An entrenched river is a river that is confined to a canyon or gorge, usually with a relatively narrow width and little or no flood plain, and often with meanders worn into the landscape. Such rivers form when the base level of erosion is rapidly lowered, so that the river begins downcutting into its channel faster than it can change course (which rivers normally do on a constant basis). This may occur due to tectonic uplift of the region, a lowering of the oceans, the collapse of a moraine-dammed lake downstream, or by capture of the river by another.
Meanders in these landscapes are collectively known as 'incised meanders and come in two forms. An ingrown meander is one where incision is slow and lateral erosion takes place resulting in an asymmetric valley. This resembles an exaggerated un-incised meander. The other sort is an entrenched meander; here rapid incision occurs creating a more symmetrical valley with a gorge like appearance. Both types are due to meanders becoming established before Rejuvenation.