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Home My WebLink AboutFIRST STOP PLAZA - BASIC DEVELOPMENT REVIEW - BDR180031 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE RELATED DOCUMENTFORT COLLINS: 301 North Howes Street, Suite 100, 80521 | 970.221.4158 GREELEY: 820 8 th Street, 80631 | 970.395.9880 | WEB: www.northernengineering.com October 31, 2018 Mr. Wes Lamarque City of Fort Collins 700 Wood Street Fort Collins, Colorado 80522 RE: Final Drainage Memorandum for 1st Stop Plaza Second Filing Fort Collins, Colorado Dear Wes: Northern Engineering Services is pleased to submit this Final Drainage Memorandum for 1st Stop Plaza Second Filing. As a result of the recent design improvements to the intersection of Suniga Drive and College Avenue, the driveway access for Lots 1 and 2 of 1st Stop Plaza will be relocated. The existing driveway is a full-service access from College Avenue. In conjunction with the improvements to Suniga Drive, the access on College Avenue will become right turn in and out only and relocated 60 feet north of the current location. A three-quarter access will be provided from Suniga Drive 390 feet east of College Avenue. A shared driveway will be constructed to allow vehicular movement between the two new access locations. As part of the improvements for Suniga Drive and College Avenue intersection, Interwest Consulting Group prepared a drainage memorandum to North East College Corridor Outfall (NECCO) Design Report dated August 13, 2018. Lots 1 and 2 of 1st Stop Plaza Second Filing coincide with Basin B of the Interwest Drainage Memorandum. Interwest assumed an impervious area of 44.4% and a runoff coefficient of 0.53 for Lots 1 and 2 of 1st Stop Plaza. The impervious area with the proposed driveway improvements is 35% and the runoff coefficient is 0.47. The proposed driveway improvements comply with assumptions used in the Interwest Drainage Memorandum for Suniga Drive. Detention for the site is part of the North East College Corridor Outfall (NECCO), but the project does not meet the City’s water quality and LID requirements. Upon redevelopment of Lots 1 and 2 for 1st Stop Minor Subdivision, the developer will need to provide the necessary water quality and LID improvements for that portion of the driveway, asphalt, parking lot, and concrete of this project that falls within their property. Table 1 below summarizes the required volumes necessary to satisfy the City’s water quality requirements for this project. FORT COLLINS: 301 North Howes Street, Suite 100, 80521 | 970.221.4158 GREELEY: 820 8 th Street, 80631 | 970.395.9880 | WEB: www.northernengineering.com Table 1: Required Water Quality Volume Description Water Quality Volume (ft3) Water Quality Volume (Acres) Lot 1 669 0.015 Lot 2 285 0.007 We feel the current proposed drainage plan for 1st Stop Plaza Second Filing is in compliance with the concepts shown in the NECCO Design Report and the Interwest Drainage Memorandum for Suniga Drive and College Avenue. Upon redevelopment of Lots 1 and 2 of 1st Stop Minor Amendment, the developer will need to provide water quality and LID improvements for that portion of the driveway improvements that fall within their property. If you have any questions, please feel free to contact me at your earliest convenience. NORTHERN ENGINEERING SERVICES, INC. Frederick S. Wegert, PE Project Engineer 1st Stop Plaza CHARACTER OF SURFACE: Runoff Coefficient 1 Percentage Impervious 2 Project: Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: Asphalt ………………… ................... .......................................................... 0.95 100% Date: Concrete ………………. ................... .......................................................... 0.95 96% Gravel (packed) ………. ................... .......................................................... 