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Home My WebLink About19 - Design Report - Ruh Building - Stormwater DESIGN REPORT STORMWATER MANAGEMENT THE RUH BUILDING Prepared for: William & Karen Ruh 439 Cranleigh Court San Ramon, CA 94583 Prepared by: C&H Engineering and Surveying, Inc, 1091 Stoneridge Drive, Bozeman, MT 59718 (406) 587-1115 Project Number: 180423 February 2019 INTRODUCTION The proposed Ruh Building is a 4-story commercial/residential development located on a 0.64- acre parcel in Section 1, Township 2 South, Range 5 East of P.M.M., Gallatin County, City of Bozeman. A combination of site grading, curb and gutter, storm inlets, piping, drywells, swales, and underground retention will be used to manage stormwater runoff on the site. Supporting stonnwater 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. RETENTION/DETENTION POND/DRYWELL DESIGN All drywells/underground retention facilities 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/drywell can be found in Appendix C. STORM SEWER FACILITIES DESIGN Stone sewer facilities were sized for the 25-yr storm using Manning's Equation. For each inlet, the contributing area, weighted C factor, and time of concentration were calculated. These values were input into Manning's Equation to check capacity and flow characteristics for inlets, storm drain pipes,and curb gutters.All curbs are designed to maintain 0.15' freeboard per C.O.B.Design Manual Section IV.C.5. For the purposes of this report, each pipe section was named to match the associated upstream structure. Pipe sizing calculations are included in Appendix D. Proposed Drywell#1 Drywell #1 is located in the southern half of the proposed parking lot. It receives runoff from Drainage Area 1, totaling 0.28 acres. The required volume of the drywell is 697 cubic feet. The proposed volume of Drywell#1 is 823 cubic feet, which is adequate to handle the runoff from this development. Sizing calculations for this drywell can be found in Appendix C. Proposed Drywell#2 Drywell #2 is located in the northern half of the proposed parking lot. It receives runoff from Drainage Area 2, totaling 0.30 acres. The required volume of the drywell is 771 cubic feet. The proposed volume of Drywell #2 is 823 cubic feet, which is adequate to handle the runoff from this development. Sizing calculations for this drywell can be found in Appendix C. Offsite Runoff The remaining runoff from the southern portion of the proposed alley will drain into the existing stormwater infrastructure within Durston Road. This system receives runoff from Drainage Area 3, totaling 0.05 acres. The runoff volume is 104 cubic feet. The existing site conditions route the majority of the runoff from the existing hardscape on site into this existing stormwater system. This new design will reduce the total amount of runoff entering the existing system as the majority of the runoff is being contained on site. Runoff calculations for this drainage area can be found in Appendix C. APPENDIX A DRAINAGE AREA MAP as SS O N O OD � 0�1 f ti O O — M.19 M..9 - — M..9 M.19 M.19 -- M.19 M..9 M.19 O ---------------------------- 3nN3Ad H1L a) ——— SS ————— f �. w � CL N N QN �ktVl1`t 4 IL OW Q L� \ LL - � _ Q Z� �C) V��, Q Z0) w a /`MWO 0 ;/\ f❑�M I z Z N ^-�- O p LL 1 V Ld i w (n � 1 Z: 00 o W ;_CL_ I �_ y _ ` I Q _ p I 9 � (� rn -- - - 0 QU O Z 0 in =x lil ; \ 7 _ �� 00 I I � � i. ". � 7n NNVI \ LLJ I I I` SON \ .. C w 7 x z ) Qzo I H � \ > �QED N� p Ul v d \ _zk(q O / 'III— -*0 co) E