158 IRRIGATION INVESTIGATIONS IN CALIFORNIA. 



through a coniparativeh' open countn'. For the next 25 miles it is a mountain 

 stream, flowing over a steep and rocky bed and through deep gorges. About 30 

 miles from the lake it passes into Capay Valle.v, through which it flows for about 20 

 miles, wlien it emerges into the main Sacramento Valley. Its course here is almost 

 directly eastward some 25 miles to the point where it discharges into the canal which 

 drains the countrj- east of Woodland. The fall for the first 3 miles after leaving the 

 lake is about 22 feet. The next 9 miles brings us to the junction with the North 

 Fork. The fall in this section is about 350 feet. The fall between this point and 

 Eumsej', where it enters the Capay Valley, some 20 miles below, is about 500 feet. 

 In Capaj' Valley the fall is about 200 feet. Through the Sacramento Vallej' the fall 

 to the slough is about 150 feet. The total fall from Clear Lake to the town of Yolo 

 is approximatel}' 1,275 feet. 



STORAGE. 



Clear Lake lies about 80 miles north of San Francisco, in one of the valleys of the 

 Coast Range, at an elevation of 1,325 feet above sea level. The lake and its watershed 

 occupy the larger portion of the county of Lake. Its area is about 80 square miles, 

 and it receives the drainage from about 420 square miles of rough, mountainous 

 country. The moisture precipitated on these slopes soon finds its waj' through the 

 steep channels of the mountain streams into the lake. The most important of these 

 streams are Scotts Creek, Middle Creek, Clover Creek, Kelsey Creek, Cole Creek, 

 and Siegler Creek. None of them contributes much water to the lake except during 

 the rainy season. The outlet is toward the southeast through a break in the eastern 

 ridge of the Coast Kange. This channel where the stream leaves the lake is through 

 a low, flat vallej', and is in this part from 30 to 100 feet wide and from 4 to 8 feet 

 deep. It is, except at the extreme lower end of this section, at the same level, and 

 is for all practical purposes a continuation of the lake. 



. At the end of this section the water passes over what is known locally as Grigsb}' 

 Riffle. The flow through this channel would naturally tend to lower the outlet and 

 to finally drain the lake, but this tendency is counteracted by Siegler Creek. This 

 stream enters from the south nearly at right angles to the outlet. It is a mountain 

 stream carrying, in times of flood, much debris of coarse gravel and small stones. 

 Grigsby Riffle is the bar which this stream has built up in the channel from the lake. 

 The fall in Siegler Creek for the last mile of its course is about 30 feet, and above 

 it is still steeper. The fall in Cache Creek below the riffle is moderate, not over 5 or 

 6 feet to the mile, and the current is nmch impeded by willows and other growth. 

 The constant flow from the lake hardly suffices to keep the channel open to its full 

 capacity. When the lake is at its low-water stage and Siegler Creek in flood, its 

 discharge is sufficient to gorge the outlet below the riffle to such an extent that the 

 water sets back into the lake with a marked current. At such times the deposit on 

 the bar or riffle accumulates faster than it can be carried away, and tends to perma- 

 nently raise the level of the lake. Some fears have been entertained bj' dwellers 

 along the shore and owners of lands Ij'ing along the lake that serious damage may be 

 caused in this way, and some attempt has been made to prevent this by changing the 

 channel of Siegler Creek near the mouth, throwing the discharge farther eastward, 

 below the riffle. Some digging and plowing has also been done on the riffle in times 



