if they can be used to measure suspended sediment concentrations in the water 

 column. 



Sediment movement, both bed load or total load, can also be measured 

 with the use of natural and artificial tracers (Dugdale 1981). Heavy minerals 

 are an example of a natural tracer which has been used in studies of sediment 

 movement (Komar et al. 1989; McMaster 1960). Natural sand can also be 

 labelled using radioactive isotopes and fluorescent coatings (Teleki 1966). 

 Radioactive tracers are not used any more because of health and safety con- 

 cerns. When fluorescent dyes are used, different colors can be used simulta- 

 neously on different size fractions to differentiate between successive experi- 

 ments at one locality (Ingle 1966). Artificial grains, which have the same 

 density and hydraulic response of natural grains, can also be used in tracer 

 studies. Aluminum cobble has been used by Nicholls and Webber (1987) on 

 rocky beaches in England. The aluminum rocks were located on the beaches 

 using metal detectors. 



As with other phenomena, the experimental design for tracer studies may 

 be Eulerian or Lagrangian. For the time integration or Eulerian method, the 

 tracer grains are injected at a constant rate over a given interval of time. For 

 space integration or the Lagrangian method, the tracers are released over an 

 area at the same time. The choice of the method depends upon the nature of 

 the problem. Field experiments must be designed carefully to isolate the 

 parameter of interest that is to be measured or traced. For example, if the 

 purpose of the study is to assess bed load transport, then care must be taken 

 not to introduce tracers into the suspended load in the water column. 



Bed forms 



Introduction. When sediment is moved by flowing water, the individual 

 grains are usually organized into morphological elements called bed forms. 

 These occur in a baffling variety of shapes and scales. Some bed forms are 

 stable only between certain values of flow strength. Often, small bed forms 

 (ripples) are found superimposed on larger forms (dunes), suggesting that the 

 flow field may vary dramatically over time. Bed forms may move in the 

 same direction as the current flow, may move against the current (antidunes), 

 or may not move at all except under specific circumstances. The study of bed 

 form shape and size is of great value because it can assist in making quan- 

 titative estimates of the strength of currents in modern and ancient sediments 

 (Harms 1969; Jopling 1966). This introduction to a complex subject is by 

 necessity greatly condensed. For details on interpretation of surface structures 

 and sediment laminae, readers are referred to textbooks on sedimentology 

 such as Allen (1968; 1985), Komar (1976), Leeder (1982), Lewis (1984), and 

 Reineck and Singh (1980). 



50 



Chapter 3 Field Data Collection and Observation 



