A NEW METHOD OF ESTIMATING STREAM-FLOW 135 
(9) The relation of this research to three important problems is briefly given. 
(10) A brief summary of conclusions is given. 
FORM OF EQUATION FOR NORMAL STREAM-FLOW 
In the present discussion, consideration will be limited to a perennial stream in 
a moist climate, which, for the present purpose, is defined as one in which the 
annual precipitation is 20 inches or more. At present, consideration will further 
be limited to what will be called the normal flow of the stream, or the flow which is 
maintained by water which travels the whole of the distance underground from the 
point where it falls as rain, or occurs as melted snow and ice, to the stream. 
On the basis of this investigation to date, it is believed that the normal flow 
of any stream in the eastern two-thirds of the United States, in any region where 
the annual rainfall is 20 inches or more, may be expressed by the following formula: 
S.+r l R\+r 2 R' i +r 3 R\+r<R\+r 6 R\+r t R' s +r 7 R'i+r a R\+r a R\+r l0 R' i0 = D' (33) 
S t is the constant part of the flow. 
r x is the change in storage in the drainage area on the current day, or day to 
which the equation pertains. Specifically, 
r Rainfall i 
n=\ + [ — (evaporation from land) — (run-off), on current day; 
I. Net melting > 
r Rainfall i 
rj=j + [ — (evaporation from land) — (run-off), on preceding day; 
I Net melting J 
r Rainfall i 
r,= l + [ — (evaporation from land) — (run-off), on day before preceding 
••Net melting J day; 
r Rainfall ] 
r 4 =| + —(evaporation from land) — (run-off), on next preceding two 
I. Net melting J days (the two days preceding r s ); 
r Rainfall i 
r,= l + [ — (evaporation from land) — (run-off), on next preceding 4 days; 
l-Net melting J 
i Rainfall > 
r, = l + [ — (evaporation from land) — (run-off), on next preceding 8 days; 
I.Net melting J 
r Rainfall i 
r 7 = I + [ — (evaporation from land) — (run-off), on next preceding 16 days; 
l-Net melting J 
r Rainfall ] 
r»=\ + [ — (evaporation from land) — (run-off), on next preceding 32 days; 
••Net melting J 
r Rainfall i 
r, = | + [ — (evaporation from land) — (run-off), on next preceding 64 days; 
I Net melting J 
Rainfall i 
ri o = -f- [ — (evaporation from land) — (run-off), on next preceding 128 days. 
Net melting J 
