I go: 



FORESTRY AND IRRIGATION. 



121 



lis realize that the cork of a champagne 

 l)ottle is worth more than the bottle. 

 One may see large cork forests in south- 

 ern Europe, especially in Spain, and also 

 in Algeria, and I know of no reason 

 why it should not be grown in our own 

 south. The removal of the bark does 

 no injury ; on the other hand, it is said 

 it facilitates growth. The illustration 

 show^s some Cork Oaks in southern 



France, from the large limbs and the 

 trunks of which the cork has been re- 

 cently removed. These old trees yield 

 cork for a long period of time, although 

 one must wait several years before the 

 first harvest. In the sandy pine lands 

 of southwestern France the foresters are 

 always elated when they can induce a 

 species of Cork Oak {Qjiejtus occident- 

 alis) to grow satisfactorily. 



EARTHEN RESERVOIRS. 



By Arthur P. Davis 



U. S. Geological Sun-ey. 



SOMETIMES a farm is provided with 

 a small water suppl}- in the form of 

 a well, equipped with a pump, or a small 

 spring, furnishing insufficient flow for 

 convenient and economical use in irriga- 

 tion. In such cases it is necessary to 

 have a small reservoir, so that the water 

 -can be accumulated and afterwards dis- 

 tributed upon the irrigated land in a 

 larger stream than the supply would 

 furnish continuously. Such a reservoir 

 must be located above, or but little below, 

 the surface of the ground, as it is neces- 

 sary to draw the water off by gravity onto 

 the land to be irrigated. It may be con- 

 structed by building a small levee or dike 

 three or four feet in height, of such form 

 as is suited to the contour of the ground 

 where it is located. The surface soil 

 should first be removed, in order that 

 there may be no great amount of grass, 

 roots, or other vegetable matter either in 

 the reservoir or along the embankments 

 surrounding it. The bank should be 

 built of loamy earth that may be com- 

 pacted into an impervious body, and 

 should, if possible, have a considerable 

 admixture of clay and of .sand. It may 

 be placed in position by .scrapers, and 

 <:ompacted by the trampling of horses 

 or other animals, or by the use of a 

 roller, the bank being kept moi.st to fa- 

 cilitate the consolidation process. The 

 height of the bank, of course, will be 

 such as will give the required capacity 

 of storage, and will be greater on the 

 -downhill edge of the reservoir than on 

 others. At the lower end or corner a 



pipe will pa.ss through the bank (pref- 

 erably of iron), with a suitable valve, 

 by which means water may be drawn 

 off when needed for irrigation. 



Particular pains will be necessary to 

 form a joint between the iron and the 

 earth, so that the water will not follow 

 the j unction and cause a leak . The best 

 practice is to imbed the pipe in concrete, 

 the rough edges of which wall make a 

 good bond with the earth embankment. 



Such reservoirs as are practicable of 

 construction on the above plan can be 

 made available only where it is desired 

 to accumulate the water into an irrigat- 

 ing head, or to save the night flow^ for 

 use in the daytime, or to store a few^ 

 days' supply until the time when most 

 needed. As a storage of storm waters, 

 or to hold irrigation water for any con- 

 siderable period, such a reservoir is im- 

 practicable. Its relation of depth to 

 area is so small that the evaporation is 

 rapid, and this, together with the per- 

 colation to be expected, soon exhau.sts 

 its capacit}'. Moreover, the reservoir 

 being entirely artificial, its cost in pro- 

 portion to its capacity' renders it im- 

 practicable, unless the capacit}^ is to be 

 utilized over and over at frequent in- 

 terv^als. 



Where it is desired to .store .storm 

 waters for a considerable period of time, 

 as from a rainy .season to a dry season, 

 for purposes of irrigation, it is usually 

 necessary to find some point where the 

 construction is assisted by the natural 

 topography, as in a broad ravine or 



