Drainage by Gravitation. 31 



In selecting the site for a sluice discharging on the sea 

 coast, as sheltered a position as practicable should be chosen, 

 where the sand is least likely to drift and fill up the outfalL 

 Shifting sands are frequently a source of great trouble, and 

 where sluices discharge on sandy fore-shores, it often becomes 

 necessary to carry the outfall from the sluice for a considerable 

 distance by means of a covered wooden tunnel. 



When the coast is flat the water, after leaving the sluice, 

 frequently has to travel through a long stretch of maish and 

 sandy foreshore. Where creeks already exist, it is generally 

 necessary to deepen and straighten them. To prevent the 

 shifting of the channel through the sand, and the sides from 

 being washed down in storms, fascines made of thorns are the 

 best materials that can be employed. These, when once 

 properly laid in their places, and bedded with the sand, 

 form inexpensive and efficient training walls, which with 

 slight care will last for a great number of years. The same 

 method has also been successfully applied to the training and 

 straightening of livers. A full account of the method of 

 fascine training channels through sandy estuaries will be 

 found in a paper by the author in the * Transactions of the 

 Institution of Civil Engineers.' * 



Where the sluice discharges into a river, the site should be 

 fixed at a concave bend, where the water is always deeper 

 than in other parts, and the sill less likely to be blocked by 

 deposit in dry weather. The position of the sluice should be 

 such that the direction of the outflowing water should join 

 the ebb current at as small an angle as practicable and so 

 that its direction should coincide with that of the river, so as 

 to cause as little disturbance or check as possible at the point 

 where the two streams meet. 



Where the district to be drained is at a low level, the sill 

 of the sluice has generally to be placed at the lowest level at 

 which the river is ever likely to be scoured out or deepened. 

 * * Fascine Work at the Outfall of Tidal Rivers,' vol. xlvi. 



