You are here:
A review on setting appropriate reach length for biological assessment of boatable rivers
Citation:
FLOTEMERSCH, J. E. A review on setting appropriate reach length for biological assessment of boatable rivers. Presented at American Fisheries Society, 2008 Western Division, Portland, OR, May 04 - 08, 2008.
Impact/Purpose:
The purpose of this research project is to provide methods, tools and guidance to Regions, States and Tribes to support the TMDL program. This research will investigate new measurement methods and models to link stressors to biological responses and will use existing data and knowledge to develop strategies to determine the causes of biological impairment in rivers and streams. Research will be performed across multiple spatial scales, site, subwatershed, watershed, basin, ecoregion and regional/state.
Description:
Researchers working on boatable rivers are presented with the task of selecting an appropriate stream length, or reach length, from which data will be collected. Ideally, the sampling effort applied is the minimum that will allow stated objectives to be addressed as required by a study. Comparisons based on insufficient sampling effort estimates can be confounded because real differences in assemblage structure may be indistingishable from method error. In general, long reaches are advantageous for describing the mean condition of a large river sec tion as they minimize the influence of small scale conditions and localized impairments. This advantage, however, can also be a disadvantage because long reach lengths may mask small scale habitat conditions and impairments. They may also decrease the sensitivity of indicators to detect linkages between local river conditins and drivers of conditions. Conversely, short reach lengths can be criticized for being too sensitive to local conditions and thus provide a biased reading of the overall system condition. Alternatively, reach lengths can be set by evaluating the biological parameter responses, as a function of geomorphology or a combination of the two. In short, what is deemed an appropriate reach length should be a balance between data cololection ntensity for a particular event, and the number of events that can be sampled; all of which is further tempered by carefulc onsideration of the question(s) beind addressed, the data quality (in part, the precision, accuracy and sensitivity) required to address the question, the statistical approach that will be used to analyze any resulting data, and present and future resource availability. This presentation will review issues related to appropriate sample unit definition, or sampling reach for rivers, and provide examples.