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HomeMy WebLinkAbout18 - Design Report - RSVP Event Center - Stormwater DESIGNP T STORMWATER MANAGEMENT RSVP EVENT CENTS Prepared for: Folkvord Investments, LLC 10778 Highway 287 Three Forks, MT 59752 Prepared by: C IS[Engineering and Surveying, Inc. 1091 Stoneridge Drive, Bozeman, MT 59718 (406) 587-1115 Project Number: 180620 November 2018 INTRODUCTION The proposed RSVP Event Center is an addition to the existing RSVP Motel located on Lot IA, Block 2, Violett Addition to Bozeman. This lot is a 1.625-acre parcel located in Section 12, Township 2 South,Range 5 East of P.M.M., Gallatin County, City of Bozeman.A combination of site grading, curb and gutter,piping, and underground retention chambers will be used to manage stormwater runoff on the site. Supporting stormwater calculations are attached to this report. A Drainage Area Map is included in Appendix A. Calculations for each individual drainage area (total area,weighted C factor, and time of concentration) are included in Appendix B. UNDERGROUND RETENTION CHAMBER DESIGN All underground retention chambers have been sized according to City of Bozeman Design Standards. Retention facilities are sized to capture the entire volume of the 10-year 2-hour storm event. Calculations used for sizing each pond can be found in Appendix C. EXISTING SUBDIVISION STORMWATER SYSTEM The existing Tom's Flooring site currently sends runoff from 9,767 square feet of hardscape,which results in 626 cubic feet of runoff during the 10-year, 2-hour event. This new RSVP Event Center proposes to reduce the amount of runoff being discharged into the existing subdivision stormwater system by 126 cubic feet due to the majority of the site runoff being handled with the underground infiltration chambers. The existing stormwater infrastructure will handle runoff from Drainage Area #2, totaling 0.18 acres. The new volume of water being discharged into the existing stormwater infrastructure is 500 cubic feet.Because this is less than the current site discharges into the existing infrastructure, there is adequate capacity to handle the runoff from this development. Supporting calculations can be found in Appendix C. PROPOSED UNDERGROUND INFILTRATION CHAMBERS The proposed underground infiltration chambers are located underneath the pavement. They receive runoff from Drainage Area 1, totaling 0.32 acres. The required volume of the chambers was calculated to be 887 cubic feet.The proposed volume of the underground infiltration chambers is 893 cubic feet,which is adequate to handle the additional runoff from this development. Sizing calculations for these chambers can be found in Appendix C. APPENDIX A DRAINAGE AREA MAP DRANVAGE A MAP RSVP EVENT CENTER 1I EXISTING BUILDING I _ / ! PROPOSED ✓ UNDERGROUND t _ - INFlLiRA-noN VI CHAMBERS 1 > 1:5,07 SF r V 75, �❑ � HDARDSCAPE ` , 1,091 SF ix" i I EXISTING^;SiDEWAU( _ r E t -777 W. SHORT STREET DSCAPE 1,391 SF N Scale In Feet 30 0 30 9 0 9 Scale In Meters Engineering and Surveying Inc. 1091 9mnomdge 0nv •Bozeman,M159718 Phone(406)587411 S•Fax(406)587-9768 mm.chengineers.com•infoVchengi-vm.com Sheet 1 of it (/16Q$2Q APPENDIX B DRAINAGE AREA CALCULATIONS DRAINAGE AREA #1 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C "Area Hardscape 0.95 13857 13164 Landscape 0.20 0 0 Total 13857 13164 A =Area(acres) 0.3181 C=Weighted C Factor 0.95 2. Calculate Tc(Time to Concentration) Tc Overland Flow Tc= 1.87 (1.1-CC)D'12/S'/3 ------------------------------ ;Storm S= Slope of Basin (%) 2.00% ;Return (yrs) Cf C = Rational Method Runoff Coefficient 0.35 i2 to 10 1 Cf= Frequency Adjustment Factor 1.1 11 to 25 1.1 D= Length of Basin (ft) 100 ,26 to 50 1.2 :51 to 100 1.25 Tc Overland Flow(minutes) 10.6 Tc Gutter Flow Tc= L/V/60 V= (1.486/n)R2i3 S112 n = Mannings Coefficient 0.013 R= Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb) S= slope (%) 1.20% L= length of gutter(ft) 0 V= mean velocity(ft/s) 3.28 Tc Gutter Flow(minutes) = 0.0 Tc Total= 10.6 (5 minute minimum) APPENDIX C RETENTION FACILITIES DESIGN DRAINAGE AREA #2 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C *Area Hardscape 0.95 7807 