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Home My WebLink About13 - Design Report - Homes at Bridger Peaks Estates - Storm STORM DRAINAGE FOR The Homes at Bridger Peaks Estates Bozeman, MT July 2013 Ae * m C= l Cx I N E E R S P E L C: { THE HOMES AT BRIDGER PEAKS ESTATES STORM DRAINAGE ENGINEERS DESIGN REPORT Introduction This report provides a design basis and hydraulic calculations for sizing storm water features for the Homes at Bridger Peaks Estates. This project is located on Block 13, Lots 4 F± 7 of the Bridger Peaks Estates Subdivision in Bozeman, Montana. The City of Bozeman Design Standards and Specifications Policy in conjunction with the City of Bozeman Modifications to Montana Public Works Standard Specifications Sixth Edition were used as the primary guideline for this storm drainage design. References for specific methods and equations used can be found throughout this document. General Design Storm water runoff generated from this site is collected by the proposed curb and gutter along the perimeter of the alley. Runoff then is directed to a curb- cut and channeled to the retention pond. Generally, the past-development drainage pattern flows to the northeast corner of the property, and the pre- development condition, flowing primarily from south to north. The existing ditch will maintain the same general flow pattern as the existing conditions through the 36" culvert that flows from the property to the west under Meagher Avenue. There with also be two 10" overflow culverts under the south driveway approach to alleviate some burden on the east ditch and to retain the same overflow pattern as pre-development. No post-development runoff will, be directed to the existing culvert. Drainage Basins This project has one distinct post-development drainage basin delineated by the property boundary and existing curb. The basin utilizes a retention pond located at the down gradient end of the basin. The retention pond was sized and designed according to the City of Bozeman Design Standards (10-year, 2- hour storm). Please refer to the Road and Storm Drainage Plans (Sheets C4.0 and C5.0) for spot elevations, overall grading of the site, and all storm water design features. Flows Peaks flows were calculated using the Modified Rational Method. A pre- development runoff coefficient of 0.2 (Table 1-1, City of Bozeman Design Standards and Specifications) was used for open Lot. A runoff coefficient of LA131871\Engineering Reports\Stonn Water-DEQ 8-081440\Report,doc Page I 0.50 was used for the post-development conditions (Table 1-1, City of Bozeman Design Standards and Specifications). The storm intensity used was the recommended value from the City of Bozeman Design Standards and Specifications of 0.41 in/hr for a 10-year, 2-hour duration design storm. The contributing areas used for the calculations were estimated from existing and proposed topographical contours using AutoCAD Civil 3D 2010. For specific calculations and references see Microsoft Excel spreadsheets in Appendix A of this report. Culverts There are two 10" culverts proposed to pass under the southern alley approach to channel a portion of the pre-development runoff in the same direction as the current flow pattern to alleviate some flow on the existing ditch on the west side of Meagher Avenue. Erosion Sediment Control During construction, sediment transportation from storm water runoff wilt be controlled by sitt fencing and or straw wattles placed along the driveway alley approaches and berm, and initial grading of swates and pond. A Storm Water Management Plan for less than I acre of disturbance is attached. Post- construction controls will consist of implementation of the landscaping plans, silt fencing and straw wattles. Treatment and Maintenance Storm water treatment will primarily consist of natural infiltration promoted by the retention pond. Maintenance of storm water structures shall include sediment/debris removal and disposal from the retention pond, and any other features (ie. curb/gutters, curb-cuts, etc.) susceptible to collection of such sediment/debris. The storm water system wilt be maintained periodically and/or as needed by the owner as described in the "City of Bozeman Storm Water Maintenance Plan" attached in Appendix B of this report. Overflow and Discharge Destination Overflow generated from a storm event greater than the design storm, wilt be routed through the retention pond and into the street via an overflow swate to the north of the pond. Summary The storm water control management plans for this site meet the City of Bozeman requirements, and are also designed to be a landscaping amenity. LA1318MEngineering Repotis\Stonn Water-DEQ 8-08144Meport.doc Page 2 Figures Storm Water -Sheet C5.0 — Grading Plan -Sheet C5.1 — Drainage Details LA131871\Engineering