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CC - DrainageReport_2020-05-05 MERIDIAN , IDAHO Pine I4 Subd iv is ion I C) s 2 Stormwater Drainage Report May 2020 1 892 OF Prepared by: CJOU@IB , JmUmB ENGINEERS , Inc . 250 South Beechwood Avenue , Suite 201 Boise , ID 83709-0944 208m376- 7330 www . JUB . com J =U = B Project No . 10 =20 =019 SITE LOCATION The project site is located approximately 1,500 feet south of E. Fairview Avenue and 350 feet E. of N. Locust Grove Road. The site is located in the NW 1/4 of Section 8, Township 3 North, Range 1 East, Boise meridian. EXISTING SITE CHARACTERISTICS The project site presently consists of relatively flat non-irrigated land and slopes gently down- gradient to the south with grades less than 1%. PROPOSED SITE IMPROVEMENTS The proposed improvements include the construction of 54 residential lots, 3 common lots, 2 commercial lots and associated streets, sidewalks, and infrastructure. SOIL CONDITIONS The following geotechnical reports were referenced during design of this stormwater system. Geotechnical Report for the Pinebridge Development. Pine Street, Eagle to Locust Groave Road, Meridian Idaho, dated 4 February 2008, prepared by Bob J. Arnold, P.E. Based upon the preliminary soils and subsurface investigation for this subdivision, the existing soils will accept the runoff. Seepage beds are designed based on assumed maximum infiltration rate of 1.0 inch per hour. Groundwater at the nearest test pit was recorded at 9 feet below the existing ground. In the event that during construction the contractor encounters groundwater or rock, or the field percolation test results are lower than the design infiltration rate, a revised design may be prepared to meet the field conditions. DRAINAGE DESIGN CONCEPT The drainage area included within these calculations encompasses portions of the development located in future phases and covers approximately 8.7 acres. The project consists of 2 catchments labeled A through B. Catchment A stormwater shall flow above grade to designed low points where it shall be collected via curb inlets. The stormwater shall then discharge into a sub-surface seepage bed for infiltration through a sand filter into the groundwater network. Catchment B stormwater shall flow above grade to designed low points where it shall be collected via existing curb inlets. The stormwater shall then discharge into an expanded sub- surface seepage bed for infiltration through a sand filter into the groundwater network. The two commercial lots are not included in the design described in this report. Stormwater in these two lots shall flow to separate infiltration system(s) which shall not collect water from the public roadway and shall not discharge water into public storm drain systems. These system(s) shall be designed during the final development of these two lots. Stormwater