.75 0.86 0.96 25-min 0.35 0.53 0.65 0.80 0.92 1.03 30-min 0.37 0.56 0.69 0.85 0.97 1.09 35-min 0.38 0.58 0.71 0.87 1.00 1.12 40-min 0.39 0.59 0.73 0.90 1.02 1.15 45-min 0.40 0.61 0.75 0.92 1.05 1.18 50-min 0.41 0.62 0.76 0.94 1.07 1.20 55-min 0.42 0.63 0.77 0.95 1.08 1.22 1-hr 0.42 0.64 0.79 0.97 1.10 1.24 2-hr 0.49 0.68 0.81 0.98 1.10 1.22 3-hr 0.56 0.74 0.86 1.01 1.12 1.23 6-hr 0.71 0.88 0.99 1.14 1.24 1.35 12-hr 0.91 1.12 1.26 1.43 1.56 1.69 24-hr 1.18 1.49 1.70 1.96 2.15 2.34 HEC-22, 4th edition Chapter 4 - Urban Hydrologic Procedures 23 4.1.3 Synthetic Design Storm Events Designers typically base drainage design on synthetic, rather than actual, rainfall events. The U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS), formerly known as the Soil Conservation Service (SCS), developed and documented 24-hour rainfall distributions, which is described in HDS-2. The SCS 24-hour rainfall distributions are widely used synthetic hyetographs and incorporate the intensity-duration relationship for the design AEP. This approach assumes that the maximum rainfall for any duration within the 24-hour duration has the same AEP. For example, a 0.1 AEP, 24-hour design storm contains the 0.1 AEP rainfall depths for all durations up to 24 hours as derived from IDF curves. Other sources of rainfall distributions exist including NOAA Atlas 14. 4.2 Peak Flow Peak flows are generally adequate for design and analysis of conveyance systems such as storm drains or open channels. This section discusses methods used to derive peak flows for both gaged and ungaged sites. The NRCS (SCS) peak flow method is another approach that calculates peak flow as a function of drainage basin area, potential watershed storage, and the time of concentration. This rainfall-runoff methodology separates total rainfall into direct runoff, retention, and initial abstraction. HDS-2 provides more detailed discussion on this method. 4.2.1 Statistical Analysis Designers use statistical analysis to evaluate peak flows where adequate gaged streamflow data exist. Frequency distributions, used in the analysis of hydrologic data, include the normal distribution, the log-normal distribution, the Gumbel extreme value distribution, and the log-Pearson type III distribution. The log-Pearson type III distribution is a three-parameter gamma distribution with a logarithmic transform of the independent variable. Designers use it widely for flood analyses because the data frequently fit the assumed population. This flexibility led the United States Geological Survey (USGS) to recommend its use as the standard distribution for flood frequency studies by all U.S. Government agencies, as documented in Bulletin 17C (England et al. 2019). Figure 4.3 presents an example of a log-Pearson type III distribution frequency curve (FHWA 2002). Designers do not commonly use statistical analysis methods in urban drainage design due to the lack of adequate streamflow data. Consult HDS-2 (FHWA 2002) for additional information on these methods. 4.2.2 Rational Method One of the most used approaches for the calculation of peak flow from small areas is the Rational Method, given as: u CIAQK= (4.1) where: Q = Flow, ft3/s (m3/s) C = Dimensionless runoff coefficient I = Rainfall intensity, in/h (mm/h) A = Drainage area, ac (ha) Ku = Unit conversion constant, 1.0 in CU (360 in SI) HEC-22, 4th edition Chapter 4 - Urban Hydrologic Procedures 27 4.2.2.2 Rainfall Intensity The Rational Method uses rainfall intensity, duration, and frequency curves. Federal, State, and local agencies have developed IDF curves for locations across the country and State highway agency drainage manuals typically document those applicable within their jurisdiction. NOAA and NRCS have created regional rainfall intensity curves that can also be used to create IDF relationships for design. 