River Processes in Different Climates

Abstract

The article contains a general discussion on river processes in different climates. It is stressed that a good knowledge of the natural river processes is of great importance, both for purely scientific reasons and in the interests of society. The prediction of future development and the forecasting of possible environmental risk factors are essential elements in the physical planning. Both the hydrological regime and the sediment production are controlled to a great extent by climate, but they are also affected by a multitude of different factors, mutually related and seldom independent. Vegetation, bedrock and soil conditions, topography and channel geometry are some of these factors.
Some typical examples are given from different climatic regions. The influence of the perennially frozen ground on the fluvial processes in arctic regions is discussed and exemplified. In humid, mid-latitude climates, the influence of, among other things, the seasonality and the possible presence of snow and ice during the winter is discussed. The partial absence of vegetation in dry climates and the occurrence of heavy flash floods is discussed, and their significance for the processes is stressed. The close relationship in the dry zones between the fluvial processes, particularly the transport of bed load, and the general geomorphological evolution of the landscape is pointed out. In the tropics, the vegetation plays a very important rôle, bòt other factors, for instance, the “lahar” activity in volcanic areas, may also be significant as regards the river characteristics.
In a concluding section, some general concepts are presented. It is pointed out that the fundamental hydrodynamic and fluvial processes are the same, irrespective of climate and other external conditions (concept of similarity), and that the rate of most river processes and their morphological and sedimentological results are directly or indirectly controlled by climate, for instance, by permafrost, river ice, snow and vegetation (concept of climatic control). There is a balance or quasi-balance in all rivers between water discharge and sediment load, determining the general character of fluvial processes and morphological development (water-sediment relationship). As the processes in a river depend on conditions and processes also in other parts of the river basin, it is necessary to treat the whole river basin as a compound unit (the river basin as the fundamental unit). The importance of geomorphological events of different frequencies and magnitudes varies with climate. This is an important topic for further studies (frequency-magnitude relationship). Man's influence on river processes is becoming more and more important. It is necessary to develop satisfactory methods for the prediction of the effects of human activities (man's influence). Process geomorphology would be a useful term to utilize, covering both the influence of climate and other factors, for example man's influence, on the long-term geomorphological development.