0.50 40% Roofs………………….. ................... .......................................................... 0.95 90% Pavers…………………. ................... .......................................................... 0.40 40% Lawns and Landscaping Sandy Soil Flat <2% ………….. ................... .......................................................... 0.10 0% Average 2% to 7% ................... .......................................................... 0.15 0% Steep >7% ………… ................... .......................................................... 0.20 0% Clayey Soil Flat <2% ………….. ................... .......................................................... 0.20 0% Average 2% to 7% ................... .......................................................... 0.25 0% Steep >7% ………… ................... .......................................................... 0.35 0% 2-year C f = 1.00 10-year C f = 1.00 USDA SOIL TYPE: C Sub-Basin ID Sub-Basin Area (sq. ft.) Sub-Basin Area (ac.) Area of Asphalt & Concrete (ac.) Area of Roofs (ac.) Area of Gravel (ac.) Area of Landscaping 2% to 7% (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff New Impervious Area 0.187 Ac. Paver Area 0.048 Ac. Traditional Pavement Area 0.139 Ac. Other Impervious Surfaces (Roofs, Concrete Walks, etc.) 0.000 Ac. Required Minimum Impervious Area to be Treated 0.094 Ac. Paver LID Treatment Paver area 0.048 Ac. Run-on area for Pavers (parking area) 0.125 Ac. Run-on area for Pavers (other - concrete walks, etc.) 0.000 Ac. Impervious Area Treated by LID Pavers 0.173 Ac. Rain Garden Treatment Rain Garden Area 0.000 Ac. Run-on area for Rain Garden 0.000 Ac. Impervious Area Treated by Rain Gardens 0.000 Ac. Total Impervious Area Treated 0.173 Ac. Percent of Impervious Area Treated 92.38 % New Pavement Area 8,165 Sq. Ft. Required Minimum Area of Permeable Pavement 2,041 Sq. Ft. Total Permeable Pavement Area 2,099 Sq. Ft. Actual % of Permeable Pavement Provided 25.7 % 50% On-Site Treatment by LID Requirement 25% Permeable Pavement Requirement Interwest Consulting Group RUNOFF COEFFICIENTS & % IMPERVIOUS LOCATION: SUNIGA PROJECT NO: 1326-069-00 COMPUTATIONS BY: ES DATE: 7/18/2018 Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I Runoff % coefficient Impervious C Streets, parking lots (asphalt): 0.95 100 Sidewalks (concrete): 0.95 96 Roofs: 0.95 90 Gravel or Pavers: 0.50 40 Landscape Areas (Flat, heavy) : 0.20 0 Landscape Areas (Steep, heavy) : 0.35 0 SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS SIDEWALK LANDSCAPE RUNOFF % DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS (ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C) A 0.98 42,631 0 42,631 0 0 0 0.95 100 NORTH HALF SUNIGA B 3.22 140,134 0 62,219 0 0 77,914 0.53 44.4 C 0.98 42,720 0 42,720 0 0 0 0.95 100 SOUTH HALF SUNIGA Equations - Calculated C coefficients & % Impervious are area weighted C = Σ (Ci Ai) / At Ci = runoff coefficient for specific area, Ai Ai = areas of surface with runoff coefficient of Ci n = number of different surfaces to consider At = total area over which C is applicable; the sum of all Ai's 7-18-18 FC Flow Suniga.xls T 3.21 ac. B B PROPOSED 15' UTILITY EASEMENT 15' DRAINAGE EASEMENT (RECEPTION NO. 199400063870) EXISTING SIDEWALK EX. COLUMN (TYP.) EXISTING BUILDING 1006 N. COLLEGE AVENUE LOT 2 1ST STOP MINOR SUBDIVISION LOT 1 1ST STOP MINOR SUBDIVISION NORTH COLLEGE AVENUE 1008 N. COLLEGE AVENUE 1010 N. COLLEGE AVENUE 1180 N. COLLEGE AVENUE CROWNE AT OLD TOWN NORTH SUBDIVISION 1108 N. COLLEGE AVENUE EX. SIDEWALK PROPOSED 20' EMERGENCY ACCESS EASEMENT PROPOSED 20' EMERGENCY ACCESS EASEMENT 22' UTILITY EASEMENT PER 1ST STOP PLAZA UTILITY EASEMENT 45' UTILITY EASEMENT 5' DRAINAGE EASEMENT PER 1ST STOP PLAZA 15' UTILITY EASEMENT PER 1ST STOP PLAZA 15' UTILITY EASEMENT 31' UTILITY EASEMENT 5' DRAINAGE EASEMENT PER 1ST STOP PLAZA PROPOSED BICYCLE RACK (RE: LANDSCAPE ARCHITECT) PROPOSED 2' WIDE