Analysis and Interpretation of Stream Channel Cross-Sectional Data

Abstract

Stream channel cross-sectional transects can be used to evaluate effects of management on stream channel morphology and therefore on fish habitat quality. We describe four indices that summarize raw data from stream channel cross sections to detect change in channel morphology over time, The net percent change in area under the transect quantifies net degradation or aggradation. The absolute percent change in area quantifies cumulative streambed or streambank material movement. The width/depth ratio is a relative index of channel shape. The Gini coefficient describes the channel cross-sectional profile, This coefficient indicates whether the channel is becoming wider and flatter or narrower and deeper, independent of change in area under the transect. These indices provide a repeatable measurement of stream channel morphology, with estimable confidence limits. They are being used to evaluate changes in channel morphology of a stream in southwestern Montana. The selection of indices depends on the information needed to evaluate management actions.