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HomeMy WebLinkAboutFRONT RANGE COMMUNITY COLLEGE, PARKING LOT EXPANSION - SITE PLAN ADVISORY REVIEW - 10-06 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPond Spillway Calculations Worksheet for Broad Crested Weir Project Description Worksheet Spillway Calcs Type Broad Crested Weir Solve For Crest Length Input Data Discharge 216.1 cfs --� Headwater Elevation 5,064.20 ft -� Crest Elevation 5,063.20 It Tailwater Elevation 5,060.00 ft Crest Surface Type Gravel Crest Breadth 5.0 ft Q 5?I« WAY To? of BERM Results 9CQU[RED Crest Length 22.0 ft-1 Headwater Height Above Crest 1.00 ft Tailwater Height Above Crest -3.20 ft Discharge Coefficient 3.00 US Submergence Factor 1.00 Adjusted Discharge Coefficient 3.00 US Flow Area 72.0 ft' Velocity 3.00 fills Wetted Perimeter 74.0 ft Top Width 72.0 ft 7revious ?ond _ QV114WAY _ INpIo%v 6�EsT LENGTH k + Currev,4 fond 1 Ki?lo w gi.8c-P + I(6, 3 c'5 = 216. I AS To? of 3eRNl So6y.Z ---- _ t (,o CkesT exe v, ,�- 7z' PMk Project Engineer: Kevin Tone j:\...\flowmaster\1352c pond spillway.fm2 JVA, Inc FlowMaster v7.0 [7.0005] 03/08/06 10:56:40 AM 0 Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Page 1 of 1 OPTIONAL CONCRETE WING WALL (TYP.) K. AND PAO (END OF PAD i0 MATCH ` END OF WING WALL) I Ls 3.-6. I 1' I � � (MIN.) 6- 6" 6" TRASH RACK 3/8' ROUND OR 51%51' GRATING iWt$iED CROSS 3/8'16' BOLT TO HOLD� �� (3/8' ROUND OR 1'13/8' HINGE IN PUCE, 2 I/4' `\ ` A B TWISTED CROSS D BEARING FROM EDGE OF GRATE . �\ EARS A7 3' O.C., BAR (TYP. OPP, SIDE) ��� WEARER 70 11AT BEARING BARS 'S AT l ` 3 A F. .. ®I�gRR�R�RI�R�RRRRmail/I �'�RRRRRRRRRRRRRRMRRtl RRRRRRRLIRRRRRRRR�won RsonsommooRRRRo�\RRR tl�R��RRRRRRRsRRRoRRB �R�RO\RRRRRORRR ���RRR�RRRRRR�RRtl RORRRRRRR�R�RRtl MRRRMMENEM RRq RR RlRRn MEMRE�Rn \R�MENEM MENEM _ t / � -t L" C \'/ L L y�i\/ ROW CONTROL WELL SCREEN TN 93 PATE STEEL FOREEOVAL) LESS A B PLAN D L TRASH RACK ELEV. C 0 03 (NOTE 5) 4 R 3 Ln 3/8'16' THREADED BOLT 1 CELEV, B TO FASTEN GRATE DOWN L O WELL SCREEN NO. 93 D (U.S, RATER $iNNLEss _ STEEL OR EQUAL) C 4 FLOW CONTROL CONCRETE PAD WITH USE 3T` 10 PLATEY PLATE OF OPTIONAL WING WALLS 100-YEAR OUTLET DOWEL WITH USE OF CONCRETE PAD 3/8'16' BOLT TO HOLD HINGE IN PUCE, 2 1/4- FROM EDGE OF GRATE SPILL ELEV. (TYP. OPP. SIDE) #4012" 3 1/2- I1 1/2" KEY PIPE STEEL CHANNEL FORMED INTO CONCRETE SIDES Wo � 1 1 3/8'.1" FLAT BAR HOLDING FRAME WELL SCREEN NO. 93 (U.S. FILTER STAINLESS STEEL OR EQUAL) ITAINLESS STEEL ANCHOR BOLTS OR NTERMITTANT WELDS ON TOP AND SIDES WELLSCREEN SECTION A -A /4 HOOP METAL OR CONCRETE PIPE 12- / / - UP 1 CLR Ir 11 LL 4% 1 jA 4% SECTION D-D Wp WATER DUALITY (WO) HOLE (TYP), SEE TABLE a 1/4' (MIN,) THICK c STEEL FLOW CONTROL PLATE p (TYP) `STNNLE55 STEEL ANCHOR BOLT (TYP.) FLOW CONTROL PLATE SECTION B-B — LEGEND A A SECTION LINE A -A (ARROWS f4012' p PRINT IN DIRECTION SECTION O.C. IS WEWEO) ABBREVIATIONS CLR. CLEARANCE TYP. TYPICAL DIA. DIAMETER Wo MOTH OF CONCRETE OPENING ELEV. ELEVATION VIP WIDTH OF PLATE INV, INVERT WO WATER DUALITY d4 DIAGONAL MAX. MAXIMUM Ls LENGTH OF STRUCTURE (TYP.) MIN. MINIMUM Ws MOTH OF STRUCTURE O.C. ON CENTER X NUMBER DPP, OPPOSITE 0 AT O.C. .GENERALNOTES -------------------- I. CONCRETE SHALL BE CLASS B. MAY BE CAST -IN -PUCE OR PRECAST. 2 REINFORCING BARS SHALL BE EPDXY COATED AND DEFORMED, AND SHALL HAVE A MINIMUM i' CLEARANCE. ]CLLR, 3, STEPS SHALL BE PROVIDED WHEN VERTICAL DIMENSION EXCEEDS Y-6' AND SHALL BE IN ACCORDANCE WITH A SHTO M 199. 