COMPREHENSIVE RIVER BASIN SEDIMENT BUDGETING: SIX DECADES’ EXPERIENCE

When sediment budgetting was introduced as a formal procedure in river basin studies in the 1950s, the discussion focused exclusively on suspended clastic sediments. The original purpose was to provide a quantitative check on basin-wide sediment balance: was the basin aggrading or degrading? The major change which has occurred in the last 50 years is an interest in incorporating bed load, dissolved load, nutrients and contaminants into the sediment budget. This increasing interest has come partly from discovery of the flexibility of the sediment budget methodology itself. But, more significantly, a whole range of new questions has been broached such as the following: (a) In what ways is the river basin sediment budget a management tool? (b) As a conceptual framework, in what respects has the river basin sediment budget reformulated traditional geomorphological questions? (c) What is the influence of spatial scale on the relative contribution of suspended sediments, bedload and dissolved load carried by rivers? (d) At what level of precision and accuracy can sediment source to sink pathways be defined? (e) What is the role of nutrients in the sediment budget? (f) What is the role of contaminants bound to the sediment load?

What is unquestionable is the fact that river basin sediment budgeting has become an interdisciplinary challenge underlining the weakness of single discipline expertise. Geomorphologists, hydrologists, geochemists, ecologists, civil engineers, modellers and Lidar specialists all occupy essential niches in forwarding comprehensive river basin sediment budgets.