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1498 because of overbank deposition triggered MY increased roughness on once-smooth .andy surfaces that are now occupied by tamarisk (Hadley, 1961). Field evidence re- vealed that some channel-side bars and is- lands that previously were 1 m(3 ft) above the annual low-water level are now 3 to 3.5 m (9 to 10 ft) above the annual low-water level. What were once barren ephemeral features are now permanent vegetated fixtures of the landscape (Fig, 10), Small floodplains (locally known as bot- W, L. GRAF toms) that existed before the tamarisk in- vasion have become enlarged, and two new floodplain sections have developed (at miles 66.8 and 72.0). New vegetated, stable is- lands have appeared at miles 31.3, 61.8, 100,0, and 106.0, The invasion of tamarisk also caused the conversion of some islands into bottoms, or floodplain sections, by eliminating the narrow, chutelike channels that separated the islands from the channel banks. The following features have de- veloped by chute elimination in the past TABLE 3, CHANNEL CHANGES, BEFORE AND AFTER INTRODUCTION OF TAMARISK, GREEN RIVER, CANYONLANDS NATIONAL PARK Site Standing Rock t Last Bend,t southwest limb Last Bend,t west limb Last Bend, t first can yon Water Tank Creekt _ork's Head Bend, southeast limb Bonita Bend, southeast limb Bonita Bend, point Bonita Bend, northwest limb Fort Bottom, south limb Fort Bottom, north limb Oak Bottom Bowknot Bend, south limb Bowknot Bend, north limb Keg Point Bottom t Trinalcove Bend, mouth Date Miles above Channel Width (m) confluence' Unstable Stable Bank to sand sand bank 1914 1975 1871 1968 1871 1968 1871 1968 1914 1975 1914 1975 1871 1975 1871 1975 1871 1975 1914 1975 1914 1975 1914 1951 1871 1951 1871 1951 1914 1951 1871 1951 !~ I, i I ,;: Trinalcove Bend, north limb 1871 1951 uth Bull Bottom 1871 1951 0.8 1.0 1.1 1.2 15.2 20,5 29.2 29,6 30.1 37,5 40,0 61.0 61.6 67,9 68,8 88,2 88.5 89,3 116 116 89 62 86 109 104 102 104 142 47 118 73 46 139 108 59 55 115 134 159 183 125 138 87 165 105 128 129 109 123 125 76 144 263 283 17 o 183 o 75 o 50 o 122 o 109 6 107 o 103 3 93 o 278 20 38 o 6 13 48 7 18 4 116 o 48 o 3 o 47 47 6 31 102 380 o 38 154 116 Change (%) -24 -20 -13 -13 -35 +25 -39 -16 -26 -55 -21 -21 -20 -37 -43 -43 -14 -43 , Mile measures based on U.S, Bureau of Reclamation survey, as mapped by Herron (1971). t Names not officially recognized by U.S, Board of Geographic Names. G ,i, i~1 I L~~__ _ 27 49 16 36 15 31 24 102 94 75 134 116 123 106 219 142 40 16 95 118 759 789 881 912 76 46 185 155 o 20 19 183 67 118 20 58 75 55 298 134 234 183 175 138 o 44 209 165 28 109 17 144 8 106 214 134 236 109 226 128 169 144 541 303 W = a(L)., century: Ruby Ranch Bottom opposi" mouth of the San Rafael River (mile an unnamed bottom (mile 90.2),' Point Bottom (mile 47.6), Saddle Bottom (mile 45.5), and Valentine B (mile 27.2), Junes Bottom (mile 87. an island in 1951~ but soon thereafter".,.",'",..,' attached to the rIver bank. " Ii Figure 11 shows several examples 0;1 ,IDI development of exaggerated point-b1: posits that convert sweeping bends o,li river into angular turns or corners. " the invasion of tamarisk, corner barS!! veloped at low water, but they were nated during flood periods when the nel made wide meanders. The develop, of permanent corner, bars precludes. ~'~ bility, so that during flood periods,~h, bank flow is dictated by the restricted ch nels. About half of the major bends ~il Green River in the study area have'<< veloped corner bars stabilized by tama ' Allometry of Islands and Bars Islands and bars (bars are defined as i aCOlmulations in the channel but atta~ to the bank) have changed in size and sh~, since the invasion of tamarisk, and; exhibit a variety of sizes and shapes a(;, one time throughout the study area.:,{ general statement that explains the.~ morphic impact of tamarisk ,must take \ account systematic changes inislands:H bars. , !!f~ Island and bar dimensions can be formulate a mathematical model des the dimensional changes through time space. Changes in length (L) and width: " are related to increases in a third varia, mass, and so are related to each otherb./ constant ratio (b): :1 , 'I dW = dL (b) 'I Wdt Ldt ,Ii The integrated form is clearer and easieti interpret: i ,~ where a is a constant (Woldenberg, 1965 If b = 1.0, length and width increase at,~ same rate, islands and bars expand whi, maintaining a constant shape, and isoll1C "'I' prevails. If b '* 1.0, changes in. sh~~, company changes in size, and aU~m, prevails (Bull, 1975), " r. 'f!l~ It seems reasonable to predict that IS~.. and bars in the Green River will ~, sh,ape as ,they gr?w .larger, because~e'1 WIdth WIll restrIct Island or bar vrd~i fore restrictions on length become app ent. As the deposits become larger" tit ,'I II I';