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HomeMy WebLinkAbout014 4-1_Storm Report_4-11-22      190 NORTHSTAR LANE  BOZEMAN, MT  59718   406‐581‐5730  www.headwatersmt.net                                                                Page 1 of 8          Storm Water Management Design Report    Bozeman Bucks Hitting Facility  901 N. Black Ave.  Bozeman, Montana                                      April, 2022      Headwaters Engineering, Inc.  Project #:  2028.001      Prepared For:  Bozeman Legion Baseball  PB Box 6054  Bozeman, MT 59771                  190 Northstar Lane, Bozeman, MT 59718                  (406) 581‐5730                 www.headwatersmt.net                         Page 2 of 8  Storm Water Management Design Report  Table of Contents      I.  Project Background……………………………………………………………………………………………….. 3    1.  Introduction………………………………………………………………………………………………………………. 3    2.  Soil and Groundwater……………………………………………………………………………………………….. 3    3.  Land Use……………………………………………………………………………………………………………………. 3    II.  Existing Conditions…………………………………………………..………………………………………………. 4    1.  Drainage Basins and Pre‐Development Peak Flows…………………………………………………… 4    III.  Proposed Drainage Plan and Post‐Development Peak Flows…………………………………. 4    1.  Major Drainage System…………………………………………………………………………………………….. 5    2.  Minor Drainage System…………………………………………………………………………………………….. 5    3.  Initial Stormwater Facility and Initial Abstraction……………………………………………………….  6    4.  Maintenance…………………………………………………………………………………………………………….. 6    IV.  Conclusion………………………………………………………………………………………….……………………. 6    List of Tables  Table 1.  Estimated Pre‐Development Peak Flows……………………………………………………………………….. 5  Table 3.  Estimated Post‐Development Peak Flows……………………………………………………………………… 5  Table 4.  Required Pond Volumes ……………………………………..………………………………………………………… 6  Table 5.  Proposed Drainage Conveyance Structures Capacities …………………………………………………… 6      Appendix A—Calculations  Grading and Drainage Exhibits  Pre/Post Development Drainage Basin Flows  Conveyance Structure Modeling  Storm Pond Calculations               List of References     City of Bozeman Design Standards and Specifications Policy, March 2004, and all addenda.          190 Northstar Lane, Bozeman, MT 59718                  (406) 581‐5730                 www.headwatersmt.net                         Page 3 of 8  I.  Project Background   Introduction  The Bozeman Bucks Hitting Facility Project consists of 1 building that will be used for baseball activities by the  non‐profit Bozeman Bucks Legion Baseball Team. The site is on the 64.7‐acre parcel described as: IMES ADD,  S06, T02 S, R06 E, ACRES 64.731, PT OF BLKS 3 & 4 & ALL BLK 5‐13 & 16‐27 PLUS VACANT STREETS & ALLEYS  LESS TRACT A, PLAT C‐41‐D. The parcel is more generally and appropriately described as a 5‐acre lease on the  northeast corner of the Gallatin County Fairgrounds, located at 901 N. Black in Bozeman, Gallatin County,  Montana. Bozeman Legion Baseball leases this site from Gallatin County. This area is home to Legion Field at  Heroes Park—a high‐quality baseball field used by the Bozeman Bucks Legion Baseball Organization.    This design report outlines the storm water analysis conducted for the site and describes the storm water  drainage and management facilities required for the project by state and local regulations. The storm water  plan follows the design standards set forth by the City of Bozeman in Design Standards and Specifications  Policy, March 2004 and subsequent addenda.      Soil and Groundwater  Four test pits were excavated at the site on June 2nd, 2021. The test pits generally included topsoil to a depth  of 8” – 14”, on top of a sandy/silty clay layer to approximately 5’, on top of a sandy‐gravel layer. Test pits were  excavated to 8’, with no groundwater present. The NRCS Soil Survey identifies the soil map areas as “Urban  Land.”      