CEA1GEKD. 



143 



Before we leave the dam it may be useful to trace a summer 

 spate, and the action of the various works throughout. 



FIG. 100 scale &. 



When the rain first begins to run off the hill after a dry 

 spell, all the sheep-drains through which it finds its way to the 

 burn are full of dust and ddbris of vegetation, and often in an 

 hour the stream comes down as thick as, and much the colour of, 

 pea-soup, long before there is more than a few inches' rise. When 

 the discoloured water first meets the leaf-screen, it falls through, 

 leaving the debris on the screen. In a short time the screen clogs ; 

 and if the burn has not risen much, as the water clears, the screen 

 cleans itself by the eddy formed by the angle of the bulk-head. If, 



