260 Irrigation and Drainage 



influence in improving the texture of the soil is quite 

 as great as that due to the fertilizers contained. 



The sediment carried by the Po is given by Lom- 

 bardini as TOO" of the volume of the river, and on 

 this account the waters are held in high esteem for 

 irrigation. 



The river Nile, during the time of the rainy season 

 of mountainous Abyssinia, comes loaded with sedi- 

 ment constituting TTT of the volume of the water; 

 and this, under the old system of the Pharoahs of 

 basin irrigation, which permitted the rich mud to col- 

 lect on the fields, kept them fertile for thousands of 

 years, and they are so today; whereas in Lower Egypt, 

 where the old practice has been abandoned in recent 

 years for an "improved" system, which does not per- 

 mit the utilization of the rich Nile mud, the fields are 

 fast deteriorating in fertility, although only half a 

 century has passed. 



The Durance, in France, is famous for its fertile 

 waters, and they carry at the ordinary maximum -33 of 

 their weight of sediment, or nearly 1.9 pounds per 

 cubic foot, equal to 82,464 pounds per each acre-foot 

 of water. In rare cases the sediment of this stream 

 rises to iV of the water by weight, and the average 

 proportion for nine years has been found to be T^O. 

 When such waters are used year after year on poor 

 lands, the improvement becomes very great, while on 

 the better lands a high and permanent degree of fer- 

 tility is maintained indefinitely, with heavy yields per 

 acre as the result. 



