Publications of Matthias Vanmaercke
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See detailPredicting gully erosion at regional scales: an empirical approach
Vanmaercke, Matthias ULiege; Poesen, Jean

Conference (2017)

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See detailMeasured soil erosion and catchment sediment yield data from Africa: an overview
Vanmaercke, Matthias ULiege; Poesen, Jean; Broeckx, Jente

Conference (2017)

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See detailA data-based landslide susceptibility map of Africa
Broeckx, Jente; Vanmaercke, Matthias ULiege; Duchateau, Rica et al

Conference (2017)

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See detailExploring the effects of seismicity on landslides and catchment sediment yield: An Italian case study
Vanmaercke, Matthias ULiege; Ardizzone, F.; Rossi, M. et al

in Geomorphology (2017), 278

Recent studies showed that contemporary average catchment sediment yields (SY, [t km− 2 y− 1]) at regional and continental scales are often strongly correlated to spatial patterns of seismic activity ... [more ▼]

Recent studies showed that contemporary average catchment sediment yields (SY, [t km− 2 y− 1]) at regional and continental scales are often strongly correlated to spatial patterns of seismic activity. Nonetheless, we currently have little insights into the mechanisms that explain these correlations. We investigated how spatial patterns of SY in Italy are linked to patterns of seismic activity. For a dataset of 103 Italian catchments with average SY measured over a period of years to decades, we extracted tectonic and none-tectonic variables that potentially explain observed differences in SY. These include proxies for vertical uplift rates and cumulative seismic moments (CSM) associated with historic earthquakes of different ranges of magnitude. Results showed that also across Italy, SY is significantly correlated to seismicity. However, SY showed much stronger correlations with proxies of seismicity relating to small but frequent earthquakes (2 ≤ Mw < 4) than with proxies relating to tectonic uplift or large, potentially landslide-triggering earthquakes (Mw ≥ 4). Analyses of a dataset of about 500,000 landslides across Italy showed very comparable trends: spatial patterns of landslides within similar lithological units generally show a significant positive correlation with CSM of weak but frequent seismicity and generally not with CSM of large earthquakes. These results suggest that, on a decadal time scale and at a regional/continental spatial scale, frequent but relatively weak seismicity may exert a more important geomorphic impact than large earthquake events or tectonic uplift. © 2016 Elsevier B.V. [less ▲]

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See detailSpatially explicit farmer population modelling in Belgium
Beckers, Veronique; Beckers, Joris; Vanmaercke, Matthias ULiege et al

Conference (2017)

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See detailEffectiveness of plant roots in controlling rill and gully erosion: A case study on vegetation communities on river dikes
Vannoppen, W.; Poesen, J.; De Baets, S. et al

Conference (2017)

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See detailModelling sediment fluxes in the Danube River Basin with SWAT
Vigiak, O.; Malagó, A.; Bouraoui, F. et al

in Science of the Total Environment (2017), 599-600

Sediment management is of prior concern in the Danube Basin for provision of economic and environmental services. This study aimed at assessing current (1995–2009) sediment fluxes of the Danube Basin with ... [more ▼]

Sediment management is of prior concern in the Danube Basin for provision of economic and environmental services. This study aimed at assessing current (1995–2009) sediment fluxes of the Danube Basin with SWAT model and identifying sediment budget knowledge gaps. After hydrologic calibration, hillslope gross erosion and sediment yields were broadly calibrated using ancillary data (measurements in plots and small catchments, and national and European erosion maps). Mean annual sediment concentrations (SSC) from 269 gauging stations (2968 station-year entries; median 19 mg/L, interquartile range IQR 10–36 mg/L) were used for calibrating in-stream sediments. SSC residuals (simulations-observations) median was 2 mg/L (IQR − 14; + 22 mg/L). In the validation dataset (172 gauging stations; 1457 data-entries, median 17 mg/L, IQR 10–28), median residual was 9 mg/L (IQR − 9; + 39 mg/L). Percent bias in an independent dataset of annual sediment yields (SSY; 689 data-entries in 95 stations; median 52 t/km2/y, IQR 20–151 t/km2/y) was − 21.5%. Overall, basin-wide model performance was considered satisfactory. Sediment fluxes appeared overestimated in some regions (Sava and Velika Morava), and underestimated in others (Siret-Prut and Romanian Danube), but unbiased elsewhere. According to the model, most sediments were generated by hillslope erosion. Streambank degradation contributed about 5% of sediments, and appeared important in high stream power Alpine reaches. Sediment trapping in reservoirs and floodplain deposition was probably underestimated and counterbalanced by high stream deposition. Factor analysis showed that model underestimations were correlated to Alpine and karst areas, whereas underestimations occurred in high seismicity areas of the Lower Danube. Contemporary sediment fluxes were about one third of values reported for the 1980s for several tributaries of the Middle and Lower Danube. Knowledge gaps affecting the sediment budget were identified in the contributions of some erosion processes (glacier erosion, gully erosion and mass movements), and in-stream sediment dynamics. © 2017 The Authors [less ▲]

