4. Existing Irrigation 



Review of 1 980 aerial photographs, infrared photogra- 

 phy and water resources data resulted in the following dis- 

 tinaions between lands on the Rosebud north of the North- 

 em Cheyenne Reservation: 



1 . sprinkler irrigation; 



2. surface irrigation, including all methods of application 

 such as border dikes and ditches, which generally re- 

 ceive at least one application a year, 



3. partial service irrigation which receives some water on 

 an intermittent basis; 



4. naturally subirrigated cropland, based on deep rooted 

 crops (alfalfa); 



5. naturally subirrigated riparian areas which are not 

 cropped; 



6. formerly irrigated cropland which has been irrigated in 

 the past but is now in dryland crops; and 



7. formerly irrigated lands now idle and not being used as 

 cropland. 



Irrigation occurring in 1 980 was calculated at approxi- 

 mately the following levels for each of these categories: 



The method used to obtain these acreages does not give 

 precise results, but does show the irrigation practices for this 

 area in 1980. More accurate information could be obtained 

 from detailed field work. 



Because of low flows and poor quality of water during 

 summer and fall, all irrigation in the Rosebud Creek basin 



is partial service. No one irrigates after mid-July. Irrigators 

 cooperate and usually only tfiree diversions operate simul- 

 taneously (GrifFidi, Holnbeck. 1982). 



A field survey by former RWRCC staff members indi- 

 cated about 1 ,900 acres were served by irrigation systems 

 downstream from the northern Reservation boundary in 

 1981 (Griffith, Holnbeck, 1982). About one-third of these 

 acres also benefited from natural flooding; most of them also 

 benefited from natural sub- irrigation (high water table). 



Around 1 ,600 acres received a second irrigation that 

 year. Pumpingwas used 88 percentandgravity diversions 12 

 percent for thesecond irrigation. Reduced streamflows were 

 the main reason for pumping (Griffith, Holnbeck, 1982). 

 The first application consisted mosdy of natural flooding 

 upstream and from gravity diversion downstream from 

 West Rosebud Creek. Acres totally dependent on natural 

 sub-irrigation were not calculated. 



The estimate of irrigated acreage south of the northern 

 reservation boundary, both on and off the Reservation, 

 ranges from 300 acres (Woessner, et al. 1981) to 543 acres 

 (Water Resources Survey, 1947). 



5. Water Availability 



Rosebud Creek is almost a fully used system. In 1 980 it 

 supported panial service irrigation for about 6,000 acres, 

 most of which are dependent on sub-irrigation. There is a 

 very small amount of additional water available during 

 March and April for early first irrigation applications. How- 

 ever, development of new irrigation systems just for one 

 application probably would be economically infeasible 

 (Greiman, 1 990) and would reduce the flow, thus probably 

 forcing some downstream irrigators to change their diver- 

 sion structures. Any other irrigation development, potential 

 reservoirs included, could adversely afFea existing practices 

 by stopping the natural flooding and changing the sub- 

 irrigation water table (Colder, 1990). 



Barring development of the Madison aquifer. Rosebud 

 Creek basin does not have enough water for significant 

 development of irrigation systems on the reservation, even 

 if all off-Reservation irrigation south of the northern reser- 

 vation boundary would cease (see Hgure 10).The total flow 

 of Rosebud Creek at the northern reservation boundary 

 exceeded 80 percent of the time for the May to September 

 irrigation season amounts to about 2,800 acre-feet 



