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Home My WebLink AboutSWM Report-Reserve ESE Consultants, Inc. 3103 W. Sheryl Drive Meridian, Idaho 83642 TEL: 208-424-0020 PRELIMINARY STORMWATER MANAGEMENT PLAN FOR THE RESERVE 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 E Homedale Road to the north, Deer Flat Caldwell Canal to the south, S. 10th Ave to the west and existing residential uses to the east. The site is primarily comprised of open agricultural fields. There are several existing residential structures to be removed at the time of construction. Project Scope The applicant proposes to construct one hundred and thirty-eight (138) single family residential homes on subdivided lots within the approximately 38.11-acre property. The development includes the construction of homes, local roads, sidewalks, stormwater management facilities, a gravity irrigation pond, and other infrastructure improvements typical of residential construction. Report Scope This report presents the preliminary stormwater management plan for The Reserve 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) The Reserve at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) = 7.12 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 190 Total Excavation Volume (cf) = 38,000 Bed Width (ft) = 25 Pipe Size (in) = 18 Bed Depth (ft) = 8 Total Pipe Length (ft) = 567 Pipe Storage (cf) = 1,002 Infiltration Area (sf) = 4750 Remaining Vol. for Stone (cf) = 36,998 Infiltration Rate (in/hr) = 4.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 14,799 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 7.51 4,507 297 4,210 15 0.25 1.78 6.34 5,703 445 5,258 30 0.50 1.24 4.41 7,946 891 7,055 60 1 0.78 2.78 9,996 1,781 8,215 120 2 0.64 2.28 16,404 3,563 12,842 180 3 0.52 1.85 19,993 5,344 14,649 360 6 0.27 0.96 20,762 10,688 10,074 720 12 0.16 0.57 24,607 21,375 3,232 1440 24 0.10 0.36 30,758 42,750 ‐11,992 MAXIMUM STORAGE VOLUME = 14,649 TOTAL REQUIRED STORAGE VOLUME = 14,649 PROVIDED STORAGE (CF) =15,801 OK DRAINAGE TIME (HRS) =8.9 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) =15,801 100‐YEAR STORM EVENTWHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME The Reserve at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) = 10.41 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 220 Total Excavation Volume (cf) = 61,600 Bed Width (ft) = 35 Pipe Size (in) = 18 Bed Depth (ft) = 8 Total Pipe Length (ft) = 657 Pipe Storage (cf) = 1,161 Infiltration Area (sf) = 7700 Remaining Vol. for Stone (cf) = 60,439 Infiltration Rate (in/hr) = 2.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 24,176 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 10.98 6,590 267 6,322 15 0.25 1.78 9.26 8,338 401 7,937 30 0.50 1.24 6.45 11,618 802 10,815 60 1 0.78 4.06 14,616 1,604 13,011 120 2 0.64 3.33 23,985 3,208 20,776 180 3 0.52 2.71 29,231 4,813 24,419 360 6 0.27 1.41 30,356 9,625 20,731 720 12 0.16 0.83 35,977 19,250 16,727 1440 24 0.10 0.52 44,971 38,500 6,471 MAXIMUM STORAGE VOLUME = 24,419 TOTAL REQUIRED STORAGE VOLUME = 24,419 PROVIDED STORAGE (CF) =25,337 OK DRAINAGE TIME (HRS) =15.8 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 2 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage + Stone Storage] (cf) =25,337 100‐YEAR STORM EVENT The Reserve at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) = 3.00 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 100 Total Excavation Volume (cf) = 16,000 Bed Width (ft) = 20 Pipe Size (in) = 18 Bed Depth (ft) = 8 Total Pipe Length (ft) = 198 Pipe Storage (cf) = 350 Infiltration Area (sf) = 2000 Remaining Vol. for Stone (cf) = 15,650 Infiltration Rate (in/hr) = 4.5 Stone Voids (%) = 40% Available Stone Storage (cf) = 6,260 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 3.17 1,899 125 1,774 15 0.25 1.78 2.67 2,403 188 2,216 30 0.50 1.24 1.86 3,348 375 2,973 60 1 0.78 1.17 4,212 750 3,462 120 2 0.64 0.96 6,912 1,500 5,412 180 3 0.52 0.78 8,424 2,250 6,174 360 6 0.27 0.41 8,748 4,500 4,248 720 12 0.16 0.24 10,368 9,000 1,368 1440 24 0.10 0.15 12,960 18,000 ‐5,040 MAXIMUM STORAGE