Geoscience Reference
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Box 13.1
A century of channel change in the Gila River, southern Arizona
The ephemeral streams and rivers of the American southwest have been a focus of geomorphological attention for
more than a century and research into their changing channel forms has been encapsulated in two seminal texts
(Leopold, Wolman and Miller, 1964; Graf, 1988), each of which has been influential in the general development of
fluvial geomorphology. Towards the end of the nineteenth century, landowners, government agencies and academics
from a number of disciplines became aware that significant changes were occurring in once flat-floored valleys.
Arroyos - deep, steep-sided river incisions - were rapidly destroying grazing lands (Cooke and Reeves, 1976).
(a)
100
vegetation
50
channel
cultivated
0
stream channel
outside the bottom land
1870
1890
1910
1930
1950
1970
(b)
1.40
1.20
1.00
1870
1890
1910
1930
1950
1970
(c)
1.5
1.0
0.5
1910
1930
1950
1970
Figure 13.31 Changes in channel morphology and land use along a subreach of the Gila River in Safford Valley, southeast
Arizona during the period 1870 to 1970. (a) Dramatic increases in channel width arose principally from floods of 1891,
1905-1917 (eight separate events), 1941, 1965 and 1967. (b) Channel sinuosity showing successive episodes of straightening
by damaging floods and the slow subsequent recovery sympathetic with gradual reduction in channel width due to the
reestablishment of in-channel bars. (c) Estimates of flood wave celerity showing the impact of increasing flow resistance
that arose from progressive reduction in channel width and increasing sinuosity following the damaging flood events of the
1905-1917 period (after Burkham, 1970, 1972).
 
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