Final answer:
Empty riverbeds in Arizona where rain flows are known as washes or arroyos, which fill with water during rainfalls. Erosion significantly influences the landscape in these regions, forming distinctive features such as 'The Wave' in the Vermillion Cliffs. Washes play a critical role in channeling water in desert ecosystems, impacting water storage and landscapes.
Step-by-step explanation:
In Arizona, the empty riverbeds where rain flows are commonly known as washes or arroyos. These are dry channels that temporarily fill with water during rainfalls, a phenomenon that is particularly common in desert environments where rain is infrequent but can be heavy, leading to sudden flows of water. Washes play a critical role in these ecosystems, as they channel the infrequent precipitation to basins like Lake Powell, where it can be stored. The white ring around Lake Powell, depicted in Figure 1, is an indication of fluctuating water levels in these reservoirs. Washes also contribute to the formation of unique landscapes like 'The Wave' in the Vermillion Cliffs (Figure 8), which was formed by wind and water erosion. Erosion plays an important role in shaping the geography of arid regions, as seen in the cross-bedding patterns of ancient sand dunes (Figure 4.7). Moreover, wetter regions with different hydraulic patterns reveal other geological features, such as large mudcracks in dried-up riverbeds (Figure 4.10) or lush floodplains as observed historically in Egypt. As a comparison, the Zayandeh River in Iran with its qanat system shows how different methods have been developed to manage water in arid regions. Similarly, the Colorado River, which flows through Arizona and other states, is a lifeline to many communities, evident from the Hoover Dam's role in distributing water (as mentioned in the latter part of the information provided).