Answer
A. Creating new, habitable land out of riverbeds
Explanation
To reclaim a land is to initiate a process of improving the land to make it suitable for a more intensive use. For example, improving a rainfall-deficient area through irrigation or removing salty and alkaline deposits on land. When you create a new land from the riverbed where a habitat can be established that reclamation! This is because maybe the river dried up or no longer exist thus the ground where the river used to flow(river bed) can be made useful again if a new habitat is established.