rn °' N m L m ID aLi z MQN / (t lly0 0 T LD SS..B SS.. p a�i Lo - '_ �MHO r �. ❑ � Lo adi iy0 c to 0'r \ N V L ww w 2 x x [ y U 000 U' I I I 0 a r- � W 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 10494 9969 Landscape 0.20 1850 370 Total 12344 10339 A =Area(acres) 0.2834 C= Weighted C Factor 0.84 2. Calculate Tc(Time to Concentration) Tc Overland Flow Tc= 1.87(1.1-CCf)D'/2/S1/3 ------------------------------ ;Storm S = Slope of Basin (%) 2.00% !Return (yrs) Cf C = Rational Method Runoff Coefficient 0.35 12 to 10 1 Cf= Frequency Adjustment Factor 1.1 111 to 25 1.1 D = Length of Basin (ft) 0 1,26 to 50 1.2 51 to 100 1.25 Tc Overland Flow(minutes) 0.0 Tc Gutter Flow Tc= L/V/60 V= (1.486/n)R2i3 S1/2 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) 200 V = mean velocity(ft/s) 3.28 Tc Gutter Flow(minutes) = 1.0 Tc Total= 5.0 (5 minute minimum) DRAINAGE AREA #2 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C *Area Hardscape 0.95 11714 11129 Landscape 0.20 1549 310 Total 13264 11439 A =Area(acres) 0.3045 C= Weighted C Factor 0.86 2. Calculate Tc(Time to Concentration) Tc Overland Flow Tc= 1.87 (1.1-CCf)D'/2/S1/3 ------------------------------ ;Storm S =Slope of Basin (%) 2.00% 'Return (yrs) Cf C = Rational Method Runoff Coefficient 0.35 12 to 10 1 Cf= Frequency Adjustment Factor 1.1 111 to 25 1.1 D = Length of Basin (ft) 0 1,26 to 50 1.2 51 to 100 1.25 Tc Overland Flow(minutes) 0.0 Tc Gutter Flow Tc= LN/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(%) 1.00% L = length of gutter(ft) 100 V= mean velocity(ft/s) 3.00 Tc Gutter Flow(minutes) = 0.6 Tc Total= 5.0 (5 minute minimum) DRAINAGE AREA #3 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C *Area Hardscape 0.95 1425 1353 Landscape 0.20 954 191 Total 2379 1544 A =Area(acres) 0.0546 C= Weighted C Factor 0.65 2. Calculate Tc(Time to Concentration) Tc Overland Flow Tc= 1.87 (1.1-CCf)D1/2/s1/3 ------------------------------ ;Storm S = Slope of Basin (%) 2.00% 'Return (yrs) Cf C = Rational Method Runoff Coefficient 0.35 12 to 10 1 Cf= Frequency Adjustment Factor 1.1 .111 to 25 1.1 D = Length of Basin (ft) 15 126 to 50 1.2 51 to 100 1.25 Tc Overland Flow(minutes) 4.1 Tc Gutter Flow Tc= LN/60 V= (1.486/n)R2/3 SI12 n = Mannings Coefficient 0.013 R = Hydraulic Radius A/P (ft) 0.13 (0.15' below top of curb) S = slope (%) 1.00% L = length of gutter(ft) 0 V= mean velocity(ft/s) 3.00 Tc Gutter Flow(minutes) = 0.0 Tc Total= 5.0 (5 minute minimum) APPENDIX C RETENTION FACILTIES CALCULATIONS DRYWELL #1 9. Calculate Area and Weighted C Factor Contributing Area C Area(ft z C *Area Hardscape 0.95 10494 9969 Landscape 0.20 1850 370 Total 12344 10339 A =Area(acres) 0.2834 C= Weighted C Factor 0.84 2. Calculate Required Volume Q=CiA V=7200Q C =Weighted C Factor 0:84 1 = Intensity(in/hr) 0.41 (10 yr, 2hr storm) A=Area (acres) 6.28' Q = Runoff(cfs) 0:10 V= REQUIRED VOL (ft) 697 3. Calculate Drywell Volume Existing Soil Condition 'Grave Percolation Rate (min/in) 6 (see Circular DEQ 4, Percolation Rate (ft/hr) 0.83 Table 2.1-1) Porous Media in Drywell Grave, l Void Ratio of Media 30,00% Gravel Offset Dist. From Drywell (ft) 6 Infiltration Drywell Gravel Area (fe) 222.5 Infi(itration Volume(ft3) 370:77 Gravel Void Volume Gravel Bed Depth (below MH) 2.00, Gravel Volume(ft3) 261:49 Gravel Storage Volume (ft3) 378.45 Manhole Volume Manhole Depth (ft) 4.00 Manhole Volume(ft) 73:29 Provided Volume Inc. Perc. (ft) 823 DRYWELL #2 9. