References of "Poesen, J"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailHow fast do gully headcuts retreat?
Vanmaercke, Matthias ULg; 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 ▲]

Detailed reference viewed: 8 (1 ULg)
Full Text
Peer Reviewed
See detailLinking landslide susceptibility to sediment yield at regional scale: application to Romania
Broeckx, J.; Vanmaercke, Matthias ULg; 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 ▲]

Detailed reference viewed: 9 (5 ULg)
Full Text
Peer Reviewed
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 ULg; 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 ▲]

Detailed reference viewed: 1 (0 ULg)
Full Text
Peer Reviewed
See detailQuantifying human impacts on catchment sediment yield: A continental approach
Vanmaercke, Matthias ULg; 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 ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
Peer Reviewed
See detailA review of the mechanical effects of plant roots on concentrated flow erosion rates
Vannoppen, W.; Vanmaercke, Matthias ULg; 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 ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
Peer Reviewed
See detailEvolution of the effectiveness of stone bunds and trenches in reducing runoff and soil loss in the semi-arid Ethiopian highlands
Taye, G.; Poesen, J.; Vanmaercke, Matthias ULg et al

in Zeitschrift für Geomorphologie (2015), 59(4), 477-493

Soil and Water Conservation (SWC) structures, in particular stone bunds and conservation trenches, have been extensively installed in Tigray since the 1980's. As the effectiveness of stone bunds and ... [more ▼]

Soil and Water Conservation (SWC) structures, in particular stone bunds and conservation trenches, have been extensively installed in Tigray since the 1980's. As the effectiveness of stone bunds and trenches in reducing runoff and soil loss depends on their retention capacities, it can be expected that this effectiveness declines over time due to infilling with sediment. However, little is known about the rate of this decline during subsequent years. We therefore assessed the effectiveness of SWC structures for two land use types, three slope classes and during three consecutive rainy seasons. Rainfall, runoff and soil loss were measured using 21 large (600-1,000m2) runoff plots at Mayleba catchment. Results show that all studied SWC structures are more effective in reducing soil loss than runoff. Conservation trenches are generally more effective in reducing runoff and soil loss than stone bunds. However, due to their infilling with sediment, their effectiveness quickly declines over time. By the end of the third rainy season, their effectiveness was reduced to about one third of their initial effectiveness. The effectiveness of stone bunds remained fairly constant during three consecutive rainy seasons. These findings have important implications, as they demonstrate that many of the installed SWC structures (especially in rangelands) are only very effective for short periods (one to two years). Regular sediment removal from conservation trenches is therefore crucial to preserve their effectiveness over longer periods. © 2014 Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany. [less ▲]

Detailed reference viewed: 7 (0 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
Peer Reviewed
See detailModerate seismic activity affects contemporary sediment yields
Vanmaercke, Matthias ULg; Kettner, A. J.; van Den Eeckhaut, M. et al

in Progress in Physical Geography (2014), 38(2), 145-172

Current models aiming to simulate contemporary sediment yield (SY) implicitly assume that tectonic effects are either irrelevant or are reflected by catchment topography. In this study we analyse the ... [more ▼]

Current models aiming to simulate contemporary sediment yield (SY) implicitly assume that tectonic effects are either irrelevant or are reflected by catchment topography. In this study we analyse the relation between SY and seismic activity, a component of tectonic processes. Results show a spatial correlation between SY and seismic activity expressed as the estimated peak ground acceleration (PGA) with a 10% exceedance probability in 50 years. PGA has a significant impact on the spatial variation of SY, even after correcting for cross-correlations with topography, lithology or other factors that may influence SY. Based on three distinct data sets, we demonstrate that this effect is significant both for small catchments in Europe (0.3-3940 km2) and for large river systems worldwide (1580-6.15×106 km2) and that seismic activity may be even more important for explaining regional variation in SY than land use or many other commonly considered factors (e.g. catchment area, climate). We show that explicitly considering seismic activity may lead to SY-estimates that easily deviate a factor 2 or more compared to estimates that do not consider seismic activity. This is not only the case for highly seismically active regions: also in regions with a weak to moderate seismic regime seismic activity helps explaining regional patterns in SY. We argue that these findings have important implications for a better understanding of SY and its sensitivity to human impacts, as well as for our comprehension of sediment fluxes at longer timescales. © The Author(s) 2014. [less ▲]

