WATER LOSSES FROM WET AREAS 75 



end of the stream. At each point of reappearance the water supports 

 a considerable amount of noneeonomic vegetation. Tn describing these 

 points in tlie rivei-, Thompson* states: 



''Wherever the water is at or close to the surface there is more or 

 less evaporation, not only from the surface streams but also from the 

 ground water supply through direct upward capillary movement and 

 by transpiration from the plants. In some places as summer approaches 

 the evaporation becomes so great that the water is disposed of more 

 rapidly than it reaches the surface, and the stream dwindles and 

 disappears. But even when the stream no longer exists water is gen- 

 erally present a few feet below the surface, except in places where the 

 ground water is not held near -the surface by submerged rock "dikes" 

 or dams. xVs the end of the dry season approaches and evaporation 

 becomes less, more water reaches the surface and the stream becomes 

 wider and deeper and has a greater linear extent. The end of the 

 stream may be seen to advance on cool daj's and at night and to retreat 

 on warm days. ' ' 



One of the moist areas adjacent to the river extends for several 

 miles above the Upper Narrows at Victorville. Both surface and under- 

 ground flow must pass over the bedrock at the Upper Xarrows, and the 

 level of the underground water immediatelv above this obstruction 

 fluctuates little, the water being brought to the surface by the con- 

 striction of the channel. The ground water, therefore, is usually at 

 or near the surface over much of the area. 



Several flood channels have been cut through this moist area by 

 the river during periods of high water. After careful consideration of 

 possible sites, one of these channels, located on the east side of the 

 river just above the Upper Narrows, was selected as the site of the 

 Victorville station. The only surface water that enters this channel is 

 flood water from the river and flood waters due to torrential rain storms 

 falling upon the adjacent higher areas. The bottom of the channel has 

 been cut down below the general ground-water level, so that there is a 

 free stream flow of the raised water and a swampy area (cienaga) is 

 formed. This channel is about 1600 feet in length and from 10 to 70 

 feet in width, is not isolated from the main moist area, and contains a 

 dense growth of tules. The outflow from the cienaga joins the main 

 channel of the river at the Narrows. The altitude of the station is 

 about 2700 feet above sea level. 



A low earth dam was built at the lower end of the channel chosen 

 and a Parshall measuring flume with a water-stage recorder was 

 installed to measure the outflow. The records obtained are not given in 

 this report but it is believed that when analyzed they may be found 

 useful in correlating the results of the tank experiments presented in 

 this chapter with the stream-flow measurements made by the U. S. 

 Geological Survey in the main channel of ]Mojave River. 



During the latter part of November, 1930, evaporation and trans- 

 piration apparatus was established for the purpose of obtaining basic 

 data. Evaporation, temperature, rainfall, and wind movement records 

 were started November 22, 1930, but no tules were planted in the tanks 



* "The Mohave Desert Region, California," by David G. Thompson, U. S. Geo- 

 logical Survey Water-supply Paper 578, p. 375. 