Drainage Report Pine 34 Subdivision No. 2 CALCULATION METHODS The site was divided into catchment areas based on the proposed grading design. These catchment areas were analyzed using the rational method to estimate the peak runoff rates in accordance with ACHD Policy Manual Sections 8000 and 8200 in effect as of August 2017. Peak storage volumes were based on the 100-year, 1-hour design storm event of 0.96 inches per hour. Peak flow rates and conveyance flow rates were calculated for each basin based on the 100-year and 25-year design storms, respectively. The time of concentration for each basin was used as the design storm duration to calculate both the peak flow and conveyance flow rates. Time of concentration values were calculated as a combination of sheet flow from the lots to the road section and gutter flow along the road. Specific equations are shown in the attached drainage calculations. The conveyance flow rate was used to size inlets and pipes and determine acceptable pipe slopes within the system. Sizing the expansion of seepage bed B was accomplished by assuming that the existing storage volume completely captures the previous design with no additional storage capacity. Flow rates for the existing pipes between the affected catch basins and the seepage bed have been recalculated and are presented to show that these pipes have not exceeded capacity. The catchment areas are shown on the Drainage Plan. Calculations are included with this report for all catchment areas. Stormwater Drainage Report Pine 34 Subdivision No. 2 Catchment A Pine 43 Phase 2 Project No.10-20-019 Gutter Flow Rational Method (TR-55) Sub- Elev. 1 Elev. 2 1-gutter Intercept Slope(Sp Vgutter T,gutter ) Lgutter catchment (ft) (ft) (ft) Coeff. (k) N (fps) (min) Tc-gutter = 60 V Al 2608.05 2610.48 527 0.619 0.46 1.38 6.36 gutter A2 2608.05 2610.98 542 0.619 0.54 1.49 6.06 0.007(nL)0.8 Tc-sheet - (p2)0.SS0.4 = 3.281kSp0'S Vgutter Tc = Tc-gutter + Tc-sheet Q = CiA Sheet Flow Calculation Total Tc Catchment Parameters Sub- n L P2 s Tc-sheet Tc C, Area, C2 Areal CT AreaT catchment (unitless) (ft) (in) (ft/ft) (min) (min) (ac) (ac) (ac) Al 0.24 60 1.2 0.01 20.4 26.8 0.50 1.30 0.50 1.30 A2 0.24 57 1.2 0.01 19.5 25.5 0.50 2.02 0.50 2.02 Total Area 3.32 Comp.C 0.5 Design Storm Intensities Design Storm Flow Rates Soil Parameters Sub- i2 i25 iso iloo Q2 Q25 Qso QZoo Infil. Rate 4.00 in/hr catchment (in/hr) (in/hr) (in/hr) (in/hr) (cfs) (cfs) (cfs) (cfs) (F) Al 0.42 1.12 1.33 1.55 0.27 0.73 0.86 1.01 A2 0.43 1.13 1.34 1.57 0.43 1.14 1.35 1.59 0.70 1.87 2.21 2.60 V.2019-05-09 10 Apr 2020 Catchment A Pine 43 Phase 2 Project No.10-20-019 Seepage Bed (BMP-20) DESIGN OPTIONS ris count for 1st hr of infiltration? Yes the bed inside the right-of-way? No PARAMETERS Design Storm frequency 100 -year Design Storm duration 1 -hour Design Infiltration rate(Fr) 4.00 in/hr Weighted