4. ALL TRASH RACKS SHALL BE MOUNTED USING STAINLESS STEEL HARDWARE AND PROVIDED WON MINCED AND LOCKABLE OR BOLTABLE ACCESS PANELS RACKS 5. TRASH SHALL BE STAINLESS STEEL. ALUMINUM, OR STEEL. STEEL TRASH RACKS SHALL BE HOT OIP GALVAN12E0 AND MAY BE HOT POWDER POINTED AFTER GALVANIZING. 1' CIR f 4012' L I-'4012- ,1p i-#4LO12" 14018- 557 TAMPER SECTION C-C 5/8'PPROOF BOLTS ~u WATER QUALITY OUTLET STRUCTURE _ P FA SIDE) J TITS 1/4 THK PLATE 26• RESTRICTOR PLATE DETAIL ELEV. A POND INV. 5058.5 FT ELEV. B WOCU ELEV 50613 FT ELEV. C 5062.3 FT SPILL ELEV. 5063.2 FT Dro 12' MIN. 2.8 FT Ls 5.0 FT WS 5.0 FT Wo 18 IN HOLE CIA, 1-1/8 IN WO OF ROWS 8 OF COLUMNS 5 0 _ 0 O 0 0� O 0000 a 0 OOO 0 IB — WOCV ELEV. 5061.3 6 PI-1/8' 10 02' INV 5058.5 L9 PERFORATED PLATE DETAIL Flow Capacity of a Riser (Inlet Control) Project: FRCC Basin ID: Larimer Campus Layer 00000 $d layer3 0 0 0 0 0 Numberofholes Layer 0 0 0 0 0n inearLlayer Layer 1 0 0 0 0 0 U YFImY Design Information (Input): Diameter of holes d = 2.000 in. Number of holes per layer n = 5 Number of layers NL = 2 Vertical distance between layers h = 4.00 in. Orifice discharge coefficient Co = 0.61 Total opening area at each layer A. = 15.7080 sq in Ao = 0.1091 sq ft Calculation of Collection Capacity The starting water surface elevation must be> the central elevation of the first layer. Enter water surface elevations in ascending order. star B 4SE FLOW ketmE WQCV ELEV,---, 506f,3 Water Surface Central Elevations of Layers of Holes in feet La er 1 La er 2 Layer 3 La er 4 Layer 5 La er 6 La er 7 La er 8 La er 9 La er 10 Flow Elevation 5058.56 5058.831 1 1 1 1 Rate ft (input) Collection Capacity for Each Layer of Holes in cfs cfs 5058.60 0.17 0.00 0.17 5058.80 0:29 0.00 0.29 5059.00 0.38 0.22 0:60 5059.20 0.45 0.33 0.78 505 40 0.51 0.41 0:92 5059.60 0.56 0.47 1.04 5059.80 0.61 0.53 1.14 5060.00 0.66 0.58 1 1.24 5060.20 0.70 0.631 1.33 5060.40 0.74 0.67 1.41 5060.60 0.78 0.72 1.49 5060.80 0.82 0.75 1.57 5061.00 0.85 0.79 1.64 5061.20 .0.88 0.83 1.71 5061.401 0.92 0.86 1.78 5061.60 0.95 0.89 1.84 5061.80 0.98 0.93 1.90 5062.00 1.01 0:96 1.96 LID-Detention_v1.03a, Riser 3/7/2006, 12:46 PM JVA, Incorporated Job Name: FRCC Larimer 1319 Spruce Street Job Number: 1352c Boulder, CO 80302 Date: 02/06/06 Ph: 303.444.1951 By: PPM Fax:303.444.1957 FRCC Larimer Campus Phase 1 Parking Volume & WQCV Calculations TOTAL Area sf) I %la I %Iwq 9892801 72.0 1 68.0 from Figure ND-1 Extended Detention Basin - EDB UDFCD Figure EDB-2 WQCV = a ' (0.911^3-1.191^2 + 0.781) 40 hour drain time a = 1.0 Iwq = 0.68 WQCV= 0.27 watershed inches Design Volume = (WQCV /12) *Area ` 1.2) Design Volume = 0.605 ac-ft REQUIRED1 26342 ft"3 Water Quality Outlet Structure Plate Design: Inv = 5058.5 Hwq= 5061.3 Dwq= 2.80 ft Area per row: Ao=Design Volume / K40 K40 = 0.013 " Dwq^2 + 0.22'Dwq - 0.10 K40= 0.62 Ao= 0.98 in^2 Figure 5 Hole Diameter = 1.12 (1-1/8") nc = 1 nr = 8 Steel Plate Thickness= 3/8" AREA = Current Lots (not accounted for) + New Lots + Future Lots WOCV ELEV. 5061.3 10 02' NV 505B.5 18 244 PERFORATED PLATE DETAIL 0 0 0 0 o 0 0000 I-? 