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Home My WebLink AboutZIGGI'S COFFEE - PDP - PDP170021 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE RELATED DOCUMENT621 SOUTHPARK DRIVE, SUITE 1600 – LITTLETON, CO 80120 - (720) 252-3484 - FAX (303) 979-1675 EMAIL: COLEH@HABERERGROUP.COM 1 HCI ENGINEERING A division of HABERER CARPENTRY INC. August 2, 2017 Attn: Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80521 Re: Drainage Conformance Letter for Ziggi’s Coffee – Fort Collins A Portion of Lot 2 – C.O.L. College and Trilby Subdivision ______________________________________________________________________ Summary The following letter is written on behalf of Ziggi’s Coffee – Fort Collins to demonstrate that the proposed site improvements are in conformance with the drainage design outlined in the Approved “Drainage and Erosion Control Report for Northwest Corner of College Avenue and Trilby Road Eckerd Drug”, dated 12/23/2003, prepared by North Star Design, Inc. – hereafter referred to as ‘Report 1’. Lot 2 is 1.63 acres or 71,003 square feet, however, the area encompassed by the limits of site improvement changes is approximately 17,376 square feet. The existing site consists of a detention pond, paved parking and drives, concrete walks, and landscape areas. The existing total impervious area within the limits of site improvement changes is 11,825 square feet. Proposed improvements will affect Basins 3, 4, and 6 from Report 1 and will generally follow existing drainage patterns. These basins have been reanalyzed for the areas experiencing site improvement changes within the limits of construction utilizing design criteria from Report 1. The proposed total impervious area within the limits of site improvement changes is 8,775 square feet. Basin 3 Runoff within the improved portion of Basin 3 will continue to sheet flow to an existing area inlet before being conveyed north via Storm 2 to the existing onsite detention pond (Pond 1). Proposed improvements within this basin include removing and replacing existing parking and walks with ADA parking and walks, which results in a minor increase in the overall area and impervious area for the basin. Basin 4 Runoff within the improved portion of Basin 4 will continue to sheet flow to concrete v-pans and curb and gutter then to an existing combination inlet before being conveyed via Storm 2 to the existing onsite detention pond (Pond 1). Demolition activities within this basin include the removal of a portion of the existing eastern parking area, landscape islands, and associated walks. Proposed improvements include increased landscape area, approximately 492 square feet of building area, and a concrete: drive-thru lane, patio, walks, curb and gutter, and v-pans. The change in site improvements results in a decrease of the impervious area for the basin. The overall area of the basin has also decreased based on the proposed ADA improvements now being tributary to Basin 3. 621 SOUTHPARK DRIVE, SUITE 1600 – LITTLETON, CO 80120 - (720) 252-3484 - FAX (303) 979-1675 EMAIL: COLEH@HABERERGROUP.COM 2 Basin 6 Runoff within the improved portion of Basin 6 will continue sheet flow offsite undetained before being captured by the existing inlet at the corner of the north access drive and S. College Avenue. Proposed improvements within the basin include removing and replacing a concrete walk and a portion of the concrete patio, which results in a minor increase of the impervious area. The majority of the basin will remain as landscape area. The total impervious area within the limits of