Detailed reference viewed: 10 (2 ULg)
Full Text
Peer Reviewed
See detailCorrigendum to "Predicting soil erosion and sediment yield at regional scales: Where do we stand?" [Earth-Sci. Rev. 127 (2013) 16-29]
De Vente, J.; Poesen, J.; Verstraeten, G. et al

in Earth-Science Reviews (2014), 133

[No abstract available]

Detailed reference viewed: 19 (1 ULg)
Full Text
Peer Reviewed
See detailSediment yield in Africa
Vanmaercke, Matthias ULg; Poesen, J.; Broeckx, J. et al

in Earth-Science Reviews (2014), 136

Several studies have compiled and analysed measured contemporary catchment sediment yield (SY, [tkm-2 y-1]) values for various regions of the world. Although this has significantly contributed to our ... [more ▼]

Several studies have compiled and analysed measured contemporary catchment sediment yield (SY, [tkm-2 y-1]) values for various regions of the world. Although this has significantly contributed to our understanding of SY, Africa remains severely underrepresented in these studies. The objective of this article is therefore: (1) to review and compile available SY data for Africa; (2) to explore the spatial variability of these SY data; and (3) to examine which environmental factors explain this spatial variability. A literature review resulted in a dataset of SY measurements for 682 African catchments from 84 publications and reports, representing more than 8340 catchment-years of observations. These catchments span eight orders of magnitude in size and are relatively well spread across the continent. A description of this dataset and comparison with other SY datasets in terms of spatial and temporal distribution and measurement quality is provided. SY values vary between 0.2 and 15,699tkm-2y-1 (median: 160tkm-2y-1, average: 634tkm-2y-1). The highest SY values occur in the Atlas region with SY values frequently exceeding 1000tkm-2y-1. Also the Rift region is generally characterised by relatively high SY values, while rivers in Western and Central Africa have generally low SY values. Spatial variation in SY at the continental scale is mainly explained by differences in seismic activity, topography, vegetation cover and annual runoff depth. Other factors such as lithology, catchment area or reservoir impacts showed less clear correlations. The results of these analyses are discussed and compared with findings from other studies. Based on our results, we propose a simple regression model to simulate SY in Africa. Although this model has a relatively low predictive accuracy (40%), it simulates the overall patterns of the observed SY values well. Potential explanations for the unexplained variance are discussed and suggestions for further research that may contribute to a better understanding of SY in Africa are made. © 2013 Elsevier B.V. [less ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
Peer Reviewed
See detailCorrigendum to "Scale-dependency of sediment yield from badland areas in Mediterranean environments" (Progress in Physical Geography 35 (3) (2011) 297-332)
Nadal-Romero, E.; Martínez-Murillo, J. F.; Vanmaercke, Matthias ULg et al

in Progress in Physical Geography (2014), 38(3), 381-386

[No abstract available]

Detailed reference viewed: 2 (0 ULg)
Full Text
Peer Reviewed
See detailImpact of earthquake-triggered landslides on catchment sediment yield
Vanmaercke, Matthias ULg; Obreja, F.; Poesen, J. et al

in IAHS-AISH Proceedings and Reports (2014), 367

This study explores the role of seismic activity in explaining spatial and temporal variation in sediment export from the Siret basin in Romania. Based on long-term (>30 years) sediment export ... [more ▼]

