IS A TREATISE ON DREDGES AND DREDGING 



of a vessel, the mean readings of the gauges were taken when the 

 vessel was light and again when loaded, difference between 

 the light and loaded readings as taken from tables gave the desired 

 information. Vessels which could not be measured on the ways 

 or in docks were measured on the water, their draft being obtained 

 by hook gauges. 



To check the calculated displacement, the load of a vessel was 

 actually weighed at frequent intervals, by means of a track scale, 

 located at the contractor's quarry. Remarkable agreements were 

 found between the two. 



In the case of dump scows it was not possible to obtain the 

 load carried by displacement, and the value of the gauge readings 

 was, therefore, determined by actually weighing the material on 

 the track scale, the readings of the gauge being taken when the scow 

 was light, and with frequent partial loads and when fully loaded. 

 The difference in feet and decimals of the gauge readings divided 

 into the total load gave the ratio per foot. This only applies to 

 full loads. Partial loads, as well as large or small-sized stone, affect 

 this ratio somewhat. 



Increase and Shrinkage of Material. There is a great difference 

 in the cost of dredging when the material is measured in place or in 

 scows. When the specification states that the material will be 

 measured in place, two important items should be considered. 

 These are the increasing of volume of the removed materials, due to 

 the fact that the soil removed from its natural position increases 

 in volume, and such an increase is by no means a transcurable quan- 

 tity. The second item is due to the work of the subcurrents, which 

 tend to stir up the material and fill up again the place of excava- 

 tion. This is caused by the leveling action of water, especially in 

 very soft soils, as fine sands and muds, and as a consequence 

 necessitates the excavation of a larger amount of material, in 

 order to obtain in a permanent way, the depth required by the 

 improvement. 



It will be almost impossible to foresee the amount of material 

 that will fall back into the excavated place, since this depends 

 upon two factors, namely the direction and strength of the currents 

 and the looseness of the material. It is very difficult to tell how 

 far the currents will affect the soil at the bottom of the improve- 

 ment, and to estimate even in an approximate way the amount of 

 material that will fall back. It will be advisable for the con- 



