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HomeMy WebLinkAboutSWM Report-Regency ESE Consultants, Inc. 3103 W. Sheryl Drive Meridian, Idaho 83642 TEL: 208-424-0020 PRELIMINARY STORMWATER MANAGEMENT PLAN FOR REGENCY AT VERBENA RANCH SUBDIVISION LOCATED IN: CITY OF CALDWELL, CANYON COUNTY, IDAHO ____________________________ Justin E. Bozovich Professional Engineer Idaho License No. 12449 May 2024 TABLE OF CONTENTS SUBJECT SECTION Narrative and Project Information 1 • Site Information • Stormwater Management Design Stormwater Facility Design 2 • Seepage Bed Design • Drainage Plan SECTION 1 Narrative and Project Information (Site Information, Stormwater Management Design) Site Information Project Location The project site is situated in the City of Caldwell, Canyon County, Idaho. The site is bound by existing agricultural uses to the north, west, and south, S. 10th Ave to the east, and the Forest Canal to the southeast. The site is primarily comprised of open agricultural fields. Project Scope The applicant proposes to construct one hundred and forty-three (143) single family residential homes on subdivided lots within the approximately 68.57-acre property. The development includes the construction of homes, support roads, sidewalks, stormwater management facilities, and other infrastructure improvements typical of residential construction. Report Scope This report presents the preliminary stormwater management plan for the Regency at Verbena Ranch Subdivision. Included within this report are all the calculations to verify that the stormwater management plan meets the regulations listed in the Caldwell Municipal Stormwater Infrastructure Design Manual from March 2024. Stormwater Management Design Design Criteria The Stormwater Management Plan described herein has been designed according to the following publications and criterion: Caldwell Municipal Stormwater Infrastructure Design Manual, March 2024. 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 peak flows. The ‘c’ coefficients for the calculations were based on “Table 1” from Section 2.3.2 in the stormwater design manual. Areas with mainly residential lots were assumed at this time to have a c value of 0.50 and weighted c values were calculated for areas with predominantly roadway area (collector roads). Weighted c summary tables can be found in Section 2 of this report. Rainfall intensities were determined from a chart labeled as “Table 2” from Section 2.3.2 in the stormwater design manual. ♦ Seepage beds have been designed to store and infiltrate the 100-year storm event. Design calculations can be found in Section 2 of this report. ♦ Infiltration rates for the design of the seepage beds were taken from a report titled, “Geotechnical Evaluation for ‘Caldwell Land Auction’” prepared by Geotek Inc., dated February 17, 2022. Per Section 5.3.1 of the stormwater design manual, the tested infiltration rates were reduced to 70% to achieve the design rates utilized in the volume calculations. Only the bottom of the seepage beds were considered for the available infiltration area. ♦ Preliminary site grading was designed to direct all residential lot area and open space areas in such a way as to be fully captured within the site and accounted for in the stormwater facilities. ♦ Sand and grease traps were not designed at this time. The appropriate sand and grease trap size, either 1,000 gallons or 1,500 gallons, will be determined and specified in future design submittals to provide adequate water quality treatment within the required design parameters. SECTION 2 Stormwater Facility Design (Seepage Beds and Drainage Map) Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho WEIGHTED RUNOFF COEFFICIENT, C Surface Type Runoff  Coefficient, C Area  (SF) Weighted C Drainage Area (Ac.) =  1.81 Asphalt 0.95 39083 37129 Runoff Coefficient 'c' = 0.57 Landscaping 0.20 40217 8043 Total 79300 0.57 Bed Length (ft) = 60 Total Excavation Volume (cf) = 14,400 Bed Width (ft) = 30 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 59 Pipe Storage (cf) = 46 Infiltration Area (sf) = 1800 Remaining Vol. for Stone (cf) = 14,354 Infiltration Rate (in/hr) = 1.