Geomorphic histories for river and catchment management

Abstract

River and catchment management usually proceeds from the identification of an undesirable state (e.g. pollution, sedimentation, excessive water extraction, dams, invasion by exotic species) to a strategy for reaching a desirable state described as a target. Desirable states are usually determined from community values, economic assessments and ecosystem functions, or a combination of these. Where a catchment is highly disturbed, the target is usually not a natural state, as that cannot be achieved while maintaining human uses, and a history is needed to document the disturbance, understand its cause and define the 'existence space', that is, the range of natural states that have occurred in the past. Where a catchment is less disturbed, a former natural state could provide a target for management. But which of the many natural (equilibrium) states that have occurred in the past should be the target? The paper reviews what is known of the quantitative difference between pre-and post-disturbance states, searches for the presence or otherwise of equilibrium and comments on the utility of this information for catchment management. The focus is on erosion and sediment transport.

The fluvial record of climate change

“…This might involve a 'no regrets' flood risk policy of relocation of housing and critical infrastructure out of floodplain areas. In subtropical and tropical catchments, it could also include assessment of water-borne diseases and of malaria, where a diverse set of hydrological and geomorphological processes govern surface water body formation and persistence that form vector breeding sites (see Wasson [113] and Whitcombe [114]). It is clear that huge advances have been made in river system and climate change research in recent years but arguably the key remaining challenge to this rapidly maturing discipline will be realizing the potential of applied fluvial palaeohydrology for mitigating water-related problems that threaten people worldwide.…”

Combining contemporary and long-term erosion rates to target erosion hot-spots in the Great Barrier Reef, Australia

“…Conversely, when the contemporary erosion rates are lower than long-term background rates, the ratio or AEF will be <1.0. We acknowledge that erosion rates are sensitive to the time period over which they are measured (Gardner et al, 1987;Sadler, 1981;Wasson, 2012). An attempt to scale the data in this study was considered.…”

“…These erosion rates can be used to benchmark short-term anthropogenically accelerated soil erosion and fill the gap between the contemporary (~100 year) and geological (~100 to >10,000 years) time scales (Heimsath, 2006;von Blanckenburg, 2005;Wasson, 2012). Increasingly, studies are combining erosion rates derived from TCN with data of contemporary sediment flux from check dams (Vanacker et al, 2014;Vanacker et al, 2007) or sediment loads (Brown et al, 1998;Gellis et al, 2004;Hewawasam et al, 2003;Siame et al, 2011) to quantify the contribution of human activity against the natural variability of landscape sediment yields (von Blanckenburg, 2005).…”

“…Where erosion rates are high, the period can be just a few centuries. Where erosion is low, the period can be up to 100 × 10 3 years (Wasson, 2012). Beryllium-10 ( 10 Be) is a very rare radioactive nuclide produced when cosmic rays strike Earth's atmosphere, producing particle reactive forms of 10 Be that either attach to an aerosol (meteoric 10 Be) or to quartz grains within (the first metre of) surface soil and rock (in-situ 10 Be) (Willenbring and von Blanckenburg, 2010).…”

River history

“…The results, together with a wide range of monitoring and modelling procedures [53], help to inform those engaged in devising river management programmes [54]. Sediment control is perhaps the most urgent issue, as it is linked to accelerated soil erosion, reservoir sedimentation and the wider impact of sediment on aquatic ecology, river morphology and water resource exploitation [55].…”