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Home My WebLink AboutStormwater Report Stormwater Report for Autumn Chase Subdivision General Location This tract is located on the on the undeveloped section of Cornell Street between Manuel Drive and Brentwood. Property Description The tract under consideration totals 8.35 acres of land and is currently vacant, abandoned pasture. It is bounded on the northwest by a developed multi - family housing subdivision KFO Addition, and on the southeast by a single - family subdivision, Brentwood. The tract is currently zoned PUD -2. Primary Drainage Basin Description The generally well - graded tract is near the highest point in the vicinity, with the top of the hill located approximately 300' from Dartmouth on the southeast side. Currently there are four drainage areas. The first area of 1.63 acres drains in a southwesterly direction in a sheet flow into the Brentwood Subdivision. Area two, which is 3.32 acres, and area three, which is 2.45 acres, drain in a northeasterly direction in a sheet flow into the Troy Subdivision. Area four which is .95 acres, drains in a southeasterly direction in a sheet flow in to the Bentwood Subdivision. Once the site has been altered for construction, the drainage areas will change, as will the direction, and amount of sheet flow across each area. The proposed project will consist of constructing two concrete detention facilities with a landscaped bottoms for the drainage from areas two and three. This project will not significantly alter the long standing drainage patterns. The Autumn Chase subdivision 8.35 acre tract is not within the flood plain as depicted on the current flood map, FEMA -FIRM Community Panel No. 48041C0144C, July 1992. The site is not generally considered to be a drainage problem. Drainage Facility Design (See Accompanying Runoff Calculations, Drawings, and Hydrographs). Drainage for Autumn Chase Subdivision is primarily sheetflow with an 18" controlled stormwater inlet. -.,,f; Zr Or r , ,� o r. S,, p , Y Y �` ar a Y a +s ,� s J� j ro�fr l C *ur w ia ♦�f#####® ® ®®®'►1 E. fl F\ 1- i- � erawnra i yy M T F O b e : :j t L Routing for Drainage Area Time - 1 Qpre Upost 18" V - Vtotal H Uweir ds/dt Vstorage Hstorage min in/hr cfs cfs cfs ft s C 0.35 0 0.00 0.00 0.00 0.00 0 0 0.00 C 0.61 5 5.75 11.59 23.22 1.00 3188 3188 0.50 A 5.76 ac 8 6.08 12.26 24.55 2.00 1853 5041 1.00 Apo, = 6.62 ac 11 6.40 12.90 25.84 2.00 1970 7011 14 7.05 14.21 28.47 2.00 2206 9217 15 9.90 19.96 39.98 2.00 1081 10298 18 ": depth flow 17 7.83 15.78 31.60 7.00 1059 11357 2.00 0.50 1.00 20 6.79 13.68 27.41 7.00 1211 12568 0.75 3.00 23 6.27 12.64 25.31 7.00 1022 13590 1.00 2.00 26 6.01 12.11 24.27 