Existing Water Rights 



Water rights in the Clark Fork Basin are of two 

 categories — those perfected after July 1973 and those in 

 place prior to that date. Water developments after 1973 were 

 subject to permitting requirements that provided a means of 

 assuring a reasonable correspondence between water rights and 

 actual use. Pre-1973 water rights were not officially 

 recorded with any degree of accuracy. The statewide 

 adjudication program was created to recognize and confirm 

 pre-1973 water rights in Montana, based on claims of actual 

 water use submitted by right-holders. 



Table 4-4 compares the water supply characteristics of 

 Clark Fork subbasins with the acres, volume, and flow of 

 irrigation claims filed for pre-1973 uses. These data are 

 compared with calculated actual water demand for acreage 

 under irrigation facilities in 1980. 



One reason that the number of acres associated with 

 adjudication claims is greater than the DNRC's estimate of 

 actual acreage in use is that the same irrigated acreage has 

 been claimed under more than one water right. For example, 

 water from two or more sources may be claimed to irrigate the 

 same ground. However, the differences that remain between 

 claims for pre-1973 uses and reasonable estimates of present 

 use and available water likely reflect a substantial 

 inflation of many claims. If the acreages and flows claimed 

 are not verified and revised where necessary to reflect 

 actual use, inflated claims will be incorporated into the 

 final decree, greatly complicating future water right 

 enforcement and water allocation efforts. For example, the 

 final decree might grant a claimant the right to irrigate 200 

 acres, when in fact only 120 acres have historically been 

 irrigated. The claimant could legally irrigate 80 addition- 

 al acres under the existing water right with a corresponding 

 increase in actual water use. Junior users could be affected 

 with little opportunity for appeal, and water available for 

 future use in or out of stream could be reduced or elimi- 

 nated. 



Ground Water 



Few aquifers in the greater Clark Fork Basin have been 

 investigated in the detail necessary to accurately determine 

 sustainable ground water yields. Certainly, large volumes of 

 water reside in storage in the valley fill sediments of the Clark 

 Fork valleys. Most of the major aquifers receive relatively 

 abundant recharge, and several possess hydraulic and depositional 

 characteristics that make them favorable targets for develop- 

 ment. All, however, are integral components of the Clark Fork 



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