Land Use  The pre‐development land use on the area of the proposed building footprint was a laydown area for baseball  field materials and equipment. The 5‐acre lease site is used as a baseball field, including supporting structures  (concessions, bathrooms, locker rooms, bleachers, dugouts, and electrical shed). The greater 64.7 acre Gallatin  County Fairgrounds property includes a number of buildings, warehouses, stockyards, parking lots, etc. on the  fairgrounds that do not impact the 5‐acre lease site. The land is currently zoned PLI and the proposed use is for  recreational indoor practice space for the non‐profit Bozeman Bucks Baseball Organization.                     190 Northstar Lane, Bozeman, MT 59718                  (406) 581‐5730                 www.headwatersmt.net                         Page 4 of 8    Figure 1 – Vicinity map.    II.  Existing Conditions   The Bozeman Bucks Hitting Facility Project lies north of Tamarack St., south of Oak St, and immediately west of  the on‐going Bozeman Public Safety Center Building Project. The site slopes generally to the north. The  average grade of the site is approximately 1.5%. The existing high point of the property is located near the  southeast boundary of the 5‐acre lease, with the low point in the northwest corner of the 5‐acre lease. The  existing grading of the site is not well established, but generally sheet flows to the north, with no well‐defined  concentrated flow paths.      Drainage Basins and Pre‐development Peak Flows   Headwaters has identified two contributing offsite drainage basins and two onsite drainage basins, as shown  on the Grading and Drainage Sheet C‐3 and Off Site Basin Exhibit 1, found in Appendix A. The 12.7‐acre Off Site  Basin C and 17.8‐acre Off Site Basin D stretch south to Beall St., and is bound perpendicular to the contours  generated from the USGS map on Montana Cadastral. The 1’ contours on the City of Bozeman’s GIS mapper  were also used, and generally matched the USGS contours. Estimates of runoff and their respective  calculations for the drainage basins were completed using the Modified Rational Method. The offsite basin is  fully developed, and consists mostly of residential lots between 1/8th and 1/4th acres, so a C value of 0.38 was  used per McCuen. The onsite basins considered the proposed building and proposed site improvements, as  well as the immediate adjacent area of the project site. The Onsite Basin A uses a pre‐development runoff  coefficient of C = 0.26, while Onsite Basin B uses a pre‐development runoff coefficient of C = 0.43.     The 10‐year, 25‐year, and 100‐yr storm intervals were used in the analysis of the existing storm water  conditions. A summary of estimated pre‐development peak runoff rates can be found in Table 1. Detailed  calculations are available in Appendix A.      190 Northstar Lane, Bozeman, MT 59718                  (406) 581‐5730                 www.headwatersmt.net                         Page 5 of 8  Table 1.    Estimated Pre‐Development Peak Flows (see sheet GD‐1)    Sub Area Description                    Area  Tc                     Q10  Q25             Q100                         (acres)                    (min)                     (cfs)  (cfs)  (cfs)  A Onsite Basin ‐ Rational 0.32  5  0.27  0.32 0.44  B Onsite Basin ‐ Rational 0.47  5  0.70  0.81 1.13  OS‐C Offsite Basin ‐ Rational 12.7  32  4.68  5.63 7.43  OSA‐D Offsite Basin ‐ Rational 17.8  32  6.55  7.89 10.41            III.  