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HomeMy WebLinkAboutPZ - Preliminary Stormwater Management Report ESE CONSULTAN T S ESE Consultants Inc. 3103 W. Sheryl Dr,ive ENGINEERING • PLANNING • SURVEYING • ENVIRONMENTAL Meridian, Idaho 83642 TEL: 208-424-0020 PRELIMINARY STORMWATER MANAGEMENT REPORT FOR SPRINGDAY SUBDIVISION 177 ` — ..,.,.,a i Basin 2 �!�j AL i� 1.29 air — Basin4 — V Ca E _ Basin 3— •� NQ o.A C. Basin 5 0.77ac. _ _ •+/ —— Basin 9 �f G 321ac. asin 12 -Basin I�� \ f, T�A, r. oO�OV\ l 0.42ac. 2.34ac. ' -- 'V L o I Basin B 7 n�sa� 1. Sac. - - - Justin E. Bozovich Professional Engineer -�02 ac Idaho License No. 12449 """a' December 2024 1� _ _ it • Revised March 2025 LOCATED IN: CITY OF MERIDIAN ADA COUNTY, IDAHO TABLE OF CONTENTS SUBJECT SECTION Project Overview 1 Stormwater Management Design 2 Stormwater Equations 3 Intensity-Duration-Frequency Curve 4 Drainage Basin Map 5 SECTION 1 - Project Overview Springday is a multi-phase residential development located in the City of Meridian, Ada County, Idaho.The development consists of 38 Acres and 171 single-family residential lots, and is situated between Black Cat Rd and McDermott Rd, and north of W Ustick Rd. The applicant proposes for the overall subdivision development to include the construction of homes and infrastructure and will include roads, sidewalks, stormwater management facilities, utilities, and other improvements typical of residential construction. This report presents the preliminary stormwater plan for the Springday Subdivision that will be included with the preliminary plat submittal. Included in this report are all the calculations to verify that the stormwater management plan meets Ada County Highway District Policy Manual Existing Conditions The project site is currently bounded by a residential neighborhood to the east, McDermott Rd to the west, and W. Ustick Rd. the south. The project site itself is comprised of an agricultural field. Geotechnical Characteristics A Geotechnical Report was prepared by GeoTek, Inc. for Springday Subdivision, dated May 10tn 2024. The surface soils were generally described as layers of silt loam and silty clay loam underlain by very gravelly sand to loam. Groundwater Groundwater monitoring of the project site was conducted by GeoTek in August 2024 through September 2024 with groundwater ranging from 4' to 10' below the existing ground at several of the test pit locations. Soil Infiltration Geo Tek, Inc. has performed soil infiltration testing at thirty (30) locations within the project site and presented their results in Appendix C of the Geotechnical Engineering Report. Soil infiltration rates noted in the report range from 2.7 in/hr to 8.9 in/hr. An infiltration rate of 1 in/hr was conservatively used in the calculations. SECTION 2 - Stormwater Management Design Design Criteria The Preliminary Stormwater Management Plan described herein has been designed according to the Ada County Highway District Policy Manual to determine the stormwater facility storage volumes that will be required for the project.The proposed Stormwater Management