Final answer:
The three manmade structures that prevent erosion are levees, retaining walls, and terraces. They help stabilize soil and manage water flow to protect against erosion and landslides caused by natural and human-induced factors.
Step-by-step explanation:
Manmade structures that prevent erosion can be vital in protecting landscapes from the natural and accelerated erosion processes caused by water, wind, and human activities. Structures like levees, retaining walls, and terraces are specific examples of human-engineered solutions to stabilize soil, manage water flow, and reduce the risk of erosion and landslides. Levees are often used to prevent the overflow of water from rivers, retaining walls support soil laterally so that it can be retained at different levels on the two sides, and terraces are used in agriculture to reduce the velocity of water runoff and thereby decrease soil erosion.
Landslides, an severe form of erosion, can cause significant damage to structures and landscapes. These events can be triggered by various factors such as heavy rainfall, earthquakes, volcanic eruptions, and human activities like deforestation. Countermeasures such as the strategic planting of vegetation and the installation of manmade structures are critical for landslide prevention and soil stabilization.