FOOTNOTES
a characterized by loose soil or sediment
b Unless specified otherwise, the term “irrigation methods” includes practices and technology related to both the application and delivery (conveyance) of irrigation water.
c Implications of changing irrigation methods discussed in this paper generally pertain to irrigated agriculture that is dependent upon and connected to river and alluvial aquifer systems, where exchange between shallow aquifers and surface water bodies takes place on relatively short time scales. The consequences of changing irrigation methods will be different in areas overlying deep aquifers that are not connected to river systems (such as the Ogallala Aquifer in the Great Plains).
d Groundwater irrigation withdrawals have significant influence on hydrology in certain watersheds in Montana and, where this is the case, groundwater irrigation must be factored into water supply considerations and decision-making.
e Conveyance refers to the collective network of canals, ditches and laterals that facilitate the transport of irrigation water between water sources and fields. In this paper, unless otherwise stated, we use the terms canal and ditch interchangeably to represent conveyance.
f There are many different types of gravity-based and mechanized irrigation methods, which, combined with variation in conveyance, leads to a broad array of irrigation systems. The authors recognize that categorizing irrigation as either ‘sprinkler’ or ‘flood’ is an oversimplification; but they found this limited characterization necessary given the scope and length of this publication.
g Prior to human settlement, fully connected floodplains and large populations of beaver and the consequent changes to hydrology may have had a similar effect on aquifer recharge.
h A small portion of this seepage may not make it into the focal aquifer and is thus referred to as non-recoverable seepage; this portion is functionally removed from the watershed (i.e., unavailable for reuse in the watershed).iThat part of the diverted flow that is not consumptively used and is returned to its original source or other body of water. See Glossary for Montana’s legal definition of return flow.
i That part of the diverted flow that is not consumptively used and is returned to its original source or other body of water. See Glossary for Montana’s legal definition of return flow.
j From a conservation of mass standpoint, water is only physically lost from a watershed through evapotranspiration or deep groundwater percolation into an aquifer system that does not result in discharge back to the watershed in some reasonable time frame. Degraded water is lost from the watershed from a functional, but not a physical, standpoint.
k For systems in which excess agricultural water largely evaporates before it can contribute to aquifer recharge or subsequent downstream water supply, increasing efficiency of conveyance and irrigation could lead to real water savings.
l In Montana, beneficial use is defined as a use of water for the benefit of the appropriator, others persons, or the public, including but not limited to agriculture, stock water, domestic, fish and wildlife, industrial, irrigation, mining, municipal, power, recreation, water leasing, instream flow, aquifer recharge for mitigation, and aquifer storage and recovery.
m The U.S. Supreme Court appoints a Special Master to oversee the litigation (discovery, briefs, and evidentiary hearings) and make recommendations to the Court.
n Current work at the Regional Hydrology Lab at the University of Montana is simulating the hydrologic impacts of advancing the period of use from April 1 to March 15
Table of Contents | Key Messages | Water and Irrigated Agriculture | Irrigated Agriculture in Montana | The Paradox of Irrigation Efficiency | Hydrology of Irrigated Agriculture | Assessing Consequences of Changing Irrigation Methods | Water Policy and Irrigated Agriculture | Adapting to Change | Conclusion | List of Contributors | Glossary | Footnotes | References