DISTINCTIONS OF DRYLAND RIVERS: IMPLICATIONS FOR ECOSYSTEM RESTORATION

Abstract

Ecosystem restoration has become an enormous undertaking with more than one billion dollars a year spent over the past decade (Bernhardt et al., 2005). Since society has recognized the necessity to restore past degradation this is likely to continue. Much of our current understanding of river systems has been developed in humid regions, in contrast much less is known about river systems in semi-arid and arid regions, or dry lands. Nineteen of the forty four projects considered for authorization in the 2007 Water Resource Development Act (WRDA) include ecosystem restoration purposes. Six of those (32%) are in dry land portions of the country. This region is also exhibiting the most rapid population growth in the country. Rivers occurring within drylands have distinct characteristics from those in humid environments. Flow variability and linked geomorphological processes in drylands determine the extent of available habitat more than in humid rivers (Kingsford, 2006). By their very nature drylands have scarce water supply, often made scarcer by development; including diversion of flows, overdraft of groundwater, and channelization of rivers for urban development. Perhaps the most important aspect of dry land river restoration is return ofhydrologic connectivity. Legal appropriation of water in dry lands often results in rivers that are wholly appropriated and acquisition of water is necessary to accomplish restoration. Although this is usually taken for granted in humid regions, it is one of the most challenging constraints in dry lands and contributes to higher project costs. This paper uses projects along the Salt River in Phoenix to illustrate some engineered solutions in dryland river restoration projects. Finally this paper challenges the practice of using cost per acre to compare ecosystem restoration projects. Measures required for restoration in dry lands, such as water supply, are not required in humid regions and increase project costs. This difference can increase the cost of restoration in a dryland environment up to 50%.