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Home My WebLink About43 Drainage Report Wal-Mart 150 Expansion 1815 Brothers BlvdDRAINAGE REPORT For College Station Wal-Mart #11 50 Expansion 1815 Brothers Bl vd College Station, Texas Report -October 10 , 2008 /o-rc-6~ Prepared by: Doucet & Associates, Inc. 7401 B Hwy. 71 W., Suite 160 Austin, Texas 78735 Project No. 001-402 TABLE OF CONTENTS Introduction ..................................................................................... 3 Existing Conditions ............................................................................. 3 Propo sed Conditions ........................................................................... 3 Conclusion ....................................................................................... 4 Appendix A -Drainage Area Map ............................................................ 5 Appendix B -Proposed/Existing Flow Chart ............................................... 6 2 INTRODUCTION The existing College Station Wal-Mart project encompasses 23.24 acres of property, lots 1-4 located at the intersection of Longmire Street and Brothers Blvd in College Station, Texas. This property is currently in the city limits and is to go through re-platting with the City of College Station to better accommodate the new development. Wal-Mart is proposing a 63 ,936SF expansion to the existing Wal-Mart Store #1150 to make it a Supercenter. There currently resides within the development an Albertson's building in which Wal-Mart is purchasing. The expansion area will occur in the direction of Albertsons engulfing approximately 6500sf of the Albertsons building. The remainder of the Albertsons building is to be converted to retail and storage. There is also proposed outlets 1 & 2 that are to be developed as well totaling 3 .4 acres. EXISTING CONDITIONS The existing drainage for the 23 .24 acre site drains into existing storm lines that intersect the property along the front of both the Albertsons and the Wal-Mart buildings. These 42" storm lines run East and across Longmire Drive and serve an 18.30 acre development to the West. This same system serves the existing Albertsons parking and Wal-Mart parking fields and the current Schlotskys and the Church 's Chicken. There are 3-48" RCP storm lines in front of the Wal-Mart that are to remain. These lines run into a City detention pond to the East. The detention pond drains into ditches within the Texas Avenue ROW. PROPOSED CONDITIONS There is currently planned a 64,000SF expansion to the Wal-Mart building. The expansion would occur to the West of the existing store and take up a portion of the Albertsons building. Approximately 238' of the two 42" storm lines that run in this area would require relocation to accommodate the proposed expansion but would tie back into the existing storm network. The proposed expansion and the ultimate development of outlets 1 &2, will create more impervious cover and would require additional detention volume to accommodate the difference. Assumptions of 80% impervious cover were 1 made to calculate the additional detention volume needed for the outlots. There are . currently no designated tenants for these outlets. There is currently not enough room to expand the existing City owned detention pond. An additional 35 ,352cf earthen pond within