River size as a factor in conservation
E.H. Stanley and A.J. Boulton
Other chapters in this book explore how physical, ecological, political and socio-economic factors influence river conservation efforts around the world. Directly or indirectly, each of these factors relates to the size of the river. In turn, definitions and perceptions of the ‘size’ of a river vary widely, and it is essential to effective legislation, for example, that these be expressed as unambiguously as possible.
In a physical sense, river size can be defined by catchment area, discharge, channel capacity and other geomorphological features (Richards, 1982; Newson, 1994). In a cultural sense, perceptions of river ‘size’ may vary, reflecting the experiences of the observer and the social values attached to the goods and services (sensu Meyer, 1997) provided by the river. Large rivers should attract the attention of conservationists because they are more threatened by exploitation and river regulation than smaller streams. However, large rivers are also more difficult to conserve because of their sheer size, the fact that they drain a variety of land uses and often different political states, and the potentially greater number of threatening processes they may face. Consequently, the more manageable nature of smaller streams means that these latter systems often receive disproportionately greater attention to their conservation and restoration.
This chapter reviews the definitions of river size, ecological scale and spatial hierarchy in a conservation context. Most studies recognize the importance of a catchment-scale approach but divide river systems into ‘sub-catchments’ or some intermediate spatial scale for assessment, management and conservation purposes. We explore the success of several of these strategies based on river size, seeking generalities that may guide future conservation efforts. We challenge water managers to consider explicitly the implications of river size in conservation of entire catchments, recognizing that selection of equal-sized areas for management along a river course (e.g. regions based on municipal boundaries) is unlikely to prove a useful strategy for ecological conservation even though this may be expedient politically.
Running waters range in size from ephemeral rills that carry run-off for hours to days after rain up to massive permanent rivers whose catchments may span several countries and whose discharge alters ocean salinity for