Proposed Drainage Plan and Estimated Post‐Development Peak Flows   The proposed drainage plan will build off of the existing or natural drainage system in place. Headwaters’  drainage plan consists of two drainage systems. The major drainage system is designed to pass the 100‐year  storm without inundating buildings, with the excess runoff continuing north as it historically has, across the  property. The minor drainage system feeds into the major drainage system, and is designed to accommodate  moderate and relatively frequent storm events without inconveniencing the public. The minor system is  comprised of the swales and parking lot valleys designed to convey runoff from the 10‐year and 25‐year  events, and retention ponds designed to attenuate the 10‐year storm event. Table 2 presents a summary of  the expected post‐development peak flow rates passing through the proposed project.     Table 2.    Estimated Post‐Development Peak Flows (see sheet GD‐1)    Sub Area Description                    Area C Tc                    Q10                    Q25                    Q100                         (acres)                    (min)                    (cfs)                    (cfs)                     (cfs)        A Onsite Basin A ‐ Rational  0.32 0.60 5  0.63  0.73  1.02        B Onsite Basin B ‐ Rational 0.47 0.61 5  0.95  1.10  1.53  OS‐C Offsite Basin ‐ Rational 12.7 0.38 32  4.68  5.63  7.43  OSA‐D Offsite Basin ‐ Rational 17.8 0.38 32  6.55  7.89  10.41     Major Drainage System  Site grading onsite shall be completed so that any runoff resulting from the 100‐year design storm will flow  through the parking lot, away from the building, and down conveyance swales or cross‐sections without  inundating any structures or causing significant erosion onsite. The combined 100‐year flow for Drainage Basin  A and the Offsite Basin C of 8.45 cfs will flow through the parking lot as it heads north from Tamarack St., then  will flow west around the building and into Retention Pond A without inundating the first floor of any building.  An existing swale at the north end of Pond A will allow the 100‐year storm to overtop the pond and flow north  toward the low‐lying baseball field without inundating any buildings. The overflow of the pond is set 2.5 feet  lower than the adjacent finished floor elevation of the Hitting Facility Building, while the section west of the  building would pass the 100‐year design storm, flowing at a depth of less than six inches as shown in the  FlowMaster Cross‐section in Appendix A.    The 100‐year combined flow for onsite Drainage Basin B  and Offsite Drainage Basin D of 11.94 cfs will flow  through the parking lot as it heads north from Tamarack St., then will flow east around the building and into  Retention Pond B without inundating the first floor of any building. The existing drainage pattern flows will  carry any runoff that overtops Retention Pond B to the north. The pond overflow elevation is 4754.5’, which is  4’ below the first floor elevation of the proposed building.     Minor Drainage System   The proposed minor drainage system includes sheet flow across respective Basins A and B, into their  respective proposed Retention Ponds A and B. The pond locations are shown on the Grading and Drainage  Sheet C‐3. The City of Bozeman Design Standards and Specifications Policy requires that retention pond  volume be adequate to accommodate the difference in peak runoff between the pre‐development and post‐ development design storm of 10‐year 2‐hour design storm volume. Using a storm intensity of 0.41 in/hr per  190 Northstar Lane, Bozeman, MT 59718                  (406) 581‐5730                 www.headwatersmt.net                         Page 6 of 8  figure I‐2 and I‐3 of the City of Bozeman Design Standards, the required volumes were calculated as shown in  Table 3. The capacity of the ponds is sufficient to retain the design storm.     Table 3.     