Runoff Coefficient(C) 0.50 Design Storm Inentsity(i) 0.96 in/hr Catchment Area (A) 3.32 ac Sediment factor(f)= 0 % Required Storage Volume(V100) 5,737 ft3 V = C * i *A * 3600 * 1 + DESIGN Width (W)= 10 ft Depth (D)= 6.5 ft Void Ratio(e)= 40 % Vol (Ve U)= 25.3 ft3 Inlet pipe size(d1)= 18 in Qty(dlq)= 1 Vol (VP1)= 1.77 ft3 Overflow pipe size(dz)= 0 in Qty(d2q)= 0 Vol (VP2)= 0.00 ft3 Infiltration/LF(Fu)= 3.33 ft3 Storage Vol/LF(Su)= 29.51 ft3 Vol based lenth (Lv)= 194.43 ft Drain based length (Lp)= 35.89 ft RESULTS DESIGN CHECKS Min Design Bed length (L)= 194.43 201.00 ft 368>_L>_Lmin PASS Bed Capacity(V)= 5,737 5,931 cf water V>_V100 PASS Time to Drain 90%(t90)= 7.7 hr t90<_48 PASS Min infil rate(F,r i,) = 0.5 0.6 in/hr OPTIONAL MULTIPLE SUB-BEDS Sub-Bed# Length Max allowed bed length= 386 ft 1 36.5 ft 2 75.5 ft 3 89 ft 4 ft Total Length (ILs b)= 201 ft EQUATIONS: F,, iT d2 • dlq rc •dz •d2q Fu = W - VP1 =12 48 VP2 — 48 V,u = e • ((W •D) — VP1 —VP2) Su = VIU +V21 + VP2 + Fu _ V100 _ V100 Lv SU LD 48 •Fu V.2019-05-09 10 Apr 2020 Catchment A Pine 43 Phase 2 Project No.10-20-019 Sand and Grease Trap Peak Flow Design Storm 100 -year Water Quality Design Storm 25 Peak Flow Rate(QPeak) 2.60 in/hr Water Quality Flow Rate(QWQ) 1.87 ac QWQ = C * iwQ *A Design Calculations Vault Size= 1500 gallon Peak Throat Velocity(VPeak)= 0.31 No.of S&G Traps= 1 WQ Throat Velocity(vN,Q)= 0.22 fps Baffle Spacing= 20 inch Throat Width= 60 inch Allowed Max Flow rate(QMax,A)= 4.15 cfs Total Throat Area= 8.33 ftz Max Flow rate(QMax)= 2.60 cfs Bypass Flow Rate= 0 cfs Checks: VWQ<0.5 PASS Bypass Required FALSE LI LI OUTLET BAFFLE WALL EL. OUT EL. IN-7 FLOW FL.. INLET BAFFLE WALL Modified rom ISPWC SO-624,2017 V.2019-05-09 10 Apr 2020 Catchment A Pine 43 Phase 2 Project No.10-20-019 Pipe Sizing Allowable Limits Velocity(ft/sec) Flow depth (%) Min 3.0 0.0 Max 10.0 90.0 Minimum Pipe Slope Maximum Pipe Slope Pipe Id Design Mannings Pipe Min. V Flow Max. V Flow Flow Size Slope' Depth Slope Depth (cfs) (n) (in) (%) (fps) (%) (%) (fps) (%) CB Al to SDMH Al 0.73 0.010 12 0.37 3.02 34.68 10.80 9.99 14.88 CB A2 to SDMH Al 1.14 0.010 12 0.27 3.03 48.37 7.42 9.99 20.28 SDMH Al through S&G A 1.87 0.010 12 0.22 3.12 71.37 4.96 9.99 28.79 -4 Pipe velocity solved using the Mannings equation at the respective flow depth. Flow depth solved using itterative solutions of the Manning's equation 1.49 2 1 Q = .A . R3 . $2 n D Cr hl Y r = — h = 2r —y 9 = 2 arccos /I _ r2(9 — sin B) A r A = TC • r2 — 2 Rh = P P = 2rcr — rO h Note: 'Slightly decreased slopes may be considered where the depth of flow will be 0.3 of the diameter or greater for design average flow. (10-State Standards, Paragraph Z Maximum slopes greater than 20%require additional restraint. (10-State Standards, Paragraph 33.46) V.2019-05-09 10 Apr 2020 Catchment B Pine 43 Phase 2 Project No.10-20-019 Gutter Flow Rational