7416 Landscape 0.20 0 0 Total 7807 7416 A =Area(acres) 0.1792 C=Weighted C Factor 0.95 2. Calculate Tc(Time to Concentration) Tc Overland Flow Tc= 1.87 (1.1-CC)D'/2/S1i3 ------------------------------ ;Storm S = Slope of Basin (%) 2.00% ;Return (yrs) Cf C= Rational Method Runoff Coefficient 0.35 ;2 to 10 1 Cf= Frequency Adjustment Factor 1.1 :11 to 25 1.1 D = Length of Basin (ft) 30 126 to 50 1.2 151 to 100 1.25 Tc Overland Flow(minutes) 5.8 Tc Gutter Flow Tc= W/60 V= (1.486/n)R213 S112 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb) S = slope (%) 1.20% L= length of gutter(ft) 80 V= mean velocity (ft/s) 3.28 Tc Gutter Flow(minutes) = 0.4 Tc Total= 6.2 (5 minute minimum) UNDERGROUND INFILTRATION CHAMBERS REQUIRED VOLUME 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft2) C *Area Hardscape 0.95 13857 13164 Landscape 0.20 0 0 Total 13857 13164 C=Weighted C Factor 0.95 2. Calculate Additional Required Volume Q = CIA V=72000 C =Weighted C Factor 0.95 1 = intensity(in/hr) 0.41 (10 yr, 2hr storm) A=Area (acres) 0.32 Q = runoff(cfs) 0.12 V= REQUIRED VOL(ft) 887 EXISTING STORMWATER INFRASTRUCTURE REQUIRED VOLUME 1. Calculate Area and Weighted C Factor Contributing Area C Area ft2) C *Area Hardscape 0.95 7807 7416 Landscape 0.20 0 0 Total 7807 7416 C=Weighted C Factor 0.95 2. Calculate Additional Required Volume Q = CIA V=72000 C =Weighted C Factor 0.95 1 = intensity (in/hr) 0.41 (10 yr, 2hr storm) A=Area (acres) 0.18 Q = runoff(cfs) 0.07 V= REQUIRED VOL(ft) 500 INSPECTION AND MAINTENANCE FOR STORMWATER MANAGEMENT FACILITIES The Property Owners Association shall be responsible for the maintenance of the stormwater drainage facilities within RSVP Motel Event Center development. Storm Water Facilities: I. Drainage swales slope toward retention and detention ponds to collect storm water runoff and channel it to the retention or detention pond. 2. Retention Ponds collect storm water runoff and store the water until it evaporates and/or infiltrates into the ground. 3. Detention ponds collect storm water runoff while allowing some water to drain to another location. 4. Culverts are pipes which channel storm water from ditches or swales under roads. 5. Pipe Networks convey storm water to different discharge locations underground. 6. Inlets are facilities where storm water runoff enters a pipe network. Inlets include storm water manholes and drains. 7. Catch Basins are sumps typically located directly below storm water inlets and allow sediment to settle before storm water enters the pipe network. 8. Outlets are points where storm water exits a pipe network. 9. Dtywells are underground storm water collection facilities that collect and temporarily store runoff from roof tops and landscaped areas before allowing storm water to infiltrate into the ground. Post Construction Inspection: 1. Observe drain time in retention ponds for a storm event after completion of the facility to confirm that the desired drain time has been obtained. If excessively slow infiltration rates are observed then excavate a minimum 5 ft by 5 ft drain to native gravels(or native well-draining material)and backfill with well-draining material (pit-run). 2. Observe that drywells, catch basins, and outlet structures are clear of any material or obstructions in the drainage slots. Inspect these structures to insure proper drainage following a storm event. Immediately identify and remove objects responsible for clogging if not draining properly. Semi-Annual Inspection: I. Check retention ponds and dry wells three days following a storm event exceeding 1/4 inch of precipitation. Failure for water to percolate within this time period indicates clogging or poor-draining soils. Clear any clogs and replace any poor-draining soils with well-draining gravely soils. 2. Check for grass clippings, litter, and debris in drainage swales, catch basins, dry wells, culverts and retention ponds. Flush and/or vacuum drywells or storm water pipes if excessive material is observed in the facilities. Standard Maintenance: 1. Remove sediment and oil/grease from retention ponds and detention 2. Inspect and remove debris from drainage swales, catch basins,dry wells, and retention ponds.Use a vacuum truck to clean catch basins and dry wells. 