SALT MARSH DRAINAGE 155 



length of culvert pipe to assure proper settlement and avoid 

 misplacement after filling over the culverts. At the other 

 slough, a battery of six gates and culverts was installed in a 

 similar manner. Owing to the fact that the culverts at the time 

 of placement would lie below water level, it was necessary in 

 both installations to lay the culverts with the gates attached. 

 Each culvert and gate unit weighed more than seven tons. Two 

 clam-shell dredges employed in the dike work were used to lower 

 them in place. 



As an auxiliary proposition, to take care of high water periods 

 and freshets, a pumping plant was provided at each slough. 

 Both installations of pumps and pipe lines were placed directly 

 over the culverts and gates. 



To enclose the 5,600 acres against high water required lYi 

 miles of dike, of an average height of 12 feet. At the culvert 

 and gate installations, the height of the embankment over the 

 top of the culverts was 20 feet. The total cubic yardage of 

 embankment amounted to 800,000. 



The appraised value of the land before improvement was 

 approximately $50 an acre, and after improvement, $250 an 

 acre. The cost of all diking, dredging and spillways, was $60 

 an acre, leaving a net profit of $140 an acre. 



OPERATION OF TIDE-GATES 



Tide-gates, like all other contrivances, need a certain amount of 

 attention. In addition to this, it is imperative that they be 

 operated intelligently. 



Tide-gates should be inspected at least once a week and pre- 

 ferably twice a week. Despite the use of racks and screens, 

 there is a certain amount of fine debris that is almost bound to 

 enter the gate and possibly interfere with its operation. Even 

 though the gate be below mean low tide level, sunken logs and 

 other like objects frequently enter and lodge in the gate. These 

 must be removed, if the gate is to function satisfactorily. 



There is also another problem in connection with tide-gates. 

 When the gates are closed, fish cannot enter the marsh and, 

 when the fish supply gets low, there is apt to be more or less 

 mosquito breeding. This is particularly the case when sewage 

 is discharged into the marsh. In order to overcome such breed- 

 ing, the practice in New Jersey has been to raise the tide-gates 

 for a week or two each month during the period of the lowest 



