River rejuvenation is the geomorphic process involving changes in river movement and its base level. Negative movement occurs with land upliftment or decrease in sea level, increasing the river’s gradient and enhancing vertical erosion. Positive movement occurs with rising sea levels or land depression, reducing the river’s gradient, diminishing its erosional capacity, and enhancing sediment deposition. River rejuvenation has been observed in River Moselle in Germany and River Wear in Durham.
Characteristic features associated with negative movement:
• Entrenched or incised meanders: Deeply cut meanders indicate vertical erosion. E.g.: Colorado River through the Grand Canyon.
• River terraces: Step-like remnants of former floodplains left at higher levels due to downward erosion by the river.
• Knickpoints: Sudden gradient changes resulting in waterfalls or rapids where the old and rejuvenated profile of the river meets.
• Rapids: Occur when a river’s longitudinal profile is disrupted, causing the water to flow over a series of steep, uneven sections, typically where hard rock layers are exposed.
• Steep-sided gorges: Deep, narrow valleys with vertical walls that form in the upper course of a river during rejuvenation as the river cuts downward through resistant bedrock.
Characteristic features associated with positive movement:
• Drowned valleys: Valleys become submerged due to rising sea levels or land subsidence, often forming estuaries and resulting in the flooding of coastal areas.
• Features of deposition in middle course: In the middle course of a river, where the gradient decreases, the river loses energy and begins to deposit more sediment. As the river reaches its lower course and stretches into the sea, sediment deposition contributes to delta formation and the widening of riverbeds.
River rejuvenation can create fertile lands, boost tourism with scenic landscapes, renew ecosystems, and provide opportunities for hydroelectric power generation.