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See detailPrevention and Mitigation of Urban Gullies (PREMITURG): Lessons learned from Failures and Successes
Vanmaercke, Matthias ULiege; Makanzu Imwangana, Fils; Cogels, Serge et al

Conference (2017)

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See detailA Global Data Analysis for Representing Sediment and Particulate Organic Carbon Yield in Earth System Models
Tan, Z.; Leung, L. R.; Li, H. et al

in Water Resources Research (2017), 53(12), 10674-10700

Although sediment yield (SY) from water erosion is ubiquitous and its environmental consequences are well recognized, its impacts on the global carbon cycle remain largely uncertain. This knowledge gap is ... [more ▼]

Although sediment yield (SY) from water erosion is ubiquitous and its environmental consequences are well recognized, its impacts on the global carbon cycle remain largely uncertain. This knowledge gap is partly due to the lack of soil erosion modeling in Earth System Models (ESMs), which are important tools used to understand the global carbon cycle and explore its changes. This study analyzed sediment and particulate organic carbon yield (CY) data from 1,081 and 38 small catchments (0.1–200 km2), respectively, in different environments across the globe. Using multiple statistical analysis techniques, we explored environmental factors and hydrological processes important for SY and CY modeling in ESMs. Our results show clear correlations of high SY with traditional agriculture, seismicity and heavy storms, as well as strong correlations between SY and annual peak runoff. These highlight the potential limitation of SY models that represent only interrill and rill erosion because shallow overland flow and rill flow have limited transport capacity due to their hydraulic geometry to produce high SY. Further, our results suggest that SY modeling in ESMs should be implemented at the event scale to produce the catastrophic mass transport during episodic events. Several environmental factors such as seismicity and land management that are often not considered in current catchment-scale SY models can be important in controlling global SY. Our analyses show that SY is likely the primary control on CY in small catchments and a statistically significant empirical relationship is established to calculate SY and CY jointly in ESMs. © 2017. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailLandslide risk reduction measures: a review of practices and challenges for the tropics
Maes, Jan; Kervyn, Matthieu; de Hontheim, Astrid et al

in Progress in Physical Geography (2017)

The overall objective of this review is to gain insights into landslide risk reduction measures that are applied or recommended in tropical landslide-prone countries, and the challenges at play. More ... [more ▼]

