Some Scale Considerations for Watercourse Restoration and Rehabilitation

Appropriate temporal and spatial scales vary between rehabilitation objectives. A scale appropriate within a physical or biological context might not be appropriate within a political or social context. For example, corporations and stockholders consider quarterly profits and losses to be an important measure of corporate health. Politicians often focus on election cycles as their measure of a program's success. Those who ignore the quarterly balance sheet or the next election may find themselves out of a job. Companyand government-sponsored rehabilitation programs, therefore, are often expected to produce interpretable results within months to a few years. For many issues, unusual events are more important than average conditions. For example, the morphology of mountainous channels and much of their diversity in aquatic habitat are shaped by infrequent large storms that may occur only once every 25 years or more. Rehabilitation programs that focus on the consequences of small "normal" storms will likely be inadequate because the critical geomorphic events that produce the physical and biological concerns are missing. Rehabilitation programs often stop at some political, social, organizational, or disciplinary boundary, although such boundaries make no sense within the physical or biological context of the issue. Relevant spatial scales also vary by issue. The appropriate area to rehabilitate the quality of a small community's water supply is defined by the boundary of the watershed supplying that water. In contrast, the area to restore salmon runs would include both freshwater and ocean habitats, encompass several large river basins, and extend far offshore.