22 
BULLETIN 181, U. S. DEPARTMENT OF AGEICULTUEE. 
of the rainfall flowing off was, as previously calculated, 56 per cent 
for this storm period. Fifty-six per cent of 3.9 inches is 2.18 inches, ^ 
or 15,950,000,000 cubic feet. The run-off which produced the 
maximum rate is equal to the total run-off, represented by the area 
maoqs, minus the above computed amount and should be equivalent 
to the area mafunrs under the hydrograph as constructed for improved 
conditions. 
320O0 
24000 
16000 
8000 
P^ 
r 

^_^ 
i 
1 
\ 
\, 
1 
•5 
\ 
k 
i 
1 
\ 
v^^ 
1 
y 
^ 
— 
^ 
^ 
1909 
'"^ 
^^___ 
' 
8 2 
2 2 
May 
6 
3 
: 
! 
' 1 
1 1 
5 19 23 27 
June 
5 9 1 
July 
3 r 
64000 
40000 -p 
32000 
Z4O00 
16000 
8000 
! 
1 i 
\ 
\ 
-^ 
^ 
\ 
\ 
\ 
/ 
/ r 
\ 
B 
r 
1 
/ 
\ 
.^ 
^ 
1 
1 
1 
1 
/ 
\ 
1 1 
ll 
il 
\ 
\ 
\^ 
IJ 
1^ 
V 
\m 
h" — 
-^-.^ 
.. .'902 
V 
- — 
J 
j.GH,del 
24 28 
March 
17 21 
April 
May 
Fig. 4. — Discharge hydrograph of Pearl River at Jackson, Miss. 
It can be seen from the figure that the area maunrs is common to 
each of the two distinct hydrographs for actual and improved con- 
ditions. Therefore the run-off to be provided for by the triangle afu 
must equal the run-off in the area aoqrnu, minus the above amount 
to be deducted for rainfall occurring subsequent to April 5. The 
area aoqrnu equals 16.76 square units, or 46,350,000,000 cubic feet, 
which diminished by 15,950,000,000 equals 30,400,000,000 cubic 
