33 



period records of the flow of eight California streams. These 

 were selected to represent a variety of drainage basins varying 

 in length and width as well as in altitude. It will be noted 

 that each hydrograph shows a well-defined daily cycle with rise 

 and fall at approximately the same time each day although not in 

 the same degree of amplitude. 



Evaporation from a water surface is an expression of the 

 combined climatic influences affecting both evaporation and tran- 

 spiration, yet because of the volume of water in an evaporation 

 pan, the solar energy necessary to cause evaporation is greater 

 than that which causes transpiration from plants, and thus evap- 

 oration lags behind transpiration. To obtain a more sensitive 

 record of transpiration opport\inity , an evaporimeter was designed 

 by Taylor (4). This consisted of a shallow, black pan attached 

 to the weighing mechanism of a recording rain gage. The depth of 

 water in the pan is limited to the maximum evaporation for a sin- 

 gle day. The chart scale is exaggerated 9 to 1, making possible 

 the reading of very small amounts of evaporation. With this 

 equipment it is feasible to determine exact hourly evaporation 

 losses. The exposed shallow pan, resting on a sensitive balance, 

 responds readily to wind movement and the resulting pan movements 

 on the chart also record the times of greater wind movement and 

 its relative intensity. 



A measuring device much used in California investigations 

 is the Parshall flume (22). The difficulty of measuring, in a 

 single device, both low and high water flows, has been met in a 

 combination Parshall flume and connected V-notch weir or by two 

 connected Parshall flumes of different throat widths, arranged by 

 Taylor (4) to pass the maximum and minimum flows respectively. 

 The difficulty of accurate measurements of low water flow in a 

 flume intended for peak flow is obvious. Design for a double 

 Parshall flume is shown in Figure 3- It should be noted that the 

 combination flume requires two water-stage recorders. 



In using the Parshall flume it should be remembered that 



