Human impact on land–ocean sediment transfer by the world's rivers

Walling, D. E.

doi:10.1016/j.geomorph.2006.06.019

Cited by 800 publications

(536 citation statements)

References 53 publications

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“…Catchment SY can be used to assess trends over time, by continuously measuring SY at a gauging station or by conducting multiple bathymetric surveys in a reservoir over different years (e.g. Walling 2006). Rivers in arid and semiarid zones generally have runoff discharges and sediment yields that are highly sensitive to any changes in the headwaters, especially changes in vegetation cover (e.g.…”

Section: Cost Effectivementioning

confidence: 99%

“…climate changes or human interventions) is generally known to be complex and difficult to predict (e.g. Schumm et al 1976;Walling & Kleo 1979;Church & Slaymaker 1989;Walling 2006;Owens et al 2010;Trimble 2010). SY at the catchment scale and its response to changes are, however, of great importance as it relates to many environmental and management issues (see Owens et al 2005 for an overview) and are also of great relevance in the framework of desertification assessment.…”

Section: Introductionmentioning

confidence: 99%

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Sediment yield as a desertification risk indicator

Vanmaercke

Poesen

Maetens

et al. 2011

Science of The Total Environment

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Soil erosion is often regarded as one of the main processes of desertification. This has lead to the use of various desertification indicators that are related to soil erosion. Most of these indicators focus, however, on small spatial units, while little attention has been given to the amount of sediment exported at the catchment scale. Such a small spatial unit approach neglects the transfer of sediment through catchments as well as the scale-dependency of erosion processes. Furthermore, this approach does not consider important off-site impacts of soil erosion, such as sediment deposition in reservoirs, flooding as well as ecological impacts.This study aims to illustrate the importance of also considering catchment sediment yield (SY, t km -2 y -1 ) in desertification assessment studies. Based on recently established databases of SY and soil loss rates in Europe and examples from previous studies, we illustrate that soil erosion rates at the plot scale are not representative for catchment SY, as they are often several orders of magnitude smaller. Also, the erosion response of catchments to changes in land use or climate often differs strongly from responses to those changes at the plot scale.We further discuss several of the impacts of SY and their link with desertification: i.e. the sedimentation of reservoirs, problems related to flooding, catchment hydrology, export of nutrients and ecological implications.Using earlier established criteria we evaluate the potential for using catchment SY as a desertification indicator and conclude that this could give an important added value to desertification studies. SY, used in combination with other indicators, allows the identification of other sediment sources than those considered at the plot scale and can reflect the results of desertification processes over longer time periods than periods over which assessments at the plot scale have been made. We argue therefore, that SY is a strong complementary indicator of desertification providing valuable information on the catchment response to changes in drivers of desertification.

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Section: Cost Effectivementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sediment yield as a desertification risk indicator

Vanmaercke

Poesen

Maetens

et al. 2011

Science of The Total Environment

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“…The implemented SWCmeasures therefore probably also have a significant effect on the reduction of sediment supply to river systems at the medium-sized catchment scale. However, several authors have reported that the response to changes in sediment supply at the catchment scale is often complex (Walling 1983(Walling , 2006Trimble 1999;de Vente and Poesen 2005;de Vente et al 2007). Other erosion and sediment deposition processes may override changes in sediment supply as scale increases from the hillslope to larger catchments.…”

Section: Suspended Sediment Yield and Soil And Water Conservation Mementioning

confidence: 99%

“…Descheemaeker et al 2006;Haregeweyn et al 2008;Nyssen et al 2009a), the integrated effect of these measures at the medium-sized catchment scale is not well understood. The response of catchments to soil erosion and human interventions is often complex due to scale effects which can buffer changes in sediment supply (Walling 1983;Trimble 1999;Verstraeten et al 2002;Walling 2006;de Vente et al 2007). Further, many rivers in the northern Ethiopian highlands have a hydrological regime characterized by flash floods.…”

Section: Introductionmentioning

confidence: 99%

Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia

et al. 2010

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Purpose The Ethiopian highlands are a fragile environment, characterized by steep slopes, intense rainfall, a sparse vegetation cover and the occurrence of flash floods. Although important efforts have been made to mitigate the ongoing soil erosion and land degradation problems, the sediment dynamics at medium-sized catchment scale (100-10,000 km²)are not fully understood. Therefore, this study aims to provide a better of sediment export processes and the importance of flash flood events in semi-arid tropical catchments. 2Methods Measuring campaigns were conducted in 10 subcatchments of the Geba, a tributary of the Tekeze, representative of the northern Ethiopian highlands. During 2 to 4 rainy seasons, the rivers were sampled for their suspended sediment concentration (SSC) and runoff discharge.Results and discussion Variations in SSC and sediment grain-size distribution indicate changes in sediment supply during the rainy season, due to the depletion of readily available sediments and the development of a vegetation cover.Also during flood events, changes in sediment supply are observed. Sediment yields (i.e. 497-6,543 t km -2 yr -1 ) are higher than suggested by previous studies and correlate with rainfall depth. The majority of sediment export occurs during a few short but intense flash floods. No clear effect of implemented soil and water conservation measures could be detected in the sediment yields of the catchments.Conclusions Sediment export rates in the Ethiopian highlands are high, are characterized by important changes in sediment supply and are mainly controlled by the occurrence and magnitude of flash flood events. Mitigation measures to reduce sediment yield at the catchment scale should therefore not only focus on the reduction of hillslope erosion rates, but also on the magnitude of these floods.

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“…Dams represent the most significant disturbance by human activities to global rivers (Nilsson et al, 2005;Walling, 2006). To reconcile expanding demand in energy and water resources consumption associated with economic development and the goal for mitigating global climate change, growing numbers of dams have been constructed or continue to be constructed since the 1950s (Vörösmarty and Sahagian, 2000).…”

Section: Introductionmentioning

confidence: 99%

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

Tang

Bao

et al. 2016

Science of The Total Environment

105

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• Hydrological regime in the reservoir fluctuation zone has been significantly altered.• Grain-size variations are diagnostic for sedimentary stratigraphy differentiation.• Post-dam sedimentation processes were reproduced by chronology determination.• Regular flow regulation controls contemporary seasonal sedimentary dynamics. Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1 cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by G R A P H I C A L A B S T R A C T a b s t r a c t a r t i c l e i n f o Contents lists available at ScienceDirectScience of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may have profound implications in affecting sedimentary equilibrium in the reservoir fluctuation zone. The results herein provide insights of how big dams have disrupted the sediment conveyance processes of large scale fluvial systems.

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Human impact on land–ocean sediment transfer by the world's rivers

Cited by 800 publications

References 53 publications

Sediment yield as a desertification risk indicator

Sediment yield as a desertification risk indicator

Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

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