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C *Area Hardscape 0.95 11714 11129 Landscape 0.20 1549 310 Total 13264 11439 A =Area(acres) 0.3045 C= Weighted C Factor 0.86 2. Calculate Required Volume Q=CIA V=7200Q C =Weighted C Factor 086 1 = Intensity(in/hr) 0.41 (10 yr, 2hr storm) A=Area(acres) 0.30 Q = Runoff(cfs) 011 V= REQUIRED VOL (ft) 771 3. Calculate Drywell Volume Existing Soil Condition ! Gravel Percolation Rate (min/in) 61, (see Circular DEQ 4, Percolation Rate (ft/hr) 0.83' Table 2.1-1) Porous Media in Drywell Gravel Void Ratio of Media ''36.00% Gravel Offset Dist. From Drywell (ft) 6 Infiltration Drywell Gravel Area (fe) 2&5 Infilitration Volume(ft) 37037 Gravel Void Volume Gravel Bed Depth (below MH) ,2.00- Gravel Volume(ft) 1261,49 Gravel Storage Volume(ft) 378.45 Manhole Volume Manhole Depth (ft) 4.00 Manhole Volume (ft) 7329. Provided Volume Inc. Perc. (ft) $23 OFFSITE FLOW 1. Calculate Area and Weighted C Factor Contributing Area C Area (ft 2) C *Area Hardscape 0.95 1425 1353 Landscape 0.20 954 191 Total 2379 1544 A =Area(acres) 0.0546 C= Weighted C Factor 0.65 2. Calculate Required Volume Q=CIA V=7200Q C =Weighted C Factor 0,65 1 = Intensity(in/hr) 0.41 (10 yr, 2hr storm) A=Area (acres) 0.05" Q = Runoff(cfs) 0.01 V= REQUIRED VOL(ft) 104 APPENDIX STORM SEWER CALCULATIONS PIPE #1 25-YR OUTFLOW RATE REQUIRED CAPACITY 1. Calculate Area and Weighted C FactoR Contributing Area C Area (ft 1) C *Area Hardscape 0.95 10494 9969 Landscape 0.20 1850 370 Total 12344 10339 A =Area(acres) 0.2834 C= Weighted C Factor 0.84 2. Calculate Rainfall Intensity(Duration =Max Tc from Contributing Drainage Areas) i =0.78XI.14(10-yr Storm, Fig. 1-3, COB Design Standards) x=storm duration (hrs) 0.08 (DA#1) i=rainfall intensity(in.1hr.) 3.83 3. Calculate 25-yr Pond Outflow Rate Q = CiA C = Rational Method Runoff Coefficient 0.84 (calculated above) i =rainfall intensity(in./hr.) 3.83 (calculated above) A=Area (acres) 0.28 (calculated above) Q =25-yr Pond Outflow Rate(cfs) 0.91 MANNING'S EQUATION FOR PIPE FLOW Pipe: Pipe 1 Project: The Ruh Building *-7 INPUT D= 12 inches d= 11.26 inches Mannings Formula dn= 0.013 manningsS0= 57.7 degrees AR Q= 1.486/n zi3 �i2( ) nS= 0.01 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rn2/3S12 n=Manning's roughness coefficient Q=V X A Solution to Mannings Equation Manning's n-values Area,ft2 Perimeter,ft Radius,ft velocity ft/s flow,cfs PVC 0.013 0.77 2.64 0.29 501 3.83 PE(<9"dia) 0.015 PE(>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 PIPE #2 25-YR OUTFLOW RATE REQUIRED CAPACITY 9. Calculate Area and Weighted C FactoR Contributing Area C Area(ffz) C *Area Hardscape 0.95 10093 9588 Landscape 0.20 1549 310 Total 11642 9898 A =Area(acres) 0.2673 C= Weighted C Factor 0.85 2. Calculate Rainfall Intensity(Duration =Max Tc from Contributing Drainage Areas) i =0.78x o.s4(10-yr Storm, Fig. 1-3, COB Design Standards) x=storm duration (hrs) 0.08 (DA#2) i=rainfall intensity(in./hr.) 3.83 3. Calculate 25-yr Pond Outflow Rate Q= CiA C = Rational Method Runoff Coefficient 0.85 (calculated above) i = rainfall intensity(in./hr.) 3.83 (calculated above) A=Area (acres) 0.27 (calculated above) Q=25-yr Pond Outflow Rate(cfs) 0.87 MANNING'S EQUATION FOR PIPE FLOW Pipe: Pipe 2 Project: The Ruh Building 0 INPUT D= 12 inches d= 11.26 inches Mannings Formula d n= 0.013 mannings D 0= 57.7 degrees AR Q= 1.486/n Zi3S�r2 ( ) n S= 0.01 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rn213SI12 n=Manning's roughness coefficient Q=V X A Solution to Mannings Equation Manning's n-values Area,fe