River and stream channels are constantly moving and changing, adjusting to their most stable form. These changes result in a stream that is in dynamic equilibrium, neither eroding nor filling over time. A stream in dynamic equilibrium is able to transport the sediment load supplied by the watershed. Land use changes within the watershed can upset this balance. If the function and the health of a stream are to be maintained, there must be an understanding of the natural stable characteristics of the stream, and the impacts that changes in land use can have on these characteristics.
In 2001, Clermont County completed a preliminary evaluation of channel conditions using the Rosgen stream classification system. The Rosgen system categorizes streams based on channel morphology. It uses a hierarchy of four assessment levels ranging from a broad characterization (Level 1) to a detailed reach-specific characterization of hydraulic and sediment relationships (Level 4). To learn more about the Rosgen classification system, visit www.wildlandhydrology.com.
A Level 1 assessment was completed on all streams in the Clermont portion of the East Fork watershed. In a Level 1 assessment, streams are categorized based on four measurable parameters, including channel slope, sinuosity, channel shape and channel patterns.
A Type B stream will have a moderately sinuous channel connected to its flood plain, and will be generally stable. A Type F stream is entrenched (flood flows are contained within the channel) and will have high bank erosion rates.
Rosgen Level 2 analyses were performed at 15 sites in the East Fork watershed. The Level 2 assessment provides a more detailed description of stream characteristics based on actual field measurements of specific channel reaches. Level 2 assigns a number (1 through 6) to each stream type describing the dominant bed material (e.g., a Type F stream with a primarily sandy bottom is assigned an F-5 classification). Information gathered from the Level 2 assessments will help the County answer questions related to sediment loadings, stream stability, biological habitat and potential for recovery.
Clermont County will be able to use the data from the Rosgen Level 1 and 2 surveys in many different ways. Data from Rosgen analyses can aid in bridge design, create flood plain maps, quantify erosion rates and sediment loss, and identify impacted streams and implement restoration projects.