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See detailIs an expert-based model able to map erosion in an agricultural catchment?
Cantreul, Vincent ULiege; Bielders, Charles; Swerts, Gilles ULiege et al

Conference (2019, May 16)

Intensive agricultural practices on sensitive soils induce high erosion rates in central Belgium. Expert-rules models quantify runoff and erosion at watershed scale avoiding over-parameterization. The aim ... [more ▼]

Intensive agricultural practices on sensitive soils induce high erosion rates in central Belgium. Expert-rules models quantify runoff and erosion at watershed scale avoiding over-parameterization. The aim of this study is to test the ability of an expert-based model, LandSoil, to quantify runoff and to locate erosion and deposition areas in a small agricultural watershed in Belgium. For that purpose, Chastre catchment behavior is modeled using LandSoil during 3 years. Measurements of runoff and observation of spatial erosion/deposition patterns permit to assess the reliability of the model. Runoff modeling gives satisfactory results with good linear adjustments (r² of 0.94, Nash-Sutcliffe criterion of 0.92). However, 3 events tend to greatly overestimate runoff production. Graduated rulers and runoff samplings demonstrate that the model is able to provide a coherent pattern of erosion/deposition. The study highlights more sensitive effect of land use compared to landscape design. Grass strips induce a deposition of eroded particles when slopes are gentle (<2%), wood strip decreases connectivity by cutting erosion stream and deposit thicker sediment layers (up to 5 cm). This modeling validation in the Belgian loess context allows us to use expert based models in other similar environments and to estimate the effect of landscape management scenarios. [less ▲]

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See detailIs an expert-based model able to map erosion in agricultural catchments?
Cantreul, Vincent ULiege; Bielders, Charles; Swerts, Gilles ULiege et al

Poster (2019, May 15)

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See detailHow pixel size affects a sediment connectivity index in central Belgium
Cantreul, Vincent ULiege; Bielders, Charles; Calsamiglia, Aleix et al

in Earth Surface Processes and Landforms (2018), 43(4), 884-893

Connectivity has become an increasingly used concept in hydrological and sediment research. In order to quantify it, various indices have been proposed since the start of the 21st century including the ... [more ▼]

Connectivity has become an increasingly used concept in hydrological and sediment research. In order to quantify it, various indices have been proposed since the start of the 21st century including the index of connectivity developed by Borselli et al. (2008). This index is based on a limited number of factors, the most important one being topography. Sediment connectivity indices values are likely to depend on the digital elevation model (DEM) resolution. The aim of this study was, first, to compare the effect of DEM pixel size (between 0.25 and 10 m, using an UAV) in the Belgian loess belt, a lowland area. We show that the index values were lower when the pixel size decreased (a difference of about 20 % in value between 0.25 and 10 m). In addition, the impact of linear features in the watershed (e.g., grass strip, bank and road) was lower with the largest pixel sizes, and the connectivity pattern was affected with a pixel size of 5 m or more. At lower pixel sizes (1 m or below), some more disconnected regions appeared. These corresponded to zones where there had been water stagnation during and after rainfalls, and was corroborated by field observations. This confirmed the need for a proper resolution according to the objectives of the study. The second aim of this study was to deduce a minimum pixel size for connectivity study, helping local erosion or sedimentation location and consequent land management decisions. In our context, 1 m stands as the optimum DEM resolution. This pixel size permitted to locate all “key areas” in terms of erosion. Very high resolutions (<0.5 m) did not generate much more information, and their calculation time was far greater. [less ▲]

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See detailHow pixel size affects a sediment connectivity index in central Belgium
Cantreul, Vincent ULiege; Bielders, Charles; Calsamiglia, Aleix et al

Conference (2017, December 05)

Connectivity has become an increasingly used concept in hydrological and sediment research. In order to quantify it, various indices have been proposed since the start of the 21st century including the ... [more ▼]