7.00 927 14517 1.25 1.80 29 5.88 11.85 23.74 7.00 880 15397 1.50 1.80 30 5.75 11.59 23.22 7.00 278 15675 2.5 2.00 7.00 31 0.00 0.00 0.00 7.00 -420 15255 3.00 9.00 34 0.00 0.00 0.00 7.00 -1260 13995 4.00 10.00 37 0.00 0.00, 0.00 7.00 -1260 12735 40 0.00 0.00 0.00 7.00 -1260 11475 43 0.00 0.00 0.00 7.00 -1260 10215 46 0.00 0.00 0.00 2.00 -360 9855 49 0.00 0.00 0.00 2.00 - 360 9495 52 0.00 0.00 0.00 2.00 -360 9135 55 0.00 0.00 0.00 2.00 -360 8775 58 0.00 0.00 0.00 2.00 - 360 8415 61 0.00 0.00 0.00 2.00 -360 8055 64 0.00 0.00 0.00 2.00 -360 7695 67 0.00 0.00 0.00 2.00 -360 7335 70 0.00 0.00 0.00 2.00 -360 6975 73 0.00 0.00 0.00 2.00 -360 6615 76 0.00 0.00 0.00 2.00 -360 6255 79 0.00 0.00 0.00 2.00 -360 5895 82 0.00 0.00 0.00 2.00 -360 5535 85 0.00 0.00 0.00 2.00 -360 5175 88 0.00 0.00 0.00 2.00 -360 4815 91 0.00 0.00 0.00 2.00 - 360 4455 94 0.00 0.00 0.00 2.00 -360 4095 97 0.00 0.00 0.00 2.00 -360 3735 100 0.00 0.00 0.00 2.00 -360 3375 103 0.00 0.00 0.00 1.00 -180 3195 106 0.00 0.00 0.00 1.00 -180 3015 109 0.00 0.00 0.00 1.00 -180 2835 112 0.00 0.00 0.00 1.00 -180 2655 115 0.00 0.00 0.00 1.00 -180 2475 Vol. (cf) 1 /3(Atop + Abottom + SQRT(Atop x Abottom)) x Depth Atop (sf) Abot. (sf) t x Ab (s Depth (ft) Volume (cf) Detention Volume Sum 1 6102 4760 29045520 1 5,412 5,412 2 7576 6102 46228752 1 6,819 12,231 3 9179 7576 69540104 1 8,356 20,587 4 10913 9179 1E+08 1 10,023 30,610 Res A 4528 440 1992320 0 - Total 30,610 O.K. Autumn Chase Subdivision 8.35 Acre Tract I. STORM WATER DETENTION BASIN SIZING: Rational Method (Q = CIA) 5 Year Storm Calculation Pre - Development Post - Development Assumptions 1 acre = 1 acre = : C = .35 I = 7.7 43560ft Assumptions: C = .85 I = 7.7 43560ft Area 0: Area 0: Description Ft Acres C I Description Ft Acres C I Grassland 174576 4.01 0.85 7.7 Grassland 174576 4.01 0.85 7.7 Q = 26.23 Q = 26.23 Area Area 1: Description Ft Acres C I Description Ft Acres C I Grassland 71177 1.63 0.35 7.7 Impervious 28883 0.66 0.85 7.7 Q = 4.40 Q = 4.34 Area 2: Area 2: Description Ft Acres C I Description Ft Acres C I Grassland 144119 3.31 0.35 7.7 Impervious 155632 3.57 0.85 7.7 Q = 8.92 Q = 23.38 Area 3: Area 3: Description Ft Acres C I Description Ft Acres C I Grassland 106621 2.45 0.35 7.7 Impervious 132736 3.05 0.85 7.7 Q = 6.60 Q = 19.94 Area 4: Area 4: Description Ft Acres C I Description Ft Acres C I Grassland 41354 0.95 0.35 7.7 Impervious 28101 0.65 0.85 7.7 Q= 2.56 Q= 4.22 Intensity Required Frequency (in/in) Cpre Cpost Qpre Qpost Vpre(cf) Vpost Storage (years) (Tc =10 (cfs) (cfs) (cf) Volume min) 5 7.7 0.35 0.85 22.48 51.89 20,228 46,701 26,473 Autumn Chase Subdivision 8.35 Acre Tract I. STORM WATER DETENTION BASIN SIZING: Rational Method (Q = CIA) 10 