Pond Volumes     Pond Type    Location                    Contributing             Initial ½” Abstraction   10‐year, 2‐hour  Provided                                Subarea                Volume (cf)      Volume (cf) Capacity (cf)___       A Retention  Basin A (C = 0.6 @ 0.32 acres)    245  321  399      B Retention  Basin B (C = 0.47 @ 0.61 acres)    155    236    250     It is required that retention ponds and storage structures drain to prevent long‐term standing water. We used  a conservative infiltration rate of .07 in/hr for sandy silt/silty clay per DEQ 8. Since the Retention Ponds are 3”  deep, it will take 42.9 hours for the surface water to drain from the pond.     At Drainage Basin A, a gentle swale/valley in the parking lot will direct the runoff to the Retention Pond A. The  proposed valley has a capacity of 7.04 cfs which passes the 10‐year onsite storm event.    At Drainage Basin B, the typical gentle swale/valley will direct the runoff to Retention Pond B. Flow generated  from storms greater than the 10‐year storm will just widen out the flow path into the 100‐year swale and  continue past the building.    Table 4.    Proposed Drainage Conveyance Structure Capacity   Description                  Contributing        Depth          Slope     Q10PST           Q100PST  Capacity   Passes                            Subareas                  (ft) (%)            (cfs)             (cfs)           (cfs)    Design Storm  10‐YR SWALE @ PARKING LOT  A & Offsite C 0.25 0.9 5.31  7.76 Y  10‐YR SWALE @ PARKING LOT  B & Offsite D 0.25 0.9 7.5  7.76 Y  100‐YR SECTION N. OF POND A  A & Offsite  C 0.4 0.5  8.45 10.03 Y  100‐YR SECTION ALONG W. OF BLDG A & Offsite  C 0.5 0.5  8.45 13.72 Y  100‐YR SECTION ALONG E. OF BLDG B & Offsite D 0.7 0.8  11.94 13.83 Y  100‐YR SWALE BLDG ENTRY  B & Offsite D 0.3 0.8  11.94 13.03 Y    Initial Stormwater Facility and Initial Abstraction  The City of Bozeman requires that the first 0.5 inch of runoff generated from the project improvements must  be captured and not be allowed to become direct runoff. At 1,597 SF, and 3 inches deep, Retention Pond A has  capacity to treat the first 0.5 inches of runoff generated from improvements in Drainage Basin A, which is  calculated to be 321 cf. At 1,000 SF, and 3 inches deep, Retention Pond B  has capacity to treat the first 0.5  inches of runoff generated from improvements from Drainage Basin B, which is calculated to be 236 cf.      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 debris from the flow path and pond will 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 owner.     All maintenance and repairs should be prioritized and scheduled in advance. Typical maintenance items  include removing obstructions, cleaning and flushing pipes, mowing grass and weeds, tree maintenance to  prevent limbs from falling and blocking swales, and establishing groundcover on bare ground. See the  Stormwater Maintenance Manual for additional information.    IV.  Conclusion  Storm water analysis and calculations indicate that the proposed storm water management plan for the  Bozeman Bucks Hitting Facility Project is adequate to safely convey the 10‐year, 25‐year, and 100‐year storm  events while satisfying state and local regulations for peak attenuation and stormwater storage. Furthermore,  190 Northstar Lane, Bozeman, MT 59718                  (406) 581‐5730                 www.headwatersmt.net                         Page 7 of 8  the proposed first floor elevations for the structure all above the estimated 100‐yr Base flood Elevation as  determined by Headwaters Engineering.      