Page:Isaiah Bowman - Desert Trails of Atacama (1924).pdf/33

 ies have become blocked, and the water collects in pools back of the obstructions. In all, there are at least fifteen principal gallerics in the Pica region. They havea total length of 12,980 meters, or cight miles, the Galeria Comifia alone being 2350 meters in length. The shortest ts the Botijeria, 100 meters long. The total discharge of the fifteen principal galleries is 36.37 liters (9.5 gallons) a second. Besides the fifteen galleries, or tunnels, there are cight principal springs with a discharge of 118.98 liters (31.5 gallons) a second, or three times as great as the discharge from the artificial tunnels or gallerics, though these have been produced at such great labor and expense.

The galleries, or tunnels, have been built in part by the vil- lage of Pica, in part by private individuals for purposes of irrigation, and in part to supply water for the pipe lines that run to desert stations and to [quiquc. Some of them have branches to augment the supply, some of them end in abrupt walls of earth from which the water oozes, others have an indefinite ending where the tunnel reaches a fault or penetrates a water-bearing stratum from which a supply of water is de- rived. Others still are terminated in a series of ascending slopes in order to furnish a larger area of * bleeding *’ surface to supply the main canal.°

The supply of water from tunnels and springs is variable; but the supply from the springs is much more constant, for the feeding spaces in the subsoil are of natural origin. This is an important point to keep in mind in interpreting the diminished flow which is reported from many of the tunnels and which has led to the abandonment of some of the cultivated fields, or chacras, that they supply.

Unlike most desert towns Pica stands in the midst of the desert without the green valley that elsewhere gives a natural basis for settlement. From its wells and springs and a reservoir in the course of a small stream descending from the piedmont the closely compacted gardens of the village are watered with scrupulous economy. We walked about the fruit orchards and irrigated patches of vegetables and grass, chatted with several

Servicio Jeol. No. 3, Minist. de Indystrias i Obras Publicas, Santiago, ror.
 * J. Briiggen; Informe sobre cl agua subterranea de la rejion de Pica, Pudbls. del