Design has been prepared to meet the following requirements and guidelines: ♦ The Rational Method (Q=CiA) has been utilized to calculate 100-year storage volumes. Runoff coefficient of 0.50 was used per the ACHD Policy Manual for residential subdivisions. Rainfall intensity of 0.96 in/hr was used using the ACHD adopted Intensity- Duration-Frequency Curve located in Section 5 of this report. ♦ An infiltration rate of 1 inch per hour has been used for the design of the stormwater swales. SECTION 3 - Stormwater Equations Coefficient of Runoff(ACHD Policy Manual 8011.2.1) Estimated Runoff Coefficients for Various Surfaces Type-of Surface RuriofF Coefficients"C" Business Downtuwfi areas 0.70.0.95 Urbannelghborhoods 0.50.0.70 Resldentkal SI ngle Faml ly 0.35.0.50 Multi family 0.60.0.75 Resldentkal rural} 0.2".40 ApartmentDwelll rig Areas 0.70 Industrial and[ommerclal Light areas 0.80 Heavy areas 0.90 Parks,Cemeterles 0.10.0.25 Playgrounds 0.20.0.35 Rallroad yard areas 0.20.0.40 UnlmpFaved areas 0,10.0.30 StFB@tS Asphalt 0.95 CaficFete 0.95 Brick D.95 Roofs D.45 GraM D.75 4elds:Sandy sail Soll Type Slope A b t U. Flat 0.2% 0.D4 0.07 0.11 0.15 Average,2.6% 0.09 0.12 0.15 0.20 Steep:,6g. 0.13 0.18 0.23 0.28 Adapted from AS[E Design Storm Runoff Volume (ACHD Policy Manual 8011.3.2) V— C1A(3600) V: Design storm runoff volume required for storage C: Coefficient of Runoff is Rainfall Intensity per IDF Curve 1-hour 100-year storm event, i=0.96 1-hour 2-year storm event, i=0.26 A: Total catchment area(acres) SECTION 4 Primary Stormwater Facility Calculations BASIN CATCHMENT AREA 1a BASIN CHARACTERISTICS Basin Area,A: 0.06 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 104 577 0.43 204 168 1.0 17 5.5 BASIN CATCHMENT AREA 1b BASIN CHARACTERISTICS Basin Area,A: 0.06 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 104 577 0.43 204 168 1.0 17 5.5 BASIN CATCHMENT AREA 2 BASIN CHARACTERISTICS Basin Area,A: 1.29 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 604 105 2.5 5.5 184 504 688 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft') (ft) (in/hr) (ft) (ft') (hrs) 2,229 1 105 1 9.5 1 5.5 1 82 1 2,162 1 1.0 1 83 1 2,327 1 24.13 BASIN CATCHMENT AREA 3 BASIN CHARACTERISTICS Basin Area,A: 1.53 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft) (ft) (ft) 716 80 4 5.5 140 648 788 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 2,644 1 80 1 14.5 1 5.5 1 62 1 2,527 1 1.0 1 97 1 2,686 1 24.62 BASIN CATCHMENT AREA 4 BASIN CHARACTERISTICS Basin Area,A: 1.69 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 791 175 3 3.4 307 591 898 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 2,920 1 175 1 11.5 1 3.4 1 137 1 2,682 1 1.0 1 168 1 2,987 1 15.67 BASIN CATCHMENT AREA 5 BASIN CHARACTERISTICS Basin Area,A: 0.77 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 360 110 3 5 193 583 776 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 1,331 1 110 1 6 1 5 1 86 1 1,286 1 1.0 1 55 1 1,426 1 21.77 BASIN CATCHMENT AREA 6 BASIN CHARACTERISTICS Basin Area,A: 2.34 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft) (ft) (ft) 1,095 150 4.5 4 