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Irrigation Water Requirement (IWR) <br />The irrigation water requirement is the depth of irrigation water required consumptively for crop <br />production, exclusive of effective precipitation and carry over soil moisture. <br />IWR=CCU-(EP+SM)-----(Eq. 3) <br />Irrigation Year <br />A one year period starting on November 1st of the previous calendar year and ending on October 31st. <br />Consequently, irrigation year 1990 starts in calendar year 1989. See also water year. <br />Isohyet <br />A line on the surface of the earth, as represented on a map, connecting all points of equal <br />precipitation. Also called isohyetal and isopluvial line. (Rice (1991)) <br />LAN -Local Area Network <br />A computer network that is confined to a small area, e.g., a single building or city block (as opposed to <br />WAN). <br />Langley <br />A unit equal to one gram calorie per square centimeter of irradiated surface, used to measure solar <br />radiation. <br />Lateral <br />A minor ditch headgating off the main ditch used to direct water onto the land. A ditch may have many <br />laterals, depending on the amount of acreage irrigated, the slope of the land, and the rate of seepage <br />losses. (Rice (1991)) <br />Law of the River <br />The name applied to the legal framework comprised of interstate and interregional compacts, state and <br />federal laws, Supreme Court decisions, and international treaties which govern the distribution of water <br />from the Colorado River system. (Rice (1991)) <br />Linearization <br />Many of the differential equations representing physical relationships are inherently nonlinear in form. <br />Such relationships are generally difficult to handle and it is often desirable to replace them with <br />approximations which have a more tractable linear form. This may be done in specific cases, by <br />neglect of small quantities, by replacing a curve with its tangent in a range of interest or by other <br />means. The process is called linearization. (Rice (1991)) <br />Loss <br />The difference between the amount of water that is actually placed on the land and the amount of <br />water that was physically diverted to the headgate. Losses usually are from seepage and evaporation. <br />See also conveyance loss. (Rice (1991)) <br />Management Allowed Depletion (MAD) <br />Management allowed depletion is the maximum amount of water that is allowed to be depleted from <br />the soil root zone without any perceived stress in the crop. <br />Makefile <br />A file used by the software and file management tool make. Targets and dependencies are listed in the <br />makefile using a standard syntax. A target is "made" by typing "make target." A target (usually a <br />program or library) depends on its dependencies (usually source code modules). If a dependency is <br />newer than a target, then the dependency is recompiled, as is the target. <br />Mapsets for GRASS <br />A mapset is a collection of maps that have some type of permission specifications associated with <br />them. GRASS uses the idea of mapsets to improve the reliability of data. Since this system is designed <br />for more than one user at any time the integrity of the data needs to be ensured by not allowing one <br />user to change another user's data. <br />Therefore, each user has a mapset that is set up in a resource file in their home directory for which the <br />user has read and write privileges. Each user also has access to the crdss maps mapset, for which <br />each user has only read privileges. <br />MOA <br />Memorandum of Agreement. <br />