Limiting Width of Meander Belts 383 



French Broad and Nolichucky 



It should be remembered that there 

 are no true maxima for incised meander 

 belts, since the cut-offs that rebuke the 

 flood-plain stream when it undertakes 

 ventures beyond its strength cannot 

 readily occur when the stream bed is 

 sunk deep in the rocks. The average 

 difference of the flood-plain meander 

 ratios from their mean is 3.3, of the in- 

 cised meander ratios 12.3. There is no 

 necessary limit to meander belts when 

 incised, and soft rocks may facilitate 

 high values. 



THE WIDTH OF STREAMS 



A brief examination either of a stream 

 or a good map shows width to be very 

 variable, not merely from foot to foot, 

 from mile to mile. The most striking 

 case that I have come across is on the 

 Prestonburg, Ky., topographic sheet, 

 where Levisa Fork of the Big Sandy 

 flows for 10 miles or so in the southeast 

 part of the map with a pretty constant 

 width of over 500 feet in a deep, narrow 

 valley. Then for 5 or 6 miles near 

 Prestonburg it is barely 300 feet wide, 

 though the valley is opener. Later it 

 again widens out to the northward. If 

 correctly mapped, it is clear that such 

 variations would be important in mean- 

 der studies. 



If examination be continued through 

 the seasons, the changes at one place 

 become very great. The fluctuations 

 in height of the water at a river gage 

 are incessant, not merely through the 

 year and month, but even through the 

 day. As the slopes that confine the 

 stream waters to right and left are gen- 

 tle, the fluctuations in width are much 

 greater than the changes on the gage. 

 At high stages particularly an inch rise 

 on the gage may increase the width of 

 the river by many feet. In drought 

 stages there is a narrow thread of water 

 meandering on its own law in the bot- 

 tom of the stream bed ; at flood time 

 the whole plain is submerged, and if 

 there is then a tendency to meander, it 

 is in long curves wholly unlike those 

 the river is familiar with. The mean- 

 ders of the maps are, of course, those 

 of the stream bed. This is confined 

 by steeper slopes, but still by slopes, 

 causing it to vary in width as the water 

 falls or rises. It is in this bed that the 

 stream is when it carves its meanders, 

 and if it varies there in width, so is the 

 stream bed the scene of varying mean- 

 der tendencies. Some of the irregu- 

 larities in the resultant meanders are 

 due to this cause. For the Preliminary 

 Map of the Lower Mississippi the stage 

 adopted for mapping is about one-third 