site improvement changes has been decreased by approximately 3,050 square feet from the existing (11,825 SF) to the proposed (8,775 SF) conditions. The 100-year peak runoff to Design Point 4 in Basin 4 slightly increased from 1.66 CFS in the existing conditions to 1.71 CFS in the proposed conditions due to an increase in the overall area and impervious area of the basin. However, the existing area inlet has the capacity (2.70 CFS) to completely capture the additional runoff. The 100-year peak runoff to Design Point 3 in Basin 3 has been decreased from 16.27 CFS in the existing conditions to 15.89 CFS in the proposed conditions due to a decrease in the overall area of the basin, increased pervious landscape areas, and Report 1 anticipating 4,500 square feet of future building to occupy space within Basin 3, however, the proposed building will now only occupy 492 square feet. The 100-year peak runoff to Design Point 6 slightly increased from 0.63 CFS in the existing conditions to 0.74 CFS in the proposed conditions due to increased concrete area by the encroaching patio. The approved hydrological calculations and calculations based on proposed improvements are attached for refence. Volume based water quality mitigation for Basins 3 and 4 was originally analyzed as part of Report 1 and is provided in the existing onsite extended detention basin (Pond 1). Basins 1 through 5 are tributary to Pond 1. Per Report 1, the required total storage volume for Pond 1 is 39,814 cubic feet and includes the required 100-year detention volume (35,937 CF) plus the required water quality capture volume (3,876 CF). The required water quality capture volume has been reanalyzed utilizing proposed conditions for modified Basins 3 and 4 and approved conditions for unchanged Basins 1, 2, and 5. The composite percent impervious for the tributary area to Pond 1 (Basins 1 through 5) decreased from the approved value, 74.0%, to the proposed value, 69.1%. This decrease in the composite percent impervious results in a direct decrease in the required water quality capture volume from the approved conditions (3,876 CF) to the proposed conditions (3,616 CF). Pond 1 provides 3,920 CF of storage for the required water quality capture volume and is adequately sized to treat the proposed runoff from Basins 3 & 4. Additional water quality is provided within Basin 3 by the increased pervious landscape areas. Level 1 - Low Impact Development (LID) will be implemented to direct runoff as sheet flow over these pervious landscape areas which increases travel time and traps suspended solids prior to runoff reaching the storm sewer system, Storm 2. This same LID measure will be utilized for Basin 6, where runoff is released offsite undetained over sloped grass buffers. The project site is located within Sub-Basin 319 of the Fossil Creek Drainage Basin. Furthermore, the proposed project meets the release requirements as analyzed in Report 1 and set forth by the Fossil Creek Basin Master Drainageway Planning Restudy, by ICON Engineering, Inc., dated 2001. Conclusion The proposed project has been analyzed utilizing the approved conditions set forth in Report 1. This drainage letter and associated calculations are limited to the project shown by the attached Drainage Plan. Based on the above findings and attached calculations HCI Engineering finds the proposed development to be in compliance with the drainage criteria set forth in Report 1. No negative impacts are anticipated as a result of this development to adjacent properties or downstream. 