26 
BULLETIN 181; U. S. DEPARTMENT OF AGEICULTUEE. 
ditch be designed to care for only the ordmary floods, it prevents a 
large number of overflows and aids materiaUy in reducing the maxi- 
mum floods. The cost of ditches designed on this basis will be much 
less than that necessary to care for the maximum conditions, while the 
land will be greatly benefited by the decrease in 
the number, durations, and heights of the floods. 
Investigations by C. E. Ramser, in Lee County, 
Miss., where conditions are quite similar to those 
existing in the Big Black watershed, seem to show 
that a ditch that has a capacity sufficient to care 
for a run-off of 55 second-feet per square mile for 
an area of 25 square miles, and a capacity of 25 
second-feet per square mile for an area of 100 
miles, is sufficient to handle a large number of the 
ffoods such as formerly had occurred, and to re- 
duce greatly the heights and durations of the 
maximum floods. Beheving that a design fulfiU- 
ing these conditions is economical in this case, the 
following formula of 
the Murphy type has 
been developed by the 
use of the above values. 
500 1000 1500 2O00 
Drainage Area in Sg. Miles 
Fig. 5.— Discharge curve used in design of levees, Big Black 
River, Miss. 
The curve for this 
equation has been plat- 
ted by substituting va- 
rious values for M and 
solving for Q; this curve (fig. 6) has been used in computing the sizes 
of aU ditches, except that no ditch had been designed for a greater 
run-off than 70 second-feet per square mile. 
DRAINAGE PLANS CONSIDERED. 
Before the final plan, as hereafter discussed, was decided upon, 
other possible methods of reclamation were carefully investigated 
and compared. These are very briefly discussed below. 
IMPROVING PRESENT CHANNEL. 
The plan of clearing the present river channel and making cut-offs 
was first investigated. It was found that the channel, even if it were 
straightened throughout and cleared of all drifts and brush, would 
not have sufficient capacity to care for the run-off as indicated by the 
curve for ditches (fig. 6), and that such improvements would not 
reduce the flood height sufficiently to prevent the summer and fall 
overflows, w^hich are very injurious to the crops. 