The overall objective of this review is to gain insights into landslide risk reduction measures that are applied or recommended in tropical landslide-prone countries, and the challenges at play. More specifically, this review aims to (i) presenting an overview of recent studies on landslides and landslide risk reduction in these countries, (ii) exploring the factors controlling the publication output on landslides and landslide risk reduction, (iii) reviewing the various landslide risk reduction measures recommended and implemented, and (iv) identifying the bottlenecks for the implementation of these strategies. A compilation of recommended and implemented landslide risk reduction measures in 99 landslide-prone tropical countries was made, based on an extensive review of scientific literature (382 publications). The documented measures are analysed Corresponding author: Jan Maes, Department of Earth & Environmental Sciences, KU Leuven, Celestijnenlaan 200E 03.256, Heverlee B-3001, Belgium. Email: maes.jan@kuleuven.be Progress in Physical Geography 1–31 ª The Author(s) 2017 Reprints and permission: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0309133316689344 journals.sagepub.com/home/ppg using a scheme of risk reduction measures that combines classifications of the Hyogo Framework for Action and the SafeLand project. Our literature review shows that the factors influencing the number of publications on landslides and landslide risk reduction per country are (in order of importance) the absolute physical exposure of people to landslides, the population number and the Human Development Index of a country. The ratio of publications on landslide risk reduction versus publications on landslides for landslide-prone tropical countries does not vary much between these countries (average: 0.28). A significant fraction (0.30) of all known landslide hazard reduction measures are neither implemented nor recommended according to our review. The most recommended landslide risk reduction component is ‘risk management and vulnerability reduction’ (0.38). However, the most implemented component is ‘risk assessment’ (0.57). Overall, the ratio of implemented versus recommended landslide risk reduction measures in the tropics is low (<0.50) for most landslide risk reduction components, except for ‘risk assessment’ (3.01). The most cited bottlenecks for implementing landslide risk reduction measures are scientific (0.30) and political (0.29) in nature. [less ▲]

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See detailVegetation cover and topography rather than human disturbance control gully density and sediment production on the Chinese Loess Plateau
Zhao, J.; Vanmaercke, Matthias ULiege; Chen, L. et al

in Geomorphology (2016), 274

The factors controlling topsoil erosion rates on the Chinese Loess Plateau (CLP) are currently relatively well understood and topsoil erosion rates can now be relatively accurately estimated. This is ... [more ▼]

The factors controlling topsoil erosion rates on the Chinese Loess Plateau (CLP) are currently relatively well understood and topsoil erosion rates can now be relatively accurately estimated. This is, however, not the case for non-topsoil erosion (sediment production by gullying and landslides): while it is well known that these processes produce significant amounts of sediment, the factors controlling their intensity and spatial distribution on the CLP are less well understood. In this study we quantified the contribution of non-topsoil erosion to total sediment production on the CLP and investigated which factors control spatial and temporal variations in non-topsoil erosion. We estimated non-topsoil erosion rates (ENT) by comparing the measured average sediment yields of 46 gauged catchments for the 1950–1970 period, when soil conservation measures were nearly absent in the area, with predicted topsoil erosion rates (using a recently developed empirical model). In addition, gully density was estimated in each catchment using Google Earth data. Our results showed that the area-weighted average catchment erosion rate (E) and ENT were 58.60 ± 51.80 and 48.68 ± 49.78 t ha− 1 yr− 1 respectively for the studied catchments. The sediment contribution of non-topsoil erosion to total sediment production ranged between ca. 0 and 97% with a mean of 70 ± 25%. Both E and ENT were significantly correlated to longitudinal river slope, land use, NDVI, and gully density. However, gully density was the only variable explaining a major part of the variance in both E (60%) and ENT (57%). Gully density itself was significantly related to topography and vegetation cover but not to rainfall erosivity. Importantly, gully density was not only related to overall slope steepness, but also to the longitudinal slope of the river network and the hypsometric integral, suggesting that not only land cover disturbance but also tectonic uplift controls gully density and erosion rates. The absence of a clear climate signal, both with respect to the variation in gully density and in E, can be explained by the overwhelming effect that climate has on vegetation cover. Our research showed that non-topsoil erosion processes are the dominant sediment sources on the CLP and are strongly controlled by natural factors. The effect of human disturbance on non-topsoil erosion processes is far less important than its effect on topsoil erosion. Given the dominance of non-topsoil erosion processes on the CLP, this suggests that the high sediment production of the CLP is mainly attributable to natural factors. © 2016 Elsevier B.V. [less ▲]

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See detailASSURE: a model for the simulation of urban expansion and intra-urban social segregation
Vermeiren, K.; Vanmaercke, Matthias ULiege; Beckers, Jacqueline ULiege et al

in International Journal of Geographical Information Science (2016), 30(12), 2377-2400

Numerous cities in developing regions worldwide are expanding at a tremendous rate. This requires adequate strategies to address the needs of these growing cities with diverse populations. Nonetheless ... [more ▼]