This study explores the role of seismic activity in explaining spatial and temporal variation in sediment export from the Siret basin in Romania. Based on long-term (>30 years) sediment export measurements for 38 subcatchments, we found that spatial variation in sediment yield (SY) is strongly correlated to the degree of seismic activity and catchment lithology. Combined, these factors explain 80% of the variation in SY. To investigate the role of earthquake-triggered landslides in explaining these correlations, we studied the temporal variability in sediment concentrations before and after the 7.4 Mw earthquake of 1977 for ten subcatchments. Despite the fact that this earthquake triggered many landslides, only one subcatchment showed a clear (3-fold) increase in sediment concentration per unit discharge after the earthquake. This shows that, although prolonged seismic activity strongly controls average SY, individual earthquakes do not necessarily affect sediment export at short timescales. Copyright © 2014 IAHS Press. [less ▲]

Detailed reference viewed: 4 (0 ULg)
Full Text
Peer Reviewed
See detailSeismic controls on contemporary sediment export in the Siret river catchment, Romania
Vanmaercke, Matthias ULg; Obreja, F.; Poesen, J.

in Geomorphology (2014), 216

While differences in catchment sediment yield (SY, [tkm-2y-1]) are generally attributed to topography, lithology, climate and land use, recent studies have highlighted that also seismic activity may have ... [more ▼]

While differences in catchment sediment yield (SY, [tkm-2y-1]) are generally attributed to topography, lithology, climate and land use, recent studies have highlighted that also seismic activity may have an important impact on SY. Nonetheless, relatively little is known about the importance of this factor and the processes and mechanisms explaining its influence. Therefore, this study explores the role of seismic activity in explaining spatial and temporal variation in sediment export within the Siret Basin (Romania, 45,000km2), a catchment with a large variability in seismic activity. Based on previously unpublished long-term (>30years) SY measurements for 38 subcatchments of the Siret, we analyze the correlation between average SY, seismic activity and various other catchment characteristics. Our results showed that spatial variation in average SY was indeed strongly correlated with the degree of seismic activity in each catchment (R2=0.74). Also catchment lithology explained an important part of the differences in SY (R2=0.67). The combination of these two factors accounted for about 80% of the observed variation in SY, while other factors (e.g. topography, land use, climate, and runoff) did not significantly contribute to the explained variance in average SY. To explore the impact of a specific earthquake event on sediment export, we analyzed daily variations in suspended sediment concentrations of 10 subcatchments, five years before and after an earthquake of Mw= 7.4 that affected the Vrancea region in 1977 and triggered a substantial number of landslides. Only one catchment showed a clear (3-fold) increase in sediment concentrations at unit discharge. For the other nine catchments, no consistent increase could be observed. This indicates that the impact of seismic activity on average SY is mainly indirect and not associated with sudden pulses of sediments, caused by earthquake-triggered landslides. Potential mechanisms that could explain such indirect responses are discussed. © 2014 Elsevier B.V. [less ▲]

Detailed reference viewed: 3 (0 ULg)
Full Text
Peer Reviewed
See detailEffects of land use, slope gradient, and soil and water conservation structures on runoff and soil loss in semi-arid Northern Ethiopia
Taye, G.; Poesen, J.; Wesemael, B. V. et al

in Physical Geography (2013), 34(3), 236-259

Land degradation and recurrent drought are the major threats to rain-fed agriculture in the semi-arid Ethiopian highlands. Water harvesting has become a priority in the Tigray region since 1990. However ... [more ▼]

