676 



ECONOMICAL ASPECTS 



especially the smaller ones, where few, if any, discharge measure- 

 ments have been made, and in such cases it is necessary to base 

 estimates of discharge on the records at other stations in the same 

 precipitation belt and watershed, and data of other systems of 

 similar nature may be also used. Rainfall data are also useful as a 

 check on flow estimates and they also show years of high and low 

 water, but care should be exercised in their use. 



The daily and seasonal distribution of stream-flow is best 

 shown graphically in the hydrographic curves, as fully explained 



140,000 

 130,000 

 120,000 



J 110,000 

 ^100,000 

 ft 90,000 

 80,000 

 O 70,000 

 S 60,000 

 > 50,000 

 | 40,000 

 p 30,000 

 20,000 

 10, 



50 100 150 200 250 300 



Days per Year 



FIG. 398. Stream-flow-Duration Curves. 



350 365 



under the section of Stream Flow, and by comparing a number of 

 such hydrographs the dryest year, i.e., the year with the minimum 

 flow, can readily be ascertained. 



For convenience in making a scientific analysis and study, the 

 stream-flows, instead of being arranged chronologically as in the 

 hydrographs, may be arranged according to magnitude, as in Fig. 

 398. The discharge is plotted as ordinate and the corresponding 

 number of days during which the respective discharge has oc- 

 curred as abscissas. Instead of recording the time in days it 

 may also be given in percentage of the entire year, and horse- 

 power values may be substituted for the discharge by making 

 allowance for any possible variation in the head at the different 

 discharges. 



