56 



Republican is above that of the Platte, and his conclusion is that 

 this water comes from local precipitation. On the other hand, the 

 water in the wells on a line passing north and south through North 

 Platte is in a gravel stratum on a level with or below the South 

 Platte, which extends to the tributaries of the Eepublican. 



Wliile these measurements are not conclusive, since the wells 

 observed west of the State line do not go below the level of the Platte, 

 and therefore do not prove that the water from the river does not get 

 away to the south on a level lower than the wells, they seem to indi- 

 cate that in Colorado the water of the Platte is retained in its own 

 valley, either in the surface stream or as an underflow, and that some- 

 where between the State line and North Platte the water begins to 

 flow away from the valley as underflow and contributes to the flow 

 of the trilDutaries of the Republican. The measurements made by Mr. 

 Follett east of North Platte showed that these conditions exist along 

 the river as far as Grand Island, where the measurements were dis- 

 continued. 



The measurements of return seepage given in the table seem to l^ear 

 out Mr. Follett's conclusions as regards the stream in Colorado. Ir- 

 rigation along the stream has brought about a gradual increase in 

 return waters which has now reached the State line. Mr. Follett's 

 measurements give reason to suppose that this increase will not be 

 as rapid in Nebraska as it has been in Colorado, on the supposition 

 that not all the water used in the valley of the Platte will be re- 

 tained within the valley, either in the surface stream or the sands of 

 the valley. The volume of return w^ater in the surface streams will 

 depend upon whether the supply added to the underground Avater by 

 irrigation is greater than that which is lost through the underflow 

 into the tributaries of the Republican and by evaporation. The 

 velocity of underflow is supposedly very slow, and a large use of 

 water in irrigation would probably supply it faster than it could be 

 carried away by this underflow and would tend to produce a flow in 

 the river. On the other hand, the bed of the stream in Nebraska is 

 broader than it is above and evaporation will always be a source of 

 great loss. 



The general conclusion regarding the efl^ect of irrigation in Colo- 

 rado upon the supply of water in Nebraska is that the use of the 

 water of the Platte in Colorado has reduced the size of the spring 

 floods, and also to a less extent the flow in the late summer, but this 

 summer flow has always been very unreliable. At present the im- 

 provement in the flow of the stream during the late summer due to 

 return seepage has reached the State line and may be expected to con- 

 tinue down the stream. In that case the conditions along the stream 

 in Nebraska w411 be better than they have ever been before. The floods 

 will be less, but the supply after the floods have subsided will be 



