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Water: WARSSS

Channel Processes

Transport physics, sediment size, sediment load, increases in the magnitude and duration of stream flow, stability of stream banks and bed all influence the contribution of sediment from channel processes. The hillslope processes reflect the potential sediment delivered to the channel. How the stream accommodates delivered sediment is then dependent on the particle size and magnitude of the delivered sediment load as well as the river competence and capacity.

Measurements of suspended and bedload sediment are not routinely obtained, thus the amount of data is limited throughout the United States. Relations based on measured sediment and flow data over a longer period of record are routinely extrapolated to rivers without sediment measurements. Bedload data, which is key for assessment of stream stability and habitat change, is rare due to the difficulty of obtaining measurements during high flows. As a consequence, the analysis of measured bedload transport magnitude and frequency has traditionally relied on modeled transport rates. The difficulty in prediction is often in selecting the appropriate model for the stream type being studied. Many models are often used without calibration, which requires measured bedload data. Without the calibration, the predicted values can vary from actual rates by many orders of magnitude. Bedload prediction is essential to maintain the natural stability and fish habitat features of rivers (e.g., glides, pools and spawning redds), the conveyance of sediment, and especially the coarser component of total sediment transport. For protecting a river's designated water uses such as recreation or aquatic life support, it is often more important to ascertain the channel response to a given sediment load and/or size than its response to total annual yield or export.

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