RESERVOIRS AND PONDS. 



Kansas, for instance, a small fraction of the precipitation 

 during the year would make a lake one -fourth of u mile 

 square and five feet deep for every section of land. This 

 could be utilized easily for irrigation. 



A grand system of reservoirs in Arid America would 

 greatly reduce the dangers of floods and rendei immunity 

 from the horrors of deluge that every year come to the 

 settlers along the lower Mississippi. The ancients under- 

 stood this principle, for, in order to remedy the incon- 

 venience of the torrential period, when the country was 

 flooded, and of the subsequent drouth for five months, 

 the Romans covered their African provinces with a net- 

 work of hydraulic structures. From the summit of the 

 mountains to the sea all the rains that fell were seized 

 upon, led here and there in channels and distributed 

 over the fields. In the smallest mountain ravines stone 

 dams were built to retain water. In the valleys they 

 arrested its progress downstream. By this means the 

 Romans prevented great floods descending the mountains 

 at times of heavy rains, and retained a larger part of the 

 precipitation in the higher reservoirs until such time as 

 the water thus preserved was needed. At the entrance 

 to each large valley was a system of works which assured 

 not only the watering of that immediate region but con- 

 ducted flowing streams through many channels, so that 

 the surrounding earth could absorb what was required. 

 At the entrance of each large stream on a plain a dam 

 was built, generally to retain the waters and prevent 

 their sudden invasion of the plain before they were 

 required. 



Location of Reservoirs. In the selection of 

 reservoir sites regard must be had to several considera- 

 tions the area and character of land to be irrigated and 

 its distance from the proposed reservoir ; the area of the 

 watershed, the drainage from which is to fill it ; and both 

 the maximum and minimum annual rainfall of the water 