Year Storm Calculation Pre - Development Post - Development 1 acre = 1 acre = Assumptions: C = .35 I = 8.6 43560ft Assumptions: C = .85 I = 8.6 43560ft Area 0: Area 0: Description Ft Acres C I Description Ft Acres C I Grassland 174576 4.01 0.85 8.6 Grassland 174576 4.01 0.85 8.6 Q = 29.30 Q = 29.30 Area 1: Area 1: Description Ft Acres C I Description Ft Acres C I Grassland 71177 1.63 0.35 8.6 Impervious 28883 0.66 0.85 8.6 Q = 4.92 Q = 4.85 Area 2: Area 2: Description Ft Acres C I Description Ft Acres C I Grassland 144119 3.31 0.35 8.6 Impervious 155632 3.57 0.85 8.6 Q = 9.96 Q = 26.12 Area 3: Area 3: Description Ft Acres C I Description Ft Acres C I Grassland 106621 2.45 0.35 8.6 Impervious 132736 3.05 0.85 8.6 Q = 7.37 Q = 22.27 Area 4: Area 4: Description Ft Acres C I Description Ft Acres C I Grassland 41354 0.95 0.35 8.6 Impervious 28101 0.65 0.85 8.6 Q = 2.86 Q = 4.72 Intensi Required Frequency (in/in) Cpre Cpost Qpre Qpost Vpre(cf) Vpost(cf) Storage ears ) (cfs) (y (Tc =10 min) (cfs Volume 10 8.6 0.35 0.85 25.10 57.96 22,592 52,160 29,568 Autumn Chase Subdivision 8.35 Acre Tract I. STORM WATER DETENTION BASIN SIZING: Rational Method (Q = CIA) 25 Year Storm Calculation Pre - Development Post - Development 1 acre = 1 acre = Assumptions: C = .35 I = 9.9 43560ft Assumptions: C = .85 I = 9.9 43560ft Area 0: Area 0: Description Ft Acres C I Description Ft Acres C I Grassland 174576 4.01 0.85 9.9 Grassland 174576 4.01 0.85 9.9 Q = 33.72 Q = 33.72 Area 1: Area 1: Description Ft Acres C I Description Ft Acres C I Grassland 71177 1.63 0.35 9.9 Impervious 28883 0.66 0.85 9.9 Q= 5.66 Q= 5.58 Area 2: Area 2: Description Ft Acres C I Description Ft Acres C I Grassland 144119 3.31 0.35 9.9 Impervious 155632 3.57 0.85 9.9 Q = 11.46 Q = 30.07 Area 3: Area 3: Description Ft Acres C I Description Ft Acres C I Grassland 106621 2.45 0.35 9.9 Impervious 132736 3.05 0.85 9.9 Q = 8.48 Q = 25.64 Area 4: Area 4: Description Ft Acres C I Description Ft Acres C I Grassland 41354 0.95 0.35 9.9 Impervious 28101 0.65 0.85 9.9 Q= 3.29 Q= 5.43 Intensity Required Frequency (in/in) Qpre Qpost Vpost (years) (Tc =10 Cpre Cpost (cfs) (cfs) Vpre(cf) (cf) Storage min) Volume 25 9.9 0.35 0.85 28.90 66.72 26,007 60,044 34,037 Autumn Chase Subdivision 8.35 Acre Tract I. STORM WATER DETENTION BASIN SIZING: Rational Method (Q = CIA) 50 Year Storm Calculation Pre - Development post- Development 1 acre = Assumptions 1 acre = Assumptions: C = .35 I = 11.1 43560ft2 : C = .85 I = 11.1 43560ft Area 0: Area 0: Description Ft Acres C I Description Ft Acres C I Grassland 174576 4.01 0.85 11.1 Grassland 174576 4.01 0.85 11.1 Q= 37.81 Q= 37.81 Area 1: Area 1: Description Ft Acres C I Description Ft Acres C I