4.2.2.3 Time of Concentration Designers use many methods to estimate time of concentration including the velocity or segment method. The velocity method calculates the flow velocity within individual segments of the flow path, e.g., sheet flow, shallow concentrated flow, and open channel flow. The time of concentration can be calculated as the sum of the travel times within the various consecutive flow segments. For additional discussion on establishing the time of concentration for inlets and drainage systems, see Section 9.2.2 of this manual. Sheet flow is the shallow runoff on a planar surface with a uniform depth across the sloping surface. This usually occurs at the headwater of streams over relatively short distances, rarely more than about 300 ft, but most often less than 100 ft (NRCS 2010). Ragan (1971) suggests sheet flow occurs for distances 72 feet or less. Designers commonly estimate sheet flow with a version of the kinematic wave equation (FHWA 2002): 0.8 ut0.5 2 K nLtPS = (4.3) where: tt = Sheet flow travel time, min n = Roughness coefficient L = Flow length, ft (m) P2 = 2-year, 24-hour rainfall depth, inches (mm) S = Surface slope, ft/ft (m/m) Ku = Unit conversion constant, 0.42 in CU (5.5 in SI) Table 4.2 summarizes Manning’s roughness coefficients. Equation 4.3 is the modified version of the sheet flow equation. An iterative version of the equation replaces rainfall depth with rainfall intensity (FHWA 2002). Shallow concentrated flow develops as sheet flow concentrates in rills and then gullies of increasing proportions. Designers can estimate the velocity of such flow using a relationship between velocity and slope, as described in HDS-2 (FHWA 2002) as follows: 0.5upV = K kS (4.4) where: V = Velocity, ft/s (m/s) k = Intercept coefficient Sp = Slope, percent Ku = Unit conversion constant, 3.28 in CU (1.0 in SI) Table 4.3 summarizes intercept coefficients for shallow concentrated flow. HEC-22, 4th edition Chapter 10 - Detention and Retention 187 10.3.1.3 Rational Method Triangular Hydrograph Method Designers can obtain a preliminary estimate of the storage volume required for peak flow attenuation from a simplified design procedure that replaces the actual inflow and outflow hydrographs with simplified triangular shapes. This method works best with the Rational Method. Figure 10.5 illustrates the procedure. The area above the outflow hydrograph and inside the inflow hydrograph represents the estimated storage volume: S ii o V =0.5 t (q q )− (10.4) where: Vs = Storage volume estimate, ft3 (m3) qi = Peak inflow rate into the basin, ft3/s (m3/s) qo = Peak outflow rate out of the basin, ft3/s (m3/s) ti = Duration of basin inflow, s The duration of basin inflow equals two times the time of concentration. The triangular hydrograph procedure, originally described by Boyd (1981), compares favorably with more complete design procedures involving reservoir routing. Figure 10.5. Triangular hydrograph method. Stormwater Drainage Report The Northern Bozeman, MT 14 APPENDIX E OPERATION, INSPECTION, & MAINTENANCE CONSIDERATIONS Operation, Inspection, and Maintenance Plan for The Northern Planning Application #24595 Bozeman, Montana April 11, 2025 Prepared For: Drake Building & Development 29785 Max Avenue, #1050 Bozeman, MT 59718 406-595-1782 Contact: Cole Nelson Prepared By: Incline Civil LLC 101 East Loucks Street, #300 Sheridan, WY 82801 970-227-0714 Contact: Ryan C. Meisel, PE 101 E. Loucks Street, #300 Sheridan, WY 82801 970-227-0714 Introduction: This Operation, Inspection, and Maintenance plan for the proposed project, The Northern, has been prepared to identify the party responsible for operations, inspection, and