621 SOUTHPARK DRIVE, SUITE 1600 – LITTLETON, CO 80120 - (720) 252-3484 - FAX (303) 979-1675 EMAIL: COLEH@HABERERGROUP.COM 3 Sincerely, Cole C Haberer, P.E. - HCI Engineering 621 SOUTHPARK DRIVE, SUITE 1600 – LITTLETON, CO 80120 - (720) 252-3484 - FAX (303) 979-1675 EMAIL: COLEH@HABERERGROUP.COM 4 ATTACHMENTS Project: 17_13 Ziggi's Coffee Project Number: 17_13 Date: 8/2/2017 Soil Type: C & D Modified Basins for Proposed Conditions Basin: 3 Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 53678 100% 0.95 0.95 0.95 0.95 492 90% 0.95 0.95 0.95 0.95 16810 0% 0.25 0.25 0.25 0.25 70980 76.2% 0.78 0.78 0.78 0.78 Basin: 4 Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 7090 100% 0.95 0.95 0.95 0.95 0 90% 0.95 0.95 0.95 0.95 414 0% 0.25 0.25 0.25 0.25 7504 94.5% 0.91 0.91 0.91 0.91 Basin: 6 Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 822 100% 0.95 0.95 0.95 0.95 0 90% 0.95 0.95 0.95 0.95 7231 0% 0.25 0.25 0.25 0.25 8053 10.2% 0.32 0.32 0.32 0.32 PROPOSED COMPOSITE IMPERVIOUS AND RUNOFF COEFFICIENT CALCULATIONS FOR AFFECTED BASINS Formula: [(Area)(C Value)+(Area)(C Value)+(Area)(C Value)]/(Total Area) Cf2 = 1.00 Cf5 = 1.00 Cf10 = 1.00 Cf100 = 1.25 Total Area Total Area Composite (SF) (Acres) % Impervious C2 C5 C10 C100 3 70980 1.63 76.2% 0.78 0.78 0.78 0.98 4 7504 0.17 94.5% 0.91 0.91 0.91 1.00 6 8053 0.18 10.2% 0.32 0.32 0.32 0.40 Total: 86537 1.99 71.7% 0.75 0.75 0.75 0.93 Cf = Coefficient Frequency Factors from Report 1 Runoff Coefficient (C) cannot be greater than 1.00 Paved Roofs Land Use or Surface Characteristics HCI ENGINEERING A division of HABERER CARPENTRY INC. Total/ Compsite Land Use or Surface Characteristics Paved Roofs Lawns, sandy soil Paved Roofs Lawns, sandy soil Total/ Compsite Lawns, sandy soil Total/ Compsite Basin I.D. Composite Runoff Coefficient, C Land Use or Surface Characteristics NRCS Hydrologic Soil Type (Per Geotech) Project: 17_13 Ziggi's Coffee Project Number: 17_13 Date: 8/2/2017 Area Area Runoff tc C x A Intensity (I) Q Design (ac) Coeff (min) (AC) in/hr (cfs) 3 1.63 0.78 5.80 1.28 4.62 5.90 4 0.17 0.91 5.00 0.16 4.87 0.76 6 0.18 0.32 5.00 0.06 4.87 0.29 Cf10 = 1.00 From Report 1 Runoff Coefficient (C) cannot be greater than 1.00 tc From Report 1 Intensity (I) From Report 1 HCI ENGINEERING A division of HABERER CARPENTRY INC. PROPOSED CONDITIONS DIRECT RUNOFF 10-YR STORM Project: 17_13 Ziggi's Coffee Project Number: 17_13 Date: 8/2/2017 Area Area Runoff tc C x A Intensity (I) Q Design (ac) Coeff (min) (AC) in/hr (cfs) 3 1.63 0.98 5.00 1.60 9.95 15.89 4 0.17 1.00 5.00 0.17 9.95 1.71 6 0.18 0.50 5.00 0.09 9.95 0.92 Cf100 = 1.25 From Report 1 Runoff Coefficient (C) cannot be greater than 1.00 tc From Report 1 Intensity (I) From Report 1 PROPOSED CONDITIONS DIRECT RUNOFF 100-YR STORM HCI ENGINEERING A division of HABERER CARPENTRY INC. Project: 17_13 Ziggi's Coffee Project Number: 17_13 Date: 8/2/2017 Soil Type: C & D Approved Basins & Modified Basins for Proposed Conditions 1Basin: 1 Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 13550 100% 0.95 0.95 0.95 0.95 0 90% 0.95 0.95 0.95 0.95 505 0% 0.25 0.25 0.25 0.25 14055 96.4% 0.92 0.92 0.92 0.92 1Basin: 2 Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 0 100% 0.95 0.95 0.95 0.95 14500 90% 0.95 0.95 0.95 0.95 0 0% 0.25 0.25 0.25 0.25 14500 90.0% 0.95 0.95 0.95 0.95 2Basin: 3 Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 53678 100% 0.95 0.95 0.95 0.95 492 90% 0.95 0.95 0.95 0.95 16810 0% 0.25 0.25 0.25 0.25 70980 76.2% 0.78 0.78 0.78 0.78 2Basin: 4 Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 7090 100% 0.95 0.95 0.95 0.95 0 90% 0.95 0.95 0.95 0.95 414 