Sediment yield in Africa

Vanmaercke, Matthias; Poesen, Jean; Broeckx, Jente; Nyssen, Jan

doi:10.1016/j.earscirev.2014.06.004

Cited by 141 publications

(161 citation statements)

References 119 publications

(57 reference statements)

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“…Figure 1 shows the frequency distribution of sediment yields for South Africa extracted from this database to which additional sources have been added (from Weaver, 1988 and. The data confirm earlier published estimates that sediment yields generally range from < 50 to > 900 t km −2 yr −1 , although the highest is a yield of over 11 000 t km −2 yr −1 not included in the Vanmaercke et al (2014) dataset but measured over 3 years in the Roxeni Dam in the former Ciskei in the 1980s (Weaver, 1988). There are significantly higher yields in the rivers database (median 230 t km −2 yr −1 ; n = 38) than in estimates from reservoir sedimentation data (median 84 t km −2 yr −1 ; n = 138).…”

Section: Introductionsupporting

confidence: 79%

“…The most recent compilation of sediment transport data for Africa was published by Vanmaercke et al (2014), including an accessible on-line database comprising sediment yield data from reservoir surveys and river monitoring. Figure 1 shows the frequency distribution of sediment yields for South Africa extracted from this database to which additional sources have been added (from Weaver, 1988 and.…”

Section: Introductionmentioning

confidence: 99%

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The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

et al. 2017

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Abstract. Several research projects undertaken by the authors and others over the last 14 years have used fallout and geogenic radionuclides for understanding erosion processes and sediment yield dynamics in South Africa over the last 100-200 years as European settlers colonised the interior plains and plateaux of the country and imported new livestock and farming techniques to the region. These projects have used two fallout radionuclides ( 210 Pb and 137 Cs) to date sediments accumulating in reservoirs, farm dams, wetlands, alluvial fans and floodouts and have used other fallout nuclides ( 7 Be) and long-lived geogenic radionuclides (e.g. 40 K, 235 U) as part of a composite fingerprint exploring contemporary sediment sources and changes to sources through time. While successful in many parts of the world, applying these techniques in Southern Africa has posed a number of challenges often not encountered elsewhere. Here we explore some of the benefits and challenges in using gamma-emitting radionuclides, especially 137 Cs, in these landscapes. Benefits include the potential for discriminating gully sidewall from topsoil sources, which has helped to identify contemporary gully systems as sediment conduits, rather than sources, and for providing a time-synchronous marker horizon in a range of sedimentary environments that has helped to develop robust chronologies. Challenges include the spatial variability in soil cover on steep rocky hillslopes, which is likely to challenge assumptions about the uniformity of initial fallout nuclide distribution, the paucity of stable (non-eroding) sites in order to estimate atmospheric fallout inventories, and the limited success of 210 Pb dating in some rapidly accumulating high altitude catchments where sediments often comprise significant amounts of sand and gravel. Despite these challenges we present evidence suggesting that the use of gamma-emitting radionuclides can make a significant contribution to our understanding of erosion processes and sediment yield dynamics. Future research highlighted in the conclusion will try to address current challenges and outline new projects established to address them more fully.

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Section: Introductionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

et al. 2017

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“…The specific sediment yield of African catchments ranges between 0.2 and 15 700 t km 2 yr -1 with median and average values of 160 and 634 t km 2 yr -1 , respectively (Vanmaercke et al, 2014). The values for the Tana , and between 0.001 and 56.9 t km 2 yr -1 for DOC (Alvarez-Cobelas et al, 2012), which are very broad ranges which encapsulate our observations.…”

Section: Comparison With Other Measurementssupporting

confidence: 62%

Seasonal and inter-annual variations in carbon fluxes in a tropical river system (Tana River, Kenya)

Geeraert

Omengo

Tamooh

et al. 2017

Preprint

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Abstract. Quantification of sediment and carbon (C) fluxes in rivers with strong seasonal and inter-annual variability 10 presents a challenge for global flux estimates as measurement periods are often too short to cover all hydrological conditions. We studied the dynamics of the Tana River (Kenya) from 2012 to 2014 through daily monitoring of sediment concentrations at three sites (Garissa, Tana River Primate Reserve and Garsen) and daily monitoring of C concentrations in Garissa and Garsen during three distinct seasons. In wet seasons, C fluxes were dominated by particulate organic C (POC) and decreased downstream. Dry season fluxes of dissolved inorganic C (DIC) and POC had a similar share in total C flux at 15 both locations while POC fluxes increased downstream. The dissolved organic C (DOC) flux did not show strong spatial nor temporal variations. The construction of constituent rating curves with a bootstrap method in combination with daily discharge data provided potential sediment and C flux ranges as a function of annual discharge. At low annual discharge, our estimates generally predict a net decrease of sediment and C storage between the upstream and downstream site. As the annual discharge increases, our simulations shift toward net retention. This analysis allowed us to infer how 20 variations in discharge regime, related to climate or human impacts, may affect riverine fluxes. Overall, we estimate that retention was dominant: integration over all simulations resulted in an average net retention of sediment (~2.9 Mt yr -1 ), POC (~18000 tC yr -1 ), DOC (~920 tC yr -1 ) and DIC (~1200 tC yr -1 ) over the 73 years of discharge measurements.

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“…Although runoff was noted to have a limited impact on the distribution of sediment yield at regional or global scales by Aalto et al (2006), Syvitski and Milliman (2007) and Vanmaercke et al (2014), the temporal variability in precipitation, runoff (or discharge) and consecutive vegetation cover was shown to be locally the main impact on fluvial sediment load (see Vanmaercke et al, 2014, p. 360). On the Wadi Abd, the yearly suspended sediment load was highly correlated with discharge (Q mean or its highest percentiles) and to its intra-annual fluctuation (Fig.…”

Section: Runoff and Sediment Yieldmentioning

confidence: 99%

Recent changes in climate, hydrology and sediment load in the Wadi Abd, Algeria (1970–2010)

Achite

Ouillon

2016

Hydrol. Earth Syst. Sci.

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Abstract.Here we investigate the changes of temperature, precipitation, river runoff and sediment transport in the Wadi Abd in northwest Algeria over a time series of 40 hydrological years . Temperature increased and precipitation decreased with the reduction in rainfall being relatively higher during the rainy season. A shift towards an earlier onset of first rains during summer was also found with cascading effects on hydrology (hydrological regimes, vegetation, etc.) and thus on erosion and sediment yield. During the 1980s, the flow regime shifted from perennial to intermittent with an amplification of the variations of discharge and a modification of the sediment regime with higher and more irregular suspended particulate flux. Sediment flux was shown to almost double every decade from the 1970s to the 2000s. The sediment regime shifted from two equivalent seasons of sediment yield (spring and fall) to a single major season regime. In the 2000s, autumn produced over 4 times more sediment than spring. The enhanced scatter of the C-Q pairs denotes an increase of hysteresis phenomena in the Wadi Abd that is probably related to the change in the hydrologic regime. At the end of the period, due to irregularity of the discharge, the ability of a rating curve to derive suspended sediment concentration from river discharge was poor.

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Sediment yield in Africa

Cited by 141 publications

References 119 publications

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

Seasonal and inter-annual variations in carbon fluxes in a tropical river system (Tana River, Kenya)

Recent changes in climate, hydrology and sediment load in the Wadi Abd, Algeria (1970–2010)

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