Connectivity has become an increasingly used concept in hydrological and sediment research. In order to quantify it, various indices have been proposed since the start of the 21st century including the index of connectivity developed by Borselli et al. (2008). This index is based on a limited number of factors, the most important one being topography. Sediment connectivity indices values are likely to depend on the digital elevation model (DEM) resolution. The aim of this study was, first, to compare the effect of DEM pixel size (between 0.25 and 10 m, using an UAV) in the Belgian loess belt, a lowland area. We show that the index values were lower when the pixel size decreased (a difference of about 20 % in value between 0.25 and 10 m). In addition, the impact of linear features in the watershed (e.g., grass strip, bank and road) was lower with the largest pixel sizes, and the connectivity pattern was affected with a pixel size of 5 m or more. At lower pixel sizes (1 m or below), some more disconnected regions appeared. These corresponded to zones where there had been water stagnation during and after rainfalls, and was corroborated by field observations. This confirmed the need for a proper resolution according to the objectives of the study. The second aim of this study was to deduce a minimum pixel size for connectivity study, helping local erosion or sedimentation location and consequent land management decisions. In our context, 1 m stands as the optimum DEM resolution. This pixel size permitted to locate all “key areas” in terms of erosion. Very high resolutions (<0.5 m) did not generate much more information, and their calculation time was far greater. [less ▲]

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See detailHow does the connectivity index change through year in an agricultural catchment?
Cantreul, Vincent ULiege; Degré, Aurore ULiege

Poster (2017)

The emerging concept of hydrological connectivity is difficult to quantify. Some indices have been proposed. The most cited is Borselli’s one. It gives the advantage to visualize connectivity at watershed ... [more ▼]

The emerging concept of hydrological connectivity is difficult to quantify. Some indices have been proposed. The most cited is Borselli’s one. It gives the advantage to visualize connectivity at watershed scale with very few inputs. But it is not a dynamic index and the resulting map is not time dependent. However, vegetation cover changes through year and possibly affects the connectivity dynamics. The objective of this poster is to show the evolution of the CI during the year looking at a few “strategic” times. Moreover, the study permits to identify a few “key locations” in the watershed, for example permanent disconnections or at the opposite constantly connected fields. The CI was calculated in a 124ha catchment (Hevillers), in the loess belt, in Belgium. Land use is agricultural with mostly cereals, sugar beets and potatoes, little area with wood, road, path or grass strip. Used weighting factor is soil loss ratio. It is between 0 and 1 and translates the protection offered to the soil by the crop. In winter (January), cereals have the most connected fields because of almost bare soils. Cover crops on sugar beets and potatoes fields decrease connectivity, except for one big field not far from the outlet. But rainfalls are generally not so erosive during this period. In spring (March and May), the cereals have a decreasing CI with plants growth covering the soil. On the opposite, sugar beets and potatoes are planted and bare soils in spring involve much higher connectivity index. The effect of grass strip is strong for sugar beet field situated uphill and underlines the importance of such mitigation measures. In summer (July), the whole watershed is much more disconnected and it does not represent the most risky part of the year in terms of erosion. The end of the year is related to harvesting and consequent bare soil in September for potatoes and November for the rest. In conclusion, the IC is an easy tool to estimate connectivity in a watershed. With the evolution during the year using soil loss ratio in the calculation, it permits to visualize dynamically the connectivity pattern and to localize erosive parts of the catchment for the crop rotation. With a global view on several years, it could be helpful to erosion managers to think about best long-term location of mitigation measures in the watershed. [less ▲]

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See detailFarms For Future: building tomorrow's agriculture
Pécheur, Emilie ULiege; Maebe, Laura ULiege; Boeraeve, Fanny ULiege et al

Poster (2016, May 20)

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See detailEffect of DEM resolution and comparison between different weighting factors for hydrologic connectivity index
Cantreul, Vincent ULiege; Cavalli, Marco; Degré, Aurore ULiege

Poster (2016, April)