Grassland 71177 1.63 0.35 11.1 Impervious 28883 0.66 0.85 11.1 Q= 6.35 Q= 6.26 Area 2: Area 2: Description Ft Acres C I Description Ft Acres C 1 Grassland 144119 3.31 0.35 11.1 Impervious 155632 3.57 0.85 11.1 Q = 12.85 Q = 33.71 Area 3: Area 3: Description Ft Acres C I Description Ft Acres C I Grassland 106621 2.45 0.35 11.1 Impervious 132736 3.05 0.85 11.1 Q = 9.51 Q = 28.75 Area 4: Area 4: Description Ft Acres C I Description Ft Acres C 1 Grassland 41354 0.95 0.35 11.1 Impervious 28101 0.65 0.85 11.1 Q = 3.69 Q = 6.09 Intensity Frequency (in/in) Qpre Qpost Vpost Required (years) (Tc =10 Cpre Cpost (cfs) (cfs) Vpre(cf) (co Storage min) Volume 50 11.1 0.35 0.85 32.40 74.80 29,159 67,322 38,163 Autumn Chase Subdivision 8.35 Acre Tract I. STORM WATER DETENTION BASIN SIZING: Rational Method (Q = CIA) 100 Year Storm Calculation Pre - Development Post - Development 1 acre = 1 acre = Assumptions: C = .35 I = 12.6 43560ft Assumptions: C = .85 I = 12.6 43560ft Area 0: Area 0: Description Ft Acres C I Description Ft Acres C I Grassland 174576 4.01 0.85 12.6 Grassland 174576 4.01 0.85 12.6 Q = 42.92 Q = 42.92 Areal: Areal: Description Ft Acres C I Description Ft Acres C I Grassland 71177 1.63 0.35 12.6 Impervious 28883 0.66 0.85 12.6 Q= 7.21 Q= 7.10 Area 2: Area 2: Description Ft Acres C I Description Ft Acres C I Grassland 144119 3.31 0.35 12.6 Impervious 155632 3.57 0.85 12.6 Q = 14.59 Q = 38.26 Area 3: Area 3: Description Ft Acres C I Description Ft Acres C I Grassland 106621 2.45 0.35 12.6 Impervious 132736 3.05 0.85 12.6 Q = 10.79 Q = 32.64 Area 4: Area 4: Description Ft Acres C I Description Ft Acres C I Grassland 41354 0.95 0.35 12.6 Impervious 28101 0.65 0.85 12.6 Q = 4.19 Q = 6.91 Fre uenc Intsity q y (in/in) (Tc =10 Cpre Cpost QPre Qpost Vpre(ct) Vpost(cf) Required Storage (years) ) (cfs) (efs) Volume 100 2n6 0.35 0.85 36.78 84.91 33,100 76,420 43,320 ENGINEER'S OPINION OF CONSTRUCTION COSTS AUTUMN CHASE - CORNELL & PURDUE DRIVE PROJECT PO2CS140 BIDDER TEXCON ITEM NO I BID ITEM DESCRIPTION 1 EST QTY 1 UNIT UNIT PRICE 1 TOTAL omeli Drive (80' ROW) - 540 LP STREET / DRAINAGE Common Excavation 1500 CY $ 3.00 $ 4,500.00 Lime Stabilization 3000 SY $ 3.00 $ 9,000.00 7" Reinforced Concrete Pavement 2280 SY $ 29.25 24" Concrete Curb & Gutter 1080 LF $ 7.00 $ 7,560.00 4" Reinforced Concrete Sidewalk 720 SY $ 22.50 $ 16,200.00 4' x 6' Precast Concrete Box 360 LF $ 100.00 $ 36,000.00 Erosion and Sediment Control 1 LS $ 2,500.00 $ 2,500.00 Type "D "Hmac, 1.5" Surface Course 2100 SY $ 5.50 $ 11,550.00 7" Flex Base 2100 SY $ 10.50 $ 22,050.00 Common Excavation 4 EA $ 80.00 $ 320.00 33" Storm Sewer 540 LF $ 16.00 $ 8,640.00 Junction Boxes 2 EA $ 80.00 $ 160.00 WATER 6" Fire Hydrant Assembly 1 EA $ 2,200.00 $ 2,200.00 8" PVC Waterline 175 LF $ 16.00 $ 2,800.00 8" PVC Waterline with Structural Fill 120 LF $ 25.00 $ 3,000.00 Connections, Single 4 EA $ 400.00 $ 1,600.00 SEWER Sanitary Sewer Manhole 6 EA $ 2,000.00 $ 12,000.00 6" Sanitary Sewer Cleanout 1 EA 6" PVC Sanitary Sewer (Duffel!) 