Ch. 20] DETERMINING POSITION ON RANGE 357 



On the completion of the sounding of a range, the instrumentman 

 boards the boat, and the boat retraces the range in order to rewind 

 the piano wire on the distance wheel. The rewinding is done by a 

 small motor at 400 feet per minute. At the bank, the end of the wire 

 is released, the iron pin is pulled, and the party heads for the next 

 range. 



The temperature of the water must be taken into consideration in 

 the operation of echo-sounding equipment. At the beginning of a 

 day's run and at other periods, if there is much change in depths of 

 the reservoir, a check is made with the sounding recorder by submerg- 

 ing a steel bar hung from chains on either end to known depths below 

 the water surface and recording the echoes therefrom. Successively 

 lowering the bar by known intervals of 10 feet gives the depths, which 

 are recorded on the chart, and the corrections that must be made to 

 reduce the chart depths to true depths. The bar check is considered 

 accurate to a depth of about 100 feet. For greater depths, corrections 

 are made on the basis of water temperature. For example, in a sur- 

 vey of Hiwassee Reservoir, temperatures at 100 feet of depth were 

 42° F., and soundings were corrected for this condition. Corrections 

 for salinity must be made where it exists. 



As in any type of sounding, there is the problem of the character 

 of the surface of the bottom where the soundings are taken. The 

 possibly unconsolidated nature of relatively new deposition introduces 

 difficulties of interpretation and application of the soundings. The 

 solution for this problem lies in methods for determination of density 

 of materials in deep water which are separate from the soundings 

 themselves. 



Determining Position on Range 



For ranges up to a length of 4,000 feet, position on range is deter- 

 mined with the distance wheel. For ranges longer than 2,000 feet, 

 the party works first from one bank and then from the other to a 

 distance of about 2,000 feet. In establishing ranges initially where 

 the length exceeds 2,000 feet and on resurveys for ranges longer than 

 4,000 feet, location on range is determined by cutting angles with a 

 plane table from the bank. If distance-wheel equipment is not avail- 

 able, position may be determined in the manner described in the suc- 

 ceeding paragraph for long ranges. 



Some reservoirs have expanses of water as wide as 2 to 3 miles. 

 These are beyond the limit of the distance wheel for position measure- 

 ment. For ranges of such great length, two instruments are used on 

 the bank. One is a transit to keep the boat on range, and the other 