000 0 JVA, Incorporated Job Name: FRCC-Larimer 1319 Spruce Street Job Number: 1352C Boulder, CO 80302 Date: 03/02/06 Ph: 303.444.1951 By: XT Fax: 303.444.1957 FRCC - Larimer Campus Orifice Plate using Headwater above opening and Previous Pond Release Rate' = 6.12 cfs Current Pond Release Rate" = 13.63 cfs Q=cA(2gH)A.5 C= 0.65 Q2 allowable release rate= 19.746 cfs Water Surface Elev 5063.20 Inv Elev 5058.50 Determine the Height of the Plate to release Allowable Flow Using the 18" RCP pipe for Area that passes Qallowable Q=cA(2gH)A.5 C= 0.65 Q 19.75 cfs Assume Dia c 0.65 Hhe d 5.31 Dia Needed Area 1.64 sf 1.45 ft 17.36 in Hole diameter needed in order to discharge the allowable release rate. USE 14-1/2" Hole Diameter NOTES: From Landmark 1997 " For Conservative Design, Allowable Release Rate = Historic 2-year runoff rate for 22.7 acre study area. 14.53 in I" CLR (TYP) 18" 5/8"¢ SST TAMPER 14-1/2" PROOF BOLTS (TYP EA SIDE) 1 I i I 1/4" THK PLATE I I 1 O O 26" RESTRICTOR PLATE DETAIL 1352c Drainage Calcs.xls 5o 6+s cn TO of Qor' 0 'bCfu" 5709! . 5063. l oo `(R. vJ5£l, 5062. Z O Q 5061.! w 50611 W wacv w > VQ co LL w 5060.! M (q W w LL W a 3 5059.t 5058.! STAGE VS. STORAGE Detention Pond — i- ggq�Sc'F 11531 � c� I I 1 � v zuuuu y. Neui Re? - UoI-WQCV 4000U 60000 POND VOLUME (CF) 80000 y 100000 y T 'rvlous Re?. Vol -too Plrk�t o �g �-f (moo rim Nfw Re7J vJQCv + Wevious R71 Vol- too lm;: c: TOTAL Vo-r i Cam. t= v-t�z OoMr_o �'� JVA, Incorporated I11\!!. /! 11 1319 Spruce Street Job Name: FRCC-Larimer `J ` J �`' I I1 Boulder, CO 80302 Job Number: 1352C _ Ph: 303.444.1951 Date: 03/02/06 Fax: 303.444.1957 By: XT POND VOLUME CALCULATION WEIGHTED INCREMENTAL CUMMULATIVE AREA AVG AREA VOLUME VOLUME ELEVATION DEPTH S.F. S.F. C.F. C.F. 5058.5 50 0.5 151 76 76 5059.0 252 1.0 846 846 921 5060.0 1,439 1.0 14,322 14,322 15,243 5061.0. 27,205 1.0 36,439 36,439 51,682 5062.0 45,672 1.0 54,358 54,358 106,039 5063.0 63,043 0.2 63,642 12,728 118,767 5063.2 64,240 4.7 TOTAL CUBIC FEET 118,767 2.73 ac-ft STAGE/STORAGE STAGE CUM VOL(CF) CUM VOL(AF) 5058.5 0 0 5059:0 '76 0.002 5060.0 921 0.021 5061.0 15,243 0.350 5062.0 51,682 1.186 5063.0 106,039 2.434 5063.2 118,767 2.727 Volume Ac-Ft Surface Elev Depth PREVIOUS POND Required Vol-100* 88975 cf 2.04 ac-ft 5064.00* 4.00 ft Provided Vol-100* 89833 cf 2.06 ac-ft 5064.00" 4.00 ft CURRENT POND New Required Vol-WQCV 26342 cf 0.60 ac-ft 5061.30 2.80 ft Previous Req Vol-100* + 115317 cf 2.65 ac-ft 5063.15 4.65 ft Current Req. Vol WQCV Total Volume Provided 118767 cf 2.73 ac-ft 5063.20 4.70 It * Includes WQCV ** From Landmark 1997 JVA, Incorporated 1319 Spruce Street Boulder, CO 80302 Ph: 303.444.1951 Fax: 303.444.1957 TABLE 2 Job Name: FRCC Larimer Job Number: 1352c Date: 02/06/06 By: PPM FRCC Larimer Campus Parking Project 2006 Developed Storm Drainage System Design (Rational Method Procedure) Design Storm Developed -10 YEAR Cf= 1.25 C100 values are determined from a weighted imperviousness on Table 1 Direct Runoff Total Runoff c N r U N („) _tt: Y U C9C d U E C O J N O 0 2 7 CDC In 0 O 3 0 X U .. «.` U w «Q U = (7 H W C `_' (1) (2) (3) (4) 1 (5) (6) (7) 1 (8) (9) (10) (11) (12) (13) (14) ou ery Portion of Site Outfall Site at East 22.71 0.69 0.87 18.3 19.64 1 2.90 1 56.97 18.3 19.64 1 2.90 56.97 Water Quality Area Design Storm Developed -100 YEAR Cf= 1.25 C100 values are determined from a weighted imperviousness on Table 1 Direct Runoff Total Runoff C C C c o a g E 76 o c d U E a 'vim c d U E E m ¢ L cf0 «� Q c W U U U C7 (1) (2) (3) (4) (5) 1 (6) (7) (8) 1 (9) 10) (11) (12) (13) (14) Southerly Portion of Site