78 



THE IRRIGATION AGE. 



After the delta or dam had separated the gulf into 

 two parts, one an inland sea, lying in that portion of 

 the United States now Imperial Valley, there is no 

 doubt that the stream continued to shift alternately 

 into the ocean and alternately into this inland sea. 

 During this period of time the silt deposits made the 

 fertile soil, which now comprises the Imperial Valley. 



It is probable that shortly before the dawn of 

 civilization in the West the Colorado River assumed 

 its present channel, leading to the Gulf of Lower Cali- 

 fornia. There was then considerable elevated land, 

 lying between Imperial Valley and the Gulf and ex- 

 tending in the direction of Volcano Lake. Evidences 

 are conclusive to show that the stream has maintained 

 this course with but slight interruption during the last 

 100 years. During this time there have been some 

 diversions of the river into the inland sea, but these 

 were not sufficient to maintain it. The inland sea dis- 

 appeared through evaporation, except a small part fed 

 by some of the channels of the Alamo river, Bee river, 

 etc., leading in 

 that direction. 



The water 

 cut off from the 

 gulf, having 

 evaporated, has 

 left the large 

 areas, known as 

 Imperial Valley, 

 forming a basin 

 below sea level, 

 with only a small 

 lake in the deep- 

 e s t impression. 

 When first viewed 

 by the people of 

 California and 

 Mexico, it was so 

 found and. this is 

 the condition in 

 which it was more 

 than 20 years ago, 



when the first plans for its reclamation were given con- 

 sideration. 



It is therefore safe to state, that the creation of 

 the valley is due to the silt carried by the water of the 

 river, and we shall further see that this silt has played, 

 and still continues to play, an important part in the 

 irrigation projects of the valley. It will also become 

 apparent that the importance of the silt problem has 

 never been fully understood and, with all the progress 

 made during the last 15 years in dealing with the sub- 

 ject, its importance is nevertheless underestimated. 



The first diversion was made into a channel of the 

 Alamo river, which terminated in Imperial Valley, and 

 thus afforded an easy method for conveying the water 

 to a point where it is diverted out of the Alamo at 

 Sharp's Heading for distribution in the Imperial Val- 

 ley. 



In the earlier plan for the utilization of the Colo- 

 rado in Imperial Valley the writer suggested its diver- 

 sion into Bee river and Volcano Lake, and thence to 

 be distributed by canals over the Imperial Valley. This 

 plan had the disadvantage of locating the intake, as 

 well as the entire main canal system, in Mexico. But 

 it possessed the advantage of having a settling basin 

 in Volcano Lake, where the troublesome part of the 



Weir on New Hamakua Ditch at Kukttihaele, Hawaii. 



silt could be eliminated from the water before turning 

 it into the distributing canals. 



The Alamo river, which was finally utilized as a 

 main canal by the promoters of the irrigation system, 

 who were not at that time informed as to the other 

 plan, has its intake in the United States, close to the 

 International boundary line, and passes entirely 

 through Mexican territory on its way to Imperial Val- 

 ley. 



The diversion of the Colorado into the Alamo, 

 which since then has become the main irrigation canal, 

 soon began to develop difficulties on account of the 

 presence of silt. Before proceeding with the discus- 

 sion of these difficulties, and the manner in which they 

 were overcome, a 'brief statement as to the condition of 

 the Colorado river water with reference to silt will 

 not be out of place. 



The appearance of the water is a dark red to 

 brown, due to the character of the silt. From this it 



has taken i t s 

 name, the Span- 

 ish word Colo- 

 r a d o, meaning 

 red. The Arizona 

 experiment sta- 

 tion on the lower 

 Colorado has in- 

 vestigated the 

 amount of silt 

 carried by the 

 stream and in this 

 way has deter- 

 mined that it de- 

 livers on the aver- 

 age from 35,000 

 to 40,000 acre 

 feet of silt per 

 annum. 



The amount 

 of silt carried 

 varies greatly at 



different times, being highest when the river is in flood, 

 and may be roughly stated to range between 80 to 

 3,500 parts per 100,000 parts of water by weight, or 

 from the one-thirtieth to the twelve-hundredth part of 

 volume of water by weight. On an average it is fair 

 to say that the Colorado river carries from nine to ten 

 tons of silt in each acre foot of water. 



In accordance with the well known law governing 

 the transporting power of water, the volume of silt 

 carried depends on the velocity of the stream. Under 

 variable conditions as to the velocity it soon became 

 apparent that irrigating canals would at times accumu- 

 late silt, as it is impossible to construct them on a suf- 

 ficiently steep grade, with safety to the banks, to in- 

 sure the carrying of all of the silt delivered, when the 

 Colorado river is at its flood stage. 



Whenever the water assumes a velocity in the 

 canals less than in the river, the lessening of the trans- 

 porting power induces the deposition of silt. These 

 difficulties soon became apparent in the Alamo river, 

 used as the main canal. The deposits first occurred in 

 the upper reaches of the main canal, until the level was 

 raised to such an extent, that diversions into it from 

 the stream were no longer possible. 



It must here be remembered, that the Colorado is 

 a navigable stream as far as the Potholes above Yuma 



