Final answer:
The primary function of a river levee is c. to control floodwaters by preventing the river from overflowing. Sandbags can be used to manage leaks in levees by creating an equilibrium in water levels which stops the flow.
Step-by-step explanation:
The primary function of a river levee, whether natural or artificial, is C) To control floodwaters. Levees are essentially raised banks or walls that run along the sides of a river.
The main objective is to keep river waters from flooding surrounding areas during times of high water levels, such as during excessive rainfall or snowmelt. This structure is crucial for protecting farmland, residential areas, and urban spaces from the potentially devastating effects of uncontrolled flooding.
As for how the small amount of water inside the column of sandbags is able to balance the much larger body of water behind the levee, it is based on the principle that water seeks its own level. According to Figure 11.38, when sandbags are placed around a leak outside a river levee, they prevent the water from flowing further, and water contained within this makeshift barrier will rise until it matches the level of the river water exerting pressure from the other side.
When the water inside reaches the same height as the river level, it reaches equilibrium, and the flow stops because there is no longer a gradient driving the flow.