Outfall Site at East 22.71 0.69 0.87 18.3 19.64 5.92 116.30 18.3 19.64 5.92 116.30 1352c Drainage Caics.xls Water Quality Area JVA, Inc. JVA, Incorporated Job Name: FRCC Larlmer 1319 Spruce Street Job Number: 1352c Boulder, CO 80302 Date: 02106/06 Ph: 303.444.1951 By: PPM Fax: 303.444.1957 FRCC Larimer Campus Parking Project 2006 Developed Composite Runoff Coefficient & Time of Concentration Calculations %I Type of Land Surface Conveyance Coefficient Cv Location: Fort Collins, Colorado Open Space 10.00 Heavy Meadow 2.5 Minor Design Storm: 10 Gravel 50.00 Tillagelfeld 5 Major Design Storm: 100 Landscaping 10.00 Short Feature and lawns 7 SOIL TYPE: C 8 D (assumed) Pavements 95.00 Nearly bare ground 10 Roof 95.00 Grassed waterway 15 Playground 25.00 . Paved areas and shallow paved swales 20 Art. Turf 25.00 Basin Design Data e a c N rn� 01 o 3 u Runoff Coeffs Initial Overland Time (Q 4=0.395(1.1•Cs)L1QS'r' Travel Time (t,) t,=Lengtht(Velocity x 60) F Computed I. Urbanized Check 4 Final Basin Aos Agovel Ar Awe Arcot p`Tv,t '4Total ATot,i Uppermost Slope A Length Slope Velocity 4 Time of Conc Total Length V(L1180)+10 Min t, = Name Design Point (SO (sf) (Sf) (so (sf) (SO (Sf) (ac) s¢ E C2 C5 C10 C100 Length (R) (No) (min) (it) (°h) C,. (fps) (min) 6+t,=t, (ft) (min.) 5min ou e y Portion of Site Outtall a[ 1 1 Site East 0 0 267.343 721,937 0 0 989,280 22.71 72.0 0,51 0.55 0.59 0.69 300 1.0 17.5 1200 1.00 20 2.0 10.0 27.5 1500 18.3 18.3 1352c Drainage Calm.xls JVA, Incorporated Job Name: FRCC Larimer 1319 Spruce Street Job Number: 1352c Boulder, CO 80302 Date: 02/06/06 Ph: 303.444.1951 By: PPM Fax: 303.444.1957 TABLE 2 FRCC Larimer Campus Parking Project 2006 Storm Drainage System Design (Rational Method Procedure) Design Storm HISTORIC - 2 YEAR Cf= 1 C100 values are determined from a weighted imperviousness on Table 1 Direct Runoff Total Runoff c d C C U � m C .O76 D_ C N U .� .� E Q o u o ❑ ❑ o: U u U C! F U w C7 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) Site :7.72 Outfall at 1 0.00 Eas 22.71 0.20 0.20 18.3 4.54 1.70 7.72 18.3 4.54 1.70 Design Storm HISTORIC - 10 YEAR Cf= 1 C100 values are determined from a weighted imperviousness on Table 1 Direct Runoff Total Runoff c m 'U o O_ 0 O E U $ '0 a2m c U E Q u y co U U C H w U (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) Historic - Southerly Site Portion of I Ouffall at 1 Site East 1 22.71 1 0.20 1 0.20 1 18.3 1 4.54 1 2.90 1 13.17 1 18.3 1 4.54 2.90 13.17 Design Storm HISTORIC - 100 YEAR Cf= 1 C100 values are determined from a weighted imperviousness on Table 1 Direct Runoff Total Runoff C C c m U N O C L14) Q c o omm ❑ m❑ of U U U f-(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (13) (14) -Fistoric - Southerly Site Portion of Outfall at Site East 22.71 0.20 0.20 18.3 4.54 5.92 26.89 1 18.3 1 4.54 1 5.92 1 26.89 1352c Drainage Calcs.xls JVA, Incorporated Job Name: FRCC Larimer 1319 Spruce Street Job Number: 1352c Boulder, CO 80302 Date: 02/06/06 Ph: 303.444.1951 By: PPM Fax: 303.444.1957 FRCC Larimer Campus Parking Project 2006 Historic Composite Runoff Coefficient & Time of Concentration Calculations % I Type of Land Surface Conveyance Coefficient Cv Location: Fort Collins, Colorado Open Space 10.00 Heavy Meadow 2.5 Minor Design Storm: 10 Gravel 50.00 Tillage/field 5 Major Design Storm: 100 Landscaping 10.00 Short Pasture and lawns 7 SOIL TYPE: C & D (assumed) Pavements 