H:\2028\001\DOCS\DESIGN\Storm\Stormwater Design Report.docx       190 Northstar Lane, Bozeman, MT 59718                  (406) 581‐5730                 www.headwatersmt.net                         Page 8 of 8        Appendix A  Exhibits & Calculations & O&M                                                                                      HW#: DATE: ENGINEER:   RAINFALL FREQ =10YR (DURATION = 1) BASIN AREA PRE =0.32AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc =5.0MIN 0.08 2 0.36 0.6 1.60 5 0.52 0.64 2.55 PRE‐DEV  C = 0.26 10 0.64 0.66 3.30 25 0.78 0.64 3.83 STORM  A = 0.64 50 0.92 0.66 4.74 B = 0.66 100 1.01 0.67 5.34 STORM INTENSITY =3.30IN/HR PRE‐DEV   Qp =0.27CFS BASIN AREA PRE =0.32AC POST‐DEV Tc =5.0MIN POST‐DEV  C =0.6 STORM INTENSITY =3.30IN/HR POST‐DEV   Qp =0.63CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 4/11/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM BASIN A H:\2028\001\DOCS\DESIGN\Storm\BASIN A FLOWS 1 OF 1 PRINTED: 4/11/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ =25YR (DURATION = 1) BASIN AREA PRE =0.32AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc =5.0MIN 0.08 2 0.36 0.6 1.60 5 0.52 0.64 2.55 PRE‐DEV  C = 0.26 10 0.64 0.66 3.30 25 0.78 0.64 3.83 STORM  A = 0.78 50 0.92 0.66 4.74 B = 0.64 100 1.01 0.67 5.34 STORM INTENSITY =3.83IN/HR PRE‐DEV   Qp =0.32CFS BASIN AREA PRE =0.32AC POST‐DEV Tc =5.0MIN POST‐DEV  C =0.6 STORM INTENSITY =3.83IN/HR POST‐DEV   Qp =0.73CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 4/11/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM BASIN A H:\2028\001\DOCS\DESIGN\Storm\BASIN A FLOWS 1 OF 1 PRINTED: 4/11/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ = 100 YR (DURATION = 1) BASIN AREA PRE =0.32AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc =5.0MIN 0.08 2 0.36 0.6 1.60 5 0.52 0.64 2.55 PRE‐DEV  C = 0.26 10 0.64 0.66 3.30 25 0.78 0.64 3.83 STORM  A = 1.01 50 0.92 0.66 4.74 B = 0.67 100 1.01 0.67 5.34 STORM INTENSITY =5.34IN/HR PRE‐DEV   Qp =0.44CFS BASIN AREA PRE =0.32AC POST‐DEV Tc =5.0MIN POST‐DEV  C =0.6 STORM INTENSITY =5.34IN/HR POST‐DEV   Qp =1.02CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 4/11/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM BASIN A H:\2028\001\DOCS\DESIGN\Storm\BASIN A FLOWS 1 OF 1 PRINTED: 4/11/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ =10YR (DURATION = 1) BASIN AREA PRE =0.47AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc =5.0MIN 0.08 2 0.36 0.6 1.60 5 0.52 0.64 2.55 PRE‐DEV  C = 0.45 10 0.64 0.66 3.30 25 0.78 0.64 3.83 STORM  A = 0.64 50 0.92 0.66 4.74 B = 0.66 100 1.01 0.67 5.34 STORM INTENSITY =3.30IN/HR PRE‐DEV   Qp =0.70CFS BASIN AREA PRE =0.47AC POST‐DEV Tc =5.0MIN POST‐DEV  C =0.61 STORM INTENSITY =3.30IN/HR POST‐DEV   Qp =0.95CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 4/11/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM BASIN B H:\2028\001\DOCS\DESIGN\Storm\BASIN B FLOWS 1 OF 1 PRINTED: 4/11/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ =25YR (DURATION = 1) BASIN AREA PRE =0.47AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc =5.0MIN 0.08 2 0.36 0.6 1.60 5 0.52 0.64 2.55 PRE‐DEV  C = 0.45 10 0.64 0.66 3.30 25 0.78 0.64 3.83 STORM  A = 0.78 50 0.92 0.66 4.74 B = 0.64 100 1.01 0.67 5.34 STORM INTENSITY =3.83IN/HR PRE‐DEV   Qp =0.81CFS BASIN AREA PRE =0.47AC POST‐DEV Tc =5.0MIN POST‐DEV  C =0.61 STORM INTENSITY =3.83IN/HR POST‐DEV   Qp =1.10CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 4/11/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM BASIN B H:\2028\001\DOCS\DESIGN\Storm\BASIN B FLOWS 1 OF 1 PRINTED: 4/11/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ = 100 YR (DURATION = 1) BASIN AREA PRE =0.47AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc =5.0MIN 0.08 2 0.36 0.6 1.60 5 0.52 0.64 2.55 PRE‐DEV  C = 0.45 10 0.64 0.66 3.30 25 0.78 0.64 3.83 STORM  A = 1.01 50 0.92 0.66 4.74 B = 0.67 100 1.01 0.67 5.34 STORM INTENSITY =5.34IN/HR PRE‐DEV   Qp =1.13CFS BASIN AREA PRE =0.47AC POST‐DEV Tc =5.0MIN POST‐DEV  C =0.61 STORM INTENSITY =5.34IN/HR POST‐DEV   Qp =1.53CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 4/11/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM BASIN B H:\2028\001\DOCS\DESIGN\Storm\BASIN B FLOWS 1 OF 1 PRINTED: 4/11/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ =10YR (DURATION = 1) BASIN AREA PRE = 12.7 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc = 32.0 MIN 0.53 2 0.36 0.6 0.52 5 0.52 0.64 0.78 PRE‐DEV  C = 0.38 10 0.64 0.66 0.97 25 0.78 0.64 1.17 STORM  A = 0.64 50 0.92 0.66 1.39 B = 0.66 100 1.01 0.67 1.54 STORM INTENSITY =0.97IN/HR PRE‐DEV   Qp =4.68CFS BASIN AREA PRE = 12.7 AC POST‐DEV Tc = 32.0 MIN POST‐DEV  C =0.38 STORM INTENSITY =0.97IN/HR POST‐DEV   Qp =4.68CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 3/31/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM OFF SITE BASIN C H:\2028\001\DOCS\DESIGN\Storm\OFF SITE BASIN C FLOWS 1 OF 1 PRINTED: 4/1/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ =25YR (DURATION = 1) BASIN AREA PRE = 12.7 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc = 32.0 MIN 0.53 2 0.36 0.6 0.52 5 0.52 0.64 0.78 PRE‐DEV  C = 0.38 10 0.64 0.66 0.97 25 0.78 0.64 1.17 STORM  A = 0.78 50 0.92 0.66 1.39 B = 0.64 100 1.01 0.67 1.54 STORM INTENSITY =1.17IN/HR PRE‐DEV   Qp =5.63CFS BASIN AREA PRE = 12.7 AC POST‐DEV Tc = 32.0 MIN POST‐DEV  C =0.38 STORM INTENSITY =1.17IN/HR POST‐DEV   Qp =5.63CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 3/31/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM OFF SITE BASIN C H:\2028\001\DOCS\DESIGN\Storm\OFF SITE BASIN C FLOWS 1 OF 1 PRINTED: 4/1/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ = 100 YR (DURATION = 1) BASIN AREA PRE = 12.7 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc = 32.0 MIN 0.53 2 0.36 0.6 0.52 5 0.52 0.64 0.78 PRE‐DEV  C = 0.38 10 0.64 0.66 0.97 25 0.78 0.64 1.17 STORM  A = 1.01 50 0.92 0.66 1.39 B = 0.67 100 1.01 0.67 1.54 STORM INTENSITY =1.54IN/HR PRE‐DEV   Qp =7.43CFS BASIN AREA PRE = 12.7 AC POST‐DEV Tc = 32.0 MIN POST‐DEV  C =0.38 STORM INTENSITY =1.54IN/HR POST‐DEV   Qp =7.43CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 3/31/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM OFF SITE BASIN C H:\2028\001\DOCS\DESIGN\Storm\OFF SITE BASIN C FLOWS 1 OF 1 PRINTED: 4/1/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ =10YR (DURATION = 1) BASIN AREA PRE = 17.8 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc = 32.0 MIN 0.53 2 0.36 0.6 0.52 5 0.52 0.64 0.78 PRE‐DEV  C = 0.38 10 0.64 0.66 0.97 25 0.78 0.64 1.17 STORM  A = 0.64 50 0.92 0.66 1.39 B = 0.66 100 1.01 0.67 1.54 STORM INTENSITY =0.97IN/HR PRE‐DEV   Qp =6.55CFS BASIN AREA PRE = 17.8 AC POST‐DEV Tc = 32.0 MIN POST‐DEV  C =0.38 STORM INTENSITY =0.97IN/HR POST‐DEV   Qp =6.55CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 3/31/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM OFF SITE BASIN D H:\2028\001\DOCS\DESIGN\Storm\OFF SITE BASIN D FLOWS 1 OF 1 PRINTED: 4/1/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ =25YR (DURATION = 1) BASIN AREA PRE = 17.8 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc = 32.0 MIN 0.53 2 0.36 0.6 0.52 5 0.52 0.64 0.78 PRE‐DEV  C = 0.38 10 0.64 0.66 0.97 25 0.78 0.64 1.17 STORM  A = 0.78 50 0.92 0.66 1.39 B = 0.64 100 1.01 0.67 1.54 STORM INTENSITY =1.17IN/HR PRE‐DEV   Qp =7.89CFS BASIN AREA PRE = 17.8 AC POST‐DEV Tc = 32.0 MIN POST‐DEV  C =0.38 STORM INTENSITY =1.17IN/HR POST‐DEV   Qp =7.89CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 3/31/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM OFF SITE BASIN D H:\2028\001\DOCS\DESIGN\Storm\OFF SITE BASIN D FLOWS 1 OF 1 PRINTED: 4/1/2022 HW#: DATE: ENGINEER:   RAINFALL FREQ = 100 YR (DURATION = 1) BASIN AREA PRE = 17.8 AC STORM EVENT INTENSITY (YR) A B (IN/HR) PRE‐DEV Tc = 32.0 MIN 0.53 2 0.36 0.6 0.52 5 0.52 0.64 0.78 PRE‐DEV  C = 0.38 10 0.64 0.66 0.97 25 0.78 0.64 1.17 STORM  A = 1.01 50 0.92 0.66 1.39 B = 0.67 100 1.01 0.67 1.54 STORM INTENSITY =1.54IN/HR PRE‐DEV   Qp = 10.41 CFS BASIN AREA PRE = 17.8 AC POST‐DEV Tc = 32.0 MIN POST‐DEV  C =0.38 STORM INTENSITY =1.54IN/HR POST‐DEV   Qp = 10.41 CFS PRE‐DEVELOPMENT MODIFIED