the parking field is proposed to accommodate the additional developed flows. Pe City of College Station requirements, the proposed detention pond has been designed to handle fully developed 1 OOyr flows and mitigate storm events 2yr through 1 OOyr flows for the 4.12 acres of additional planned impervious development. The pond will utilize an outlet structure consisting of a V-Notch Weir and orifices to control flows out of the pond with an emergency overflow weir. The maximum water surface elevation within the pond will be 1' below the top of the pond providing 1' of freeboard. Since direct access to this pond isn't feasible, a portion of the existing parking field has been routed to the proposed pond and detained to match the flow characteristics of the fully developed 4.12acre. Portions of the existing parking field are the be re-graded also to accommodate 3 the expansion area to the front of the Wal-Mart and new sump curb inlets have been added to the site with an additional storm network further north in the parking field. This line would remove some of the drainage from the 3-48" existing storm lines directly in front of the Wal-Mart building as well as serve the outlet from the proposed lOOyr detention pond . The proposed network would tie back into the existing storm network just before the existing detention pond. Please refer to Appendix A for drainage area map . CONCLUSION With the proposed 35,352 cubic feet detention pond, the future proposed expansion/development will not adversely impact the existing drainage system. Developed runoff from the additional 4.12acre impervious development including the Wal-Mart expansion and developed outlots 1 & 2 have been accounted for in the pond calculations. The proposed flows will be detained to match existing flows to the existing pond and downstream drainage system. Bentley, Pond Pack was used to design the detention pond with an SCS Type III 24hr storm event and rainfall intensities and storm characteristics were input with storm data for College Station, Brazos County. A master network summary has been provided for reference under Appendix B including Tc, C values and resulting flow rates. 4 APPENDIX A 1. Drainage Area Map. 5 APPENDI X B 1. Master Network Summary & Calculations for Proposed Detention Pond 6 Table of Contents i ********************** MASTER SID.fMA.RY ********************** Watershed ....... Master Network Summary ............ . 1. 01 ********************** TC CALCULATIONS ********************* OUTLOTS 1&2 ..... Tc Cales 2.01 ********************** CN CALCULATIONS ********************* OUTLO TS 1&2 ..... Runoff CN-Area 3.01 *********************** POND VOLUMES *********************** POND 10 ......... Vol: Elev-Area .................... . 4.01 ******************** OUTLET STRUCTURES ********************* Outlet 1 ........ Outlet Input Data ................. . 5 .01 *********************** POND ROUTING *********************** POND 10 ......... Pond E-V-Q Table .................. . 