maintenance of the proposed stormwater facility in accordance with the City of Bozeman Design and Construction Standards (Revised October 2024). Responsible Party or Entity: The responsible party or entity for operation, inspection, and maintenance as well as replacement of storm drainage facilities is: Drake Building & Development 29785 Max Avenue, #1050 Bozeman, MT 59718 406-599-8677 drakebuilding.com List of Contact Names and Information: Cole Nelson Address: 29785 Max Avenue, #1050 Phone: 406-595-1782 Email: cnelson@drakebuilding.com Site Plan: A drainage plan illustrating the storm drainage facilities can be found in Appendix G of the Stormwater Drainage Report. 101 E. Loucks Street, #300 Sheridan, WY 82801 970-227-0714 Required Maintenance and Inspection Activities: The following maintenance and inspection activities shall be performed for each facility listed at the frequency specified. Roof Drain Catch Basins All roof drain catch basins shall be inspected every 6 months or after storm events with 0.5 inches of precipitation or greater. Sediment and debris shall be cleaned from catch basin grates at a minimum once every 2 years or as needed upon inspection. Parking Garage Area Drains All area drains in the parking garage shall be inspected every 6 months or after storm events with 0.5 inches of precipitation or greater. Sediment and debris shall be cleaned from area drain grates and sumps within the facility at a minimum once every 2 years or as needed upon inspection. Sand/Oil Separator The sand/oil separator shall be inspected every 6 months or after storm events with 0.5 inches of precipitation or greater. If it is determined that the sand/oil separator is not functioning as intended, a qualified professional shall be contacted to service the facility as needed to ensure proper operation. Stormwater Detention Vault The stormwater detention vault shall be inspected every 6 months or after storm events with 0.5 inches of precipitation or greater. Sediment and debris shall be removed at a minimum once every 2 years or as needed upon inspection. Stormwater Pump Vault The stormwater pump vault shall be inspected every 6 months or after storm events with 0.5 inches of precipitation or greater. Sediment and debris shall be removed at a minimum once every 2 years or as needed upon inspection. Pump shall be inspected and tested to ensure it is functioning properly. If it is determined that the pump is not functioning, a qualified professional shall be contacted to service or replace the pump to ensure proper operation. Stormwater Facility Inspection Form: A Stormwater Facility Inspection Form illustrating maintenance inspection requirements has been obtained from the City of Bozeman Design and Construction Standards and is attached at the end of this plan. Chapter 6 - Storm Drainage Design 6-44 City of Bozeman Design and Construction Standards Stormwater Facility Inspection Form Section 1: General Information Facility ID: Facility Type: Choose an item. Date/Time: Click or tap to enter a date. Owner: Contact: Inspector’s Name, contact info: Choose an item. Location/Access info: Type of Inspection: ☐ Routine, Dry Weather ☐ Routine, Wet Weather ☐ Complaint Driven ☐ Other: __________________ Section 2: Weather and Discharge Information Most recent precipitation or melt: Temperature: Is a stormwater discharge occurring? ☐ Yes ☐ No If yes, what is the source and quality of discharge? Is an illegal discharge occurring? ☐ Yes ☐ No If yes, what is the source and quality of discharge? Section 3: Facility Maintenance Priority ☐ Low: Stormwater facility appears to be functioning as designed. Continue scheduled maintenance. ☐ Medium: Stormwater facility requires minor to moderate sediment and vegetation maintenance to