3. Monitor health of vegetation and revegetate as necessary to maintain full vegetative cover. 4. Inspect for the following issues:differential accumulation of sediment,drain time,signs of petroleum hydrocarbon contamination (odors, oil sheen in pond water), standing water, trash and debris. Sediment accumulation: In most cases,sediment from a retention pond does not contain toxins at levels posing a hazardous concern. However, sediments should be tested for toxicants in compliance with current disposal requirements and if land uses in the drainage area include commercial or industrial zones, or if visual or olfactory indications of pollution are noticed. Sediments containing high levels of pollutants should be disposed of in accordance with applicable regulations and the potential sources of contamination should be investigated and contamination practices terminated. m t3 ® e o o a e B EEN Underground stormwater detention and infiltration systems must Maintenance be inspected and maintained at regular intervals for purposes of CMP detention systems should be cleaned when an inspection reveals performance and longevity. accumulated Sediment or trash is clogging the discharge orifice. Inspection Accumulated sediment and trash can typically be evacuated through Inspection is the key to effective maintenance of CMP detention the manhole over the outlet orifice. If maintenance is not performed systems and is easily performed. Contech recommends ongoing, as recommended, sediment and trash may accumulate in front of the quarterly inspections. The rate at which the system collects pollutants outlet orifice. Manhole covers should be securely seated following will depend more on site specific activities rather than the size or cleaning activities. Contech suggests that all systems be designed with configuration of the System. an access/inspection manhole situated at or near the inlet and the outlet orifice. Should it be necessary to get inside the system to perform Inspections should be performed more often in equipment washdown maintenance activities, all appropriate precautions regarding confined areas, in climates where sanding and/or salting operations take space entry and OSHA regulations should be followed. place, and in other various instances in which one would expect higher accumulations of sediment or abrasive/corrosive conditions. A Systems are to be rinsed, including above the spring line, annually record of each inspection is to be maintained for the life of the system. soon after"the spring thaw, and after any additional use of salting agents, as part of the maintenance program for all systems where salting agents may accumulate inside the pipe. Maintaining an underground detention or infiltration system is easiest when there is no flow entering the System. For this reason, it is a good idea to schedule the cleanout during dry weather. The foregoing inspection and maintenance efforts help ensure underground pipe systems used for stormwater storage continue to function as intended by identifying recommended regular inspection and maintenance practices. Inspection and maintenance related to the structural integrity of the pipe or the soundness of pipe joint connections is beyond the scope of this guide. i NOR d b " °v }y3 1 NOTHING IN THIS CATALOG SHOULD BE CONSTRUED AS A WARRANTY APPLICATIONS t/�r SUGGESTED HEREIN ARE DESCRIBED ONLY TO HELP READERS MAKE THEIR OWN EVALUATIONS ���®► o ,. AND DECISIONS,AND ARE NEITHER GUARANTEES NOR WARRANTIES OF SUITABILITY FOR ANY CMP DETENTION SYSTEMS APPLICATION.CONTECH MAKES NO WARRANTY WHATSOEVER,EXPRESS OR IMPLIED,RELATED TO THE APPLICATIONS,MATERIALS,COATINGS,OR PRODUCTS DISCUSSED HEREIN,All IMPLIED WARRANTIES OF MERCHANTABILITY AND ALL IMPLIED WARRANTIES OF FITNESS FOR ANY PARTICULAR PURPOSE ARE DISCIAIMED BY CONTECH"SEE CONTECIS CONDITIONS OF SALE (AVAILABLE AT WWW CONTECHES.COM/COS)FOR MORE INFORMATION ENGINEERED SOLUTIONS 2017 Contech Engineered Solutions IIC CMP MAINTENANCE GUIDE 2/17 PDF All rights reserved.Printed in USA. 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