Numerous cities in developing regions worldwide are expanding at a tremendous rate. This requires adequate strategies to address the needs of these growing cities with diverse populations. Nonetheless, the development of urban policies is often hampered by the lack of reliable data or insight in the socio-spatial dynamics of this urban expansion. This paper therefore presents ASSURE, a spatially and temporally explicit model that can simulate urban growth and intra-urban social segregation, taking into account alternative policy strategies and expected social dynamics. The model has a flexible structure that allows incorporating specific city conditions that influence residential decision-making and adapting the simulation to the data available. This, in combination with the transparent model structure, makes ASSURE a potentially valuable decision support tool for urban planning. The potential is demonstrated with an example where the urban growth of and social segregation in Kampala (Uganda) is simulated based on (semi-)quantitative and qualitative data for ca. 800 households collected through interviews. The results of the simulations show that depending on the scenario, the spatial segregation and accessibility problems will evolve highly differently. © 2016 Informa UK Limited, trading as Taylor & Francis Group. [less ▲]

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See detailLinking landslide susceptibility to sediment yield at regional scale: application to Romania
Broeckx, J.; Vanmaercke, Matthias ULiege; Bălteanu, D. et al

in Geomorphology (2016), 268

It is generally accepted that catchment sediment yield (SY, t km− 2 y− 1) can be strongly influenced by landsliding. Nevertheless, due to data requirements, only few studies investigated this effect at a ... [more ▼]

It is generally accepted that catchment sediment yield (SY, t km− 2 y− 1) can be strongly influenced by landsliding. Nevertheless, due to data requirements, only few studies investigated this effect at a regional scale. The objective of this study is therefore to explore the potential of a landslide susceptibility map for explaining the spatial variation of SY in Romania. We selected 133 catchments in Romania for which SY was measured during a period of at least 10 years. For each catchment, we derived a variety of proxies that potentially explain SY, including several indicators of landslide occurrence. The latter were derived from a published landslide susceptibility map. Results show that SY is significantly correlated with mean landslide susceptibility (r2 = 0.30). Estimates of average sheet and rill erosion rates showed a much weaker correlation with SY (r2 = 0.06). Further analyses showed that the strong correlation between SY and landslide susceptibility is mainly attributed to regional variations in lithology and seismicity. Especially the latter may play a crucial role in understanding denudation rates at regional scales, e.g. by facilitating the occurrence of landslides. Using landslide proxies that also account for sediment connectivity did not result in stronger correlations. Overall, our results show that landslide susceptibility maps can be a highly useful tool to predict SY at regional scales, provided that they incorporate all relevant factors. © 2016 Elsevier B.V. [less ▲]

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See detailHow fast do gully headcuts retreat?
Vanmaercke, Matthias ULiege; Poesen, J.; Van Mele, B. et al

in Earth-Science Reviews (2016), 154

Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these ... [more ▼]

Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these led to important site-specific and regional insights, the overall importance of this erosion process or the factors that control it at a global scale remain poorly understood. This study aims to bridge this gap by reviewing research on GHR and conducting a meta-analysis of measured GHR rates worldwide. Through an extensive literature review, GHR rates for 933 individual and actively retreating gullies have been compiled from more than 70 study areas worldwide (comprising a total measuring period of >19 600 years). Each GHR rate was measured through repeated field surveys and/or analyses of aerial photographs over a period of at least one year (maximum: 97 years, median: 17 years). The data show a very large variability, both in terms of gully dimensions (cross-sectional areas ranging between 0.11 and 816 m2 with a median of 4 m2) and volumetric GHR rates (ranging between 0.002 and 47 430 m3 year- 1 with a median of 2.2 m3 year- 1). Linear GHR rates vary between 0.01 and 135 m year- 1 (median: 0.89 m year- 1), while areal GHR rates vary between 0.01 and 3628 m2 year- 1 (median: 3.12 m2 year- 1). An empirical relationship allows estimating volumetric retreat rates from areal retreat rates with acceptable uncertainties. By means of statistical analyses for a subset of 724 gullies with a known contributing area, we explored the factors most relevant in explaining the observed 7 orders of magnitudes of variation in volumetric GHR rates. Results show that measured GHR rates are significantly correlated to the runoff contributing area of the gully (r2 = 0.15) and the rainy day normal (RDN; i.e. the long-term average annual rainfall depth divided by the average number of rainy days; r2 = 0.47). Other factors (e.g. land use or soil type) showed no significant correlation with the observed GHR rates. This may be attributed to the uncertainties associated with accurately quantifying these factors. In addition, available time series data demonstrate that GHR rates are subject to very large year-to-year variations. As a result, average GHR rates measured over short (<5 year) measuring periods may be subject to very large (>100%) uncertainties. We integrated our findings into a weighted regression model that simulates the volumetric retreat rate of a gully headcut as a function of upstream drainage area and RDN. When weighing each GHR observation proportional to its measuring period, this model explains 68% of the observed variance in GHR rates at a global scale. For 76% of the monitored gullies, the simulated GHR values deviate less than one order of magnitude from their corresponding observed value. Our model clearly indicates that GHR rates are very sensitive to rainfall intensity. Since these intensities are expected to increase in most areas as a result of climate change, our results suggest that gully erosion worldwide will become more intense and widespread in the following decades. Finally, we discuss research topics that will help to address these challenges. © 2016 Elsevier B.V. [less ▲]

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See detailHoe zijn ravijnen in oude bossen ontstaan? Studiegeval Neigembos
Schotmans, Jeroen; Poesen, Jean; Vanmaercke, Matthias ULiege

in Jaarboek ...: de Aardrijkskunde (2015)

Het onderzoek naar ravijnvorming onder akkerland kreeg recent veel aandacht binnen de geomorfologie. Ravijnen onder bos komen echter ook voor, maar deze werden minder bestudeerd. Een belangrijke motivatie ... [more ▼]

Het onderzoek naar ravijnvorming onder akkerland kreeg recent veel aandacht binnen de geomorfologie. Ravijnen onder bos komen echter ook voor, maar deze werden minder bestudeerd. Een belangrijke motivatie voor onderzoek naar ravijnen onder bos is dat dit nieuwe inzichten kan aanreiken over het historisch landgebruik en mens-milieu interacties. Deze studie onderzocht grote ravijnen in het Neigembos, een oud bos nabij Ninove. De huidige hypothese stelt dat deze ravijnen ontstaan zijn door smeltwatererosie tijdens de klimaatsopwarming na het einde van de laatste ijstijd. Onderzoek van ravijnen in andere bossen van Vlaanderen heeft echter aangetoond dat dergelijke ravijnen ook kunnen ontstaan door menselijk toedoen in een recenter verleden. Dit artikel toont op basis van een geomorfologische analyse en de studie van oud kaartmateriaal aan dat het ontstaan van de ravijnen in Neigembos met grote waarschijnlijkheid het gevolg is van landgebruiksveranderingen in historische tijden. Deze bijdrage levert nuttige achtergrondinformatie voor een excursie over geomorfologische processen in oude bossen. [less ▲]

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See detailQuantifying human impacts on catchment sediment yield: A continental approach
Vanmaercke, Matthias ULiege; Poesen, J.; Govers, G. et al

in Global and Planetary Change (2015), 130

Both from a scientific and environmental management perspective, there is a large need to assess the magnitude and controlling factors of human impacts on catchment sediment yield. Quantifying this impact ... [more ▼]