Land degradation and recurrent drought are the major threats to rain-fed agriculture in the semi-arid Ethiopian highlands. Water harvesting has become a priority in the Tigray region since 1990. However, the success of water harvesting in reservoirs is limited due to reduced inflow. The aim of this study was to investigate the effects of typical land-use types, slope gradients, and different soil and water conservation (SWC) structures on runoff and soil loss at the runoff-plot scale. Six runoff measuring sites, corresponding to three slope gradients, were established for cropland (cultivated land for annual crop production) and rangeland (heavily grazed land on hillslopes with high rock-fragment cover) at Mayleba catchment in Tigray, Ethiopia. SWC structures tested were stone bunds, trenches, and stone bunds with trenches, in addition to control plots. In total, 21 large runoff plots (with lengths of 60 to 100 m) were monitored daily for runoff production and soil loss during the main rainy season (July-September) in 2010. The results show that the seasonal runoff coefficient (RCs) representing the fraction of rainfall measured as runoff was much higher for rangeland (0.38 < RCs < 0.50) compared to that for cropland (0.11 < RCS < 0.15). Seasonal soil loss (SLs) values were five to six times larger on rangeland (28.6 < SLs < 50.0 ton ha-1) compared to that for cropland (4.6 < SLs < 11.4 ton ha-1). Stone bunds with trenches were the most effective SWC structures in reducing runoff and soil loss. With the same SWC structures installed, RCs and SLs for both rangeland and cropland tend to decrease with increasing slope gradient mainly due to a corresponding increase in rock-fragment cover. The effects of SWC structures on runoff production and soil loss are considerable; hence, it is crucial to consider these effects for optimal design of water-harvesting schemes such as micro-dams that collect and store surface runoff for irrigation development in the Ethiopian highlands. © 2013 Taylor & Francis Group, LLC. [less ▲]

Detailed reference viewed: 21 (1 ULg)
Full Text
Peer Reviewed
See detailSpatial and temporal variability of river flows in the degraded semi-arid tropical mountains of northern Ethiopia
Zenebe, A.; Vanmaercke, Matthias ULg; Poesen, J. et al

in Zeitschrift für Geomorphologie (2013), 57(2), 143-169

Water availability has for long been a critical issue in many developing countries. Despite its enormous potential of water resources, Ethiopia is suffering from a lack of water availability and ... [more ▼]

Water availability has for long been a critical issue in many developing countries. Despite its enormous potential of water resources, Ethiopia is suffering from a lack of water availability and threatened by the consequences of climate change. Well-considered planning to develop these resources is crucial. However, very few observational runoff data exist for this type of environments. Especially runoff data for catchments at the intermediate scale (100- 10,000 km2) are lacking. This study assesses the runoff from 10 medium-sized catchments in the Geba river basin, a subcatchment of the Nile in the semi-arid degraded northern Ethiopian highlands. Flow depth records were automatically obtained every 10 minutes during the rainy seasons (July-September) of 2004-2007 and converted to continuous runoff discharge records. Cumulative annual runoff depths (46-395 mm) are mainly correlated with rainfall depth. Estimated runoff coefficients (9-47%) and are negatively correlated with the areal fraction of limestone outcrops in the catchments, indicating runoff transmission losses. Throughout the rainy season, increases in runoff depth and runoff coefficient were observed, which is partly attributed to an increase in baseflow throughout the season. The majority of the runoff occurs during flash floods, i. e. relatively short runoff events with often very high peak discharges. Characteristics of these floods are discussed with some examples, including an exceptionally large flood. Taking into account the difficult conditions for river discharge measurements, this study provides one of the most comprehensive analyses so far of the magnitude and dynamics of river discharges in Ethiopia. © 2012 Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany. [less ▲]

Detailed reference viewed: 9 (1 ULg)
Full Text
Peer Reviewed
See detailPredicting soil erosion and sediment yield at regional scales: Where do we stand?
De Vente, J.; Poesen, J.; Verstraeten, G. et al

in Earth-Science Reviews (2013), 127

Assessments of the implications of soil erosion require quantification of soil erosion rates (SE) and sediment yield (SSY) at regional scales under present and future climate and land use scenarios. A ... [more ▼]