0% 0.25 0.25 0.25 0.25 7504 94.5% 0.91 0.91 0.91 0.91 1Basin: 5 Land Use or Surface Characteristics Area (SF) % Imp. C2 Value C5 Value C10 Value C100 Value 0 100% 0.95 0.95 0.95 0.95 4500 90% 0.95 0.95 0.95 0.95 21392 0% 0.25 0.25 0.25 0.25 Total/ Compsite 25892 15.6% 0.37 0.37 0.37 0.37 COMPOSITE IMPERVIOUS AND RUNOFF COEFFICIENT CALCULATIONS Formula: [(Area)(C Value)+(Area)(C Value)+(Area)(C Value)]/(Total Area) Cf2 = 1.00 Cf5 = 1.00 Cf10 = 1.00 Cf100 = 1.25 Total Area Total Area Composite (SF) (Acres) % Impervious C2 C5 C10 C100 1 14055 0.32 96.4% 0.92 0.92 0.92 1.00 2 14500 0.33 90.0% 0.95 0.95 0.95 1.00 3 70980 1.63 76.2% 0.78 0.78 0.78 0.98 4 7504 0.17 94.5% 0.91 0.91 0.91 1.00 5 25892 0.59 15.6% 0.37 0.37 0.37 0.46 Total: 132931 3.05 69.1% 0.74 0.74 0.74 0.88 Cf = Coefficient Frequency Factors from Report 1 Runoff Coefficient (C) cannot be greater than 1.00 1Basin information per approved Report 1 2Basin information under proposed conditions Roofs Lawns, sandy soil Total/ Compsite Land Use or Surface Characteristics Paved Roofs Lawns, sandy soil Total/ Compsite Basin I.D. Composite Runoff Coefficient, C Paved Lawns, sandy soil Project: 17_13 Ziggi's Coffee Project Number: 17_13 Date: 8/2/2017 1, 2, 3, 4, & 5 (Pond 1) 3.06 69.1% 0.29 0.069 1.00 0.083 3616 0.65 1 Information per approved Report 1 2 Information under proposed conditions Tributary Area (Acres) Basin I.D. Water Quality Capture Volume for Approved Basins & Modified Proposed Basins Composite % Impervious 1 Req. Storage (in. of runoff) from Fig, EDB-2 WQCV (ac-ft) 1 DWQ (ft) Req. Vol. WQCV*1.2 (ac-ft) 1 Req. area/row (in 2 / row) Req. Vol. WQCV*1.2 (cf) HCI ENGINEERING A division of HABERER CARPENTRY INC. STOP ENTER WEST TRILBY ROAD (75.51' R.O.W.) SOUTH COLLEGE AVENUE (HIGHWAY 287) (R.O.W. REC. NO. 2004002682 & BOOK 1066 PAGE 184 & BOOK 1059 PAGE 402) 3 1.63 0.78 0.98 3 4 0.17 0.91 1.00 4 6 0.18 0.32 0.50 6 INFLOW C&G 2' CONCRETE V-PAN (TYP.) 2' CONCRETE V-PAN OUTFALL C&G 5032 5033 5034 5034 5034 5034 5034 5033 5034 5034 REVISIONS: Drawn By: Sheet Sheet Name: No. Date: Description: FILENAME: 17_13 UP DrainagePlan.dwg PLOTDATE: 2017-08-02 PLOT TIME: 4:53 PM Checked By: Date Issued: Project No: CALL 811 2-BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE, OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. Know what's below, Call before you dig. ZIGGI'S COFFEE - FORT COLLINS UTILITY PLANS 6533 S. COLLEGE AVE. FORT COLLINS, CO 80525 Number: A DIVISION OF HABERER CARPENTRY INC. This unofficial copy was downloaded on Jun-01-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA This unofficial copy was downloaded on Jun-01-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA 621 SOUTHPARK DR., SUITE 1600 LITTLETON CO, 80120 INFO@HABERERGROUP.COM 1 6/21/17 PDP SUBMITTAL #1 ZAH CCH 8/02/2017 2 8/02/17 PDP SUBMITTAL #2 DRAINAGE LEGEND EX. MAJOR CONTOUR EX. MINOR CONTOUR FLOW ARROW DRAINAGE BASIN BASIN ID AREA (AC) C100 B3-6 2.80 0.47 0.76 C10 LIMITS OF SITE IMPROVEMENT CHANGES BASIN BOUNDARY 5421 5420 NOTES: 1. THE SITE LIES WITHIN THE FOSSIL CREEK DRAINAGE BASIN. FOSSIL CREEK IS LOCATED APPROXIMATELY 1.35 MILES EAST OF THE SITE. PR. MAJOR CONTOUR PR. MINOR CONTOUR B4-6A DESIGN POINT 0' 20' 40' 60' SCALE: 1" = 20' N 17_13 DRAINAGE PLAN C1.4 LIMITS OF CONSTRUCTION Paved Roofs Lawns, sandy soil Total/ Compsite Paved Roofs Lawns, sandy soil Total/ Compsite Land Use or Surface Characteristics HCI ENGINEERING A division of HABERER CARPENTRY INC. NRCS Hydrologic Soil Type (Per Geotech) Land Use or Surface Characteristics Land Use or Surface Characteristics Paved Roofs