Boulders will be placed in strategic locations to protect the stream banks from future erosion. The boulders have to lock together to effectively hold the bank. If they don't, the water will slowly edge the boulders away from each other, slowly gaining access to the soil behind, and eventually washing the soil away, leaving individual boulders where the bank used to be. Previous failed attempts at boulder treatment used rocks that were too round and so didn't lock together. Since we don't have a source for angular boulders, the contractor broke very large round boulders into smaller pieces. As this photo shows, the resulting pieces have lots of sharp edges--perfect for locking.
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