6.01 S I N: 7AYXYW J3CNA2 Bentley PondPack (10 .00.023.00) 9:14 AM Bentley Systems, Inc. 10 /10 /2008 Table of Contents i MASTER DESIGN STORM SUMMARY Network Storm Collection: College Station Total Depth Rainfall Return Event in Type RNF ID -------------------------------------------------- Dev 2 Dev 10 Dev 25 DevlOO 3.4400 Synthetic Curve TypeIII 6.1000 Synthetic Curve TypeIII 7.6400 Synthetic Curve TypeIII 10.2000 Synthetic Curve TypeIII MASTER NETWORK SUMMARY SCS Unit Hydrograph Method (*Node=Outfall; +Node=Diversion;) 24hr 24hr 2 4hr 24hr (Trun= HYG Truncation: Blank=None; L=Left; R=Rt; LR=Left&Rt) Return HYG Vo l Qpeak Qpeak Node ID Type Event ac-ft Trun hrs cf s -------------------------------------------------- *OUT 10 JCT 2 .760 12.3500 3 .72 *OUT 10 JCT 10 1. 621 12.2000 12.86 *OUT 10 JCT 25 2.134 12 .1500 17.93 *OUT 10 JCT 100 2.996 12.1500 25 .13 OUTLOTS 1&2 AREA 2 .760 12.1000 9.31 OUTLOTS 1&2 AREA 10 1. 621 12.1000 19.05 OUTLO T S 1&2 AREA 25 2 .134 12.1000 24.63 OUTLOTS 1&2 AREA 100 2.997 12.1000 33.83 PO ND 10 IN POND 2 .760 12.1000 9 .31 POND 10 IN POND 10 1. 621 12.1000 19.05 POND 10 IN POND 25 2 .134 12.1000 24.63 PO ND 10 IN POND 100 2.997 12.1000 33 .83 S I N: 7AYXYWJ3CNA2 Bentley PondPack (10.00.023.00) 9 :14 AM Max Max WSEL Pond Storage ft ac-f t -------------------- Bentley Systems, Inc. 10 /10 /2008 Type .... Master Network Swrnnary Page 1.01 Name .... Watershed File .... P:\001-402 \en.gineering \drainage \pondpack \001-402 College Station Post Cond.ppw MASTER NETWORK SUMMARY SCS Unit Hydrograph Method (*Node=Outfall; +Node=Diversion;) (Trun= HY G Truncation: Blank=None; L=Left; R=Rt; LR=Left &Rt) Return HYG Vol Qpeak Qpeak Node ID Type Event ac-ft Trun hrs cfs -------------------------------------------------- POND 10 OUT POND 2 .760 12.3500 3.72 POND 10 OUT POND 10 1. 621 12.2000 12 .86 POND 10 OUT POND 25 2 .134 12 .1500 17.93 POND 10 OUT POND 100 2.996 12.1500 25 .13 S /N: 7AYXYWJ3CNA2 Bentley PondPack (10.00.023.00) 9:14 AM Max Max WSEL Pond Storage ft ac-ft -------------------- 272 .4 7 .241 273.26 .396 273 .58 .464 274 .06 .571 Bentley Systems, Inc . 10 /10 /2008 Type .... Master Network Summary Page 1.02 Name .... Watershed File .... P:\001-402 \engineering \dra inage \pondpack \001 -4 02 College Station Post Cond.ppw : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : TIME OF CONCENTRATION CA LCULATOR ....................................................... " ............... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Segment #1: Tc: User Defined Segment #1 Time: .0833 hrs Total Tc: .0833 hrs Calculated Tc < Min.Tc: Use Minimum Tc ... Use Tc = .0833 hrs S I N: 7AYXYWJ3CNA2 Bentley Systems, Inc. Bentley PondPack (10.00.023.00) 9:14 AM 10 /10 /2 008 Type .... Tc Cales Page 2.01 Name .... OUTLOTS 1&2 File .... P:\001-402 \engineering \drainage\pondpack\001-402 College Station Post Co n d.ppw Tc Equations used ... User Def ined ====================================================== Tc = Valu e entered by user Where: Tc = Time of concentration S /N: 7AYXYWJ3CNA2 Bentley PondPack (10 .00.02 3 .0 0) 9:14 AM Bentley Systems, Inc. 10 /10 /2008 Type .... Tc Cales Page 2.02 Name .... OUTLOTS 1&2 File .... P:\001-402 \engineering \drainage \pondpack \001-402 College Station Post Cond.ppw RUNO FF CURVE NUMBER DATA .......................................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soil /Surface De scription CN Parking Field Equivalent to Out lets 88 COMPOSITE AREA & WEIGHT ED CN ---> Area acre s 4.120 4.120 Impervious Adj u stme n t %C %UC Adj u sted CN 88.00 88.00 (88) ........................................