132 KANSAS ACADEMY OF SCIENCE. 



because during each Platonic winter there may be many summer seasons when the Kaw 

 is bound in ice that the Arkansas is free to run. 



The greatest future change of surface will take place along the headwaters of the 

 Kaw, where erosion is at present most brisk ; the least future change will take place in 

 the valley of the Arkansas, where erosion at present is but slight. 



The earth that is carried down by the Kaw finds its way into the river mostly by 

 the action of water. On the other hand, the earth that is carried down by the Arkan- 

 sas from the surface of Kansas is carried into the river mostly by the wind. The clayey 

 and alkaline portions are carried away quite readily ; the sand goes out slowly. In 

 winter, when north winds prevail, the Arkansas is dry, and the wind blows considerable 

 sand out of the bed of the river, and makes ranges of sand-hills all along south of the 

 river. In summer, when the prevailing winds are south, the river is filled with water 

 and no sand is blown out. From Hutchinson to Arkansas City, over which course the 

 river runs nearly south and is seldom dry, there are no sand-hills. 



AREA. 



The area drained by the Arkansas is 22,000 square miles in Kansas, and 26,000 in 

 Colorado — 48,000 square miles in all. This does not include the territory drained by 

 the Cimarron, etc. The area drained by the Kaw is 63,000 square miles, of which 

 36,000 square miles are in Kansas, 18,000 square miles in Nebraska, and 9,000 square 

 miles in Colorado. The area drained by all other rivers is 24,000 square miles, all of 

 which rivers have their headwaters within the State, except the Missouri and the Cim- 

 arron, neither of which need be considered except as on the borders of the State. 



RAINFALL. 



The rainfall of the basin drained by the Arkansas averages a depth of 22i inches per 

 annum, being 24 inches within the State, and 21 inches in Colorado. The rainfall of 

 the Kaw basin averages 26 inches per year in Kansas, 23 inches in Nebraska, and 18 

 inches in Colorado — 24 inches for the entire basin. The rainfall of all other sections 

 averages 30 inches per annum. 



PRECIPITATION. 



This would show that the average rainfall of the entire Arkansas basin, as far down 

 as Arkansas City, Kas., is 2,450 billion cubic feet per annum, of which 1,269 billions 

 fall in Colorado. The rainfall of the entire Kaw basin is -3,515 billion cubic feet, of 

 which amount 1,340 billions fall in Nebraska and Colorado. The rainfall of all other 

 streams is figured at 1,673 billion cubic feet, all of which is precipitated in the State. 

 According to this, then, the total precipitation in Kansas amounts to 5,075 billion cubic 

 feet in a year. 



EVAPORATION. 



Were evaporation and permeability of soil equal all over the State, discharge through 

 the rivers would be in proportion to the rainfall. But it is well known that evaporation 

 is greatest in the western part of the State, and permeability is greatest in the central 

 part. From many experiments and constant observation made in Barton county, from 

 1874 to 1880, I determine that, though in many years, from Ellinwood west to the Colo- 

 rado line, evaporation is greater than the rainfall, yet ordinarily there is a small excess 

 of rainfall. Evaporation in the Arkansas valley averages 95 per cent, in Kansas, and 

 94,^ per cent, in Colorado, averaging 94§ for that basin. Evaporation is 94 per cent, in 

 the Kaw basin in Kansas, and 94J in Nebraska and Colorado, thus averaging 94} for the 

 whole basin. The evaporation in the valleys of the Neosho, Osage, and other streams, 

 is estimated at 92 per cent., which may possibly be too low. I have no means of know- 

 ing the proportion of seepage separately. It is included in the above figures for evapora- 

 tion. 