SIDEWALK CULVERT MATCH INTO EXISTING LIP OF GUTTER EX. TRASH ENCLOSURE MATCH INTO EXISTING CONCRETE PAD FOR TRASH ENCLOSURE SAWCUT LINE (TYP.) EX. CONCRETE BLOCK RETAINING WALL EX. CONCRETE VALLEY PAN EX. CONCRETE VALLEY PAN 2 SAWCUT LINE (TYP.) PROPOSED STORM INLET PROPOSED STORM SEWER MANHOLE PROPOSED STORM SEWER PROPOSED STORM INLET PROPOSED 20' STORM SEWER EASEMENT PROPOSED 30" STORM SEWER BY INTERWEST CONSULTING GROUP (SEE SHEET 11 OF SUNIGA DRIVE IMPROVEMENTS PREPARED BY INTERWEST CONSULTING GROUP),. PROPOSED STORM INLET BY INTERWEST PROPOSED STORM INLET BY INTERWEST CONSULTING GROUP (SEE SHEET 11 OF SUNIGA DRIVE IMPROVEMENTS PREPARED BY INTERWEST CONSULTING GROUP),. PROPOSED SIDEWALK BY INTERWEST CONSULTING GROUP (SEE SHEET 4 OF SUNIGA DRIVE IMPROVEMENTS PREPARED BY INTERWEST CONSULTING GROUP). PROPOSED SIDEWALK BY INTERWEST CONSULTING GROUP PROPOSED TRAFFIC LIGHT BY INTERWEST CONSULTING GROUP (TYP.) Sheet 1ST STOP PLAZA SECOND FILING These drawings are instruments of service provided by Northern Engineering Services, Inc. and are not to be used for any type of construction unless signed and sealed by a Professional Engineer in the employ of Northern Engineering Services, Inc. NOT FOR CONSTRUCTION REVIEW SET E NGINEER ING N O R T H E RN FORT COLLINS: 301 North Howes Street, Suite 100, 80521 GREELEY: 820 8th Street, 80631 970.221.4158 northernengineering.com of 10 PROPOSED CONCRETE FLATWORK PROPOSED INFLOW CURB & GUTTER PROPOSED 8' CURB AND GUTTER TRANSITION C5.0 DRAINAGE PLAN 7 CALL UTILITY NOTIFICATION CENTER OF COLORADO Know what'sbelow. Call before you dig. R LEGEND: ( IN FEET ) 0 1 INCH = 20 FEET 20 20 40 60 PROPERTY BOUNDARY EXISTING RIGHT-OF-WAY EXISTING EASEMENTS NOTES: 1. EXISTING UNDERGROUND AND OVERHEAD PUBLIC AND PRIVATE UTILITIES AS SHOWN ARE INDICATED ACCORDING TO THE BEST INFORMATION AVAILABLE TO THE ENGINEER. THE ENGINEER DOES NOT GUARANTEE THE ACCURACY OF SUCH INFORMATION. EXISTING UTILITY MAINS AND SERVICES MAY NOT BE STRAIGHT LINES OR AS INDICATED ON THESE DRAWINGS. THE CONTRACTOR SHALL BE RESPONSIBLE TO CALL ALL UTILITY COMPANIES (PUBLIC AND PRIVATE) PRIOR TO ANY CONSTRUCTION TO VERIFY EXACT UTILITY LOCATIONS. 2. REFER TO THE "FINAL DRAINAGE MEMORANDUM FOR FIRST STOP PLAZA" BY NORTHERN ENGINEERING, DATED OCTOBER 31, 2018 FOR ADDITIONAL INFORMATION. PROPOSED OUTFALL CURB & GUTTER T PROPOSED INFRASTRUCTURE BY OTHERS EXISTING MAJOR CONTOUR EXISTING MINOR CONTOUR PROPOSED STORM SEWER PROPOSED STORM INLET PROPOSED MAJOR CONTOUR PROPOSED MINOR CONTOUR PROPOSED PERMEABLE PAVERS A DRAINAGE BASIN LABEL BASIN DESIGNATION BASIN AREA (AC) DRAINAGE BASIN BOUNDARY B2 1.45 ac DESIGN POINT FLOW ARROWS PROPOSED STORM SEWER PROPOSED UNDERDRAIN UD THIS PROJECT DOES NOT MEET THE CITY'S LID REQUIREMENTS. UPON REDEVELOPMENT OF LOTS 1 & 2 FOR 1ST STOP MINOR SUBDIVISION, THE DEVELOPER SHALL PROVIDE LID IMPROVEMENTS FOR THAT PORTION OF THE DRIVEWAY, ASPHALT, PARKING LOT, AND CONCRETE THAT FALLS WITHIN THEIR PROPERTY. OFFSITE DRAINAGE FROM THE NORTH MUST BE MAINTAINED, CONVEYED, OR RE-ROUTED TO FLOW INTO THE NORTH EAST COLLEGE CORRIDOR OUTFALL STORM SEWER SYSTEM WITHIN SUNIGA DRIVE. REQUIRED WATER QUALITY VOLUME DESCRIPTION WATER QUALITY VOL. (FT3 ) WATER QUALITY VOL. (ACRES) LOT 1 669 0.015 LOT 2 285 0.0070 Coefficient Composite % Imperv. B 139,891 3.21 0.94 0.21 0.00 2.07 0.47 0.47 0.58 35% 2) Percent impervious are taken from Suniga Road Design, College Avenue to Blondel Street Drainage Memorandum prepare by Interwest Consulting Group. 100-year C f = 1.25 1) Runoff coefficients are taken from the Fort Collins Stormwater Criteria Manaual, Table 3.2.1 and Table 3.2.2. Composite Runoff Coefficient with Adjustment PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS 1st Stop Plaza F. Wegert September 12, 2018 9/12/2018 2:30 PM D:\Projects\1564-001\Drainage\Hydrology\1564-001_Rational Fort Collins.xlsx\Composite C