205 LF $ 20.00 $ 4,100.00 6" PVC Sanitary Sewer 400 LF $ 20.00 $ 8,000.00 6" PVC Sanitary Sewer with Structural Fill 60 LF $ 29.00 $ 1,740.00 Connections, Double 2 EA $ 500.00 $ 1,000.00 CORNELL SUBTOTAL $ 154,920.00 urdue Drive (50' ROW) - 340 LF STREET / DRAINAGE Common Excavation 1059 CY $ 3.00 $ 3,178.33 Lime Stabilization 2119 SY $ 3.00 $ 6,356.67 6" Reinforced Concrete Pavement 1892 SY $ 27,00 24" Concrete Curb & Gutter 994 LF $ 7.00 $ 6,958.00 4" Reinforced Concrete Sidewalk 227 SY $ 22.50 $ 5,100.00 Type "D" Hmac, 1.5" Surface Course 1707 SY $ 4.50 $ 7,679.57 6" Flex Base 1707 SY $ 7.50 $ 12,799.28 Common Excavation 4 EA $ 80.00 $ 320.00 33" Storm Sewer 540 LF $ 16.00 $ 8,640.00 Junction Boxes 2 EA $ 80.00 $ 160.00 WATER 6" Fire Hydrant Assembly 1 EA $ 2,200.00 $ 2,200.00 6" PVC Waterline 415 LF $ 18.00 $ 7,470.00 6" PVC Waterline with Structural Fill 60 LF $ 27.00 $ 1,620.00 Connections, Single 4 EA $ 400.00 $ 1,600.00 Connections, Double 5 EA $ 500.00 $ 2,500.00 SEWER 6" PVC Sanitary Sewer 260 LF $ 20.00 $ 5,200.00 6" PVC Sanitary Sewer with Structural Fill 35 LF $ 29.00 $ 1,015.00 6" Sanitary Sewer Cleanout 1 EA $ 750.00 $ 750.00 Connections, Single 2 EA $ 400.00 $ 800.00 Connections, Double 3 EA $ 500.00 $ 1,500.00 PURDUE SUBTOTAL $ 73,546.85 TOTAL $ 228,000 ENGINEER'S OPINION OF CONSTRUCTION COSTS AUTUMN CHASE • CORNELL & PURDUE DRIVE PROJECT PO2CS140 BIDDER TEXCON ITEM NO I BID ITEM DESCRIPTION I EST QTY I UNIT UNIT PRICE I TOTAL omelt Drive (70' ROW) - 540 LF I I I STREET /DRAINAGE Common Excavation 1980 CY $ 3.00 $ 5,940.00 Lime Stabilization 3960 SY $ 3.00 $ 11,880.00 7" Reinforced Concrete Pavement 3240 SY $ 29.25 24 "Concrete Curb & Gutter 1080 LF $ 7.00 $ 7,560.00 4" Reinforced Concrete Sidewalk 720 SY $ 22.50 $ 16,200.00 4' x 6' Precast Concrete Box 360 LF $ 100.00 $ 36,000.00 Erosion and Sediment Control 1 LS $ 2,500.00 $ 2,500.00 Type "D" Hmac, 1.5" Surface Course 3000 SY $ 5.50 $ 16,500.00 10" Flex Base 3000 SY $ 12.50 $ 37,500.00 Common Excavation 4 EA $ 80.00 $ 320.00 33" Storm Sewer 540 LF $ 16.00 $ 8,640.00 Junction Boxes 2 EA $ 80.00 $ 160.00 WATER 6" Fire Hydrant Assembly 1 EA $ 2,200.00 $ 2,200.00 8" PVC Waterline 175 LF $ 16.00 $ 2,800.00 8" PVC Waterline with Structural Fill 120 LF $ 25.00 $ 3,000.00 Connections, Single 4 EA 400 $ 1,600.00 SEWER Sanitary Sewer Manhole 6 EA $ 2,000.00 $ 12,000.00 6" Sanitary Sewer Cleanout 1 