j. Shores and Shoals with low surf or breakers (Waves 
less than one foot high on breaking) 
k. Shores and Shoals with medium surf or breakers 
(Waves between one and 3 feet high on breaking) 
1. Shores and Shoals with severe surf or breakers 
(Waves over 3 feet high on breaking) 
mo ice covered lakes and rivers 
The data thus developed indicate that about 40 per cent of 
the shallow water surveys done by the various Districts consists 
of surveys made on slow and medium rivers (velocities from 0 to 
3 feet per second and 3 to 7 feet per second, respectively; with 
little or no tidal influence). The approximate percentage of 
the total work load of all Districts for the rivers, lakes and 
oceans surveyed are shown in Figure 1. 
The surveys usually are made to accomplish two general 
types of work. One is the general coverage work done in con- 
nection with preliminary examinations and similar type surveys; 
the other is the contract work done in connection with contract 
dredging. Two methods are employed generally in making the 
necessary surveys; the soundings are obtained by contact using 
a lead line to determine the depths, or by an echo sounder. 
The data from the questionnaire show that throughout all 
Districts of the Corps water depths are determined by contact 
soundings in 75 per cent of all surveys and by echo sounder in 
the remaining 25 per cent. A further breakdown of the data 
shows: 
Percentage of Surveys 
No. of Districts made by Contact Method 
20 100 
6 tp) — LOO 
6 50) = 125 
v 25> © 
The questionnaire develops the fact that the interval 
between soundings and the distance between ranges varies con- 
siderably for the surveys made by both methods. Table 1 lists 
average, maximum, and minimum sounding interval and range 
distance for all surveys. It is to be understood that the 
lines of soundings taken with the echo sounder are continuous, 
and the distances given in the table represent the interval at 
which spot soundings were taken from the record. 
