FLOW OF WATER IN IRRIGATION DITCHES 



247 



2. It is difficult if not impossible to assign values to n for canals 

 in which there is much aquatic growth. In the Thompson Mfg. Co. 

 canal, for example, the mean velocity was 1.58 per second, while the 

 surface velocity was 3 . 7 feet per second. This discrepancy was due to 

 the choking of the channel by milfoil. 



3. Rough and uneven banks have as much influence on the flow as an 

 uneven bottom. 



4. It seems that cross-currents and internal friction exercise a con- 

 siderable influence on the velocity. These are not directly provided for 

 in Kutter's formula. It appears, therefore, that if the flow is without 

 cross-currents and internal friction, there is not much variation in the 

 value of n whether the channel through which the water flows is of 

 earth, gravel or some smooth material such as cement. For this reason 

 cobblestones and other projections exercise considerable influence in 

 small canals but cut very little figure in the larger ones. 



Tabulation of Results 



