SELECTION OF THE SAMPLE TRANSECTS 



Sample points were plotted on a map 

 (scale: 2 inches/miles) . Aerial photos (scale: 

 1/20,000) were used to determine what tribu- 

 taries or portions of the main streams were 

 dry. This was necessary because most maps 

 don't distinguish between dry, intermittent, 

 and flowing streams. Dry streambeds were 

 eliminated from consideration as sample 

 points. If there was any doubt as to whether 

 a channel contained flowing water, the channel 

 was included in the sample. 



The beginning and end points of each 

 flowing channel were identified on photos and 

 then plotted on the map. The beginning point 

 was defined as the origin, such as a lake or 

 a stream, or as the point above which the 

 streambed was obviously dry. The end of a 

 stream was defined as the point where it 

 drained into another stream or reached the 



drainage unit boundary. These decisions were 

 based on aerial photo interpretation. 



In some instances, inspection of the photos 

 revealed flowing streams that were not shown 

 on the map. Such channels were sketched as 

 accurately as possible on the map. 



Sample points were then .selected and 

 marked at ^/4-mi\e intervals along the channels 

 showTi on the corrected map. The points were 

 numbered as shown in figure 2. Dividers were 

 used to measure the distance between these 

 points. Each point was then located on the 

 appropriate aerial photo and marked with the 

 same number used on the map. 



- The map. rather than the aerial photos, uas 

 used for selecting the sample transects, because dif- 

 ferences in scale between individual photos would 

 have made equal spacing of the sample points diffi- 

 cult and time consuming to do on photos. 



Figure 2. — Numbering system used to identify the 

 locations of sample tr.insects within drainage units is 

 shown on this sketch of a hypothetical drainage. For 

 example, 10 denotes the number assigned to the drainage 

 unit and 10-1 denotes the first sample transect on the 

 main stream of the drainage unit, while 10-T.\-1 denotes 

 the first sample transect on Tributary .\ in the drain- 

 age unit. 



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