RECLAIMING OVEEPLOWED LANDS IN MISSISSIPPI. 

 APPLICATION OF RUN-OFF RESULTS. 



25 



The followmg is a summary of the results obtained for the three 

 drainage areas discussed: 



Drainage area. 



Probable 

 run-off. 



Square miles. 



3,120 



1,200 



100 



Second-feet per 



square mile. 



24.0 



31.5 



93.7 



In order to utHize these results as a basis for determining run-off 

 from other areas, it is necessary to incorporate them into a formula 

 which will give the probable run-off from any desired drainage area. 

 A formula of the Murphy type seems best adapted to the use of the 

 above data. 



The Murphy formula is 



/)__ 46790 



in which Q equals the discharge in second-feet from each square 

 mile, and M the watershed area ui square miles. Adopting a general 

 formula of the above form, viz., 



the values of X, Y, and Z were derived by substituting for Q and M 

 the following values obtained for the Big Black watershed: 



Where M= 100, ^ = 95 

 Where li= 1200, Q = Z2 

 Where ilf=3000, Q = 24 



Substituting the above values, and solving, the following formula 

 was obtained: 



^ 18700 



if +144 



+ 18 



For convenience in the use of this equation its curve has been 

 platted (fig. 5). It is beheved that this curve represents the max- 

 imum nito of run-off that may be expected under improved condi- 

 tions, and the design of all levee improvements has been based upon 

 it, although no rate of run-off greater than 90 second-feet per square 

 mile has been used. 



If a levee system be insuilicicnt to care for the flood conditions, 

 great damage may be done to the land presumed to be protected 

 and to tlu! levees themselves; grxiut care should therefore ])0 taken to 

 provide for maximum run-off conditions. On the other hand, if a 



