A species-poor community of oligochaetes occurring in estuarine conditions where sands and gravel are associated with the lower shore river channel in estuaries. The sediment is relatively coarse and mobile due to strong river flow and subject to variable salinity. There is usually very little mud in the sediment. Oligochaetes, including enchytraeid oligochaetes, constitute the infaunal assemblage. Nemerteans may be present, and nematodes may be frequent. Situation: This unit occurs in channels of very fast flowing river mouths at the bottom of otherwise sheltered estuarine shores. In this situation, biotopes under the A2.31 and A2.32 biotope complexes may be present above the river channel. Unit A2.211 may be found on the upper shore where driftlines of decomposing seaweed and other debris accumulate.