Restoring mediterranean-climate rivers

Abstract

Mediterranean-climate rivers (med-rivers) have highly variable flow regimes, with large, periodic floods shaping the (often-braided) channels, which is different from stable humid-climate rivers, whose form may be dominated by the 1.5-year flood. There is a fundamental challenge in attempting to “restore” such variable, ever-changing, dynamic river systems, and the most effective restoration strategy is to set aside a channel migration zone within which the river can flood, erode, deposit, and migrate, without conflicting with human uses. An apparent cultural preference for stable channels has resulted in attempts to build idealized meandering channels, but these are likely to wash out during large, episodic floods typical of med-rivers. Med-rivers are more extensively dammed than their humid-climate counterparts, so downstream reaches are commonly deprived of high flows, which carry sediments, modify channel morphology, and maintain habitat complexity. Restoration of the entire pre-dam hydrograph without losing the benefits of the dam is impossible, but restoration of specific components of the natural hydrograph (to which native species are adapted) can restore some ecosystem components (such as native fish species) in med-rivers.