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...s in thessemi-arid southwestern United States, where many aquifer systems are characterized by a large volumesof water in storage, but a relatively small rate of natural annual recharge and discharge =-=[1]-=-.sBecause groundwater also supports natural systems such as wetlands, riparian systems, lakes, streams,sand rivers, it has become increasingly difficult for water managers in this region to meet boths...

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...ationssabove the EPA maximum contaminant levels in southwestern alluvial basins (Robertson,s1991).sGroundwater helps to sustain base flow to some surface waters in the semi-aridssouthwestern US (e.g. =-=Webb and Leake, 2006-=-; Simpson, 2007; Zlatos, 2008); forsexample, shallow groundwater in the Upper San Pedro Basin has been shown to be as11smajor contributor to base flow of the San Pedro River (Simpson, 2007), one of th...

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... and endangered species, and arid-land vertebrate species. Riparian vegetation in arid lands can occur at scales from isolated springs to ephemeral and intermittent watercourses, to perennial rivers (=-=Webb and Leake 2006-=-). The rivers and riparian zones of arid lands are dynamic ecosystems that are highly responsive to changing hydrology, geomorphology, human utilization, and climate change. As such, river and riparia...

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...s of river channel morphology and flood routing processes (Speight, 1965; Beven et al., 1988; Carson and Griffiths, 1989; Wharton et al., 1989; Marston et al., 1995; Wyzga, 1997; Lee and Chang, 2005; =-=Webb and Leake, 2006-=-). One of the distinctive features of flood disasters in the middle Yellow River is that they mostly result water from backing up from downstream to upstream (Qian, 1992; Wang, 2004). Backwater from d...

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...s flux can be reversed, bringing stream water into the aquifer (e.g. Theis,s1940; Sophocleous, 2002) and can ultimately dewater the riparian system and lead to theselimination of riparian vegetation (=-=Webb and Leake, 2006-=-).sMore recently, research onssemiarid rivers has shown that seasonal floods can recharge the shallow riparian aquifers(Baillie et al., 2007) and even regional aquifer systems (Plummer et al., 2004a&b...