Final answer:
River levees can erode due to river currents or deposition of sediment. Regular maintenance is necessary to keep levees effective in preventing flooding.
Step-by-step explanation:
River levees are structures built alongside rivers to prevent flooding by containing the water within the river and preventing it from overflowing onto adjacent land. Over the years, river levees can undergo several changes and maintenance activities:
- Erosion: River currents can erode the levees over time, weakening their structure. This erosion can be caused by the force of the flowing water or by the presence of debris carried by the river.
- Deposition: On the other hand, the river can also deposit sediment and debris onto the levees, which can build up over time and raise the levee's height. This can happen during flood events when the river carries and deposits sediment as it overflows onto the levees.
- Maintenance: Levees require regular maintenance to ensure their effectiveness in protecting against flooding. This can involve activities such as inspecting for signs of erosion or cracks, repairing any damages, and clearing any debris that accumulates on the levee's surface.