Assessments of the implications of soil erosion require quantification of soil erosion rates (SE) and sediment yield (SSY) at regional scales under present and future climate and land use scenarios. A range of models is available to predict SE and SSY, but a critical evaluation of these models is lacking. Here, we evaluate 14 models based on 32 published studies and over 700 selected catchments. Evaluation criteria include: (1) prediction accuracy, (2) knowledge gain on dominant soil erosion processes, (3) data and calibration requirements, and (4) applicability in global change scenario studies. Results indicate that modelling of SE and SSY strongly depends on the spatial and temporal scales considered. In large catchments (>10,000km2), most accurate predictions of suspended sediment yield are obtained by nonlinear regression models like BQART, WBMsed, or Pelletier's model. For medium-sized catchments, best results are obtained by factorial scoring models like PSIAC, FSM and SSY Index, which also support identification of dominant erosion processes. Most other models (e.g., WATEM-SEDEM, AGNPS, LISEM, PESERA, and SWAT) represent only a selection of erosion and sediment transport processes. Consequently, these models only provide reliable results where the considered processes are indeed dominant. Identification of sediment sources and sinks requires spatially distributed models, which, on average, have lower model accuracy and require more input data and calibration efforts than spatially lumped models. Of these models, most accurate predictions with least data requirements were provided by SPADS and WATEM-SEDEM. Priorities for model development include: (1) simulation of point sources of sediment, (2) balancing model complexity and the quality of input data, (3) simulation of the impact of soil and water conservation measures, and (4) incorporation of dynamic land use and climate scenarios. Prediction of the impact of global change on SE and SSY in medium sized catchments is one of the main challenges in future model development. No single model fulfils all modelling objectives; a further integration of field observations and different model concepts is needed to obtain better contemporary and future predictions of SE and SSY. © 2013 Elsevier B.V. [less ▲]

Detailed reference viewed: 19 (1 ULg)
Full Text
Peer Reviewed
See detailA comparison of measured catchment sediment yields with measured and predicted hillslope erosion rates in Europe
Vanmaercke, Matthias ULg; Maetens, W.; Poesen, J. et al

in Journal of Soils and Sediments (2012), 12(4), 586-602

Purpose: This study aims to understand better the relationship between measured soil loss rates due to sheet and rill erosion (SL), predicted SL rates and measured catchment sediment yields (SY) in Europe ... [more ▼]

Purpose: This study aims to understand better the relationship between measured soil loss rates due to sheet and rill erosion (SL), predicted SL rates and measured catchment sediment yields (SY) in Europe. Materials and methods: Analyses were based on a recently established database of measured annual SY for 1794 catchments, a database of 777 annual SL rates measured on runoff plots and two recent maps of predicted sheet and rill erosion rates in Europe (i. e. one based on empirical extrapolations of measured SL data and one based on the PESERA model). To identify regional trends, all data were grouped into eight climatic zones. Results and discussion: Measured SL rates are generally a factor of five to ten times larger than predicted SL rates and are strongly biased towards erosion-prone situations in terms of land use. Also measured SY are generally higher than predicted SL rates, especially in the Mediterranean and Alpine regions where SY is generally ten times higher than predicted SL rates. This illustrates the importance of other erosion processes contributing to SY. Regional differences in the importance of these processes and their implications are discussed. Conclusions: This study confirms previous findings indicating the relatively low sheet and rill erosion rates compared to SY in the Mediterranean region and illustrates the importance of other erosion processes contributing to SY in most regions of Europe. This indicates that hillslope erosion rates cannot be used directly to estimate SY, and consequently soil conservation programmes should focus more on the dominant erosion processes in each catchment. © 2012 Springer-Verlag. [less ▲]

Detailed reference viewed: 12 (1 ULg)
Full Text
Peer Reviewed
See detailHow long should we measure? An exploration of factors controlling the inter-annual variation of catchment sediment yield
Vanmaercke, Matthias ULg; Poesen, J.; Radoane, M. et al

in Journal of Soils and Sediments (2012), 12(4), 603-619

Purpose: Although it is well-known that catchment suspended sediment yields (SY; tons per square kilometre per year) can vary significantly from year to year, little information exists on the magnitude ... [more ▼]

