Hydro35_reading - APPENDIX A DEVELOPMENT OF RAINFALL INTENSITY CURVES AND EQUATIONS l Precipitation Intensitz-Duration—Freguencz Curves

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Unformatted text preview: APPENDIX A. DEVELOPMENT OF RAINFALL INTENSITY CURVES AND EQUATIONS l. Precipitation Intensitz-Duration—Freguencz Curves Precipitation intensity-duration—frequency {I—D-F) informa- tion is necessary for the specific locality in which the Rational Method for estimating runoff is to be used. The two examples which follow illustrate the development of I—D~F curves from HYDRO—35 and NCAA Atlas 2. HYDRO—35 HYDRO-35 maps included in this Appendix as figures 28 through 33 are for 2vyear and lfiB—year frequencies and durations Of 5! 15 and 66 minutes. To estimate intensities for lfl-minutes and 3B-minutes, the following equations are provided: : 19—min value = 0.59 (15—min valua) + 3.41 (5-min) (25} g 36-min value = 9.49 (63-min value) + 6.51 (15-min) (27) Use equations (28) through (31) to compute values for return intervals intermediate to the 2-year and lflfl—year frequen01e5- I 5-yr = 0.278 (lflB-yr) + 6.674 (2—yr) (28} ! lB-yr = 6.449 (lag—yr) + 9.495 (2-yr) (29) 25—yr = 6.669 (lflfi-yr) + 3.293 (2-yr) (3B) Sfi-yr = 9.335 (leg—yr) + 6.146 (2—yr) (31) Example 26: Given: Location — Charlotte, North Carolina DeVelop: I-D-F Curve for 2— to lflB—year frequencies Step 1: Read 5-min, 15-min and 66—min rainfall volume values for 2-yr and lea—yr frequencies from figures 28-33 (table 6): Table 6. Rainfall volumes, 2- and lflB—yr. IIIIIIIIEIHEHIIIIEIMEHIHIHIIEIH -yr 3.4' 3.97 1.72 133- r 6.81 1.75 3.63 197 Anni—=52: 523.33.- 3-=_BI_= annals .au 9...!“— .=ux 19.3.... EH 5:555 n u \ I. I‘I\ pill 11> 1.33. How... .3. an .. . L .l _ ._ 595:: I . JrVu. “tuna... .. C. _ . It. . “fl.. 20.; Elam—unWHD-SE a n who.” he. a ’9... ~I! q §..¢«v§afim? 5&3?» \ . . nxvv‘tfimmx "'ni 103 . III]!.IJ|.....IJ.1! III. .111; «nu-u..- ...... --.... , .. . .__ .w-_.....--..»-m..........-,.. ...........__.... .. 139‘ \ fig!!! 23-. wamaa flammmmflmaflm {mum-as). I “but win. no man um: umunnm: our unsung In: ENE”! i-MINUTE PRECIFi‘I'ATION IINCHISI' - = i _ “Jasm- l'llll “fl! 2-yeat. 5-minute pnclpltatlln (annu-a 5L Fig-u 3D. r; . 23 0- _E m E; R 1' J I a :1" a ;.' y! " g >-.: E- I: I I. E-IIIIII mclpita I; 111 _.-{-' hecug‘yynou _ a nu +1! KEYS. \ . \ m 5: S 1.49 E g; E 1: " FE El § -,I 35 fig 0 "' z - _.——--+"' 2.2:: _________.’-'-" .J -\ 1 If, t . .I. Z-nar. 15-min“: ptuipitatlnn [HYDRO-35L Figure 32. \mecwfidfioud I 1.— Tani N '\ ’E- fl. :2 5' 5? L P- ‘-2 ‘5 I. * l'. a. i E" -k 5 “fed :u-u “A! q u 3x . : Figme 33. Inn-year. Iii-minim precipitation [HYDRO-35L m 1---‘n=; — Step 2: Use equations (28) — (31) to compute 5-, lfi-, 25—, and SB-yr frequency values (table 7): Table ?. Rainfall volumes, intermediate frequencies. _ a. 4 . ‘ Step 3: Use equations (26) and (27) to compute lfl-min and 36-min values; complete table 8: Table-8. Rainfall volumes. . :' ll 4 Step 43' Cbnvert values 1h.the table‘s to intensity in in/hr (table 9): Table 9. Lrbifi‘ufilues, Charlotte} NC. 2-yr . 5-yr laryr: $25;yr; '= 53-)”: lflfl¥yr' Step 5:: Plot I—DBF"Curve for'Charlotte, North Carolina, figure 34. 114 NAINFALI. INTENSITY i (INIIIIIII BI'IAIILBTTE NORTH CAROLINA 20 30 DURATION t (Ill) Flynn 34. Intlnsity-Illrltion-frequancytunes for Charlotte. Ninth Carolina. 115 60 ...
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This document was uploaded on 10/29/2011 for the course CWR 4306 at University of Florida.

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Hydro35_reading - APPENDIX A DEVELOPMENT OF RAINFALL INTENSITY CURVES AND EQUATIONS l Precipitation Intensitz-Duration—Freguencz Curves

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