RATIONAL METHOD (CITY OF BOZEMAN)i = A * (Tc/60) ‐B     STORM i COEFF 2028.001 GPS 3/31/2022 POST‐DEVELOPMENT Qp = C i A FLOW FROM OFF SITE BASIN D H:\2028\001\DOCS\DESIGN\Storm\OFF SITE BASIN D FLOWS 1 OF 1 PRINTED: 4/1/2022 4/11/2022 On‐site Drainage Areas Post Development A: Area Draining West Impervious West Half of Building 4320 Impervious P Lot Sidewalk 597 Impervious Sidewalk along building 967 Impervious Viewing Pad 465 Light Pad 16 Gravel Parking Lot 2666 Grass 4908 Total Area 13939 B: Area Draining East Impervious Overhang 1500 Impervious East Half of Building 4320 Impervious Sidewalk to High Point 197 Shed 279 Gravel Parking Lot 2218 Verizon Gravel and Equipment 888 Millings area 3672 Dirt Warning Track 790 Grass 2668 Unimproved 3841 Total Area 20373 H:\2028\001\DOCS\DESIGN\Storm\Impervious Area Calcs 1 of 1 4/11/2022 On‐site Drainage Areas Pre‐Development Impervious Areas A: Area Draining West Light Pad 16 Gravel Parking Lot 3146 Grass 10777 Total Area 13939 B: Area Draining East Shed 279 Gravel Parking Lot 2218 Verizon Gravel and Equipment 888 Millings area 5961 Dirt Warning Track 790 Grass 6396 Unimproved 3841 Total Area 20373 H:\2028\001\DOCS\DESIGN\Storm\Impervious Area Calcs 1 of 1 POST DevelopmentFINAL TCBASIN A250 0.015 1.13 0.011 5.00 0 0.015 1 0.00 0.000 0.031944 0.05 0.005BASIN B250 0.015 1.13 0.011 5.00 0 0.015 1 0.00 0.000 0.031944 1.05 0.005OFFSITE C300 0.015 1.13 0.011 5.51 300 0.015 2.5 2.00 2100 0.015 0.24 0.05 24.8332OFFSITE D300 0.015 1.13 0.011 5.51 300 0.015 2.5 2.00 2100 0.015 0.24 0.05 24.8332BOZEMAN BUCKS HITTING FACILITYn6TtcTcTtL3ELEV. START (ft)ELEV. END (ft)S (ft/ft)r5 (ft)BASIN IDInitial / Sheet Flow1Shallow Concentrated Flow2Concentrated Flow2,3L1ELEV START (ft)ELEV END (ft)S (ft/ft)P2 (in)n6Tt‐ Sheet FlowL2ELEV. START (ft)ELEV. END (ft)S (ft/ft)V4        (ft/s) 1 Manning's Kinematic Solution 2 Shallow Concentrated Flow Equation 3 Manning's Equation for Concentrated Flow4Velocity vs. Slope for Shallow Concentrated Flows5 Geometric Elements of Channel Sections6ze Bucks Hitting Facility 4/8/2022 Bucks Hitting Facility 4/8/2022 PRE DEVELOPMENT PRE DEVELOPMENT Basin A Basin B Weighted C Weighted C Area (sf) 13939 Area (sf) 20373 Area (Acres) 0.32 Area (Acres) 0.47 Area Impervious (0.9) 16 Area Impervious (0.9) 279 Area Gravel (0.8) 3146 Area Gravel (0.8) 9067 Area Packed Soil (0.3) 0 Area Packed Soil (0.3) 790 Area Unimproved (0.2) 0 Area Unimproved (0.2) 3841 Area Landscaped (0.1) 10777 Area Landscaped (0.1) 6396 Weighted C= 0.26 Weighted C= 0.45 Bucks Hitting Facility 4/8/2022 Bucks Hitting Facility 4/8/2022 POST DEVELOPMENT POST DEVELOPMENT Basin A Basin B Weighted C Weighted C 0.4677 Area (sf) 13939 Area (sf) 20373 Area (Acres) 0.32 Area (Acres) 0.47 Area Impervious (0.9) 6365 Area Impervious (0.9) 6296 Area Gravel (0.8) 2666 Area Gravel (0.8) 6778 Area Packed Soil (0.3) 0 Area Packed Soil (0.3) 790 Area Unimproved (0.2) 0 Area Unimproved (0.2) 3841 Area Landscaped (0.1) 4908 Area Landscaped (0.1) 2668 Weighted C= 0.60 Weighted C= 0.61 TTTTTTTTTEEEEEEEEG G G G G G G G G G G G G G E E E E E E E E E E E E EEEEEEEEEEEEEE E E E E E ETTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT15.0025.0'60.0'6.0'81'31.0'15.8 '86.0 '114.0'22'6.0'EEE E GGGG G EXISTINGELECTRICALTRANSFORMER6' WIDE X 4"THICKCONCRETESIDEWALKBUILDINGFOOTPRINT,TYPEXISTING SHED25' ASPHALT MILLINGSEXISTING GRAVELPARKING LOT FORUSECHAIN LINK FENCE, 6-FT TALL4'-TALL CHAIN LINK FENCE6' CHAINLINK FENCEGATE6-FT TALL FENCEEXISTING50 KVA 1PH120/240 VTRANSFORMEREXISTINGLIGHT POLEAND CELLTOWEREXISTING 10'NON-EXCLUSIVEUTILITY ANDACCESSEASEMENTELECTRICAL EQUIPMENTFOR CELL TOWEREXISTINGBURIEDUTILITIES TOCELLTOWER24'X40'VERIZONLEASEAREA30'X30''VERIZONLEASEAREAEXISTINGWOODENOUTFIELDFENCEEXISTING 20'NON-EXCLUSIVEACCESSEASEMENTEXISTINGELECTRICALJ-CANEXISTINGCOMMBOXEXISTING3 PHASE277/480 VSERVICETO 