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HomeMy WebLinkAboutDrainage Reports - 01/21/2016MARTIN/MARTIN CONSULTING ENGINEERS January 18, 2016 Mr. Shane Boyle . Fort Collins Utilities - Stormwater 700 Wood Street Fort Collins, CO 80522 City of Fort Coll Approv tans Aprovei by. Re: Avago Technologies — Building 3 Drainage Letter describing changes for new stair tower addition Martin/Martin, Inc Project No.: 14.0833 Dear Mr. Boyle, This letter serves to inform you of the proposed changes to the approved "Avago Technologies —Building 3 and Site Development Drainage Report" by Martin/Martin, Inc. dated March 13, 2015 due to the addition of a stair tower. Specifically, the revised drainage report with a date of January 18, 2016 addresses the following revisions: Y Site tributary basins to the North and South Ponds showed an increase of imperviousness due to the stair tower addition and additional sidewalk paving adjacent.to stair tower addition. o The attached Proposed Impervious Area Exhibit summarizes the increase in impervious area and updates the required detention volumes for both ponds. Y Calculations were performed and determined that both the North and South Ponds would require no alterations to the pond size or outlet structure with the addition of the stair tower. I o The additional stormwater runoff created by the new impervious surface can be accommodated by the existing tolerances in the stormwater detention ponds. Please do not hesitate to call at 303.431.6100 or email at pbuckley@martinmartin.com should you have any questions or concerns. Sincerely, 1 Ryan Stratman, Peter Buckley, PE EIT Associate Attachments: 1— Proposed Impervious Area Exhibit Revised for Stair Tower Addition MARTIN/MARTIN, INC. 12499 WEST COLFAX AVENUE LAKEWOOD, COLORADO 80215 MAIN 303.431.6100 MARTINMARTIN.COM NORTH 412.630 SF DRIVES/WALKS= 67,786 SF (1.56 AC) +1,150 SF @ ® 90% IMP.= 1.40 AS 0 1.42 AC POROUS PAVERS= 22,639 SF (0.52 AC) ® 40% IMP.= 0.21 AC ROOF= 0 SF (0 AC) ® 90% IMP.=O AC LANDSCAPE= 322,205 SF (7.40 AC)-1,150 SF @ Oi ® 0% IMP.= 0 AC 71,098 1.63 AC NET IMPERVIOUS ACRES= 78,1132 SF (NET PROP. % IMP.=494-32-/^'n2,630=1 ) 71,098 413,780 17.18% 1 PRE -DEVELOPMENT NET IMPERVIOUS ACRES = 0.52 AC POST DEVELOPMENT NET IMPERVIOUS ACRES = 1.61- A 1.63 AC NET = + 1.09--AC 1.11 AC REQ'D DET. VOLUME = 0z42 (AG 0.246 AC - IMP. 1 I III SOUTH 656.570 SF +605 SF @ 90% IMP. DRIVES/WALKS- 225,564 SF (5.18 AC) ® 90% IMP. = 4.66 AG 4.67 AC a POROUS PAVERS= 29,045 SF (0.67 AC) J� 40% IMP. = 0.27 AC ROOF= 74,917 SF (1.72 AC)+574 SF @ 90% IM @ 90% IMP. = 1.55 AG -- 0- 1.56 AC LANDSCAPE= 327,044 SF (7.51 AC)-1,179 SF @ 0% IMP. ® 0% IMP. = 0 AC / i 283,112 6.50 AC NET IMPERVIOUS ACRES= 20269 (� SF 6AC) (NET PROP. % IMP.= 282-,2fT9/656�76=42.99%) 283,112 657,749 43.04% PRE -DEVELOPMENT NET IMPERVIOUS ACRES = 4.92 AC POST DEVELOPMENT NET IMPERVIOUS ACRES = 6.4=8-AG 6.50 AC NET = +1.56 A 1.58 AC REQ'D DET. VOLUME = 9.346 (AGFT) a Q A POST -DEVELOPMENT NORTH AREA 1 0.350 -FT POST -DEVELOPMENT SOUTH AREA 1 REVISED FOR STAIR TOWER 1 ADDITION 1 1 1 1 New Stair Tower I I 1 o PROPOSED IMPERVIOUS AREA ANALYSIS EXHIBIT FOR USE IN DETERMINING THE ADDED IMPER VIO US AREA FOR THE B3 DEVELOPMENT 0 KEY MAP DRIVES/WALKS l I ROOF L \ POROUS PAVERS f OVERALL 1.069.200 SF 295,105 SF (6.78 A( DRIVES/WALKS= 2-9��9�F 1 ��1 ® 90% IMP. = 6-66 AG 6.10 AC POROUS PAVERS= 51,684 SF (1.19 AC) o @ 40% IMP. = 0.48 AC 75,491 SF (1.73 Al >o ROOF= © 90% IMP. - 1.55-AE 1.56 AC LANDSCAPE- ) ® 0% IMP. = 0 AC 646,920 SF (14.85) NET IMPERVIOUS ACRES= $799Ae 8.14 AC PRE -DEVELOPMENT NET IMPERVIOUS ACRES = 5.44 AC POST DEVELOPMENT NET IMPERVIOUS ACRES = -8-69-Ae NET = +2765-A0 2.70 AC rollE .12r, REV. 1/18/16 11/15 _MARTIN/MARTIN CONSULTING ENGINEERS 12499 WEST COLFAX AVENUE, LAKEWOOD, COLORADO 80215 303.431,6100 MARTINMARTIN.COM