Reports\5torcn Water-DEQ 8-081440\Report.doc Page 3 Appendix A Storm Water -Pond Calculations LAI 31871\Engineering Reports\Storm Water-DEQ 8-081440\Report.doc Page 4 HE#: 131871 DATE: 7/10/2013 ENGINEER: Erika Chaney HYALITE E N G I N E E R S P L L C The Homes at Bridger Peaks Estates MODIFIED RATIONAL METHOD Qp=CiA PRE-DEVELOPMENT RAINFALL FREQ= 10 YR(DURATION=1) i=A*(Tc/60)"a (CITY OF BOZEMAN) BASIN AREA PRE= 1.9 AC STORM EVENT STORM i COEFF INTENSITY YR_ A_ B IN/HR PRE-DEV Tc= 28.6 MIN 2 0.36 0.6 0.13 5 0.52 0.64 0.18 PRE-DEV C= 0.20 (fable 1-1,COB Design Standards) t0 0.64 0.65 0.22 25 0.78 0.64 0.27 STORM A= 0.64 50 0.92 0.66 0.31 B= 0.65 1 100 1.01 0.67 0.34 STORM INTENSITY= 1.04 IN/HR PRE-DEV Qp= 0.39 CFS POST-DEVELOPMENT POND VOLUME: CONST.RELEASE , BASIN AREA PRE= 1.9 AC 744.61 POST-DEV Tc= 19.1 MIN TRIANGLE RELEASE' DETENTION (CF) . POST-DEV C= 0.5 (Table 1-1,COB Design Standards) 125876 STORM INTENSITY= 1.35 IN/HR AVERAGE VOLUME {e POST-DEV Qp= 1.28 CFS 1001,68, OUTLET STRUCTURE DESIGN RETENTION {0�, POND: The Homes at Bridger Peaks Estates 2804 40 REQUIRED VOL= 1001.68 CF (AVG.BIW CONST.&TRIANGLE RELEASE) DIAMETER= 10.00 IN LENGTH OF PIPE= 10.00 FT QPRE= 0.39 CFS HEAD WATER= 1.50 FT AREA= 0.07 SF N= 0.013 ORIFICE= 3 1/2 IN Kc= 0.50 ORIFICE FLOW= 0.39 CFS SLOPE OF PIPE= 0.020 FT/FT FLOW OUT= 2.96 CFS "NEED ORIFICE AVE SURF AREA= 667.79 SF L:\131871\Computations\STORM\10yr-Retention-Pond.xls 1 OF 2 PRINTED: 7/12/2013 NVALU E N G I N E E R S . P LL L C The Homes at Bridger Peaks Estates POND VOLUME CALC'S OUTLET STRUCUTRE CALC'S Triangle Release Constant Release SLOPE OF ENERGY ORIFICE DURATION INTENSITY QP POND VOLUME POND VOLUME PIPE FLOW OUT (MIN) (IN/HR) (CFS) (CF) (CF) (FT/FT) (CFS) (CFS) 18.10 1.39 1.33 1000.16 695.12 0.000 2.595 0.394 19.10 1.35 L28 1015.69 703.60 0.001 2.614 20.10 1.30 1.24 1030.31 711.08 0.002 2.633 21.10 1.26 1.20 1044.08 717.63 0.003 2.652 22.10 1.23 1.16 1057.08 723.33 0.004 2.671 23.10 1.19 1.13 1069.36 728.24 0.005 2.690 24.10 L 16 1.10 1080.97 732.42 0.006 2.709 25.10 1.13 1.07 1091.96 735.91 0.007 2.728 26.10 1.10 1.04 1102.36 738.76 0.008 2.746 27.10 1.07 1.02 1112.22 741.00 0.009 2.764 28.10 1.05 1.00 1121.56 742.68 0.010 2.783 29.10 1.02 0.97 1130.42 743.82 0.011 2.801 30.10 1,00 0.95 1138.82 744.45 0.012 2.819 31.10 0.98 0,93 1146.79 744.61 0.013 2.836 32.10 0.96 0.91 1154.36 744.31 0.014 2.854 33.10 0.94 0.90 1161.53 743.58 0.015 2,872 34.10 092 0.88 1168.33 742.44 0.016 2.889 35.10 0.91 0.86 1174.79 740.91 0.017 2.907 36.10 0.89 0.85 1180.90 739.01 0.018 2.924 37.10 0.87 0.83 1186,70 736.75 0.019 2.941 38.10 0.86 0.82 1192.19 734.15 0.020 2.958 39.10 0.85 0.80 1197.39 731.22 0.021 2.975 40.10 0.83 0.79 1202.31 727.98 0.022 2.992 41.10 0.82 0.78 1206.96 724.43 0.023 3.009 42.10 0.81 0.77 1211.35 720.60 0.024 3.026 43.10 0,79 0.75 1215.49 716.49 0.025 3.043 44.10 0.78 0.74 1219.40 712.12 0.026 3.059 45.10 0.77 0.73 1223,07 707.48 0.027 3.076 46,10 0.76 0.72 1226.52 702.60 0.028 3,092 47.10 0.75 0.71 1229.76 697.48 0.029 3,108 48.10 0.74 0.70 1232.79 692.12 0.030 3.124 49.10 0.73 0.69 1235.63 686.54 0.031 1141 50.10 0.72 0.68 1238.27 680.75 0.032 3.157 51.10 0.71 0.67 1240.72 674.74 0.033 3.173 52.10 0.70 0.67 1243.00 668.53 0.034 3.188 53.10 0.69 0.66 I245.10 66113 0.035 3.204 54.10 0.68 0.65 1247.03 655.53 0.036 3.220 55.10 0.68 0.64 1248.79 648.75 0,037 3,236 56.10 0.67 0.64 1250,40 641.79 0.038 3.251 57.10 0.66 0.63 1251.85 634.65 0.039 3.267 58.10 0.65 0.62 1253.15 627.35 0.040 3.282 L:\131871\Computations\STORM\10yr-Retention-Pond.xls 2 OF 2 PRINTED: 7/12/2013 Appendix Storm Water -City of Bozeman Storm Water Maintenance Flan LA13187 REngincering Reports\5tonn Water-DEQ 8-081440\RMort.doc Page 5 STORM WATER MAINTENANCE PLAN Site name: The Homes at Brid eg r Peaks Estates Location: Bozeman, MT OWNERS RESPONSIBILITIES FOR ROUTINE INSPECTION AND MAINTENANCE: I. Retention pond and swales shall be kept free of trash, and the berms/slopes shall be mowed or otherwise maintained to provide for a pleasant appearance. 2. A cleanout stake(2" x 4" treated wood) shall be installed near the center of the pond(s). The cleanout elevation shall be clearly marked on the stake. 3. The owner shall inspect the retention pond and swales monthly from May to October to insure that the original design capacity is in order. Records shall be kept in a separate log book of the inspections of said retention ponds, indicating the bottom:elevation and condition of the pond(s). 4. Sediment and debris shall be removed and the pond restored to original dimensions when sediment and debris build-up reach the elevation marked on the cleanout stake(s). 5. Maintenance of the retention pond and swales shall be the responsibility of the property owner or the property owner's association if applicable. Dated this day of ,2013 Signed: Title: