K. Juracek | USGS Science

USGS2013

An investigation of element ratios for assessing suspended-sediment sources in small agricultural basins

Various sediment properties previously have been investigated for the purpose of determining sources of suspended sediment. A remaining research need is an assessment of element ratios for the determination of suspended-sediment sources in different terrestrial environments. In this study, 253 element ratios were assessed to determine which, if any, were potentially useful for sediment-source determinations in six small agricultural basins in northeastern Kansas, USA. Samples of surface soils (cropland and grassland), channel banks, and reservoir bottom sediments were collected, analyzed for 23 elements, and compared. Of the 253 element ratios assessed, only the Co/Pb and Co/Zn ratios were substantially and consistently different between the channel banks and surface soils for all six basins. For three of four reservoirs for which data were available, sediment-source estimates provided by Co/Pb ratios were in agreement with estimates previously provided using 137Cs. For two of the four reservoirs, sediment-source estimates provided by Co/Zn ratios were consistent with the 137Cs estimates. Thus, the Co/Pb ratio potentially may be more useful. Additional research is needed to ascertain whether or not the use of Co/Pb and Co/Zn ratios as tracers is widely applicable or restricted to specific terrestrial environments.

Physical Geography↗

USGS2012

How well do the rosgen classification and associated "natural channel design" methods integrate and quantify fluvial processes and channel response?

Over the past 10 years the Rosgen classification system and its associated methods of "natural channel design" have become synonymous (to many without prior knowledge of the field) with the term "stream restoration" and the science of fluvial geomorphology. Since the mid 1990s, this classification approach has become widely, and perhaps dominantly adopted by governmental agencies, particularly those funding restoration projects. For example, in a request for proposals for the restoration of Trout Creek in Montana, the Natural Resources Conservation Service required "experience in the use and application of a stream classification system and its implementation." Similarly, classification systems have been used in evaluation guides for riparian areas and U.S. Forest Service management plans. Most notably, many highly trained geomorphologists and hydraulic engineers are often held suspect, or even thought incorrect, if their approach does not include reference to or application of a classification system. This, combined with the para-professional training provided by some involved in "natural channel design" empower individuals and groups with limited backgrounds in stream and watershed sciences to engineer wholesale re-patterning of stream reaches using 50-year old technology that was never intended for engineering design. At Level I, the Rosgen classification system consists of eight or nine major stream types, based on hydraulic-geometry relations and four other measures of channel shape to distinguish the dimensions of alluvial stream channels as a function of the bankfull stage. Six classes of the particle size of the boundary sediments are used to further sub-divide each of the major stream types, resulting in 48 or 54 stream types. Aside from the difficulty in identifying bankfull stage, particularly in incising channels, and the issue of sampling from two distinct populations (beds and banks) to classify the boundary sediments, the classification provides a consistent and reproducible means for practitioners to describe channel morphology although difficulties have been encountered in lower-gradient stream systems. Use of the scheme to communicate between users or as a conceptual model, however, has not justified its use for engineering design or for predicting river behavior; its use for designing mitigation projects, therefore, seems beyond its technical scope. Copyright ASCE 2005.

Conference Paper↗