Method (TR-55) Sub- Elev. 1 Elev. 2 1-gutter Intercept Slope(Sp Vgutter T,gutter ) Lgutter catchment (ft) (ft) (ft) Coeff. (k) N (fps) (min) Tc-gutter = 60 V 61 2610.98 2608.87 241 0.619 0.87 1.89 2.13 gutter B2 2610.98 2608.87 241 0.619 0.87 1.89 2.13 0.007(nL)0.8 Tc-sheet - (p2)0.SS0.4 = 3.281kSp0'S Vgutter Tc = Tc-gutter + Tc-sheet Q = CiA Sheet Flow Calculation Total Tc Catchment Parameters Sub- n L P2 s Tc-sheet Tc C, Area, C2 Areal CT AreaT catchment (unitless) (ft) (in) (ft/ft) (min) (min) (ac) (ac) (ac) 131 0.24 52.5 1.2 0.01 18.4 20.5 0.50 0.66 0.50 0.66 B2 0.24 52.5 1.2 0.01 18.4 20.5 0.50 0.61 0.50 0.61 Total Area 1.27 Comp.C 0.5 Design Storm Intensities Design Storm Flow Rates Soil Parameters Sub- i2 i25 iso iloo Q2 Q25 Qso QZoo Infil. Rate 4.00 in/hr catchment (in/hr) (in/hr) (in/hr) (in/hr) (cfs) (cfs) (cfs) (cfs) (F) 131 0.48 1.28 1.52 1.79 0.16 0.42 0.50 0.59 B2 0.48 1.28 1.52 1.79 0.15 0.39 0.46 0.55 0.31 0.81 0.96 1.14 V.2019-05-09 10 Apr 2020 Catchment B Pine 43 Phase 2 Project No.10-20-019 Seepage Bed (BMP-20) DESIGN OPTIONS ris count for 1st hr of infiltration? Yes the bed inside the right-of-way? No PARAMETERS Design Storm frequency 100 -year Design Storm duration 1 -hour Design Infiltration rate(Fr) 4.00 in/hr Weighted Runoff Coefficient(C) 0.50 Design Storm Inentsity(i) 0.96 in/hr Catchment Area (A) 1.27 ac Sediment factor(f)= 0 % Required Storage Volume(V1oo) 2,195 ft 3 V = C * i *A * 3600 * 1 + DESIGN Width (W)= 32 ft Depth (D)= 6.5 ft Void Ratio(e)= 40 % Vol (Ve U)= 81.8 ft3 Inlet pipe size(d1)= 18 in Qty(dlq)= 2 Vol (VP1)= 3.53 ft 3 Overflow pipe size(dz)= 0 in Qty(d2q)= 0 Vol (VP2)= 0.00 ft3 Infiltration/LF(F,)= 10.67 ft3 Storage Vol/LF(Su)= 94.22 ft3 Vol based lenth (Lv)= 23.30 ft Drain based length (Lp)= 4.29 ft RESULTS DESIGN CHECKS Min Design Bed length (L)= 23.30 24.00 ft 368>_L>_Lmin PASS Bed Capacity(V)= 2,195 2,261 cf water V>_V100 PASS Time to Drain 90%(t90)= 7.7 hr t90<_48 PASS Min infil rate(F,r i,) = 0.5 0.6 in/hr OPTIONAL MULTIPLE SUB-BEDS Sub-Bed# Length Max allowed bed length= 386 ft 1 ft 2 ft 3 ft 4 ft Total Length (ILs b)= ft Single bed design EQUATIONS: F,, 7T d2 • dlq rc •dz •d2q Fu = W - VP1 =12 48 VP2 — 48 VeU = e • ((W •D) — VP1 —VP2) Su = Veu +V21 + VP2 + Fu _ V100 _ V100 Lv SU LD 48 •Fu V.2019-05-09 10 Apr 2020 Catchment B Pine 43 Phase 2 Project No.10-20-019 Sand and Grease Trap Peak Flow Design Storm 100 -year Water Quality Design Storm 25 Peak Flow Rate(QPeak) 1.14 in/hr Water Quality Flow Rate(QWQ) 0.81 ac QWQ = C * iWQ *A Design Calculations Vault Size= 1500 gallon Peak Throat Velocity(VPeak)= 0.14 No.of S&G Traps= 1 WQ Throat Velocity(vN,Q)= 0.10 fps Baffle Spacing= 20 inch Throat Width= 60 inch Allowed Max Flow rate(QMax,A)= 4.15 cfs Total Throat Area= 8.33 ftz Max Flow rate(QMax)= 1.14 cfs Bypass Flow Rate= 0 cfs Checks: VWQ<0.5 PASS Bypass Required FALSE LI LI OUTLET