Rivers naturally shift course over time as sediment builds up and erodes banks. Human infrastructure, such as levees, is often built to control this natural movement. While levees can reduce flooding in the short term, they may worsen it elsewhere. Restricting a river's natural flow can also disrupt surrounding wetland ecosystems. Some engineers now advocate for allowing rivers more room to move naturally. According to the passage, what is one drawback of levees mentioned in the text?
