3. Hydrogeomorphic Variability and River Restoration

—Hydrogeomorphic processes play key roles in creating, modifying, or destroying aquatic habitat and act as ecological disturbances that shape ecosystem characteristics and dynamics. Within the broad regional context set by general patterns of climate, physiography (geology and topography), and vegetation, the combined influences of the hydrologic, geomorphic, and vegetation regimes dominate the variability of river systems. Interactions among these regimes can strongly influence river ecosystems, and an understanding of the nature of these regimes and disturbance histories is crucial for setting restoration targets and interpreting the long-term ecological influences of hydrogeomorphic processes. It is difficult to design effective stream and channel restoration measures, or evaluate project performance, without an understanding of the pertinent geomorphic context, habitat-forming processes, and disturbance history. Of particular relevance are the main processes that transport and store water, sediment, and wood, and how differences in current and potential conditions are related to local conditions, basin-wide contexts, and the influences of human activities. Because stream and channel processes and characteristics vary regionally and throughout a drainage basin, there is no universal template for guiding restoration efforts. In designing restoration measures, it is essential to address trends and differences between current and potential conditions to ensure that restoration efforts are neither futile nor poorly matched to the site or system in question. You cannot step in the same river twice, for the second time it is not the same river — Heraclitus (535-475 BC)