Since rivers in the area are very different than they were 150 years ago, floods and natural recharge occur differently now than in the past. Increased urbanization, use of flood control structures, natural recharge and artificial recharge are interrelated issues that need careful consideration. According to Webster's dictionary, a flood occurs when water overflows onto normally dry land. In this arid region the term often is used to describe a situation when an unusual amount of water flows in usually dry rivers, whether or not it overflows the banks. In Arizona an unusual amount of water flowing in a river with sufficient force to erode its banks is almost invariably referred to as a flood.
Floods provide both benefits and problems.
Floods can be beneficial when they recharge groundwater, but the same flow also can damage buildings and roads, erode land, and carry pollutants that may reach the groundwater. Years of bountiful rain and snow alternate with years of little precipitation. Heavy river flows occur occasionally and are essential for the growth of riparian vegetation. During flood years new cottonwood seedlings sprout and take hold. Traditional farming took advantage of the summer rainy season when water overflowed river banks bringing both moisture and nutrients to the soils.