BAFFLE WALL EL. OUT EL. IN-7FLOW FLOW III— INLET BAFFLE WALL Modified rom ISPWC SO-624,2017 V.2019-05-09 10 Apr 2020 Catchment B Pine 43 Phase 2 Project No.10-20-019 Pipe Sizing Allowable Limits Velocity(ft/sec) Flow depth (%) Min 3.0 0.0 Max 10.0 90.0 Minimum Pipe Slope Maximum Pipe Slope Pipe Id Design Mannings Pipe Min. V Flow Max. V Flow Flow Size Slope' Depth Slope Depth (cfs) (n) (in) (%) (fps) (%) (%) (fps) (%) Ex CB 131 to Ex SDMH B3 0.53 0.010 12 0.47 3.00 27.60 14.19 9.99 11.95 Ex CB B2 to Ex SDMH B3 0.54 0.010 12 0.46 3.00 28.02 13.96 9.99 12.10 EX SDMH B3 to Ex SDMH B2 1.07 0.010 12 0.28 3.02 46.15 7.83 9.99 19.40 EX SDMH B2 to Ex SDMH B1 2.70 0.010 12 0.30 3.65 89.17 3.73 9.99 37.62 Pipe velocity solved using the Mannings equation at the respective flow depth. Flow depth solved using itterative solutions of the Manning's equation 1.49 2 1 Q = .A . R3 . $2 n D Cr hl Y r = - h = 2r -y 9 = 2 arccos /I _ r2(9 - sin B) R A r A = TC • r2 - 2 h = P P = 2rcr - rO h Note: 'Slightly decreased slopes may be considered where the depth of flow will be 0.3 of the diameter or greater for design average flow. (10-State Standards, Paragraph Z Maximum slopes greater than 20%require additional restraint. (10-State Standards, Paragraph 33.46) V.2019-05-09 10 Apr 2020 ACHD Intensity-Duration-Frequency Intensity(inches per hour) Design Storm 2 5 10 25 50 100 Tc(hr) Tc(min) 0.17 10 0.69 1.15 1.48 1.85 2.20 2.58 0.25 15 0.59 0.97 1.22 1.56 1.86 2.18 0.33 20 0.49 0.81 1.01 1.30 1.54 1.81 0.42 25 0.43 0.71 0.89 1.14 1.35 1.58 0.50 30 0.41 0.67 0.85 1.08 1.29 1.51 0.58 35 0.34 0.56 0.70 0.90 1.07 1.25 0.67 40 0.31 0.51 0.64 0.82 0.98 1.15 0.75 45 0.29 0.48 0.60 0.77 0.91 1.07 0.83 50 0.27 0.45 0.56 0.72 0.85 1.00 0.92 55 0.26 0.43 0.54 0.69 0.82 0.96 1.00 60 0.26 0.43 0.54 0.69 0.82 0.96 2.00 120 0.16 0.25 0.31 0.39 0.46 0.54 3.00 180 0.13 0.19 0.23 0.29 0.34 0.40 6.00 360 0.09 0.12 0.14 0.18 0.21 0.25 12.00 720 0.06 0.08 0.10 0.12 0.14 0.16 24.00 1440 0.04 0.06 0.06 0.08 0.09 0.10 Intensity Duration Frequency 3.00 2 -)K-5 -x-10 2.50 -�25 t 50 2.00 100 i t 1.50 c ' x 1.00 � \x x\X,x\x--x� \)K- _ x� 0.50 - � � )\ -.-.- -------------x------ � =�„ 0.00 1--- 10 15 20 25 30 35 40 45 50 55 60 120 180 360 720 1440 Duration (minutes) Table 3.2. Manning's Roughness Coefficient(n)for Overland Sheet Flow." Estimated Runoff Coefficients for VafiOUS Surfaces Surface Description n Type of Surface Runoff Coefficients"C" Smooth asphalt 0.011 Business Smooth concrete 0,012 Downtown areas 0.70-0.95 -Ordionary concrete lining p_013 Urban neighborhoods 0.50-0.70 Good wood 0.014 Residential Brick wqh cement mortar 0.014 Sirtgie Family 0.35-0-50 Multi-family 0.60-0.75 Vitrified clay 0.015 Residential(rural) 0.25-0.40 Cast iron 0.015 Apartment Dwelling Areas 0.70 -Corrugated rnetal pipe 0.024 Industrial and Commercial Cement rubble surface 0,024 Light areas 0.80 