13 



and limited groundwater data, the water table within the glacial till 

 is rising an average four to ten inches a year and the basin is storing 

 considerably more water than it did prior to farming. More complete 

 discharge data from both the Missouri and Yellowstone Rivers reveal 

 that the Missouri River Basin is storing 4. 3 million acre-feet of water 

 a year over that being stored by the Yellowstone River Basin, a basin 

 of much less extensive farming (22). If the annual 4-to- 10-inch water 

 table rise is projected over all the cultivated farm area of the Missouri 

 Basin, it accounts for most of the excess storage. 



The discharge of the Missouri River, and presumable direct 

 runoff into the river, was significantly greater from I89I to 1915 than 

 from 1915 to 1940. Since 1940, discharge has been gradually rising 

 as excess water began seeping into tributary drainages. The decline 

 from 1915 to 1940 was undoubtedly accentuated by extended drought. 

 Even so, groundwater buildup associated with the crop-fallow system 

 appears to be the most plausible explanation for the reduced discharge. 



Saline seep development is most pronounced where the glacial 

 till is less than 30 feet thick. Excess water appears to be accumulating 

 over large areas where the till is much thicker, but has not yet reached 

 the surface. Along with the extensive loss of valuable farmland, wide- 

 spread deterioration of surface and shallow groundwater resources 

 seems inevitable as long as factors contributing to this process are 

 maintained. 