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 5,741 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage Volume  Needed (cf) 10 0.17 2.11 2.18 1,305 38 1,268 15 0.25 1.78 1.84 1,652 56 1,595 30 0.50 1.24 1.28 2,301 113 2,189 60 1 0.78 0.80 2,895 225 2,670 120 2 0.64 0.66 4,751 450 4,301 180 3 0.52 0.54 5,790 675 5,115 360 6 0.27 0.28 6,013 1,350 4,663 720 12 0.16 0.16 7,127 2,700 4,427 1440 24 0.10 0.10 8,908 5,400 3,508 MAXIMUM STORAGE VOLUME = 5,115 TOTAL REQUIRED STORAGE VOLUME = 5,115 PROVIDED STORAGE (CF) =5,788 OK DRAINAGE TIME (HRS) =25.7 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm Basin 1 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =5,788 100‐YEAR STORM EVENTWHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  11.62 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 160 Total Excavation Volume (cf) = 64,000 Bed Width (ft) = 50 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 159 Pipe Storage (cf) = 125 Infiltration Area (sf) = 8000 Remaining Vol. for Stone (cf) = 63,875 Infiltration Rate (in/hr) = 4.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 25,550 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 12.26 7,355 500 6,855 15 0.25 1.78 10.34 9,308 750 8,558 30 0.50 1.24 7.20 12,968 1,500 11,468 60 1 0.78 4.53 16,314 3,000 13,314 120 2 0.64 3.72 26,772 6,000 20,772 180 3 0.52 3.02 32,629 9,000 23,629 360 6 0.27 1.57 33,884 18,000 15,884 720 12 0.16 0.93 40,159 36,000 4,159 1440 24 0.10 0.58 50,198 72,000 ‐21,802 MAXIMUM STORAGE VOLUME = 23,629 TOTAL REQUIRED STORAGE VOLUME = 23,629 PROVIDED STORAGE (CF) =25,675 OK DRAINAGE TIME (HRS) =8.6 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 2 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =25,675 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  3.24 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 120 Total Excavation Volume (cf) = 21,000 Bed Width (ft) = 25 Pipe Size (in) = 12 Bed Depth (ft) = 7 Total Pipe Length (ft) = 119 Pipe Storage (cf) = 93 Infiltration Area (sf) = 3000 Remaining Vol. for Stone (cf) = 20,907 Infiltration Rate (in/hr) = 1.6 Stone Voids (%) = 40% Available Stone Storage (cf) = 8,363 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 3.42 2,051 67 1,984 15 0.25 1.78 2.88 2,595 100 2,495 30 0.50 1.24 2.01 3,616 200 3,416 60 1 0.78 1.26 4,549 400 4,149 120 2 0.64 1.04 7,465 800 6,665 180 3 0.52 0.84 9,098 1,200 7,898 360 6 0.27 0.44 9,448 2,400 7,048 720 12 0.16 0.26 11,197 4,800 6,397 1440 24 0.10 0.16 13,997 9,600 4,397 MAXIMUM STORAGE VOLUME = 7,898 TOTAL REQUIRED STORAGE VOLUME = 7,898 PROVIDED STORAGE (CF) =8,456 OK DRAINAGE TIME (HRS) =21.1 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 3 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =8,456 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  4.11 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 100 Total Excavation Volume (cf) = 28,600 Bed Width (ft) = 26 Pipe Size (in) = 12 Bed Depth (ft) = 11 Total Pipe Length (ft) = 99 Pipe Storage (cf) = 78 Infiltration Area (sf) = 2600 Remaining Vol. for Stone (cf) = 28,522 Infiltration Rate (in/hr) = 1.6 Stone Voids (%) = 40% Available Stone Storage (cf) = 11,409 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 4.34 2,602 58 2,544 15 0.25 1.78 3.66 3,292 87 3,205 30 0.50 1.24 2.55 4,587 173 4,413 60 1 0.78 1.60 5,770 347 5,424 120 2 0.64 1.32 9,469 693 8,776 180 3 0.52 1.07 11,541 1,040 10,501 360 6 0.27 0.55 11,985 2,080 9,905 720 12 0.16 0.33 14,204 4,160 10,044 1440 24 0.10 0.21 17,755 8,320 9,435 MAXIMUM STORAGE VOLUME = 10,501 TOTAL REQUIRED STORAGE VOLUME = 10,501 PROVIDED STORAGE (CF) =11,487 OK DRAINAGE TIME (HRS) =33.1 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 4 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =11,487 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  2.16 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 140 Total Excavation Volume (cf) = 13,860 Bed Width (ft) = 9 Pipe Size (in) = 12 Bed Depth (ft) = 11 Total Pipe Length (ft) = 139 Pipe Storage (cf) = 109 Infiltration Area (sf) = 1260 Remaining Vol. for Stone (cf) = 13,751 Infiltration Rate (in/hr) = 1.6 Stone Voids (%) = 40% Available Stone Storage (cf) = 5,500 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 2.28 1,367 28 1,339 15 0.25 1.78 1.92 1,730 42 1,688 30 0.50 1.24 1.34 2,411 84 2,327 60 1 0.78 0.84 3,033 168 2,865 120 2 0.64 0.69 4,977 336 4,641 180 3 0.52 0.56 6,065 504 5,561 360 6 0.27 0.29 6,299 1,008 5,291 720 12 0.16 0.17 7,465 2,016 5,449 1440 24 0.10 0.11 9,331 4,032 5,299 MAXIMUM STORAGE VOLUME = 5,561 TOTAL REQUIRED STORAGE VOLUME = 5,561 PROVIDED STORAGE (CF) =5,610 OK DRAINAGE TIME (HRS) =33.4 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 5 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =5,610 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  1.58 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 80 Total Excavation Volume (cf) = 9,600 Bed Width (ft) = 15 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 79 Pipe Storage (cf) = 62 Infiltration Area (sf) = 1200 Remaining Vol. for Stone (cf) = 9,538 Infiltration Rate (in/hr) = 4.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 3,815 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 1.67 1,000 75 925 15 0.25 1.78 1.41 1,266 113 1,153 30 0.50 1.24 0.98 1,763 225 1,538 60 1 0.78 0.62 2,218 450 1,768 120 2 0.64 0.51 3,640 900 2,740 180 3 0.52 0.41 4,437 1,350 3,087 360 6 0.27 0.21 4,607 2,700 1,907 720 12 0.16 0.13 5,460 5,400 60 1440 24 0.10 0.08 6,826 10,800 ‐3,974 MAXIMUM STORAGE VOLUME = 3,087 TOTAL REQUIRED STORAGE VOLUME = 3,087 PROVIDED STORAGE (CF) =3,877 OK DRAINAGE TIME (HRS) =8.6 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 6 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =3,877 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  7.08 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 90 Total Excavation Volume (cf) = 45,000 Bed Width (ft) = 50 Pipe Size (in) = 12 Bed Depth (ft) = 10 Total Pipe Length (ft) = 89 Pipe Storage (cf) = 70 Infiltration Area (sf) = 4500 Remaining Vol. for Stone (cf) = 44,930 Infiltration Rate (in/hr) = 2.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 17,972 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 7.47 4,482 156 4,325 15 0.25 1.78 6.30 5,671 234 5,437 30 0.50 1.24 4.39 7,901 469 7,433 60 1 0.78 2.76 9,940 938 9,003 120 2 0.64 2.27 16,312 1,875 14,437 180 3 0.52 1.84 19,881 2,813 17,068 360 6 0.27 0.96 20,645 5,625 15,020 720 12 0.16 0.57 24,468 11,250 13,218 1440 24 0.10 0.35 30,586 22,500 8,086 MAXIMUM STORAGE VOLUME = 17,068 TOTAL REQUIRED STORAGE VOLUME = 17,068 PROVIDED STORAGE (CF) =18,042 OK DRAINAGE TIME (HRS) =19.2 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 7 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =18,042 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  5.37 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 110 Total Excavation Volume (cf) = 35,200 Bed Width (ft) = 40 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 109 Pipe Storage (cf) = 86 Infiltration Area (sf) = 4400 Remaining Vol. for Stone (cf) = 35,114 Infiltration Rate (in/hr) = 2.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 14,046 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 5.67 3,399 153 3,246 15 0.25 1.78 4.78 4,301 229 4,072 30 0.50 1.24 3.33 5,993 458 5,535 60 1 0.78 2.09 7,539 917 6,623 120 2 0.64 1.72 12,372 1,833 10,539 180 3 0.52 1.40 15,079 2,750 12,329 360 6 0.27 0.72 15,659 5,500 10,159 720 12 0.16 0.43 18,559 11,000 7,559 1440 24 0.10 0.27 23,198 22,000 1,198 MAXIMUM STORAGE VOLUME = 12,329 TOTAL REQUIRED STORAGE VOLUME = 12,329 PROVIDED STORAGE (CF) =14,131 OK DRAINAGE TIME (HRS) =15.4 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 8 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =14,131 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  2.25 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 100 Total Excavation Volume (cf) = 12,000 Bed Width (ft) = 15 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 99 Pipe Storage (cf) = 78 Infiltration Area (sf) = 1500 Remaining Vol. for Stone (cf) = 11,922 Infiltration Rate (in/hr) = 4.