Tributary confluence bar (channel junction bar, eddy bar)

Position: In-channel

 

Form

Formed at, and immediately downstream of, the mouth of tributaries. These delta-like features have an avalanche face. They generally comprise poorly sorted gravels and sands with complex and variable internal sedimentary structures. They represent a form of slackwater deposit (interbedded sands and mud) that is not elevated above the channel and is prone to reworking.

 

Process description

Typically form at high flood stage in reaches where a comparatively minor tributary enters the trunk channel. Flow separation and generation of secondary currents in the backwater zones promote sedimentation in sheltered areas under low flow velocity conditions.