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F ..- --..._~- .~=,...,.~~~"."'''''_......~.~~-~~...~;fii~''''''_ A set of nomenclature, loosely borrowed from Catastrophe Theory (Graf, 1979), may be described through the fish example. The fish represents the WATER-RELATED RESOURCE ATTRIBUTE of interest. The habitat area represents the RESPONSE VARIABLE which can be estimated using scientific tools. Other RESPONSE VARIABLES which might, of necessity, be used include water temperature, water quality, and available food sources. The flow regime, defined in terms of either quantity, quality or timing, represents the CONTROL VARIABLE. In summary, the Departure Analysis describes the changes (departures), from existing conditions, of certain response variables (those that can be associated with changes in selected water-related resource attributes) due to changes in water-related control variables. The departures in response variables are, in turn, evaluated to estimate the probable effect upon the water-related resource attribute of interest. ZION HArIONAL PARX The Park SettiDg Zion National Park (Zion), located in southwestern Utah, is characterized by ~olorful mesas and pinnacles, and narrow canyons hundreds of feet deep. Its principal w~ter sources are springs and seeps, and the East and North Forks of the Virgin River. These rivers, and their principal tributaries, are perennial and of crucial importance to wildlife and visitors alike. The park is mostly semi-arid, making the lush bottom lands, the result of runoff and spring flow, quite distinctive. Even more so are the swamps which are found near large springs. Other important features 10 Zion include hanging gardens and the 'Zion Canyon Snail' . Hanging gardens are unique assemblages of plants which cling to canyon walls where water seeps through fractures in water-bearing strata. These plant communities, "relictual refugia," (Welsh and TOft, 1981) are composed of plant species ....from other southwest locations, boreal forests, and earlier epochs" (Malanson, 1980). The 'Zion Canyon Snail' (Physa zionsisPlsbry, 1905) is about one centimeter in length, and has been found only in a few isolated populations of no more than a couple of hundred individuals each. The snail is listed as a category 2 endangered species by the US Fish and Wildlife Service (Federal Register, 1984) because of a lack of information to assess its vulnerability. Based upon its very limited distribution it appears that this organism has very specific environmental needs. The North and East Forks of the Virgin R1 ver support populations of nongame fish. One of these is called the 'Virgin Spinedace' (Le idomeda mollis inis mollis inis Cross, 1975). This fish has also been given a category 2 classification Federal Register, 1985) for the same reason as the 'Zion Canyon Snail'. Though lacking much information, researchers generally feel that the fish will not successfully compete with certain introduced fish species (HOlden, et aI, 1974). Because of its unique physical and biotic attributes, Zion has important habitat values for many terrestrial and avian inhabitants.. It is important to emphasize the critical role of water, both surface and ground, in these unique resource values. . , -':'"'"";"~ '.~ ~:': :-~-:.:.;:. '1l .ji ..~.... .::. - ~....... t~ ~-Q .~~ .. ~ ' 450 . ~, .~ ;c:i}fI -......-..