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 4,769 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 2.37 1,424 94 1,331 15 0.25 1.78 2.00 1,802 141 1,662 30 0.50 1.24 1.40 2,511 281 2,230 60 1 0.78 0.88 3,159 563 2,597 120 2 0.64 0.72 5,184 1,125 4,059 180 3 0.52 0.59 6,318 1,688 4,631 360 6 0.27 0.30 6,561 3,375 3,186 720 12 0.16 0.18 7,776 6,750 1,026 1440 24 0.10 0.11 9,720 13,500 ‐3,780 MAXIMUM STORAGE VOLUME = 4,631 TOTAL REQUIRED STORAGE VOLUME = 4,631 PROVIDED STORAGE (CF) =4,847 OK DRAINAGE TIME (HRS) =8.6 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 9 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =4,847 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  6.33 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 100 Total Excavation Volume (cf) = 36,000 Bed Width (ft) = 45 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 99 Pipe Storage (cf) = 78 Infiltration Area (sf) = 4500 Remaining Vol. for Stone (cf) = 35,922 Infiltration Rate (in/hr) = 3 Stone Voids (%) = 40% Available Stone Storage (cf) = 14,369 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 6.68 4,007 188 3,819 15 0.25 1.78 5.63 5,070 281 4,789 30 0.50 1.24 3.92 7,064 563 6,502 60 1 0.78 2.47 8,887 1,125 7,762 120 2 0.64 2.03 14,584 2,250 12,334 180 3 0.52 1.65 17,775 3,375 14,400 360 6 0.27 0.85 18,458 6,750 11,708 720 12 0.16 0.51 21,876 13,500 8,376 1440 24 0.10 0.32 27,346 27,000 346 MAXIMUM STORAGE VOLUME = 14,400 TOTAL REQUIRED STORAGE VOLUME = 14,400 PROVIDED STORAGE (CF) =14,447 OK DRAINAGE TIME (HRS) =12.8 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 10 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =14,447 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  2.95 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 90 Total Excavation Volume (cf) = 21,600 Bed Width (ft) = 30 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 89 Pipe Storage (cf) = 70 Infiltration Area (sf) = 2700 Remaining Vol. for Stone (cf) = 21,530 Infiltration Rate (in/hr) = 1.3 Stone Voids (%) = 40% Available Stone Storage (cf) = 8,612 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 3.11 1,867 49 1,819 15 0.25 1.78 2.63 2,363 73 2,290 30 0.50 1.24 1.83 3,292 146 3,146 60 1 0.78 1.15 4,142 293 3,849 120 2 0.64 0.94 6,797 585 6,212 180 3 0.52 0.77 8,284 878 7,406 360 6 0.27 0.40 8,602 1,755 6,847 720 12 0.16 0.24 10,195 3,510 6,685 1440 24 0.10 0.15 12,744 7,020 5,724 MAXIMUM STORAGE VOLUME = 7,406 TOTAL REQUIRED STORAGE VOLUME = 7,406 PROVIDED STORAGE (CF) =8,682 OK DRAINAGE TIME (HRS) =29.7 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 11 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =8,682 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  6.82 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 230 Total Excavation Volume (cf) = 41,400 Bed Width (ft) = 20 Pipe Size (in) = 12 Bed Depth (ft) = 9 Total Pipe Length (ft) = 229 Pipe Storage (cf) = 180 Infiltration Area (sf) = 4600 Remaining Vol. for Stone (cf) = 41,220 Infiltration Rate (in/hr) = 3 Stone Voids (%) = 40% Available Stone Storage (cf) = 16,488 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 7.20 4,317 192 4,125 15 0.25 1.78 6.07 5,463 288 5,175 30 0.50 1.24 4.23 7,611 575 7,036 60 1 0.78 2.66 9,575 1,150 8,425 120 2 0.64 2.18 15,713 2,300 13,413 180 3 0.52 1.77 19,151 3,450 15,701 360 6 0.27 0.92 19,887 6,900 12,987 720 12 0.16 0.55 23,570 13,800 9,770 1440 24 0.10 0.34 29,462 27,600 1,862 MAXIMUM STORAGE VOLUME = 15,701 TOTAL REQUIRED STORAGE VOLUME = 15,701 PROVIDED STORAGE (CF) =16,668 OK DRAINAGE TIME (HRS) =14.5 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 12 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =16,668 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) =  4.73 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 95 