VOLUME = 6,174 TOTAL REQUIRED STORAGE VOLUME = 6,174 PROVIDED STORAGE (CF) =6,610 OK DRAINAGE TIME (HRS) =8.8 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 3 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage + Stone Storage] (cf) =6,610 100‐YEAR STORM EVENT The Reserve at Verbena Ranch PrePlat City of Caldwell Canyon County, Idaho Drainage Area (Ac.) = 11.37 Runoff Coefficient 'c' = 0.5 Bed Length (ft) = 180 Total Excavation Volume (cf) = 64,800 Bed Width (ft) = 45 Pipe Size (in) = 18 Bed Depth (ft) = 8 Total Pipe Length (ft) = 537 Pipe Storage (cf) = 949 Infiltration Area (sf) = 8100 Remaining Vol. for Stone (cf) = 63,851 Infiltration Rate (in/hr) = 4 Stone Voids (%) = 40% Available Stone Storage (cf) = 25,540 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 12.00 7,197 450 6,747 15 0.25 1.78 10.12 9,107 675 8,432 30 0.50 1.24 7.05 12,689 1,350 11,339 60 1 0.78 4.43 15,963 2,700 13,263 120 2 0.64 3.64 26,196 5,400 20,796 180 3 0.52 2.96 31,927 8,100 23,827 360 6 0.27 1.53 33,155 16,200 16,955 720 12 0.16 0.91 39,295 32,400 6,895 1440 24 0.10 0.57 49,118 64,800 ‐15,682 MAXIMUM STORAGE VOLUME = 23,827 TOTAL REQUIRED STORAGE VOLUME = 23,827 PROVIDED STORAGE (CF) =26,489 OK DRAINAGE TIME (HRS) =9.8 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 4 Contributing Area Data Percolation Bed Data Total Bed Volume [Pipe Storage + Stone Storage] (cf) =26,489 100‐YEAR STORM EVENT The Reserve 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.) = 1.89 Asphalt 0.95 50228 47717 Runoff Coefficient 'c' = 0.66 Landscaping 0.20 31957 6391 Total 82185 0.66 Bed Length (ft) = 85 Total Excavation Volume (cf) = 14,960 Bed Width (ft) = 22 Pipe Size (in) = 18 Bed Depth (ft) = 8 Total Pipe Length (ft) = 84 Pipe Storage (cf) = 148 Infiltration Area (sf) = 1870 Remaining Vol. for Stone (cf) = 14,812 Infiltration Rate (in/hr) = 3 Stone Voids (%) = 40% Available Stone Storage (cf) = 5,925 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 2.63 1,575 78 1,497 15 0.25 1.78 2.21 1,993 117 1,877 30 0.50 1.24 1.54 2,777 234 2,544 60 1 0.78 0.97 3,494 468 3,027 120 2 0.64 0.80 5,734 935 4,799 180 3 0.52 0.65 6,988 1,403 5,586 360 6 0.27 0.34 7,257 2,805 4,452 720 12 0.16 0.20 8,601 5,610 2,991 1440 24 0.10 0.12 10,751 11,220 ‐469 MAXIMUM STORAGE VOLUME = 5,586 TOTAL REQUIRED STORAGE VOLUME = 5,586 PROVIDED STORAGE (CF) =6,073 OK DRAINAGE TIME (HRS) =13.0 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm Percolation Bed Data Contributing Area Data Basin 5 WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Total Bed Volume [Pipe Storage + Stone Storage] (cf) =6,073 100‐YEAR STORM EVENT The Reserve 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.) = 1.57 Asphalt 0.95 38592 36662 Runoff Coefficient 'c' = 0.62 Landscaping 0.20 29675 5935 Total 68267 0.62 Bed Length (ft) = 90 Total Excavation Volume (cf) = 14,400 Bed Width (ft) = 20 Pipe Size (in) = 18 Bed Depth (ft) = 8 Total Pipe Length (ft) = 89 Pipe Storage (cf) = 157 Infiltration Area (sf) = 1800 Remaining Vol. for Stone (cf) = 14,243 Infiltration Rate (in/hr) = 1 Stone Voids (%) = 40% Available Stone Storage (cf) = 5,697 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 2.07 1,240 25 1,215 15 0.25 1.78 1.74 1,569 38 1,532 30 0.50 1.24 1.21 2,187 75 2,112 60 1 0.78 0.76 2,751 150 2,601 120 2 0.64 0.63 4,514 300 4,214 180 3 0.52 0.51 5,502 450 5,052 360 6 0.27 0.26 5,713 900 4,813 720 12 0.16 0.16 6,771 1,800 4,971 1440 24 0.10 0.10 8,464 3,600 4,864 MAXIMUM STORAGE VOLUME = 5,052 TOTAL REQUIRED STORAGE VOLUME = 5,052 PROVIDED STORAGE (CF) =5,854 OK DRAINAGE TIME (HRS) =39.0 Drainage Time >>> within 48 hours of 2‐year storm >>> within 120 hours of 100‐yr storm Percolation Bed Data Contributing Area Data Basin 6 WHICH IS LESS THAN THE ALLOWABLE 120‐HOUR DRAIN TIME Total Bed Volume [Pipe Storage + Stone Storage] (cf) =5,854 100‐YEAR STORM EVENT April 26, 2024 - Caldwell, IdahoTHE RESERVE AT VERBENA RANCHDRAINAGE CATCHMENT PLANGRAPHIC SCALE0FEET1 inch = ft. Horizontal200100200200Basin 17.12 ac.Basin 210.41 ac.Basin 33.00 ac.Basin 411.37 ac.Basin 17.12 ac.Basin 51.89 ac.Basin 61.57 ac.