For the reservation of the water-partings in the past considerably denuded by lumbermen and ranchmen the increase of the forest areas, and the creation of reservoirs along the rivers, to control their erratic flow 2 and impound their flood waste for purposes of irrigation, much has been done by the national government.
The highest dams of this class in the British islands impound water to a level of about IIo ft.
Of these the highest is the Hagglee, on the Ashop, a tributary of the Derwent, which will impound water to about 136 ft.
In length and will impound water to a depth of 114 ft.
In New South Wales thirteen thin concrete dams, dependent upon horizontal curvature for their resistance to water pressure, have been constructed in narrow gorges at comparatively small cost to impound water for the use of villages.