Fallow no residue) 0.05 keavyareas 0.90 Cultivated soils Parks,Cemeteries 0.10-0.25 Residue covers 20/ 0.06 Playgrounds 0.20-0.35 Residue covers 200l 0,17 Railroad yard areas 0.20-0.40 Unimproved areas 0.10-0.30 Range(natural) D-13 Streets Grass Asphalt 0.95 Short grass prairie 0.15 Concrete 0.95 Dense grasses 0,24 Brick 0.95 Bermuda rass 0.41 Roofs 0.95 Woo d s' Gravel 0.75 Light underbrush 0-40 Fields:Sandy soil soirType Dense underbrush ❑-190'When selecting n,consider cover to a height of about 30 m Slope A B C ❑ m- This is only part of the plant Cover that will obstruct sheet flow. Sly:0-2% 0.007 D.11 0.15 0.15 0.15 Average:2-6°d 0.094 0. Table 3-3. Intercept Coefficients for Velocity vs.Slope Relationship of Equation 3-V" Steep:>696 0.13 0-18 0.23 0.29 Land Cover)Flow Regime k Adapted from ASCt` Forest with heavy ground litter:hay meadow{overland flowh 0-076 Recommend Standards for Wastewater Facilities Trash fallow or minimum tillage cultivation:contour or strip cropped:wowiland OA52 overland Row Table 33.41 Recommended Minimum Slopes Short grass pasture overland flaw] 0,213 Minnnum Slope m Feet Cultivated straig hi raw[overland fknv) 0,274 Nominal Seger Size Per 10D Feet mi( '100 m) Nearly bare and unfilled[overland flow);alluvial fans in wastem mountain ions 0.305 8 i -h(200 mm) 0 40 Grassadwaterwa shallow omcentrated now 0.457 Unpaved(shallow oonoentrated flow) 491 ID nch(25D nun) D.28 Paved area shallow concentrated flow);small upland gullies O.St9 12 inch(300 rnm) 0.22 Tabra S4. TyPlell Rargh o!Llannlny^1 C-M.Iara 4.)for Ch.-U■.a Pip- 14 inch(350 nun) 0.17 Conduit moreael Mvnnina'* - 15 inch(375 rnm) 0.15 a-d cendwls 16 inch(4DO nun) 0.14 c_ a.ura-a.ass ISuich(450mm) 0.12 CIWP 0.011-0.o37 vleasic am Dour a.aos-a.ofs 21mch(525nun) O.1D Plli.i -etas)) o.ora-0.026 24=h(6DO nun) 0.08 Paw Vpunar aaalona O.er2-0.016 smau own cnanaels 27 inch(675 nun) 0.067 co..car t. a.or+-o.o1a 30 inch(750 nun) 0.058 punele era p a.020.-tr.oas 33 inch(825 nun) 0.052 V -ion 01.020 sere Seal e.urd-0-026 36 inch(900 nun) 0.D46 Racy cut 0,025-0.043 Natwal ctfennsls(rnlnw aVearna-Sop width er flood siege tsa m(TOO it)) 39 inch(975 tnm) 0.041 Fain . ularsecnpn a.o2s-e-oaa 42mch(1D50mm) 0.037 lOQWOI srarion wlrn pools [ILLY:/r lwldl-Ldnudl u­UIIirwdxewdrelxdnudl ub.pui t Owar valusa era usuaNy rpr wee-C4neVu clad arw mai nteiaaQ Is^tpplharl pipes anO chann.as • 0 50 100 SCALE IN FEET LEGEND Al ® , •• 1.30 \\ — — PROJECT BOUNDARY • ♦ \ \ \ CATCHMENT BOUNDARY wl — — — — — — — SUB-CATCHMENT BOUNDARY 1 —� FLOW DIRECTION INFILTRATION BED LOCATION x o1 2.02 , \ \ m \ Al I CATCHMENT ID o ♦ \ 1.24 CATCHMENT AREA (AC) LLII Al \ \ ® zl � ♦ \ \ x x x _I E. STATE AVENU ♦ B1 �� o � B2 ♦�, �, 0 w i , ' At w ` a � w �♦ o � U i 2 Z f VU lz Y 6 U �O a U DELAWARE PARK, SUBDIVISION NO. 2, UNIT 5 B � CALDWELL, IDAHO o o STORM DRAIN CATCHMENT MAP a J-U-B ENGINEERS,INC.