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PZ - Storm Drainage Calculations :CKENGINEERING P . C . Civil Engineering * Project Management DRAINAGE CALCULATIONS FOR: Settlers Park Subdivision Meridian, Idaho April 15, 2022 p%AI ,F E o � Cr'�jE E F NOp��Q yqo S. KEN Q r1� Prepared for: Alturas Homes 50o E. Shore Drive, Suite too Eagle, ID 83616 (208)-391-4445 Prepared by: CK Engineering, P.C. Chad Kinkela, P.E. 130o E. State St. Ste 102 Eagle, ID 83616 (208)-639-1992 CK Engineering 13oo E.State St Suite 102 Eagle,ID 83616 208.869.0590 mobile chad@ck-engineers.com ENGINEERING P . C . - Civil Engineering * Project Management Drainage Narrative for Settlers Park Subdivision Settlers Park Subdivision consists of 4 drainage areas.All 4 drainage areas are within the site and will drain to a privately owned storm drain pond to handle the drainage along Settlers Park Dr and within the townhomes area of the site. Please see the attached drainage area exhibit.Venable Ln. storm drain plan, calculations and exhibit will be submitted separately with the submittal for the Venable Ln Improvements. All drainage areas used a time of concentration of 10 minutes. Per the attached Geotechnical Report prepared by Atlas, ground water is deemed to be between 6.2 and 10.76 feet across the site. Stabilized soil percolation rates varied from greater than 12"/hr to 4.8"/hr across the site.Atlas gave a design percolation rate of 2.4"/hr at test pit #2 which is nearest to Private Storm Drain Pond #1 so the 2.4"/hr percolation rate was used in the design of this storm drain pond. This percolation rate will be field verified when the pond is fully excavated. Further groundwater monitoring in 2021 was conducted by Natural Resource Solutions, LLC. Per their groundwater monitoring report, groundwater in TP3, which is closest to Private Storm Drain Pond #1, showed groundwater to be at 6.5' from ground surface. Private Storm Drain Pond #i: Drainage Areas #1-#4 generate runoff that will be directed to Private Storm Drain Pond #1.ACHD's stormwater spreadsheet was utilized to calculate the runoff volume for the pond and calculate the required pond volume. The required pond volume for the runoff from Drainage Areas #1-#4 was 11,689 CF. The provided pond volume is 11,86o CF. With a sand window of 1,200 sq.ft. and a percolation rate of 2.4"/hr,the pond will drain go% of the runoff volume in 43.83 hours. The peak flow was 8.73 CFS which will require 3 — l000 gallon sand and grease traps. Please see the attached storm drain calculations. Calculations for new storm drain systems. A. ACHD's storm water spreadsheets were utilized to calculate run off volumes for the site. B. ACHD's storm water spreadsheets were utilized to calculate pond volume and the required number of sand and grease traps. CK Engineering 1300 E.State St Suite 102 Eagle,ID 83616 208.869.0590 mobile chad@ck-engineers.com ENGINEERING P . C . .0 Civil Engineering * Project Management Attached: 1. Storm drain calculations. 2. 11"x17" colored drainage area exhibit. 3. Geotechnical report from Atlas. 4. 2021 Final Groundwater Report from Natural Resource Solutions, LLC. End of Narrative CK Engineering 1300 E.State St Suite 102 Eagle,ID 83616 208.869.0590 mobile chad@ck-engineers.com EXHIBIT A July 06, 2022 SETTLER PARK SUB Assumptions for calculations: Runoff coefficient varies for drainage areas. (see below) DRAINAGE AREAS # DA#1-DA#4 Tc=10 MIN Intensity2= 0.69 in/hr Intensity25= 1.85 in/hr Intensityloo= 2.58 in/hr 100 Yr Peak Flow= C * I *A in/hr Runoff Volume= Area of Hydrograph (0.5*Base*Height) = 0.5 * 1 hr storm(3600sec) * (Peak Flow) Drainage Area 2-yr 25-yr 100-yr Area (ft) Acres C-value Flow cfs Flow cfs Flow cfs Drainage Area#1 35936 0.82 0.90 0.51 1.37 1.92 CB#1 Drainage Area #2 86667 1.99 0.95 1.30 3.50 4.88 Future Drainage Area#3 6506 0.15 0.20 0.02 0.06 0.08 Pond 1 Drainage Area#4 33000 0.76 0.95 0.50 1.33 1.86 Future CK Engineering, PC 1300 E.State Street Ste 102 Eagle, ID 83616 (208)869-0590 ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted. �t c F User input in yellow cells. 