95.00 Nearly bare ground 10 Roof 95.00 Grassed waterway 15 Playground 25.00 Paved areas and shallow paved swales 20 Art. Turf 25.00 Basin Design Data a y ar L ,Q 2 3 E Runoff Coeff Initial Overland Time (Q ,rp 113 t;=0.395(1.1-Cs)L S' Travel Time t (�) t,=Length/(Velocity x 60)Urbanized I. Computed 4 Check t� Final Basin Aos Agravei Als Avave %{root ATurt Arotal Arotal Uppermost Slope 4 Length Slope Velocity t, Time of Conc Total Length F=(L/180)+10 Min t, _ Name Design Point (5f) A (So (Sf) (So (Sf) (so (ac) e o C Length (ft) (%) (min) (ft) N C, (fps) (min) t;+t,=t� (ft) (min.) 5min istoric - Southerly Portion of Site Outfall at Site East 0 0 989,280 0 0 0 989,280 22.71 10.0 0.20 300 1.0 28.6 1200 1.00 20 2.0 10.0 38.6 1500 18.3 18.3 1352c Drainage Calcs.xls , I r•. ti6.S e�6 0 6 V) 1-4 FF 9 lr F 870 SV FF c 15, ccr Fc 87"0 FF 970 870- - &c.o 18 17 - 16 15- 95 I 1 •, u I ` I Q. a 3 conk , vAN Z "V £E I I a1 r1 J �l 0.93 V S _✓ \ {TT ED 96.0- � � ci In I I I w S `; 1 , _ 0 I 1 I 0 CF 18b.5 FF = 88.5 wcl Itk. :-)%• O 7\ 1 --MnL\ f7 Y 85"4 - - • $5 15 �� j " , IF/ 7ER �� ` Z 47 - =s -- GRAVEL PUT_ / 1 I 6 Ip�ca#Z ��� $,I too- Iz.04, oc 114V: BO.6 FL,564.50 f, 5cj 0 # FC 4-.50 �y 1 Nv�l Inr�=74-5 c8 3 I1JJc 19l Z�" i---� I I �-S EXi57. MP j l O\) / GRA V E C L R -_ NEW IB RCP _T" N_ 1 • I 1 /� I IINV 77-4 l lj I I uj I ZO W117 PUIVD,_—_ 0Ve1-1=LOw 6P/Lewn-"/ I a I /--�T EL d I J / E1//� IIJ N SE CTION OELO'.✓) N o I I �r I uN i COIo N.9GE IN✓: 8p.¢¢�I11_ ✓a,l CAS �. -z 0 4 _51TE IS IN M, CLELLAND I ARE,) of 70THL VEST 24 5 f? c GROSS HISTORIC C = 0.20 DEVELOPED G = 0.5 -SECTIU/v T'-ROUGE+ 5PILLw/--�Yl DETENTIo,✓ PROViv /✓. j. 5. DETENTIGTJ REQU)KZ C1'a1::ICIT✓ TO G"OCOT+ = 17 -T-s RELCf3SE RATE = /� / 0 4 ��'--t (TnP.)_'_',. IENGTH�41 FT. :7��.a4ERGENCY OVERFLOW y. UTFLOW PEAK 0 IN 5064.00 DETENTION TABLE CURRENT CONDITION 4,5 O / 9 /A 1./ e5:�al� ll�- // W W W W_ W _W 000 aoo .- N N It a^a revel N N N .ro 1112c-��a uvO�i �•,vFi1 �%ilE.J- _ 2 B.Z� /9c TM>�E,�criovS %�iLFit%� .sTUOctiT Chit �T.2�iC' To mac. _ O. 0,1� 7 w z_sZ,s- S `f `Z fo T o,SG3 �. ZZ} 7 /�= = Z 8. z 4�D - //. ; S42 = A:o, i 3 zv7 CxO,9S ,�l6.y'f-3 zs` O.S3 bMP�3 iTi� G .'Z �- �O T = Sf,1 ys - 0.53 �i00 = C�/,/,e1 O. S3 u /. Z S x 3 . Sao >e ZS zC) 7,6 FINAL DRAINAGE STUDY AND EROSION CONTROL REPORT FOR THE FRONT RANGE COMMUNITY COLLEGE ADDITION LARIMER CAMPUS Prepared For: The Front Range Community College 4616 South Shields Fort Collins, CO 80527 April 30, 19% Project No. DAVP-5J1D-01-303A1 CONSULTING ENGINEER Landmark Engineering Ltd. 3521 West Eisenhower Boulevard Loveland, Colorado 80537 FRCC Larimer Campus — State Project No. FR070518 March 30, 2006 Page 3 of 3 vegetated ditch leaving the vegetation intact. This allows the existing trees, shrubs and cattails in the ditch to thrive and assist with the water quality enhancement. For this project, the 22.7-acre southerly area has been analyzed in order to provide with water quality features. As shown by the attached calculations, historic runoff patterns were analyzed for this area, and it was found that the total historic runoff rates at 20% impervious before the existing campus was built were 13.2 CFS and 26.9 CFS for the 10-year and 100-year storm events, respectively. Developed runoff patterns were analyzed for this area, and it was found that the total developed runoff rates at 72% impervious will be 56.9 