A GEOMORPHIC CONCEPTUAL MODEL IS A NECESSARY FIRST STEP IN NATURALISTIC CHANNEL DESIGN

Specifying the geometry of a river channel, given relevant values of controlling parameters, is a classic problem in fluvial geomorphology and river mechanics that has resisted solution despite more than a century of focused scientific study. This implies that “naturalistic channel design” for restoring rivers is founded on an incomplete scientific understanding. Fortunately, the goal of engineering is to satisfy design objectives, not to achieve or implement scientific understanding. However, if restoration cannot be completely guided by scientific principles, how can the science of geomorphology support river restoration design? The answer to this question follows immediately from the observation that any restoration design requires, as a fundamental initial step, an understanding of the fluvial system to be restored. For rivers, this understanding involves defining a stream's history, morphology, and relevant processes, and integrating this information into a thorough conceptual model of river channel behavior. While geomorphic models are often qualitative and insufficient by themselves to solve site specific design problems, the science of geomorphology provides objective and well developed methods for developing profound conceptual understanding of fluvial systems. Conceptual models of fluvial systems may be typically applied regionally, so geomorphic models do not necessarily need to be developed for each particular restoration site. Unfortunately, many restoration designs are based on conceptual models that were popular decades ago, and that have been supplanted by recent scientific advances. Furthermore, informative conceptual models of fluvial systems (particularly those with a strong historical, stratigraphic basis) require sophisticated geomorphic training. Geomorphologists, rather than apologizing for their inability to design restored rivers, should focus on their strongest achievement: established methods that allow a river's history, morphology, and relevant processes to be encapsulated in regionally valid conceptual models.