Stream Stability Analysis

This Fluvial Geomorphology Module Section will introduce Rosgen Level III classification of river Reaches. This Level 3 Stream state or condition assessment is mostly field-based, and requires in and out of channel observation and measurement. Measurement and classification of channel geomorphological pattern, profile, and dimension was the primary focus of Rosgen Level I and II analysis. Assessment of channel condition and stability is the primary focus of Level III. Note that a channel classification does not imply stability.

A stable channel will maintain its morphologic pattern, profile, and dimension, with Erosion and Deposition at levels below excessive Aggradation and Degradation. In this FGM Module Section, field based indicators of stability are introduced. Most important to Level III analysis is monitoring of indicators across time with regular return to the field, so as to note trends in river stability.

Operational and flood forecasting can benefit from stability assessment. For example, an understanding of stability helps anticipate the change in width to depth ratios and the drifting of stage-discharge relationships, or the change in Sinuosity and entrenchment ratios, and the movement of lag estimates.

A stable channel will distribute flow and sediment to maintain its pattern, profile and dimension. Channel stability is influenced by channel and watershed factors of hydrologic, biological, ecological and human nature. When a channel is self-maintaining its stability, and has a good ecologic condition, it is considered to be operating at its full potential. While Level III analysis attempts to compare a channel's existing condition and its full potential, this section will focus mainly on issues of stability.

Flood analysis is directly linked to channel stability. Completion of this FGM Module Section will help you understand the important field indicators of channel stability and provide you with exposure to methods for quantifying such indicators.

Image courtesy of Rosgen