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S/N: 7AYXYWJ3CNA2 Bentley PondPa ck (10 .00.023.00) 9 :14 AM Bentley Systems, Inc. 10 /10 /2008 Type .... Runoff CN-Area Page 3.01 Name .... OUTLOTS 1&2 File .... P :\001-402 \engineering \drainage \pondpack\001-402 College Station Post Cond .ppw Elevation (ft) 2 71 .00 272.00 273.00 27 4 .00 275.00 Planimeter (sq.in) Area Al+A2+sqr(Al*A2) (acres) (acres} .1449 .0000 .171 3 .4739 .1995 .5557 .2293 .6426 .2609 .734 7 POND VOLUME EQUATIONS Volume (ac-ft} .000 .158 .185 . 214 .245 Volume Sum (ac -f t} .000 .158 .343 .557 .802 * Incremental volume compu ted by the Conic Method for Reservoir Vol umes . Volume = (1 /3) * (EL 2-EL1} * (Areal + Area2 + sq.rt. (Areal*Area2}} where: ELl, EL 2 Areal,Area2 Volum e S /N: 7AYXYWJ3CNA2 = Lower and upper elevations o f the increment Areas computed for ELl, EL 2, respectively = Incremental volume between ELl and EL2 Bentley PondPack (10.00 .0 23.00) 9 :14 AM Bentley Systems, Inc. 10 /10 /2008 Type .... Vo l : Elev-Area Page 4 .01 Name .... POND 10 File .... P :\001-402 \engineering \d ra inage \pondpack \001 -4 0 2 College Station Post Cond.ppw REQUESTED POND WS ELEVATIONS: Min. Elev.= Increment = Max. Elev.= 271. 00 ft .5 0 ft 275 .00 ft ********************************************** OU TLET CO NNECTI VITY ********************************************** ---> F orward Fl ow Only (Upstream to DnStream) <---Reverse Flow Only (DnStream to Ups tream) <---> Forward and Reverse Both Allowed Structure No . Out fa ll El, ft E2, f t ------------------------------------------ Or if ice-Circular 01 ---> CV 271. 000 2 75.00 0 Weir-Vnotch Wl ---> CV 271. 750 275 .000 Or if ice-Circular 02 ---> CV 272 .4 00 275.000 Culvert-Circular CV ---> TW 269.500 275 .0 00 TW SETUP, DS Channe l S /N: 7AYXYWJ3CNA2 Bentley PondPack (10.00.023.00) 9 :14 AM Bentley Systems, Inc . 10 /1 0 /2008 Type .... Outlet Input Data Page 5.01 Name .... Outlet 1 File .... P:\001-402 \engineering \drainage \pondpack \001-402 College Station Post Cond.ppw OUTLET STRUCTURE INPUT DATA Structure ID Structure Type # of Openings Invert Elev. Diameter Orifice Coeff. Structure ID Structure Type # of Openings No tch Elev. Not ch Angle Wei r Coeff. Weir TW effects Structure ID Structure Type # of Openings Invert Elev. Diameter Orifice Coeff. S /N: 7AYXYWJ3CNA2 Bentley PondPack (10.00.0 23 .00) = 01 = Orifice-Circular = Wl 1 271.00 ft .8333 ft .600 = Weir-Vnotch 1 271.75 ft 30 .000 degrees 2 .000000 (Use adjustment equation) = 02 = Orifice-Circular 1 272.40 ft 1 .5 000 ft .600 9:14 AM Bentley Systems, Inc . 10 /10 /2008 Type .... Outlet Inpu t Data Pag e 5.0 2 Name .... Outlet 1 OUTLET STRUCTUR E INPUT DATA = CV Structure ID Structure Type = Culvert-Circular No. Barrels Barrel Diameter Up stream Invert Dnstream Invert Horiz. Length Barrel Length Barrel Slope OUTLET CONTROL DATA ... Mannings n Ke Kb Kr HW Convergence INLET CONTROL DATA ... Equation form Inl et Control K Inlet Control M Inlet Control c Inlet Con trol Y Tl ratio (HW /D} T2 ratio (HW /D) Slope Factor 1 2.0000 269.50 268.00 100.00 100.01 .01500 . 0130 .5000 . 012411 .5000 .001 1 .0078 2.0000 .03 790 .6900 1.128 1. 