Which practice is not associated with protecting physical structures from erosion?

Answer: C — Channel widening

Channel widening is not typically associated with protecting physical structures from erosion. Instead, it often exacerbates erosion by increasing the flow velocity of water and reducing the stability of the banks, which can lead to greater erosion. In contrast, the use of riprap involves placing large stones along shorelines or riverbanks to absorb the energy of moving water, thereby protecting the structure from erosive forces. Building guide banks can help direct the flow of water, reducing side erosion and preventing undercutting of banks along channels. Installing gabions—wire mesh baskets filled with rocks—also serves to stabilize soil and protect against erosion by dissipating energy from water flow and reinforcing the banks. These practices are all designed with the intent of minimizing erosion and protecting structures, which highlights the distinction between them and channel widening.