In the hot season there is almost no surface water.
Where the trade-winds heap up the surface water against the east coasts of the continents the currents turn poleward.
Dams Any well-made earthen embankment of moderate height, and of such thickness and uniformity of construction as to ensure freedom from excessive percolation at any point, will in the course of time become almost impermeable to surface water standing against it; and when permeable rocks are covered with many feet of soil, the leakage through such soil from standing water newly placed above it generally diminishes rapidly, and in process of time often ceases entirely.
The great warming and abundant rainfall of the island regions of the western Pacific, and the low temperature of the surface water in the east, cause a displacement of the southern tropical maximum of pressure to the east; hence we have a permanent " South Pacific anticyclone " close to the coast of South America.
The cultivation of the cane was greatly encouraged by the Reciprocity Treaty of 1875, which established practically free trade between the islands and the United States, and since 1879 it has been widely extended by means of irrigation, the water being obtained both by pumping from numerous artesian wells and by conducting surface water through canals and ditches.