W. Cully Hession

The influence of riparian vegetation on stream width, eastern Pennsylvania, USA

We surveyed adjacent reaches with differing riparian vegetation to explain why channels with forested banks are wider than channels with nonforested banks. Cross sections and geomorphic mapping demonstrate that erosion occurs at cutbanks in curving reaches, while deposition is localized on active floodplains on the insides of bends. Our data indicate that rates of deposition and lateral migration are both higher in nonforested reaches than in forested reaches. Two dimensionless parameters, α and E , explain our observations. α represents the influence of grassy vegetation on rates of active floodplain deposition; it is 5 times higher in nonforested reaches than in forested reaches. E is proportional to rates of cutbank migration; it is 3 times higher in nonforested reaches than in forested reaches. Differences in width between forested and nonforested reaches are proportional to E/ α. In forested reaches, channels are wide with banks that are difficult to erode. Dense tree roots create a low value of E , and the channel migrates slowly. E/ α is high, however, because α is very low: shade from trees inhibits the growth of grass on active floodplains. In nonforested reaches, channels are narrow with banks that are easy to erode. E is high, and the channel migrates rapidly. E/ α is low, however, due to a very large value of α: grass grows readily on nonforested convex bank floodplains. Thus, differences in width between forested and nonforested reaches are related to a balance between rates of cutbank erosion and rates of deposition on active floodplains, implying that equilibrium widths develop to equalize rates of cutbank erosion and vegetation-mediated rates of deposition on active flood-plains. These results suggest that accurate models of width adjustment should consider the combined effects of bank erodibility and floodplain depositional processes, rather than focusing on these processes in isolation from one another.

Ecological engineering: A rationale for standardized curriculum and professional certification in the United States

Abstract The demand for engineering solutions to ecosystem–level problems has increased as the impact of human activities has expanded to global proportions. While the science of restoration ecology has been developed to address many critical ecosystem management issues, the high degree of complexity and uncertainty associated with these issues demands a more quantitative approach. Ecological engineering uses science-based quantification of ecological processes to develop and apply engineering-based design criteria for sustainable systems. We suggest that in the United States ecological engineering curricula should be offered at the graduate level and should require rigorous Accreditation Board of Engineering and Technology-accredited (or equivalent) undergraduate preparation in engineering fundamentals. In addition to strengthening students’ mastery of engineering theory and application, the graduate curriculum should provide core courses in ecosystem theory including quantitative ecology, systems ecology, restoration ecology, ecological engineering, ecological modeling, and ecological engineering economics. Advanced courses in limnology, environmental plant physiology, ecological economics, and specific ecosystem design should be provided to address students’ specific professional objectives. Finally, professional engineering certification must be developed to insure the credibility of this new engineering specialization.

Sediment and Phosphorus Loads from Streambank Erosion in Vermont, USA

Streambank erosion is a poorly characterized, though potentially important, nonpoint source of sediment and phosphorus contributing to water quality degradation in Vermont. We conducted field research to obtain quantitative estimates of sediment and phosphorus loads due to streambank erosion on ten stream reaches in the Lake Champlain Basin of Vermont. Results were placed in context by comparison to simulated phosphorus and sediment loads from other nonpoint sources using the EUTROMOD watershed model and loading coefficients. Streambank erosion rates, while variable between stream reaches, were moderate (average 0.26 m/year) compared to published results for similarsized watersheds. The importance of streambank erosion relative to other nonpoint sources of sediment and phosphorus was also highly variable between stream reaches, ranging from the smallest to the largest single contributor.

Assessment of Urban Streams in Fairmount Park, Philadelphia, PA

A variety of methods exist for the rapid assessment of stream reaches. They vary widely in the type of data collected, the complexity of the methods, and the conclusions that can be drawn from the results. Relying on a variety of these methods as a basis, the we developed a method to assess streams based on geomorphic, habitat and riparian features. Over 60 km of streams including 426 stream reaches were assessed during a 2 month field effort. Analysis of the data produced an overall Stream Quality Index (SQI) used to classify streams into four major categories: severely impaired, impaired, moderately impaired, and slightly or non-impaired. The SQI rating was used in conjunction with other natural resource inventory data to aid in restoration planning and overall management of the Fairmount Park System, Philadephia, PA.