CFS and 116.3 CFS for the for the 10-year and 100-year storm events, respectively. Utilizing these results, a required water quality capture volume (WQCV) of 26,342 CF was calculated for this area. The proposed outlet structure is based on outlet details provided by the City staff and includes a water quality plate and well screen. The release rate at the WQCV elevation (2.8' deep) is calculated at 1.71 CFS, which includes a base flow of 1 CFS for release of nuisance flows in the ditch, using Urban Drainage and Flood Control District flow capacity worksheet. An armored forebay is included at the main 36" RCP outfall into the pond to collect silt and trash before the runoff can enter the pond. The proposed pond will have a new maximum 100-year volume of approximately 118,760 CF, which is an increase of approximately 28,930 CF over the volume of the current pond. This volume is based on a water surface at the proposed spillway elevation. Additional volume over the 118,760 CF is provided within the one foot of freeboard to the top of the proposed berm. In addition, an engineered/armored spillway has been incorporated into the pond which has the capacity to convey the total 100-year flow to the downstream ditch. CONCLUSIONS In summary, this project was designed to improve numerous drainage conditions at the FRCC site. The existing pond, which has an unsafe berm and lacks water quality features, will be rebuilt and consolidated with a new larger water quality/detention pond. The new pond will detain approximately 28,930 CF more than the existing pond. The previous release rate for the existing northerly pond was designed with an allowable release rate of 6.12 CFS per the Landmark report. The new pond will now capture both the southerly and northerly portion of the site and has a limited release orifice which has a conservatively -designed allowable release rate of 7.72 CFS. The lushly vegetated ditch will remain in tact and will be improved by redirecting sediment -laden tributary runoff from the ditch to the forebay and water quality basin via an upgraded storm system. Please note that this drainage analysis was prepared under my direct supervision. JVA, Inc. understands that the City of Fort Collins does not and will not assume liability for drainage facilities designed by others. If you have any questions or comments regarding this drainage letter submission, please feel free to call us to discuss. JVA, INCORPORATED Xavier Torrents Design Engineer 0 Re *sees*. `v��S R H,y ••F9�Q Mtn i 37146 Charles R. ger IV, .E. #37 Associate/P t Manager ���•.,�������,.•`�` FRCC Larimer Campus — State Project No. FR070518 March 30, 2006 Page 2 of 3 portion of the site flows directly to this ditch or is conveyed via a storm drainage system to the ditch at the east end of the site. There is an 8" diameter PVC outlet pipe at the westerly, upstream end of the ditch. The beginning point of this pipe could not be found; however, it is our understanding based on discussions with FRCC and City staff that this pipe is an outfall line for a groundwater underdrain system somewhere to the west. It is our understanding that direct rainfall runoff does not enter this 8" pipe. Further to the west and tributary to the ditch there are two right-of-way outfall pipes that release runoff from Shields Street. All runoff from the southerly portion of the site and the