Total Excavation Volume (cf) = 30,400 Bed Width (ft) = 40 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 94 Pipe Storage (cf) = 74 Infiltration Area (sf) = 3800 Remaining Vol. for Stone (cf) = 30,326 Infiltration Rate (in/hr) = 2 Stone Voids (%) = 40% Available Stone Storage (cf) = 12,130 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 4.99 2,994 106 2,889 15 0.25 1.78 4.21 3,789 158 3,630 30 0.50 1.24 2.93 5,279 317 4,962 60 1 0.78 1.84 6,641 633 6,008 120 2 0.64 1.51 10,898 1,267 9,631 180 3 0.52 1.23 13,282 1,900 11,382 360 6 0.27 0.64 13,793 3,800 9,993 720 12 0.16 0.38 16,347 7,600 8,747 1440 24 0.10 0.24 20,434 15,200 5,234 MAXIMUM STORAGE VOLUME = 11,382 TOTAL REQUIRED STORAGE VOLUME = 11,382 PROVIDED STORAGE (CF) =12,204 OK DRAINAGE TIME (HRS) =19.3 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Basin 13 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =12,204 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho WEIGHTED RUNOFF COEFFICIENT, C Surface Type Runoff  Coefficient, C Area (SF) Weighted C Drainage Area (Ac.) =  3.53 Asphalt 0.95 64819 61578 Runoff Coefficient 'c' = 0.51 Landscaping 0.20 86430 17286 Total 153829 0.51 Bed Length (ft) = 100 Total Excavation Volume (cf) = 24,000 Bed Width (ft) = 30 Pipe Size (in) = 12 Bed Depth (ft) = 8 Total Pipe Length (ft) = 99 Pipe Storage (cf) = 78 Infiltration Area (sf) = 3000 Remaining Vol. for Stone (cf) = 23,922 Infiltration Rate (in/hr) = 1.3 Stone Voids (%) = 40% Available Stone Storage (cf) = 9,569 Storm Duration  (mins) Storm  Duration (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage  Volume  Needed (cf) 10 0.17 2.11 3.82 2,292 54 2,238 15 0.25 1.78 3.22 2,900 81 2,819 30 0.50 1.24 2.24 4,041 163 3,878 60 1 0.78 1.41 5,084 325 4,759 120 2 0.64 1.16 8,343 650 7,693 180 3 0.52 0.94 10,168 975 9,193 360 6 0.27 0.49 10,559 1,950 8,609 720 12 0.16 0.29 12,514 3,900 8,614 1440 24 0.10 0.18 15,642 7,800 7,842 MAXIMUM STORAGE VOLUME = 9,193 TOTAL REQUIRED STORAGE VOLUME = 9,193 PROVIDED STORAGE (CF) =9,647 OK DRAINAGE TIME (HRS) =29.7 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm Contributing Area Data Percolation Bed Data Basin 14 WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =9,647 100‐YEAR STORM EVENT Regency at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho WEIGHTED RUNOFF COEFFICIENT, C Surface Type Runoff  Coefficient, C Area (SF) Weighted C Drainage Area (Ac.) =  1.00 Asphalt 0.95 23698 22513 Runoff Coefficient 'c' =0.61 Landscaping 0.20 19852 3970 Total 43550 0.61 Bed Length (ft) =200 Total Excavation Volume (cf) =8,000 Bed Width (ft) =5 Pipe Size (in) =12 Bed Depth (ft) = 8 Total Pipe Length (ft) =199 Pipe Storage (cf) = 156 Infiltration Area (sf) =1000 Remaining Vol. for Stone (cf) =7,844 Infiltration Rate (in/hr) =1.5 Stone Voids (%) = 40% Available Stone Storage (cf) =3,137 Storm Duration  (mins) Storm Duration  (hrs) Intensity  (in/hr) (1)Peak Flow (cfs)Runoff Volume  (cf) (2) Percolated  Volume (cf) (3) Storage Volume  Needed (cf) 10 0.17 2.11 1.28 770 21 749 15 0.25 1.78 1.08 974 31 943 30 0.50 1.24 0.75 1,357 63 1,295 60 1 0.78 0.47 1,707 125 1,582 120 2 0.64 0.39 2,802 250 2,552 180 3 0.52 0.32 3,414 375 3,039 360 6 0.27 0.16 3,546 750 2,796 720 12 0.16 0.10 4,202 1,500 2,702 1440 24 0.10 0.06 5,253 3,000 2,253 MAXIMUM STORAGE VOLUME = 3,039 TOTAL REQUIRED STORAGE VOLUME = 3,039 PROVIDED STORAGE (CF) =3,294 OK DRAINAGE TIME (HRS) =26.4 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm Basin 15 Percolation Bed Data Contributing Area Data WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Total Bed Volume [Pipe Storage +  Stone Storage] (cf) =3,294 100‐YEAR STORM EVENT Basin 211.62 ac.Basin 77.08 ac.Basin 85.37 ac.Basin 106.33 ac.Basin 9 2.25 ac.Basin 112.95 ac.Basin 126.82 ac.Basin 134.73 ac.Basin 44.11 ac.Basin 143.53 ac.May 28, 2024 - Caldwell, IdahoREGENCY AT VERBENA RANCHDRAINAGE CATCHMENT PLANGRAPHIC SCALE0FEET1 inch = ft. Horizontal200100200200Basin 11.04 ac.Basin 11.81 ac.Basin 151.00 ac.Basin 61.58 ac.Basin 52.16 ac.Basin 33.24 ac.