INTRODUCTION

River channels and their floodplains have a long record of human use, modification, and environmental consequences, e.g., as compared with groundwater (Figure 8.1). A river channel is defined here as any linear depression on the earth's surface that regularly conveys surface runoff from a watershed to a natural outlet in a lake, inland sea, or ocean. This definition excludes ephemeral rills that range in width from millimeters to centimeters on a hillslope (addressed in Chapter 5 on soil moisture where their freshwaters mix with salt waters in estuarine and deltaic coastal environments.

The geographer and regional planner Patrick Geddes (1949) described the human importance of these flows from headwaters through riparian corridors and deltas in a theory known as the “valley section of human civilization.” Geddes hypothesized different patterns of human occupance and resource utilization in the upper, middle and lower reaches of a river valley, and he argued for coordinating these upstream–downstream relationships in a regional approach to planning – an idea subsequently applied by environmental planners like Ian McHarg in the Potomac, Susquehanna, and Delaware rivers in the eastern USA (Spirn, 2000). Although this chapter recognizes a much greater diversity in river forms, processes, and uses, it shares the continuing concern for coordinating human uses, hazards, and management of rivers and floodplains (Figures 8.2 and 8.3).