1991-06-17_REPORT - M1977286

• Permit No: M1977286
• IBM Index Class Name: Report
• Doc Date: 6/17/1991
• Doc Name: DESIGN REPORT JOHNSON & SCHOOL SECTION PITS
• Media Type: D
• Archive: No

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15 Estimating Rainfall Runoff from Soil and Cover Data 543
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AMC-II.-The average case for annual floods, may be converted to a different antecedent
' that is, an average of the conditions which have moisture condition by the use of table A-7.
preceded the occurrence of the maximum an- For example, the computations in table A-6
nual flood on numerous watersheds. give an AMC-II number of '73. The corre-
AMC-III.-When heavy rainfall or light rain- sponding curve number for APQC-I and AMC-
fall and low temperatures have occurred during III can be obtained from columns 2 and 3 of
the 5 days previous to the given storm, and the table A-7. The curve numbers for AMC-I
soil is nearly saturated. and AMC-III are 54 and 87, respectively.
The numbers on tables A-2, A-3, A-4 and (b) Thunderstorm Rainfall.-Estimates of
A-5 and figures A-2 and A-3 are for the aver- direct runoff from thunderstorm rainfall are
age watershed condition, AMC-II. Curve more difficult than for general storm rainfall
numbers for one antecedent moisture condition because data for thunderstorm-caused floods
' are meager. Type and density of vegetative
cover on a watershed, as well as the time-
TABLE A-7.-Curve numbers (CN) and constants sequence of rainfall, appear to have more in-
[For the ease 1,=0.2S] fluence on thunderstorm runoff' than do ante-
cedent moisture condition and soil group.
(n (2) (3) (4) (5) l (u (2) (3) I a) (5) A definite time-sequence of 15-minute in-
' CS C.v for C.".. CN C. for Currr, cremental rainfall has been assigned for each
for eonditi oe S etaro for rcm.m. S .taro designated geographical zone for thunderstorm
rnndi- relunu rvhe,,..ndi- ,valnnl whets
t.on nehea r- nort Inehee r- precipitation values given in this text. A sim-
11 1 II[ inches 11 1 111 inrhee
--- -� --- plified "Thunderstorm Cover Index" relating
110 1181 1W) U. 0. W) 41) 78 6.67 1..33 to vegetative cover type and ground cover
99 07 100 .101 .02 SU 39 77 6.9.i 1.39 0
98 '94 99 :'f14 .04 58 38 7G 72 1.45 density for watersheds west of the 105 merid-
97 91 99 .3119 .06 57 37 ..5 7.5.1 1.51 ian has been developed. After design thun-
' 96 89 rec
'J'J .117 .UB _U 3n 75 7,86 1,57 derstorm precipitation values have been
95 87 98 .526 .11 55 35 74 8.18 1.114 P P
94 83 is .638 .13 54 34 73 8.52 1.70 arranged in respective time-sequence magni-
113 83 98 .870 .17 iA 33 2 8.87 1.77 tude (see table A-8), direct runoff increments
1I't el 97 .970 .I7 3^_ 71 U.2J 1.85
' 91 80 97 .989 .201 ail 31 70 'J.61 1.92 are computed by the procedure in the examples,
'Jn 78 9n 1.11 .221 -In 31 70 10.0 2.Uf1 nsl❑
89 7H 96 1.24 .2.51 49 30 C.9 10.4 2.09 section 58(C), g a ppropria:e runoff curve
88 7.5 95 1.30 .27 : 48 21 68 Us 2.16 number, table A-9, and minirflum 15-minute
87 73 95 1.411 30 47 28 67 11.3 226 retention loss rate for res ec:ive hydrologic
96 72 94 1.63 .33 411 27 HH LL7 2.34 p
85 70 94 1.7fi .35 45 16 1t5 12.2 2.44 soil group, table A-10.
94 n8 93 1.90 .38 44 64 12.7 2...4
U 67 93 2.05 .41 43 25 63 13.2 2.64
82 66 02 2.20 .44 42 21 1i2 13.8 2.76 TABLE A-s.-Design, thunderstorm precipitation time-
s[ rN 92 2.34 .47 41 23 61 14.4 2.88 sequence in 15-minute intervals
80 IQ 91 2.50 .JAI 40 2 rA 15.0 3.01)
79 n2 '91 2.66 3 In 21 .59 15.6 3.12
1D 78 INI 9n 2.82 .5(1 1 38 21 58 16.3 3.2n Ordrr of nutaitude
77 59 89 2.99 .fU :I7 -0 17.0 :1.41) Time.Wo,
u
70 58 89 3.10 n3 :IG I'J .511 17.8 3.513
75 .55 I8.6 3.7^ %unn 1 and III %one II
S7 88 3.33 .07 95 18 -
7J iHl 88 3.51 .70 34 I8 54 19.4 3.88
3 54 1 871 3.70 .74 33 17 53 20.3 4.06 0.0.. . ...... ..... ... .... 0 0
.53 1 861 3.89 .78 32 IC. .51 21.2 4.24 0.25. ...... .. ... ..... .. 4 3
' 71 5 4.28 .89 31 15 ail 23.3 4.66 .75 3 2
70 .51 85 4.Y8 .Bn 30 15 50 ^_3.J l.fifi .7:1...... I
On :a) 84 4.49 .90 1.00... .. 1 .4
Hs 48 94 4.70 .94 25 12 43 30.0 11.00 t.25...... .. .. ... 1
67 47 83 4.92 .98 20 'J 37 40.0 8.00 1.50... ...... . . ... . ..... 6
11H 415 82 5.15 1.03 15 11 30 .16.7 11.34 1.73............. ... . ... 7
115 45 82 5..18 1.08 IU 4 22 '".a 18.00 2.I0 .. ... .... .. 8
1" 44 81 5.112 1.12 5 2 13 190.0 38.00 2.25.... ..... .. .. 9
;1- uu' JJ BO 5.87 1.17 0 0 0 in. m- 2.:A. .... ..... 10
62 42 79 n.13 123 finitr finny 2.75.. ............... ....... 11
17- 61 41 78 0.39 1.29 3.00.. .. ....... ............ 112
l� For CN in column 1. Duration limit of zone rainfall.
1