289 -.500 ft ft ft ft ft ft /ft (forward entrance loss) (per ft of ful l flow) (reverse entrance loss) +/-ft Use unsubmerged inlet control Form 1 equ. below Tl elev. Use submerged inlet control Form 1 equ. above T2 elev. In transition zone between unsubmerged and submerged inlet control, interpolate b etween flows at Tl & T2 ... At Tl Elev 271 .76 ft ---> Flow 15.55 cfs At T2 Elev= 2 72.08 ft ---> Flow= 17.77 cfs = TW Structure ID Structure Type = TW SETUP, DS Channel FREE OUTFALL CONDITIONS SPECIFI ED CONVERGENCE TOLERANCES ... Maximum Iterations= 40 Min. TW tolerance .01 ft Max. TW tolerance .01 ft Min . HW tolerance .01 ft Max . HW tolerance .01 ft Min. Q tolerance .00 cf s Ma x . Q tolerance .00 cf s S /N: 7AYXYWJ3CNA2 Bentley PondPack (10.00.023.00 ) 9:14 AM Bentley Systems, Inc. 10 /10 /2008 Type .... Outlet Input Data Name .... Outlet 1 HYG Dir Inflow HYG file Outflow HYG file Pond Node Data Pond Volume Data Pond Outlet Data No Infiltration INITIAL CONDITIONS Starting ws Elev Starting Vol ume Starting Outflow Starting Infiltr. LEVEL POOL ROUTING DATA P:\001-402 \engineering \drainage \pondpack\ work_pad.hyg POND 10 IN Dev 2 work_pad.hyg -POND 10 OUT Dev 2 POND 10 POND 10 Outlet 1 271. 00 .000 .00 .00 ft ac-ft cfs cfs Starting Total Qout= .00 cfs Time Elevation ft Increment Outflow cfs .0500 Storage ac-f t hrs Area acres Infilt. cf s Q To tal cf s Page 5.03 2S /t + 0 cf s ------------------------------------------------------------------------------ 271. 00 .00 .000 .144 9 271. 50 .68 .07 6 .1579 271. 75 1. 37 .116 .1645 272 .00 2.07 .158 .1713 272 .40 3.38 .229 .1823 272 .50 3 .89 .247 .1851 273.00 8.69 .343 .1995 273 .50 16.65 .447 .2141 274.00 24 .7 0 .557 .2293 274.50 28.44 . 676 .2448 275.00 31. 47 .802 .2 609 S /N: 7AYXYWJ3CNA2 Bentley PondPack (10.00.023.00) .00 .00 .00 .68 .00 1. 37 .00 2 .07 .00 3.38 .00 3 .89 .00 8.69 .00 16.65 .00 24.70 .00 28 .44 .00 31.47 9:14 AM .00 37.30 57.50 78.52 114. 06 123.46 174.79 232.78 294.47 355.58 419 .79 Bentley Systems, Inc. 10 /10 /2008 Type .... Pond E-V-Q Table Page 6 .01 Name .... POND 10 File .... P:\001-402 \engineering \drainage \pondpack \001-402 College Station Post Cond.ppw -----0 ----- Outlet 1 ... 5 .0 1 OUTLOTS 1&2 ... 2.01, 3.0 1 -----p POND 10 ... 4.01, 6.01 -----w ----- Watershed ... 1.01 S I N: 7AYXYWJ3CNA2 Bentley PondPack (10.00.023.00) 9:14 AM Bentley Systems, Inc. 10/10 /2008 PondMaker Design Wizard R t I Target I Peak J Peak OJt I Maxinu:l Freeboard I Maxinum E~~~J Peak 1 OJtflow I vs f Elevation Depth Storage ___ ·--<:~>_j_(cfs) __ .L Target ·"~~----~tt._> ____ _J_~~c-ft~) -· 2 3.9276 3.7184 PASS 272 .46628 PASS 0.24083 10 11.7710 12 .8563 PASS 273.26187 PASS 0.39641 25 16 .7526 17 .9312 PASS 273 .57986 PASS 0.46376 100 25 .2666 25.1267 PASS 274 .05756 PASS 0.57064 PondMaker Design Wizard R 1 1· Pre Dev J Pre Dev 1 : Post Dev 1 • P~ Total I Estirrated I l nterp. W.S . f Freeboard e um Peak · Volurre Peak Volurre Storage j Elev. ! Depth Event J' (cfs) i (ac-ft) (cfs) I (ac-ft) (ac-ft) (ft) I (ft) ·-----·'·-··-·---~·------····-.l-.---~-1--··------'----··-·----·· ---·-·--··-----~· --·---··---- 2 3.9276 0.37146 9 .3083 0 .76011 0.23665 272.4249 PASS 10 11.7710 1.05589 19.0486 1.62125 0 .33734 272.9684 PASS 25 16.7526 1.50392 24.6342 2 .13433 0.41473 273 .3340 PASS 100 25 .2666 2.29004 33.8284 2.99668 0.51085 273 .7827 PASS (i) 13 40 · 30 - -; 20 T 0 ' u::: I 10 1 0 I ,.~ -, i--t--1- Hydrograph ROUTE10 I ' DEV100 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Time (hrs ) 40 · 30 ·1 :§' I ; 20 4 ..Q LL I 10 - Hydrograph POND 10 OUT DEV100 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Time (hrs)