Both from a scientific and environmental management perspective, there is a large need to assess the magnitude and controlling factors of human impacts on catchment sediment yield. Quantifying this impact is difficult, since it requires knowing both the actual sediment yield (SY<inf>a</inf>, [tkm-2 y-1]) as well as the corresponding "pristine" value of a catchment (SY<inf>p</inf>, [tkm-2 y-1]; i.e. the sediment yield that can be expected if the catchment was not affected by humans). Here we address this problem by comparing measured SY<inf>a</inf> values for 165 European catchments that were unaffected by dams or reservoirs with their corresponding SY<inf>p</inf>, which were predicted using a recently developed regression model. The ratio between these two values is expected to reflect the degree of human impact on catchment sediment yield (HIF).Correlation and partial correlation analyses showed that spatial variability in HIF is mainly explained by differences in land use (i.e. the fraction of arable land) and catchment area. The effect of these two factors was clearly linked in western and central Europe: whereas SY<inf>a</inf> can be easily 40 times higher than SY<inf>p</inf> in intensively cultivated small (≤1km2) catchments, the difference is negligible for large (>1000km2) catchments with the same land use. While, this concurs with our knowledge that the effects of land use (change) on erosion rates can be buffered at the catchment scale, this study provides a first robust quantification of this effect.Apart from a potential climatic effect (i.e. a correlation between HIF and the average annual air temperature) no other factors could be identified that are significant in explaining observed differences in HIF. This indicates that HIF is mainly controlled by catchment scale and land use, while other factors may be only of secondary importance at an intra-continental scale. Nonetheless, more accurate quantifications of these HIF values and more refined characterizations of the catchments in terms of (historical) land use, soil types/lithology, weather conditions and topography may reveal additional trends. 1000km2. © 2015 Elsevier B.V. [less ▲]

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See detailAdapting SWAT hillslope erosion model to predict sediment concentrations and yields in large Basins
Vigiak, O.; Malagó, A.; Bouraoui, F. et al

in Science of the Total Environment (2015), 538

The Soil and Water Assessment Tool (SWAT) is used worldwide for water quality assessment and planning. This paper aimed to assess and adapt SWAT hillslope sediment yield model (Modified Universal Soil ... [more ▼]

The Soil and Water Assessment Tool (SWAT) is used worldwide for water quality assessment and planning. This paper aimed to assess and adapt SWAT hillslope sediment yield model (Modified Universal Soil Loss Equation, MUSLE) for applications in large basins, i.e. when spatial data is coarse and model units are large; and to develop a robust sediment calibration method for large regions. The Upper Danube Basin (132,000km2) was used as case study representative of large European Basins. The MUSLE was modified to reduce sensitivity of sediment yields to the Hydrologic Response Unit (HRU) size, and to identify appropriate algorithms for estimating hillslope length (L) and slope-length factor (LS). HRUs gross erosion was broadly calibrated against plot data and soil erosion map estimates. Next, mean annual SWAT suspended sediment concentrations (SSC, mg/L) were calibrated and validated against SSC data at 55 gauging stations (622 station-years). SWAT annual specific sediment yields in subbasin reaches (RSSY, t/km2/year) were compared to yields measured at 33 gauging stations (87station-years). The best SWAT configuration combined a MUSLE equation modified by the introduction of a threshold area of 0.01km2 where L and LS were estimated with flow accumulation algorithms. For this configuration, the SSC residual interquartile was less than +/-15mg/L both for the calibration (1995-2004) and the validation (2005-2009) periods. The mean SSC percent bias for 1995-2009 was 24%. RSSY residual interquartile was within +/-10t/km2/year, with a mean RSSY percent bias of 12%. Residuals showed no bias with respect to drainage area, slope, or spatial distribution. The use of multiple data types at multiple sites enabled robust simulation of sediment concentrations and yields of the region. The MUSLE modifications are recommended for use in large basins. Based on SWAT simulations, we present a sediment budget for the Upper Danube Basin. © 2015 The Authors. [less ▲]

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See detailA review of the mechanical effects of plant roots on concentrated flow erosion rates
Vannoppen, W.; Vanmaercke, Matthias ULiege; De Baets, S. et al

in Earth-Science Reviews (2015), 150

Living plant roots modify both mechanical and hydrological characteristics of the soil matrix (e.g. soil aggregate stability by root exudates, soil cohesion, infiltration rate, soil moisture content, soil ... [more ▼]