263 975 1,238 di Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 4,044 1 150 1 16 1 4 1 117 1 3,793 1 1.0 1 200 1 4,110 1 18.20 1 BASIN CATCHMENT AREA 7 BASIN CHARACTERISTICS Basin Area,A: 1.28 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 599 70 5 4.5 122 581 703 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 2,212 1 70 1 18 1 4.5 1 54 1 2,246 1 1.0 1 105 1 2,405 1 18.96 BASIN CATCHMENT AREA 8 BASIN CHARACTERISTICS Basin Area,A: 1.89 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 885 180 5 3.2 316 1,026 1,342 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 3,266 1 180 1 14.5 1 3.2 1 141 1 3,285 1 1.0 1 218 1 3,643 1 13.51 BASIN CATCHMENT AREA 9 BASIN CHARACTERISTICS Basin Area,A: 3.21 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft) (ft) (ft) 1,502 85 13.5 3.2 148 1,409 1,558 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 5,547 1 85 1 49.5 1 3.2 1 66 1 5,359 1 1.0 1 351 1 5,776 1 14.24 BASIN CATCHMENT AREA 10 BASIN CHARACTERISTICS Basin Area,A: 2.02 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 945 90 6 4.6 157 931 1,088 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 3,491 1 90 1 20 1 4.6 1 70 1 3,284 1 1.0 1 150 1 3,504 1 20.94 BASIN CATCHMENT AREA 11 BASIN CHARACTERISTICS Basin Area,A: 2.14 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 1,002 100 5 4.5 175 830 11005 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft) (ft) (in/hr) (ft) (ft) (hrs) 3,698 1 100 1 20 1 4.5 1 78 1 3,569 1 1.0 1 167 1 3,813 1 19.97 BASIN CATCHMENT AREA 12 BASIN CHARACTERISTICS Basin Area,A: 0.42 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity,is 0.26 in/hr 100 YR Rainfaill Intensity,is 0.96 in/hr Infiltration Rate,r: 1.0 in/hr STORAGE VOLUMES Chamber 1 Rock Void Volume, Storage Volume, Req'd Volume, V2-YR Ll Wi dl Pipe Volume,VPi VRl Vl (ft) (ft) (ft) (ft) (ft') (ft) (ft') 197 80 4 5 140 584 724 Chamber 2 Design Rock Void Volume, Infiltration Rate, Bed Infiltration Storage Time to Req'd Volume,V100-YR L2 W2 d2 Pipe Volume,VP2 VR2 I Volume,V2i Volume,V2 Drain 90% (ft') (ft) (ft) (ft) (ft') (ft) (in/hr) (ft) (ft') (hrs) 726 1 80 1 4.5 1 5 1 62 1 695 1 1.0 1 30 1 787 1 21.77 BASIN CATCHMENT AREA 13a BASIN CHARACTERISTICS Basin Area,A: 0.21 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft) (in/hr) (ft3) (hrs) 363 1406 0.43 505 411 1.0 42 7.8 BASIN CATCHMENT AREA 13b BASIN CHARACTERISTICS Basin Area,A: 0.18 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 311 1447 0.43 520 423 1.0 43 6.5 BASIN CATCHMENT AREA 14a BASIN CHARACTERISTICS Basin Area,A: 0.10 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 173 708 0.43 252 206 1.0 21 7.4 BASIN CATCHMENT AREA 14b BASIN CHARACTERISTICS Basin Area,A: 0.10 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 173 919 0.43 328 268 1.0 27 5.7 BASIN CATCHMENT AREA 15a BASIN CHARACTERISTICS Basin Area,A: 0.15 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 259 1063 0.43 381 310 1.0 32 7.3 BASIN CATCHMENT AREA 15b BASIN CHARACTERISTICS Basin Area,A: 0.13 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 225 1204 0.58 435 475 1.0 36 5.6 BASIN CATCHMENT AREA 16a BASIN CHARACTERISTICS Basin Area,A: 0.13 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft) (ft) (ft) (ft) (ft') (in/hr) (ft') (hrs) 225 762 0.43 271 222 1.0 23 9.0 Gravel Storage Gravel Volume, Req'd Volume, V100-YR Li W d1 VRi Req.Vol- Pond Vol.