Purpose: Although it is well-known that catchment suspended sediment yields (SY; tons per square kilometre per year) can vary significantly from year to year, little information exists on the magnitude and factors controlling this variability. This is crucial to assess the reliability of average SY values for a given measuring period (MP) and is of great geomorphic significance. This paper aims to bridge this research gap. Materials and methods: A worldwide database was compiled with time series of measured SY values. Data from 726 rivers (mostly located in Europe, the Middle East and the USA) were collected, covering 15,025 annual SY observations. The MPs ranged between 7 and 58 years, while catchment areas (A) ranged between 0.07 and 1.84 × 106 km2. For 558 catchments, the annual runoff depths corresponding to the SY observations were also available. Based on this database, inter-annual variability was assessed for each catchment, and relationships with factors potentially explaining this variability were explored. Results and discussion: Coefficients of variation of SY varied between 6% and 313% (median 75%). Annual SY data were generally not normally distributed but positively skewed. Inter-annual variability generally increased with increasing average SY. No significant relationship was found between the inter-annual variability of SY and A, while weak but significant relationships were noted with the variability in annual runoff and rainfall depths. Detailed analyses of a sub-dataset corresponding to 63 catchments in Romania revealed no clear relationships between inter-annual variability of SY and land-use or topographic characteristics. Nevertheless, indications were found that variability was larger for catchments with erosion-prone land-use conditions. Using a Monte Carlo simulation approach, the effect of inter-annual variability on the reliability of average SY data was assessed. Results indicate that uncertainties are very large when the MP is short, with median relative errors ranging between -60% and 83% after 5 years of monitoring. Furthermore, average SY values based on short MPs have a large probability to underestimate, rather than to overestimate, the long-term mean. For instance, the SY value of a median catchment after a 1-year MP has a 50% probability of underestimating the long-term mean by about 22%. Uncertainties quickly decrease after the first few years of measurement but can remain considerable, even after 50 years of monitoring. Conclusions: It is important to consider uncertainties associated with average SY values due to inter-annual variability, for example when attempting to predict long-term average SY values using a steady-state model, as such uncertainties put fundamental limits to the predictive capabilities of such models. © 2012 Springer-Verlag. [less ▲]

Detailed reference viewed: 8 (1 ULg)
Full Text
Peer Reviewed
See detailEffects of land use on annual runoff and soil loss in Europe and the Mediterranean: A meta-analysis of plot data
Maetens, W.; Vanmaercke, Matthias ULg; Poesen, J. et al

in Progress in Physical Geography (2012), 36(5), 599-653

The largest currently compiled database of plot runoff and soil loss data in Europe and the Mediterranean was analysed to investigate effects of land use on annual soil loss (SL), annual runoff (R) and ... [more ▼]

The largest currently compiled database of plot runoff and soil loss data in Europe and the Mediterranean was analysed to investigate effects of land use on annual soil loss (SL), annual runoff (R) and annual runoff coefficient (RC). This database comprises 227 plot-measuring sites in Europe and the Mediterranean, with SL for 1056 plots (PL) representing 7024 plot-years (PY) and R for 804 PL representing 5327 PY. Despite large data variability, continental-wide trends are observed. Construction sites have the highest mean annual RC (57%) and SL (325 Mg.ha -1.yr -1). Bare soil, vineyards and tree crops have high mean annual RC (5-10%) and SL (10-20 Mg.ha -1.yr -1). Cropland and fallow show similar mean annual RC (8.0 and 7.3%), but lower SL (6.5 and 5.8 Mg.ha -1.yr -1). Plots with (semi-)natural vegetation cover show lowest mean annual RC (<5%) and SL (<1 Mg.ha -1.yr -1). Plot length and slope gradient correlations with R and SL depend on land-use type and are not concurrent for R and SL. Most land-use types show positive correlations between annual R and SL. Plots in cold climates have higher annual RC than plots in temperate and pan-Mediterranean climates. Annual SL in the pan-Mediterranean is less than in temperate zones, due to stony or clayey soils having a low erodibility. Annual RC in the pan-Mediterranean was higher than in temperate zones. Annual R increases strongly with increasing annual precipitation (P) above 500 mm.yr -1, while annual SL was found to stabilize at P > 500 mm.yr -1. For shrubland, annual SL was found to decrease for P > 250-500 mm.yr -1, which is attributed to an accompanying increase in vegetation cover. However, no such trend was found for R. The results allow a rapid assessment of the impact of land-use changes on annual R, RC and SL, based on field-measured plot data. © The Author(s) 2012. [less ▲]