mitigate the risk of flooding, waterway pollution, and infrastructure failure. ☐ High: Stormwater facility requires significant sediment dredging, vegetation removal, and/or infrastructure repairs to restore function. Notes, Findings & Recommendations: Inspector’s Signature: ________________________________ Date: ___________________ Chapter 6 - Storm Drainage Design 6-45 City of Bozeman Design and Construction Standards Section 4: Qualitative Analysis Components # Items Conditions Results Notes and Required Actions General Degraded, missing, or inadequate Yes 1.1 Accessibility maintenance access? No ☐☐ Trash, sediment, and waste within 1.2 Debris ☐Yes and around the facility? ☐ No Overgrown or dead cattails, Yes 1.3 Vegetation woody shrubs, weeds, grass, and ☐ trees? ☐ No Infrastructure Damaged inlet pipe, outlet pipe, Yes1.4 ☐ Condition outfall structure, or fencing? ☐ No Facility Condition Pretreatment Bay Clogged, obstructed, or filled 2.1 ☐ Yes or Facility pretreatment forebay or facility? ☐ No 2.2 Storage Bay Clogged or filled storage bay? ☐ Yes ☐ No Stagnant water with infiltration Groundwater or Yes 2.3 greater than 48 hours post-rain ☐ Standing Water event? ☐ No 2.4 Flow Path Clogged or obstructed flow path? ☐ Yes ☐ No Barren or exposed surfaces on Yes 2.5 Side Slopes ☐ Facility’s side slopes and bottom? ☐ No Maintenance Maintenance Plan Is there a written plan specific to ☐ Yes 3.1 or Agreement this facility? ☐ No Yes 3.2 Implementation Is there evidence of maintenance? ☐ ☐ No Chapter 6 - Storm Drainage Design 6-46 City of Bozeman Design and Construction Standards Section 5: Quantitative Analysis Vegetation Cover type % Within facility Notes Bare ground Aquatics Grasses/Herbaceou Trees >3” DBH Shrubs Total 100 Elevation Analysis Location Reading (ft) Elevation (ft) Notes SRV#CP Control Point SRV#1 Inlet SRV#2 Outlet SRV#3 Center SRV#4 North of Center SRV#5 East of Center SRV#6 South of Center SRV#7 West of center SRV#8 Berm or overflow SRV#9 Summary Chapter 6 - Storm Drainage Design 6-47 City of Bozeman Design and Construction Standards Section 6: Facility Maintenance Inspection Exhibit Chapter 6 - Storm Drainage Design 6-48 City of Bozeman Design and Construction Standards Photo 1 description Photo 2 description Section 7: Photo Log Stormwater Drainage Report The Northern Bozeman, MT 15 APPENDIX F ACKNOWLEDGEMENT OF STORMWATER FACILITY MAINTENANCE REQUIREMENTS 101 E. Loucks Street, #300 Sheridan, WY 82801 970-227-0714 Acknowledgement of Stormwater Facilities Maintenance Requirements: Property Owner: Drake Building & Development Name of Planned Development: The Northern Lot/Block/Subdivision: Remainder Portion of Lot 20, Lots 19-16, & West 9’ of Lot 15 of Tracy’s Second Addition, City of Bozeman, Gallatin County Montana Property Owner hereby acknowledges that they are required to maintain all stormwater facilities on the Property pursuant to Bozeman Municipal Code sec. 40.04.720. This requirement is binding on any successor or assign of the Property Owner listed above. The City requires stormwater facilities be constructed and adequately maintained on the Property in order to maintain the health, safety and welfare of City residents. Adequate maintenance is defined as keeping the stormwater facilities and all components thereof in good working condition so that these stormwater facilities continue to perform in accordance with the design intent. Should the Property Owner fail to adequately maintain stormwater facilities, the City may enter upon the Property and take such steps as are necessary to correct deficiencies. The City may assess against the Property Owner for the cost of any repairs or necessary maintenance by any means provided for in the Bozeman Municipal Code. By signing below Property