Sediment exchange between groin fields and main-stream

- Sediment exchange between groin fields and main-stream is investigated.
- A novel method is used to quantitatively characterize the sediment exchange.
- Different sediment exchange processes exist between emerged and submerged groin fields.

Sediment exchange between groin fields and the main-stream influences the transport and distribution of polluted sediment that represents a hazard for rivers and neighboring floodplains. Despite its practical significance, little research has been done on the sediment exchange process itself, and existing studies used to estimate the sediment exchange by morphological change. The sediment exchange process, however, differs from morphological variation and includes two behaviors: the entrance of main-stream sediment into groin fields and the movement of groin field sediment out of groin fields. Therefore, this study aims at examining this exchange process and exploring the mechanisms of different exchange phenomena. Experiments were conducted in a mobile-bed laboratory flume by using a novel experimental method that successfully separates the movement of groin fields sediment from that of main-stream sediment. In addition to traditional measurements, such as measurements of morphological changes, surface flow velocities, and bed-form propagation, the deposition of main-stream sediment in groin fields is measured in detail. The results demonstrate that morphological change cannot reflect the sediment exchange process. The deposition of main-stream sediment in groin fields is determined by the dynamics of sediment movement, in which bedload- and suspended-sediment-dominated processes exhibit different deposition patterns. The movement of groin field sediment out of groin fields is determined mainly by local scouring around groins.