3PHASEPANELEXISTINGBURIEDFIBEREXISTINGBURIEDFIBERMAN DOOR W/ STEPBLDG=58.50MILLINGS=57.83GRADE TYPICAL VALLEYTO DRAIN TO PONDEXISTINGDRAINAGEPATHNORTH -NORTHWESTGRADE AWAY FROMBUILDING. SEE TYPICALSECTION.RETENTION POND BCAPACITY: 250 CFDESIGN STORM: 236 CFDEPTH: 3"RETENTION POND ACAPACITY: 399 CFDESIGN STORM: 321 CFDEPTH: 3"THIS AREA NOT SURVEYED DUE TO TEMPORARYEXISTING PILES IN PLACE. PILES TO BE MOVED UNDERSEPARATE PROJECT AND AREA TO BE GRADED TOFLOW WATER AWAY FROM THE BUILDING.HITTING FACILITY BUILDINGFFE=4758.5'OUTFLOW EXISTING TOPOGRAPHY WILL ALLOW 100-YEARSTORM TO FLOW NORTH AS IT HAS IN THE PAST100-YEAR STORM FROM DRAINAGE A AND OFFSITEBASIN C REQUIRED= 8.05 CFSCAPACITY OF 0.4' DEEP SECTION = 10.03 CFSSEE STORM REPORT FOR CROSS SECTIONBLDG=58.50SW=57.83SLOPE=0.54%BLDG=58.50SW=58.17BLDG=58.50MILLINGS=57.83OVERHEAD AND MAN DOORSBLDG=58.50SW=58.50OVERHEAD DOORBLDG=58.50SW=58.50MAN DOORBLDG=58.50SW=58.50MAN DOORBLDG=58.50SW=58.50BLDG=58.50MILLINGS=57.83SW=58.20GRASS=55.00BLDG=58.50MILLINGS=55.00MILLINGS=57.33MILLINGS=57.33BLDG=58.50MILLINGS=57.83GB=57.40MILLINGS=57.11SW=57.83GRAVEL=57.80SW=58.38GRAVEL=58.38SW=58.38GRASS=58.05SW=58.05GRASS=58.00SW=57.47GRASS=57.14SW=57.35GRASS=57.02SW=58.22GRASS=57.89SW=58.16GRAVEL=57.836' SIDEWALK6' SIDEWALK6' SIDEWALK 15' PATIOBASIN ABASIN BPROPOSEDCONTOURSBASIN B11"X17": 1"= 40 ftNGRAPHIC SCALE1 inch = ft.0( IN FEET )10202020SERPOFSTNMOAANGNDR SCHULTZGARRETT41803 PEATNIGSIEOLEREEERIEN HEADWATERSPROJECT NUMBERDRAWING NUMBERDRAWN BY:DATE:2022VERIFY SCALETHESE PRINTS MAY BEREDUCED. LINE BELOWMEASURES ONE INCH ONORIGINAL DRAWING. MODIFY SCALE ACCORDINGLYH:\2028\001\ACAD\SHEETS\C-3 GRADING AND DRAINAGE PLAN.dwg Plot Date: 4/11/2022 11:41 AM© HEADWATERS ENGINEERING, INC.REVISION DATE:190 NORTHSTAR LANE, BOZEMAN, MT 59718HEADWATERSMT.NET406-581-5730PROJECT LOCATIONMONTANABOZEMAN04/11/2022GPSGRADING AND DRAINAGE PLANBUCKS HITTING FACILITY SITE PLANBOZEMAN LEGION BASEBALL2028.001C-3RIGHT FIELD FOUL LINENOTES:1.LOW=LOW POINT, HI=HIGH POINT, GB=GRADEBREAK, SW=SIDEWALK.2. THE CONTRACTOR IS TO VERIFY THE CROSSWALKS AND ACCESSIBLE PARKING SPACES HAVE ACROSS SLOPE LESS THAN 2%.MAINTENANCEREGULAR MAINTENANCE OF STORM WATER FACILITIES IS NECESSARY FOR PROPER FUNCTIONING OF THE DRAINAGESYSTEM. IN GENERAL, REGULAR MOWING OF ANY GRASS SWALES AND STORAGE PONDS WILL BE REQUIRED TO PREVENTSTANDING WATER, CLOGGING, AND THE GROWTH OF WEEDS AND WETLAND PLANTS. MORE SUBSTANTIAL MAINTENANCE,SUCH AS SEDIMENT REMOVAL WITH HEAVY EQUIPMENT, MAY BE REQUIRED IN COMING DECADES TO RESTORE RETENTIONPOND VOLUME.ALL MAINTENANCE AND REPAIR SHOULD BE PRIORITIZED AND SCHEDULED IN ADVANCE. TYPICAL MAINTENANCE ITEMSINCLUDE REMOVING OBSTRUCTIONS FROM FENCING, MOWING GRASS AND WEEDS, TREE MAINTENANCE TO PREVENT LIMBSFROM FALLING AND BLOCKING SWALES, AND ESTABLISHING GROUNDCOVER ON BARE GROUND. RETENTION POND A CROSS SECTIONNTSCONNECT POND BOTTOM TOSOIL THAT DRAINS SO THATPOND FULLY DRAINS WITHIN 48HOURS AFTER A STORMPOND BTM4:1 3"4:14:1EXISTINGGROUNDDRAINAGE BASIN LEGENDAREA HATCHED IN RED IS DRAINAGE BASIN A.AREA HATCHED IN BLUE IS DRAINAGE BASIN B.SEE OFFSITE DRAINAGE BASIN EXHIBIT FOR OFFSITE BASINS.SECTION A-A: TYPICAL SWALE AWAY FROM BUILDINGNTSGRAVEL*-2%*EG 1%BUILDING FACESIDEWALK*LENGTH VARIES, SEE PLAN VIEWA A AA RETENTION POND B CROSS SECTIONNTSCONNECT POND BOTTOM TOSOIL THAT DRAINS SO THATPOND FULLY DRAINS WITHIN 48HOURS AFTER A STORMPOND BTM4:1 3"4:14: 1 EXISTINGGROUND3"STEP POND DOWN AS REQUIREDTO FIT EXISTING CONTOURSPOND BTM N DRAWN BY: DATE: Plot Date: 4/1/2022 9:33 AM H:\2028\001\ACAD\CONCEPT\OFF SITE BASINS.dwg REVISION DATE: 190 NORTHSTAR LANE, BOZEMAN, MT 59718 HEADWATERSMT.NET 406-581-5730 PROJECT #: LOCATION: BOZEMAN LEGION BASEBALL HITTING FACILITY OFF SITE BASINS GPS 03/31/22 2028.001 BOZEMANNTS 12.7 ACRE OFF-SITE BASIN C 17.9-ACRE OFF-SITE BASIN D BEALL ST. PROJECT SITE