Owner acknowledges they have read this document and the applicable provisions of the Bozeman Municipal Code, and they agree to the maintenance requirements for all stormwater facilities on their Property. BY: _________________________________________ (Property Owner) DATE: _________________________________________ Stormwater Drainage Report The Northern Bozeman, MT 16 APPENDIX G DRAINAGE PLAN T 4" 4" PROPOSED BUILDING 621 W. MENDENHALL STREET BOZEMAN, MT 59715 FFE = 4821.77N00°04'35"E 120.04'W. MENDENHALL STREET (50' ROW) ALLEY (20' ROW)S00°04'52"E 140.13'N89°38'30"E 144.94' S89°39'46"W 126.32' 4820 4820 4820 4820 482 0 482048214822482 2 4822 4821 48 2 1 4820 4820482148214821 PARKING GARAGE INGRESS/EGRESS FFE = 4821.77N. 7TH AVENUE1 PROPERTY LINE PROPERTY LINE PROPERTY LINE PROPERTY LINE L = 30.34' R = 20.00' Δ = 86°55'29" PROPERTY LINE EXISTING PUBLIC SIDEWALK CURB RAMP CONSTRUCTED PER MDT FEDERAL AID PROJECT CMDP 118-1(5)0 PROPOSED STANDARD CATCH CURB & GUTTER RE: COB DWG. NO. 02528-1 PROPOSED ALLEY APPROACH RE: COB DWG. NO. 02529-7A PEDESTRIAN INGRESS/EGRESS FFE = 4821.50 PEDESTRIAN INGRESS/EGRESS FFE = 4821.77 PEDESTRIAN INGRESS/EGRESS FFE = 4821.77 PEDESTRIAN INGRESS/EGRESS FFE = 4820.64 PROPOSED DRIVE APPROACH RE: COB DWG. NO. 02529-5A PROPOSED SIDEWALK CHASE RE: COB DWG. NO. 02720-11A PROPOSED STORMWATER DETENTION VAULT VOLUME = 623.10 CUBIC FEET INTERNAL STORM SEWER PIPE FROM VAULT TO SIDEWALK CHASE PARKING GARAGE INGRESS/EGRESS FFE = 4820.87 DR-1 1 DRAINAGE MAP0'10'20' SCALE: 1" = 10' N FOR THE MARKING OF UNDERGROUND BEFORE YOU DIG, GRADE, OR EXCAVATE CALL 2 BUSINESS DAYS IN ADVANCE CENTER OF MONTANA CALL UTILITY NOTIFICATION 1-800-424-5555 MEMBER UTILITIES. SHEET NUMBER:THE NORTHERN621 WEST MENDENHALL STREETBOZEMAN, MT 597151 CHECKED BY: DESIGNED BY: DRAWN BY:DESCRIPTION:DATE:REVISED BY:REVIEWED BY:REVISION #1234567PROJECT #: 2024017 DATE: OF DRAWING NAME:PROJECT NAME & LOCATION:RECORD DRAWING BY: 101 E. Loucks Street, #300 Sheridan, WY 82801 PHONE: 970-227-0714 RCM RCM RCMOWNER:4/29/25DRAKE BUILDING & DEVELOPMENT4/29/25 BENCHMARK: ELEVATION DATUM IS NAVD 88 BASIS OF BEARING: BOBCAT LDP COORDINATE SYSTEM POINT NORTHING EASTING ELEVATION DESCRIPTION 30 120391.19 380214.59 4821.11 MDT Cu Plug LS59853 96 120340.70 380215.51 4822.33 CH MAG DISK 97 120549.24 380217.82 4819.94 MAG NAIL 98 120536.01 380339.37 4820.54 MAG NAIL 99 120440.54 380329.09 4821.26 MAG NAIL CONTROL POINT TABLE: DRAINAGE LEGEND PROPOSED DRAINAGE FLOW ARROW BASIN DESIGNATION BASIN AREA IN ACRES RUNOFF COEFFICIENT 0.33 AC 0.95 1 PROPOSED DRAINAGE BASIN DRAINAGE DESIGN POINTDRAINAGE DESIGN POINT1 0.46 AC 0.95 1 PROPOSED MINOR CONTOURS5024 5025 PROPOSED MAJOR CONTOURS EXISTING MINOR CONTOURS5024 5025 EXISTING MAJOR CONTOURS 6226. 4 2 2.0% PROPOSED SPOT ELEVATION PROPOSED SLOPE PROPOSED SANITARY SEWER LINE PROPOSED WATER SERVICE PROPOSED WATER VALVE EXISTING FIRE HYDRANT EXISTING WATER VALVE EXISTING POWER POLE EXISTING GUY WIRE EXISTING WATER METER EXISTING LIGHT POLE EXISTING FIBER OPTIC LINE EXISTING GAS LINE EXISTING WATER LINE EXISTING OVERHEAD POWER LINE EXISTING SANITARY SEWER LINE EXISTING UNDERGROUND POWER LINE EXISTING UNDERGROUND TELEPHONE LINE PROPOSED CURB BOX PROPOSED CORP STOP PROPOSED BACKFLOW PREVENTER EX RIGHT-OF-WAY/ PROPERTY BOUNDARY LEGEND: CONTROL POINT PROPOSED SANITARY SEWER MANHOLE PROPOSED FIRE HYDRANT PROPOSED SEWER CLEANOUT PROPOSED ELECTRIC SERVICE PROPOSED TELEPHONE SERVICE PROPOSED GAS SERVICE PROPOSED FIRE DEPARTMENT CONNECTION NOTES: 1.THERE ARE NO 100-YEAR FLOOD PLAINS ON OR ADJACENT TO THE PROPERTY. 2.THERE ARE NO MAJOR DRAINAGE WAYS ON OR NEAR THE SITE. DETENTION BASIN SUMMARY TABLE BASIN AREA 1 0.46 DESIGN POINT (ACRES) 10-YEAR Q 1.2 RUNOFF 0.95 COEFFICIENT (CFS) 1 BASIN 100-YEAR Q 2.3 (CFS)