Living plant roots modify both mechanical and hydrological characteristics of the soil matrix (e.g. soil aggregate stability by root exudates, soil cohesion, infiltration rate, soil moisture content, soil organic matter) and negatively influence the soil erodibility. During the last two decades several studies reported on the effects of plant roots in controlling concentrated flow erosion rates. However a global analysis of the now available data on root effects is still lacking. Yet, a meta-data analysis will contribute to a better understanding of the soil-root interactions as our capability to assess the effectiveness of roots in reducing soil erosion rates due to concentrated flow in different environments remains difficult. The objectives of this study are therefore: i) to provide a state of the art on studies quantifying the effectiveness of roots in reducing soil erosion rates due to concentrated flow; and ii) to explore the overall trends in erosion reduction as a function of the root (length) density, root architecture and soil texture, based on an integrated analysis of published data. We therefore compiled a dataset of measured soil detachment ratios (SDR) for the root density (RD; 822 observations) as well as for the root length density (RLD; 274 observations). A Hill curve model best describes the decrease in SDR as a function of R(L)D. An important finding of our meta-analysis is that RLD is a much more suitable variable to estimate SDR compared to RD as it is linked to root architecture. However, a large proportion of the variability in SDR could not be attributed to RD or RLD, resulting in a low predictive accuracy of these Hill curve models with a model efficiency of 0.11 and 0.17 for RD and RLD respectively. Considering root architecture and soil texture did yield a better predictive model for RLD with a model efficiency of 0.37 for fibrous roots in non-sandy soils while no improvement was found for RD. The unexplained variance is attributed to differences in experimental set-ups and measuring errors which could not be explicitly accounted for due to a lack of additional data. Based on those results, it remains difficult to predict the effects of roots on soil erosion rates. However, by using a Monte Carlo simulation approach, we were able to establish relationships that allow assessing the likely erosion-reducing effects of plant roots, while taking these uncertainties into account. Overall, this study demonstrates that plant roots can be very effective in reducing soil erosion rates due to concentrated flow. © 2015 Elsevier B.V. [less ▲]

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See detailImpact of papyrus wetland encroachment on spatial and temporal variabilities of stream flow and sediment export from wet tropical catchments
Ryken, N.; Vanmaercke, Matthias ULiege; Wanyama, J. et al

in Science of the Total Environment (2015), 511

During the past decades, land use change in the Lake Victoria basin has significantly increased the sediment fluxes to the lake. These sediments as well as their associated nutrients and pollutants affect ... [more ▼]

During the past decades, land use change in the Lake Victoria basin has significantly increased the sediment fluxes to the lake. These sediments as well as their associated nutrients and pollutants affect the food and water security of millions of people in one of Africa's most densely populated regions. Adequate catchment management strategies, based on a thorough understanding of the factors controlling runoff and sediment discharge are therefore crucial. Nonetheless, studies on the magnitude and dynamics of runoff and sediment discharge are very scarce for the Lake Victoria basin and the African Rift region.We therefore conducted runoff discharge and sediment export measurements in the Upper Rwizi, a catchment in Southwest Uganda, which is representative for the Lake Victoria basin. Land use in this catchment is characterized by grazing area on the high plateaus, banana cropping on the slopes and Cyperus papyrus L. wetlands in the valley bottoms. Due to an increasing population pressure, these papyrus wetlands are currently encroached and transformed into pasture and cropland. Seven subcatchments (358km2-2120km2), with different degrees of wetland encroachment, were monitored during the hydrological year June 2009-May 2010.Our results indicate that, due to their strong buffering capacity, papyrus wetlands have a first-order control on runoff and sediment discharge. Subcatchments with intact wetlands have a slower rainfall-runoff response, smaller peak runoff discharges, lower rainfall-runoff ratios and significantly smaller suspended sediment concentrations. This is also reflected in the measured annual area-specific suspended sediment yields (SYs): subcatchments with encroached papyrus swamps have SY values that are about three times larger compared to catchments with intact papyrus vegetation (respectively 106-137tonkm-2y-1 versus 34-37tonkm-2y-1). We therefore argue that protecting and (where possible) rehabilitating these papyrus wetlands should be a corner stone of catchment management strategies in the Lake Victoria basin. © 2014 Elsevier B.V. [less ▲]

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See detailSediment yield variability at various catchment scales and its impact on reservoirs in the Ethiopian highlands
Haregeweyn, Nigussie; Poesen, Jean; Tsunekawa, Atsushi et al

in Billi, Paolo (Ed.) Landscapes and Landforms of Ethiopia (2015)

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