SALT MARSH DRAINAGE 153 



the bulk-heads are fitted with slots, in which planking can be dropped to 

 form a coffer-dam. The water between the two bulk-heads has merely 

 to be pumped out, when these dams are in place to expose the gate for 

 repairs and the sluice-way for cleaning. The top of the sluice-way thus 

 formed is left open." 



Frequently in salt marshes, areas are found separated from the 

 main body of water by sand-bars. The outlets from these areas 

 are channels through shifting sands. Ordinary tide-gates 

 quickly fill up. A satisfactory way of dealing with such places, 

 according to Carroll, 1 is to construct a planked well on the inner 

 side of the bar; the well is connected with the marsh area in 

 question by a planked ditch; at the entrance of this ditch into the 

 well, a tide-gate is hung; the well discharges at low tide through 

 a terra-cotta pipe that passes under the sandy beach and connects 

 with an iron pipe running out under the water, so as to deliver the 

 water from the well a foot or two below mean low tide. The iron 

 pipe is protected against drifting ice, etc., by means of heavy 

 piling and cross-timbers. 



For small streams having a firm sub-soil, a single line of sheet 

 piling, well braced with large piles, is suggested by Fuchs. 2 

 In this case, the gate would fit over a hole cut in the piling. This 

 type of gate would have the advantage of cheapness and 

 simplicity, but it would have to be extremely well-braced 

 to withstand the recurring pressure at high tide, which would 

 have the effect of loosening it, causing leaks. Fuchs 2 reports 

 that one gate of this design that he tried out failed as a result 

 of this tide pressure. 



THE CALCO GATE 



The Calco automatic drainage gate, made by an iron-culvert 

 company, has given satisfaction on several large diking and 

 drainage projects. This gate is attached to one end of a corru- 

 gated iron culvert, somewhat after the fashion that a wooden 

 gate is attached to a sluice-box. These gates are said to be 

 sensitive to a difference of head of less than an inch. 



The method of installing these gates is similar to that outlined 

 for wooden gates, except that it is sometimes advisable to put 



1 Transactions of the First Annual Conference of Sanitary Engineers, 

 U. S. Public Health Service, 1919. 



2 Transactions of the First Annual Conference of Sanitary Engineers, 

 U. S. Public Health Service, 1919. 