Perimeter,ft Radius,ft velocity ft/s flow,cfs PVC 0.013 0.77 2.64 0.29 5.01 3.83 PE(<9"dia) 0.015 PE(>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 PIPE #3 25-YR OUTFLOW RATE REQUIRED CAPACITY 1. Calculate Area and Weighted C FactoR Contributing Area C Area(ft`) C *Area Hardscape 0.95 1621 1540 Landscape 0.20 "0 0 Total 1621 1540 A =Area(acres) 0.0372 C= Weighted C Factor 0.95 2. Calculate Rainfall Intensity(Duration =Max Tc from Contributing Drainage Areas) i =0.78x0.64(10-yr Storm, Fig. 1-3, COB Design Standards) x = storm duration (hrs) 0.08 (DA#2) i=rainfall intensity(1n.1hr.) 3.83 3. Calculate 25-yr Pond Outflow Rate Q =CiA C = Rational Method Runoff Coefficient 0.95 (calculated above) i =rainfall intensity(in./hr.) 3.83 (calculated above) A=Area (acres) 0.04 (calculated above) Q=25-yr Pond Outflow Rate(cfs) 0.14 MANNING'S EQUATION FOR PIPE FLOW Pipe: Pipe 3 Project: The Ruh Building e INPUT D= 12 inches d= 11.26 inches Mannings Formula d n= 0.013 mannings D 0= 57.7 degrees 1.486/nAR Q= v3S�i2 ( ) n S= 0.02 slope in/in R=A/P A=cross sectional area P=wetted perimeter S=slope of channel V=(1.49/n)Rn2i3Sii2 n=Manning's roughness coefficient Q=V X A Solution to Mannings Equation Manning's n-values Area,ft2 Perimeter,ft Radius,ft velocity ft/s flow,cfs PVC 0.013 0.77 2.64 0.29 708 5.42 PE(<9"dia) 0.015 PE(>12"dia) 0.02 PE(9-12"dia) 0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 INSPECTION AND MAINTENANCE FOR STORMWATER MANAGEMENT FACILITIES The Property Owners Association shall be responsible for the maintenance of the stonnwater drainage facilities within the The Ruh Building development. Storm Water Facilities: 1. Drainage swales slope toward retention facilities to collect storm water runoff and channel it to the retention or detention pond. 2. Culverts are pipes which channel storm water from ditches or swales under roads. 3. Pipe Networks convey storm water to different discharge locations underground. 4. Inlets are facilities where stone water runoff enters a pipe network. Inlets include storm water manholes and drains. 5. Catch Basins are sumps typically located directly below storm water inlets and allow sediment to settle before storm water enters the pipe network. 6. Outlets are points where storm water exits a pipe network. 7. Drywells 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 facilities 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 backfrll 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: 1. Check dry wells three days following a stone event exceeding '/ 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, and culverts. Flush and/or vacuum drywells or stone water pipes if excessive material is observed in the facilities. Standard Maintenance: 1. Remove sediment and oil/grease from retention facilities. 2. Inspect and remove debris from drainage swales, catch basins, and dry wells. 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 facility 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. Equipment Type/Access: All drywells will be cleaned using vacuum trucks. All vacuum trucks will access the site through the proposed alley and parking lot. Cost Estimate: Depending on the amount of rainfall in the given year, the cost to maintain the stormwater infrastructure will vary. It is estimated that the drywells will need to be vacuumed out once per year,with an estimated cost of$1,500 to do so. The applicant will be responsible for financing the maintenance of the stormwater infrastructure.