83« Curirent Measurements . - Measurements of littoral current may 

 sometimes give an indication of the direction of littoral drift, but they 

 require much time and are frequently unreliable. They must be made at 

 frequent intervals over a full year to be of value, and if reversals in 

 direction and wide velocity variations are observed, they cannot be ev- 

 aluated in terms of littoral drifto The most common mettiods used to ob- 

 tain the direction and velocity of the currents are by use of floats 

 outside the breaker zone and fluorescein inside the breaker zone. 



8I4.. Fluorescein is a yellowish-red crystalline compound which re- 

 ceives its name from the brilliant yellowish-green fluorescence of its 

 alkaline solutions. Fluorescein can be purchased at moderate cost from 

 most chemical firms in quantities of one pound or more. A common method 

 of employing fluorescein is to place a handful of dry sand in a paper 

 towel, or other substance, which would disintegrate readily, with a heaping 

 teaspoon of fluorescein crystals. The entire mass is twisted within the 

 towel, and tossed seaward into the breaker zone. As the towel disintegrates 

 and the crystals disolve, a small patch of water is dyed an easily dis- 

 tinguishable brilliant yellowish-green. The movement of this patch of 

 colored water in a longshore direction can be traced from the beach, noting 

 the distance traveled and the time required for the travelo All measure- 

 ments should be to the center of the colored area, which will gradually 

 disperse until no longer distinguishable. From the distance moved and 

 time for movement, the velocity of the current can be computed. Time 

 permitting, 3 readings should be taken at each station and averaged. For 

 the best effect, these readings should be taken twice a day at regular 

 intervals along the beach under study, with concurrent measurements of 

 wave height^ period and direction. 



S^e Current measurements seaward of the breaker zone are generally 

 made with floats. In general^, these react still more erratically than 

 does the fluorescein. In the low current velocities common to this area, 

 wind conditions have considerable bearing on the floats unless great care 

 is taken. Although many tsrpes of floats have been used, most of them 

 follow the same general pattern of movement. Floats should be low in the 

 water and designed to offer the least wind resistance and the maximum 

 water resistance possible. The floats should be released in sequence along 

 the entire length of a profile, spaced at regular intervals from 200 to 

 UOO feet. Each float should have a distinctive color flag or marker to 

 permit its identification. Locations of the floats at regular time 

 intervals may be made by transit intersection. These measurements are 

 generally continued through one or more tidal cycles. Because of the 

 short time interval^ this type of current measurement does not represent 

 the seasonal changes and can be used only in connection with other ob- 

 servations . 



86, Two general types of subsurface floats are usedj the rod float 

 and the vaned float. The rod float, of uniform dimensions, gives an 

 approximation of the integrated values over the depth covered by the 

 float. The vaned float, which is the type generally recommended, gives an 



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