Intermittent streams are the most difficiilt to identify on aerial photos, especially in the 

 upper reaches where flow is strongly influenced by periodic rainfall. A small channel may con- 

 tain a live stream on the date of photography and be dry immediately thereafter. Similarly, 

 field surveys may find water where none was present at the time of photography. Nevertheless, 

 experience indicates that If the photo interpreter "sees" water in a channel when he is viewing 

 photos stereoscopically, a field check will usually confirm his judgment. This probability is 

 raised by the fact that most resource photos are taken during late summer and autumn, when 

 stream levels are lowest. 



When streams are identified, obviously dry channels can be eliminated from the inventory. 

 Any later fieldwork can be concentrated on streams that remain questionable after the photo 

 interpretation has been completed. 



Most drainage units contain one main channel and one or more channels tributary to it. 

 Although most of the main stream channels are named, the smaller tributaries are frequently 

 nameless. For convenience in reference, it is desirable to use some system of numerical and 

 alphabetical identification. In this study, the main channel was given the same number as that 

 of the drainage unit in which it was located. Tributary streams were then identified with the 

 letter "T" following the unit designation number. The first tributary was labeled TA, the second 

 TB, and so on, until each flowing tributary was identified. In the example shown in figure 5, the 

 third tributary in drainage unit 10 is identified as lOTC . 



RECORDING STREAMS BY DRAINAGE UNITS 



Figure 5. - -Typical drainage unit, showing 

 pattern and identification of streams . 



14 