Detailed reference viewed: 12 (1 ULg)
Full Text
Peer Reviewed
See detailHow effective are soil conservation techniques in reducing plot runoff and soil loss in Europe and the Mediterranean?
Maetens, W.; Poesen, J.; Vanmaercke, Matthias ULg

in Earth-Science Reviews (2012), 115(1-2), 21-36

The effects of soil and water conservation techniques (SWCTs) on annual runoff (R a), runoff coefficients (RC a) and annual soil loss (SL a) at the plot scale have been extensively tested on field runoff ... [more ▼]

The effects of soil and water conservation techniques (SWCTs) on annual runoff (R a), runoff coefficients (RC a) and annual soil loss (SL a) at the plot scale have been extensively tested on field runoff plots in Europe and the Mediterranean. Nevertheless, a comprehensive overview of these effects and the factors controlling the effectiveness of SWCTs is lacking. Especially the effectiveness of SWCT in reducing R a is poorly understood. Therefore, an extensive literature review is presented that compiles the results of 101 earlier studies. In each of these studies, R a and SL a was measured on field runoff plots where various SWCTs were tested. In total, 353 runoff plots (corresponding to 2093 plot-years of data) for 103 plot-measuring stations throughout Europe and the Mediterranean were considered. SWCTs include (1) crop and vegetation management (i.e. cover crops, mulching, grass buffer strips, strip cropping and exclosure), (2) soil management (i.e. no-tillage, reduced tillage, contour tillage, deep tillage, drainage and soil amendment) and (3) mechanical methods (i.e. terraces, contour bunds and geotextiles). Comparison of the frequency distributions of SL a rates on cropland without and with the application of SWCTs shows that the exceedance probability of tolerable SL a rates is ca. 20% lower when SWCT are applied. However, no notable effect of SWCTs on the frequency distribution of RC a is observed. For 224 runoff plots (corresponding to 1567 plot-year data), SWCT effectiveness in reducing R a and/or SL a could be directly calculated by comparing measured R a and/or SL a with values measured on a reference plot with conventional management. Crop and vegetation management techniques (i.e. buffer strips, mulching and cover crops) and mechanical techniques (i.e. geotextiles, contour bunds and terraces) are generally more effective than soil management techniques (i.e. no-tillage, reduced tillage and contour tillage). Despite being generally less effective, no-tillage, reduced tillage and contour tillage have received substantially more attention in the literature than the other SWCTs. Soil and water conservation techniques are generally less effective in reducing R a than in reducing SL a, which is an important consideration in areas where water is a key resource and in regions susceptible to flooding. Furthermore, all SWCTs show a more consistent and effective reduction of both R a and SL a with increasing R a and SL a magnitude, which is attributed to the reduced influence of measurement uncertainties. Although some significantly negative correlations between SWCT effectiveness and plot slope length, slope gradient or annual precipitation were found, the importance of these factors in explaining the observed variability in effectiveness seems limited. Time-series analyses of R a during multiple years of SWCT application strongly indicate that no-tillage and conservation tillage become less effective in reducing R a over time. Such an effect is not observed for SL a. © 2012 Elsevier B.V. [less ▲]

Detailed reference viewed: 10 (1 ULg)