Sheilds Street right-of-way tributary to the vegetated ditch exits the site without detention or significant water quality enhancement. This existing condition is potentially hazardous and detrimental to the environment and downstream waterways. DEVELOPED (PROPOSED) DRAINAGE The proposed development consists of a minor expansion of Lot 1 and paving of gravel parking Lots 2 and 5 as shown on the attached Figure 1 - Drainage Map and referenced JVA storm system plans. Site construction will include demolition of an existing asphalt road, removal of wheel stops, demolition of storm sewer, minor regrading, realignment of the Shields Street intersection, replacement of a Type R inlet with a double Type 13 surface inlet near the library, public sidewalk reconstruction, and all associated utility infrastructure work. As shown on the drainage map, a future lot was discussed during the recent design process (Lot 7 at the south side of the site); however, this lot will not be built as a part of this project nor in the foreseeable future. To produce a more conservative design, the construction of Lot 7 was included in the attached runoff calculations. For drainage design of this project, an existing large 22.7-acre study area has been delineated by JVA as shown on the drainage map. As discussed above, this area currently drains overland to the existing vegetated ditch, or to an inlet/storm pipe system that conveys runoff directly to the existing vegetated ditch. This ditch runs through the southerly portion of the site from west to east and then flows directly offsite without detention. The motivation of our design is to improve the water quality of the runoff from the site and provide as much detention as possible for the 22.7-acre study area. To accomplish this, it is necessary to reshape and redesign the existing pond with more volume and a new updated water quality enhancement outlet structure, as is typically required by the City of Fort Collins. The proposed pond as shown on JVA's plans will now capture the previously undetained runoff from the southerly portion of the site by encompassing the east end of the existing vegetated ditch. In addition, water quality enhancement will be provided to both the northerly and southerly portions of the site where none existed before. Another goal of the project is to protect the existing vegetated ditch. This ditch will not be modified with this project. The plans require portions of the existing drainage ditch near the work areas to be protected by silt fence. Any use of this swale by wildlife will not be hindered, as the existing parking lot extents will not be changed along the swale. In addition, FRCC will be improving the drainage characteristics near the existing drainage swale. Silt- and trash -laden storm runoff from the existing large unpaved lots (Lots 2 and 5, which currently drain directly to the existing drainage swale and leave the site undetained) will be rerouted via curbs, inlets and storm pipes to the new consolidated water quality enhancement/detention facility. Furthermore, no wetlands areas will be disturbed during this project. Proposed grading at the new water quality enhancement/detention facility only requires the removal the berms at the sides of the "' NIncorporated 1319 Spruce Street ' Boulder, CO 80302 March 30, 2006 Ph: 303.444.1951 Fax: 303.444.1957 Mr. Basil