46 PREVENTIVE AND REMEDIAL WORK AGAINST MOSQUITOES. 



even with waders. A considerable part of the area was submerged to the depth of a 

 foot or more, thus concealing from view the cracks and tidal creeks, which one was 

 likely to fall into at every step, and which made any attempt at rapid progress some- 

 what discouraging. 



It was at once evident, under these conditions, that if the area was to be controlled, 

 the dike must be either cut through in a number of places in order to allow a freer 

 circulation of water, or the breaks must be repaired and the gates put in operation, 

 and the water kept out. The latter scheme was the one followed, because it would be 

 possible to make the area thoroughly dry, and thus the results would be more certain. 

 In attempting to operate the gates we were made to appreciate the effect of a ten or 

 twelve years' coating of rust on the large screws by which the gates were manipulated. 

 After the gates were put in operation the breaks in the dike were repaired and the weak 

 places strengthened. The largest break repaired was immediately joining the upper 

 gate. This was 30 feet wide, and by the action of the water had worn down so that at 

 high tide there was a depth of 10 feet of water. A double wall of sheet piling about 

 6 feet apart was sunk here and the space between filled in with earth. The other 

 breaks were repaired by sinking a single wall of sheet piling in the center and filling 

 in on both sides with dirt. 



After these repairs were completed the gates were operated, opened at low tide and 

 closed at high tide, for a week, but at the end of this time there was still much water 

 in the area, because the gate floors were not low enough to lower the water level suffi- 

 ciently. This made it necessary to lower the gate floors and add an extension to the 

 gates to reach the lower level. This being done the gates were again operated for 

 several days, but it was found that, due to seepage of water through the dike in 

 many places, hand operating would have to be kept up almost indefinitely. It was 

 therefore necessary to replace these old-style gates, operated by hand, by automatic 

 ones, and these were, consequently, put in at both the upper and lower gates, and the 

 floors lowered 32 and 20 inches, respectively. These gates were made to swing on an 

 axle at the top, the lower end being free and easily moved by the pressure of the 

 water, so that at low tide it was opened by the pressure of water on the inside, and 

 closed as the water from the high tide rose on the outside. 



This tidal creek, which served as an outlet for the lower gate, had become filled in 

 to a depth of 2 or 3 feet during the period the gate was closed, and this was cleaned 

 out for 300 or 400 yards toward the bay in order to drain out the area enclosed by the 

 dike. 



With this work done upon the dike the area enclosed by it was treated in much the 

 same way as that outside, except that the network of cracks, already mentioned, had 

 to be filled in in many places, and several of the tidal creeks deepened. The reward 

 for all this work came later in the season when the area was changed from a veritable 

 breeding ground to the safest portion of the marsh. Indeed, this area was the key to 

 the situation, and the excessive abundance of mosquitoes in this particular territory 

 was without doubt due to this extensive breeding ground. 



It is appropriate to mention here the connection of this work with the reclamation 

 of marsh lands. This tract of 500 or 600 acres, which had been useful only for duck 

 hunting, is now thoroughly dry and could be put to agricultural uses at very little 

 additional expense. Such work has already been extensively taken up on the marshes 

 below San Mateo, and it had been found that a good crop of grain can be raised on such 

 land in the second year of its cultivation. It is safe to predict that all the marsh land 

 involved in the present campaign will be under cultivation before many years, and 

 because of its proximity to the metropolis of the coast should be very valuable. 



Besides the marshes already mentioned, permanent control work was done on the 

 marsh about Millbrae and northward to San Bruno, and also some drainage work at 

 Coyote Point, opposite San Mateo. The work at these places was much the same as 

 that already described, and further details are unnecessary. 



