Veins of the EarthTWO SELECTIONS FROM THIS CHAPTER.
Rivers of LifeToo often, however, rivers are seen in terms of just two basic ‘services’ – as channels to contain flood waters and pass them as fast as possible downstream and through to the sea; and as waste disposal conduits to dilute and transport away our ‘wastes’. Given these aims, it is hardly surprising that the techniques of management then result in straightened rivers, fewer and sharper margins, less or more uniform riverside vegetation and restricted or completely prevented river-to-floodplain exchanges. All of which degrades the river environment by constraining and/or modifying river processes and thereby altering and suppressing the ecology and life of rivers.
Rivers are flows of water, and water is essential for life, mediating all the exchanges of living systems, while the spiralling form of its flow is repeated throughout life, both in the structural form of organs and organisms – shells, bones, muscles etc – and in the way they function. Life also takes place at the margins, where exchanges can occur. Rivers are flows of water and provide complex extended margins. They are thus corridors of life, and life is always more abundant along rivers. The drier the land, the more obvious the relative abundance of life along waterways, with ribbons of trees following the water courses. In the riparian vegetation, on the river banks and beaches, in the water, on the bed of the river, there is life, varying in its form, relationships and ecological structure, and interacting as the river channel moves and migrates across its floodplain.
Rivers are the veins of the Earth, the powerhouses of life, providing the means and the margins for life to develop and flourish. As they are degraded so life withers, not only along the rivers themselves, but because of their inter-connections to all of life, just like restricting or cutting the veins of a body causes its life to seep away.
The physical processes of rivers must function properly, and then life and its ecological processes will flourish.
Dynamic IntegrationRivers work through multi-functional integrated processes. There is not simply a flow of water down the river channel, nor even a flow of water plus a flow of sediments and of nutrients. They all flow together in a complex and dynamically varying way. The sediments move as suspended material within the flowing water, partly suspended and partly flowing over the bed of the river and in a jumping tumbling movement along the bed. Nutrients move as dissolved ions, in fine suspended flocs and in organic debris that floats or is tumbled along the bed. It is a mixing system which retains its stability through the inter-connectedness of its processes, through feedback dependence.
You can look at the same overall process in different ways, by focusing on a given aspect: water flowing in converging and diverging spirals; sediment moving from bank to bank by erosion and deposition; meandering channels migrating; nutrient exchanges varying as relative temperatures change, etc. The water flows in pulses from pool to riffle to pool – deeper, slower and more uniform flow to shallower, faster and more turbulent flow and back again. Channel sediments move in pulses from flood to flood and from steep eroding banks to gently sloping depositional beaches. The main channel(s) of the river move in floods, following the eroding banks and away from the deposition beaches. As the land and water temperatures vary differently over day and night and as flows vary the pattern of nutrient exchanges alters in a pulsating way.
These aspects of the overall river process vary down the river – in space – as well as over time, and give rise to a meta-stability that has both continuity and sudden transitions.
Rivers, then, have inter-connected processes, which are linked by systemic feedback and display a dynamically varying and pulsating rhythm. They are an essential part of the landscape and reflect its character in their own form and the functional intensities of their multifaceted processes. There is though a commonality in the characteristics of rivers, and a scale repetition of the same patterns – of form and behaviour. They have complex diffuse margins where soils and nutrients are exchanged and vegetational cover is very variable and continually changing as the channel edges move. This gives rise to a corresponding variation in the aquatic life of rivers, of plants, insects, fish etc, which is affected by but also alters the physical processes of the river.
They are both dynamic and constrained, continually altering but within a definable pattern, with uniformity and sudden extreme changes, in an ever-lasting dance of growth and decay, expansion and contraction, divergence and convergence.