Harridan, Utilities- Stormwater Engineer Toll Free: 877,444.1951 City of Fort Collins — Engineering Development Review Web site: 281 N. College / 700 Wood Street www.ivajva.com Fort Collins, CO 80521 E-mail: info®jvajva.com RE: Drainage Summary Letter for "Reconfiguration & Expansion Of Parking Lots And Traffic Flow Improvements" Principals State Project No. FR070518 David M. Houdeshell Front Range Community College-Larimer Campus, Fort Collins CO Robert B. Hurries JVA Job No. 1352c Thomas P. Skinner Thomas S. Soell Dear Mr. Hanldan: Kevin A. Tone As requested by the City of Fort Collins Public Works, JVA Inc. has prepared this Cinders L. Ward drainage summary letter regarding the proposed improvements and the existing and developed drainage conditions for the above referenced parking lot project at Front Structural Engineering Range Community College Larimer Campus (FRCC) in Fort Collins, Colorado. We have Daniel E. Cooke attached the related storm and erosion control plan portions of the final construction plans Mark C. Cormier for the project for your information. We have also attached excerpts from the previous Kathy A.Gilhooly drainage report by Landmark Engineering dated April 30, 1996. and runoff and structure Heidi M. Hall design calculations by JVA, Inc. Derek D. Henderson Michael R. Hope GENERAL LOCATION AND PROJECT DESCRIPTION Craig M. Kobe Front Range Community College proposes to pave two existing gravel/road base parking Michael J. McDonald lots and enlarge and consolidate the existing detention pond at the Larimer Campus David M. Mier within the City of Fort Collins. The parking lots and the detention pond expansion are Derek M. Pedersen bounded by Shields Street, Harmony Road and the existing Larimer Campus. The total Thomas M. Smith campus/library site is approximately 44.0 acres. Sarah E. Watts EXISTING DRAINAGE Charles B. Wilkerson The existing site slopes from west to east between two and seven percent. At the Civil Engineering northerly and northwesterly side of the campus, existing runoff travels to the east via an Jon C. Driggers existing swale and storm culverts along Harmony Road until it reaches an existing Charles R. Hager detention pond. An existing outlet structure releases the runoff into the easterly Howard M. McHenry downstream end of a vegetated ditch that runs from west to east through the southern Carolyn A. Sullivan portion of the site. Existing runoff rates and detention pond facility features were Melissa F. Tolve calculated in the Landmark report to be 99.8 CFS for the peak inflow and 6.12 CFS for the peak outflow (release rate for the I00-year event). The 100-year required volume for Administration the existing pond was 88,975 CF and the actual volume of the existing pond was Andrew P Krizman calculated to be 89,833 CF. During our site visits, it was noted that the 100-year outfall/top of structure elevation of this existing concrete outlet structure is higher than the top of the existing berm that forms the pond creating a hazardous condition. Furthermore, no water quality enhancement orifice, well screen, or other features were noted, and there is no engineered spillway present. At the southerly side of the campus, there is an existing vegetated ditch that runs through the site from west to east beside the existing parking areas. Runoff from the southerly B 0 U L D E R I FORT COLLI N S I W I N T E R P A R K