(ft3) (ft) (ft) (ft) (ft') 3 130 2 0.5 52 Total Volume Provided (ft') 274 BASIN CATCHMENT AREA 16b BASIN CHARACTERISTICS Basin Area,A: 0.07 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft3) (ft) (ft) (ft) (ft3) (in/hr) (ft3) (hrs) 121 1056 0.43 378 308 1.0 32 3.5 BASIN CATCHMENT AREA 17a BASIN CHARACTERISTICS Basin Area,A: 0.23 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft) (ft) (ft) (ft) (ft') (in/hr) (ft') (hrs) 397 1223 0.43 439 357 1.0 37 9.8 Gravel Storage Gravel Volume, Req'd Volume, V100-YR Li W d1 VRi Req.Vol- Pond Vol.(ft3) (ft) (ft) (ft) (ft) 40 219 2 0.5 88 Total Volume Provided (ft') 445 BASIN CATCHMENT AREA 17b BASIN CHARACTERISTICS Basin Area,A: 0.20 ac Runoff Coefficient,C: 0.5 25 YR Rainfaill Intensity, is 0.26 in/hr 100 YR Rainfaill Intensity, is 0.96 in/hr Infiltration Rate, r: 1.0 in/hr STORAGE VOLUMES 100-Year Event(Roadside Swale Volume) Design Infiltration Bed Infiltration Req'd Volume, V110-YR Top Area Depth Bottom Area Pond Volume Rate, I Volume,V21 Time to Drain 90% (ft') (ft) (ft) (ft) (ft') (in/hr) (ft') (hrs) 346 1077 0.43 386 315 1.0 32 9.7 Gravel Storage Gravel Volume, Req'd Volume, V100-YR Li W d1 VRi Req.Vol- Pond Vol.(ft3) (ft) (ft) (ft) (ft') 31 190 2 0.5 76 Total Volume Provided (ft') 391 SECTION 5 Intensity-Duration-Frequency Curve 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 60 0.26 0.43 0.54 0.69 0.82 0.96 2 120 0.16 0.25 0.31 0.39 0.46 0.54 3 180 0.13 0.19 0.23 0.29 0.34 0.40 6 360 0.09 0.12 0.14 0.18 0.21 0.25 12 720 0.06 0.08 0.10 0.12 0.14 0.16 24 1440 1 0.04 0.06 1 0.06 0.08 1 0.09 0.10 Intensity Duration Frequency ------ 2 3 -)K-5 -x-10 2.5 25 t 50 2 ---0-100 L H u 1.5 c c c �X�X X----X_X\X_X- --~-- \X-_)K X- �X-X 0.5 ------ ---------X-X-X- \ _ 0 - - ---- 10 15 20 25 30 35 40 45 50 55 60 120 180 360 720 1440 Duration(minutes) SECTION 6 Drainage Basin Map r ,'--Basin 1b Basin 1a 0.06 ac. a.06 ac. Basin 2� \ I / Basin 4 1.29 ac. — 1.69 ac. Basin 3 1.5 — 3 ac. / I Basin 13b "Basin 13a I I I I I I I I I 0.21ac. Basin 5 r /0.18 ac. I I I 0.77 ac. Basin 9 Basin 12 —Basin 6 3.21 ac. I III 0.42 ac. 2.34 ac. I III — — Basin 8 II I Basin 14b 1.89 ac. 0.10 ac. Basin 14a III - LEGEND Basin 7 — — - - - - Basin 15a — — — — h 0.15 ac. 1.28 ac. — Ilil Basin Boundary Line Basin 1 JI 5b _ 1.44 ac. Inlet Drainage Area Info Basin 1 0.13ac. \ e d Roadway Inlet -Basin 10 _ I III A Basin 16a 2.02 ac. II 0.13 ac. III �I hBasin 16b1 0.07 ac. \ — _Basin 11 2.14 ac. — Basin 17b Basin 17a � 0.20 ac. 0.23 ac. 11vA\ A I I FEET 150 0 75 150 L— GRAPHIC SCALE 1 inch A50 ft.Horizontal CESCE QOH2UL4La14Z SPRINGDAY PRELIMINARY PLAT Toll Brothers ENGINEERING PLANNING SURVEYING ENVIRONMENTAL DRAINAGE CATCHMENT PLAN ESE Consultants,Inc. 3103 W.Sheryl Drive- uite100•Meridian,IDS3642 March 5, 2025 - Meridian, Idaho AMERICA'S LUXURY HOME BUILDER* T:20SS-424-0020