1 Project Name SETTLERS PARK-DAS 1-4-PRIVATE SO POND Nl 2 Is area drainage basin map provided? YES (map must be included with stormwater calculations) 3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100 4 Enter number of storage facilities(25 max) Click to Show More Subbasins ❑ Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin 1 Subbasin 2 3 4 5 6 7 8 9 10 5 Area of Drainage Subbasin(SF or Acres) SF 35,936 86,667 6,506 33,000 Acres 3.72 6 Determine the Weighted Runoff Coefficient(C) 0.90 0.95 0.20 0.95 C=((C1xA1)+(C2xA2)+(CnxAn)J/A Weighted Avgl 0.91 7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 user Calculate min 10 Min. Estimated Runoff Coefficients for Various Surface Type of Surface Runoff Coefficients"I Business Downtown areas 0.70-0.95 Hydraulic Urban neighborhoods 0.50-0.70 Radius Flow Flow Residential Intercept A/Wet Velocity V Time Single Family 0.35-0.50 ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) (min) Multi-family 0. Residential(rural) 0.25-0.25-0.4040 Segment 1:Pipe Flow Apartment Dwelling Areas 0.70 a Industrial and Commercial Light areas 0.80 Heavy areas 0.90 Segment 2:Gutter Shallow Concentrated Flow 10 Parks,Cemeteries 0.10.0.25 b Playgrounds 0.20.0.35 Railroad yard areas 0.20-0.40 Segment 3:Overland Sheet Flow By TR-55,<300-ft C Computed Tc= 0.0 User-Entered Tc= 10.0 8 Tc 1 2.58 2.58 in/hr 9 Calculate the Post-Development peak discharge(QPeak) Cyp.k 8.73 cfs 10 Calculate total runoff vol(V)(for sizing primary storage) V 11,689 fta V=Ci(Tc=60)Ax3600 11 Calculate Volume of Runoff Reduction Vrr Enter Percentile Storm I(95th percentile=0.60 in) 95th 0.60 in Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vr, 7,305 ft3 12 Detention:Approved Discharge Rate to Surface Waters(if applicable) 0.00 cfs 13 Volume Summary Unimproved areas 0.10-0.30 Surface Storage:Basin Streets Basin ForebaY V 1,169 fit 0.95 Concrete 0.95 Primary Treatment/StorageBasin V 10,520 ft' Brick 0.95 Subsurface Storage Roofs 0.95 Gravel 0.75 Volume Without Sediment Factor(See BMP 20 Tab) V 11,689 fta Fields:Sandy soil Soil Type Slope A 8 C D Flat:0-2% 0.04 0.07 Average:2-6% 0.09 0.12 0.15 0. Steep:>6% 0.13 0.18 0.23 0. Adapted from ASCE D:\BRIGHTON CORP\Settlers Park Sub\Documents\DRAI NAG E CALCS\SP-POND#1 07-06-22.xlsm 7/6/2022,4:02 PM Version 10.0,May 2018 ACHD Calculation Sheet for Sand/Grease Traps NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology. These calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted. User input in yellow cells. 1 Project Name SETTLERS PARK-DAS 1-4-PRIVATE SD POND#1 2 Enter number of Sand/Grease Traps(25 max) 1 Number Peak Baffle Throat Velocity Is the Vault Size of S/G Flow Q. Spacing width Area(ft2) 0.5 fps Velocity Traps cfs (inch) (inch) max. ok? 1000 G 3 8.73 20 48 20.00 0.44 Reference for Throat widths(inch) Boise ADS Vault Lar-ken WQU, BMP 16 1000 G 48.0 50.5 n/a 1500 G 60.0 61.5 n/a WQU1000 n/a n/a 60 WQU1500 n/a n/a 60 D:\BRIGHTON CORP\Settlers Park Sub\Documents\DRAI NAG E CALCS\SP-POND#1 07-06-22.xlsm 7/6/2022,4:03 PM Version 10.0, May 2018 L L I �I N I I I I I I I I I I I I I DA #4 DA #4 DA #4 DA #4 pq #4 E'I C=0.95 - C=0.95 C=0.95 _C=0.95 C=0.95 IF O 000 00 O FUTURE O O 0 000 0 � I s O - 0 SETTLERS PARK 0 80 160' TOWNHOMES DA #4 0 I I I 1 I I I I I C=0.95 O SCALE 1" = 80' DA #4 DA #4 DA #4 4DA #4 C=0.95 C=0.95 C=0.95 C=0.95 O 0 O O DA #2 0 O C=0.95 0 f)� r v 11P6 1111 r ODA #4 DA #4 DA #4 I DRAINAGE AREA #1 ENTRY ROAD = 35,936 SF - PRIVATE SD POND #1 7- 0 LIT C=0.95 C=0.95 C=0.95 DRAINAGE AREA #2 PARKING/DRIVELANE/SW (FUTURE) = 86,667 SF - PRIVATE SD POND #1 DA #4 I 1 I I 1 I I 1 DRAINAGE AREA #3 POND AREA = 6,506 SF - PRIVATE SD POND #1 DA #4 C=0.95 C=0.95 0 DRAINAGE AREA #4 OF TOWNHOME ROOFS (FUTURE) = 33,000 SF - PRIVATE SD POND #1 id TOTAL= 162,109 SF PRIVATE SD O DA #1 IN ° POND #1 C=0.90 loon � DA.#3. . C=0.20 1 11 ❑ I �, ®® mm mm 3 Ld i J N I Q ZI 1 SRO NA L , -^' 1 �`� G\STE VC - - _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -_� - - - _ - 9412 7/06/22 ''STICK RD. sT �o C gTEOF\VP P SETTERS PARK SUBD SON D RA NAG E REVISIONS: DRAWN BY: JSF CHECKED BY: CSK CK ENGINEERING MERIDIAN , D DATE: 04/19/22 1300 E. STATE ST., SUITE 102 E X H B T 300-SPS-STREETS.DWG EAGLE, ID 83616 [� PHONE 208-639-1992 DIR: D:\BRIGFRON CORP\SEfRERS PARK SUB�CK WK'S