What are the large stones placed at culverts or water edges to prevent erosion called?

The large stones placed at culverts or water edges to prevent erosion are referred to as riprap. Riprap serves a crucial function in civil engineering and environmental management by stabilizing soil and reducing the velocity of water flow. This helps in minimizing the potential for erosion caused by water runoff or river currents. The heavy stones, often ranging from small boulders to larger rocks, are strategically placed to absorb and deflect the energy of flowing water, ultimately protecting the bank or culvert from being washed away.

Other options, while related to construction or landscaping, do not perform the same protective function as riprap. Aggregate is typically used as a component in concrete or as a base material but does not specifically refer to the erosion control context. Ballast is generally used in railroad construction or as a stabilizing material in various applications, while fill pertains to material used to raise the ground level or fill voids, lacking the specific qualities needed to address erosion in the way riprap does. Thus, riprap is the correct term for this essential erosion control method.