The Hydrodynamics and Morphodynamics of Rivers

Rivers are a crucial part of the water cycle on the Earth. They transport water and sediment over many scales from the Amazon River to a small stream or ditch. The necessity of water to human existence means that civilization has always been intimately connected to rivers. They are used for water supply, agriculture through irrigation or flood plain cultivation, industry, transport, recreation, and even as discharge routes for polluted water. This close connection brings risks as well as benefits. Dangers include erosion, flood risk, and health risk. Benefits and dangers mean that human society has adapted rivers and floodplains over many centuries. Human intervention has accelerated since the industrial revolution and in many cases, such changes have been unsustainable, leading to severe negative impacts. The latter have led to a change from a paradigm of river engineering to one of river management, where there is greater attention paid to the effects at different scales and to working with natural processes. This move to greater sustainability has also brought in perspectives from ecology and the concept of environmental water allocation. In addition to the physical aspects of rivers, they also have great significance in cultural, political, and religious terms. All these reasons mean that modern river management must involve a wide range of stakeholders. In order to manage our rivers we need an understanding of the fundamental processes that govern their shape, processes, and impacts. This requires an understanding of the behavior of rivers at a range of scales, both spatial and temporal. This chapter outlines this understanding by looking at the various scales. This presents the state of the art of scientific understanding and then put forward issues that need to be addressed in the future.