122 THE UNIVERSITY OF OKLAHOMA 



of the huiDid region is in t?ie way in which it changes its course. 

 Sometimes because cf storms higher up the stream a wall of water 

 several feet high reaching from bank to bank will rush down the 

 river. At such times the stream is apt to change its course very 

 suddenly by cutting a new channel in the soft material of the lower 

 terrace. Such a flood in 1915 cut a channel a short distance above 

 the Normar bridge about one-third of a mile wide and a mile long 

 and left an is'and of several acres betv/een the old and new chan- 

 nels. The bed of the new channel was nor cut as low as that of the 

 old and now at low water the stream runs in the old channel. 

 Drift material has been deposited to some extent in the upper end 

 of the new channel and is being covered somewhat with dune? ^".o 

 that under the right conditions the stream may remain in the eld 

 channel. 



At times of low water much sand is picked up from the river 

 bed and blown about by the wind. As the prevailing winds are from 

 the south this has resulted in a line of sand dunes on the north side 

 of the river valley. This material is sometimes carried back from 

 the river for a distance of two or three miles. The presence of 

 sand dunes along the north banks of the rivers of Oklahoma has 

 been mentioned by Gould in Water Supply Paper, No. 148 and it 

 was suggested that because oi this continuous drift of the sard to 

 the north bank that most of the rivers of Oklahoma are migrating 

 southward. Sand dunes are also found just at the north edge of 

 the present stream bed. Remnants of lines of sand dunes are 

 common on both old terraces and are apparently always situated 

 on the north side of old river channels. During periods of low 

 water dunes also form at places in the channel itself and it is 

 probable that sometimes these lines of dunes are an important fac- 

 tor in changing the course of the stream. A line of sand dunes 

 on the river bed wou'd act as a dam and be quite effective when 

 the water is slowly rising. This is the case in holding the water 

 back from the old channel above the island. Along the north side 

 of the lake above mentioned there is a line of large dunes. Their 

 situation with regard to the old stream course is such that it is 

 probable that a line of dunes formed across the old stream bed 

 during a long dry spell and turned the stream aside and resulted 

 in its cutting its present channel from there to some distance below 

 the bridge. 



A broad, flat, sandy flood-plain elevated only a small 

 amount above the stream bed seems to be the usual condition in 

 Oklahoma streams. This is due to the great difference between 

 scour and fill at periods of high and low water and to a soil which 