EA 6" PVC Sanitary Sewer (Outfall) 205 LF $ 20.00 $ 4,100.00 6" PVC Sanitary Sewer 400 LF $ 20.00 $ 8,000.00 6" PVC Sanitary Sewer with Structural Fill 70 LF $ 29.00 $ 2,030.00 Connections, Double 2 EA $ 500.00 $ 1,000.00 CORNELL SUBTOTAL $ 179,930.00 urdue Drive (50' ROW) 340 LF STREET /DRAINAGE Common Excavation 1059 CY $ 3.00 $ 3,178.33 Lime Stabilization 2119 SY $ 3.00 $ 6,356.67 6" Reinforced Concrete Pavement 1892 SY $ 27.00 24" Concrete Curb & Gutter 994 LF $ 7.00 $ 6,958.00 4" Reinforced Concrete Sidewalk 227 SY $ 22.50 $ 5,100.00 Type "D" Hmac, 1.5" Surface Course 1707 SY $ 4.50 $ 7,679.57 7" Flex Base 1707 SY $ 7.50 $ 12,799.28 Common Excavation 4 EA $ 80.00 $ 320.00 33" Storm Sewer 540 LF $ 16.00 $ 8,640.00 Junction Boxes _ 2 EA $ 80.00 $ 160.00 WATER 6" Fire Hydrant Assembly 1 EA $ 2,200.00 $ 2,200.00 8" PVC Waterline 415 LF $ 18.00 $ 7,470.00 8" PVC Waterline with Structural Fill 60 LF $ 27.00 $ 1,620.00 Connections, Single 4 EA $ 400.00 $ 1,600.00 Connections, Double 5 EA $ 500.00 $ 2,500.00 SEWER 6" PVC Sanitary Sewer 260 LF $ 20.00 $ 5,200.00 6" PVC Sanitary Sewer with Structural Fill 35 LF $ 29.00 $ 1,015.00 6" Sanitary Sewer Cleanout 1 EA $ 750.00 $ 750.00 Connections, Single 2 EA $ 400.00 $ 800.00 Connections, Double 3 EA $ 500.00 $ 1,500.00 PURDUE SUBTOTAL $ 73,546.85 TOTAL $ 253,000 SI GROUP LP Engineering ♦ Environmental Science 7010 Northwest 100 Drive Suite A -107 Houston, TX 77082 PH (713) 895 -7999 November 11, 2002 FAX (713) 895 -9214 1701 Southwest Parkway Suite 100 College Station, TX 77840 PH (979) 695-91 Development Services Department FAX (979) 696-4513 City of College Station 8245 Gladys Avenue P.O. Box 9960 Suite 206 College Station, Texas 77842 Beaumont, TX 77706 PH (409 861 -4772 Attn: Bridgette George, Assistant Development Manager FAX (409) 861 -4773 Ref: Request for Oversize Participation for Final Plat of Autumn Chase Subdivision 8.353 Acre Tract Morgan Rector League, A -46 College Station, Brazos County, Texas SI Group Proj. No. 02CS140.8 Dear Ms. George: This letter serves as a notice of the request for oversize participation. The request consists of going from a 60 foot Right -of -Way (R.O.W.) to a 70 foot R.O.W. This increase results in street oversize of 38 feet to 54 feet. Unique Strategies understands that the City of College Station pays for any additional costs due to the oversize participation. The additional cost of oversize participation is approximately $25,000. The details of the these costs can be found in our Costs spreadsheet. If you have any questions or comments, please contact me at 695 -9100. Sincerely, SI Group, LP Edward R. McDow, Jr., P.E., R. .L.S. Senior Engineer xc: Dan Bensimon, Autumn Chase L.L.P.