Which of the following best describes the impact of levees on river systems?

Levees play a critical role in managing river systems by providing flood protection to upstream areas. However, one significant consequence of their presence is that they can lead to increased flooding downstream. This occurs because levees confine the river to a narrower channel, which can enhance the speed of the water flow. When excessive rainfall or runoff occurs, the water is unable to spread out naturally across floodplains due to the levee’s restrictions, resulting in higher water levels that can exceed the capacity of the river downstream. Consequently, levees can alter the natural hydrology of river systems and ultimately contribute to more severe flooding in areas located downstream from the levees.

While levees may enhance some aspects of flood control and can provide recreational opportunities, their impact on biodiversity and water quality is often complex and can be detrimental rather than beneficial. Thus, the assertion that levees can lead to increased flooding downstream accurately captures a critical aspect of how they affect river systems.