The emerging concept of hydrological connectivity is difficult to quantify. Some indices have been proposed. The most cited is Borselli’s one. It mainly uses the DEM as input. The pixel size may strongly ... [more ▼]

The emerging concept of hydrological connectivity is difficult to quantify. Some indices have been proposed. The most cited is Borselli’s one. It mainly uses the DEM as input. The pixel size may strongly impacts the result of the calculation. It has not been studied yet in silty areas. Another important aspect is the choice of the weighting factor which strongly influences the index value. The objective of this poster is so to compare 8 different DEM’s resolutions (12, 24, 48, 72, 96, 204, 504 and 996cm) and 3 different weighting factors (factor C of Wischmeier, Manning’s factor and rugosity index) in the Borselli’s index calculation. The IC was calculated in a 124ha catchment (Hevillers), in the loess belt, in Belgium. The DEM used is coming from a UAV with a maximum resolution of 12 cm. Permanent covered surfaces are not considered in order to avoid artefact due to the vegetation (2% of the surface). Regarding the DEM pixel size, the IC increases for a given pixel when the pixel size decreases. That confirms some results observed in the Alpine region by Cavalli (2014). The mean difference between 12 cm and 10 m resolution is 35% with higher values up to 100% for higher connectivity zones (flow paths). Another result is the lower impact of connections in the watershed (grass strips…) at lower pixel sizes. This is linked to the small width of some connections which are sometimes comparing to cell size. Furthermore, a great loss of precision is observed from the 500 cm pixel size and upper. That remark is quite intuitive. Finally, some very well disconnected zones appear for the highest resolutions. Regarding the weighting factor, IC values calculated using C factor are lower than with the rugosity index which is only a topographic factor. With very high resolution DEM, it permits to represent the fine topography. For the C factor, the zones up to very well disconnected areas (grass strips, wood…) are well represented with lower index values than downstream zones. On the contrary, areas up to very well connected zones (roads, paths…) are higher and much more connected than downstream areas. For the Manning’s factor, the values are very low and not very well contrasted. This factor is not enough discriminant for this study. In conclusion, high resolution DEM (1 meter or higher) is needed for the IC calculation (precison, impact of connections…). Very high resolution permits to identify very well disconnected areas but it multiplies the calculation time. For the weighting factor, rugosity index and C factor have each some advantages. It is planned to test other approaches for the IC calculation. [less ▲]

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See detailEfficiency of thermography in the study of hydrological connectivity
Cantreul, Vincent ULiege; Leemans, Vincent ULiege; Burgeon, Victor ULiege et al

Conference (2016, April)

Hydrologic connectivity is an emerging concept which permits deeper understanding of catchments behavior. However, the measurements of functional connectivity is complex and still needs new developments ... [more ▼]

Hydrologic connectivity is an emerging concept which permits deeper understanding of catchments behavior. However, the measurements of functional connectivity is complex and still needs new developments in order to approach the « dynamic » part of the story. This study aims at assessing the efficiency of thermography to analyze hydrologic connectivity in an agricultural catchment in Belgium (loamy soils). Tests have been performed on experimental tubs at first and on field at second. Under controlled conditions, hot milk was spread on an experimental tub with bare soil and grass. The hot milk permits to compare color tracer with thermic one. The results are quite good. The binarization of pictures from usual camera and from thermic one gives similar percentage of runoff coverage at same locations. The mean difference is about 8% for bare soils and 10% for planted grass. There is a slight overestimation with thermic camera because of time delay of soil cooling after milk passing. In the same time in the planted grass, there are some runoff pixels which are hidden by vegetation. On field, blue colored water was used to simulate a rainfall on a field covered with mustard and on the same field without any coverage. Where runoff flows, the soil appears warmer because of heat extracted by water in the soil. The results comparing visual and thermic pictures are more nuanced. The mean difference reaches 30% on bare soil. Indeed, (i) the rainfall drops seem to hide the runoff during the rain; (ii) the vegetation density (mustard) is quite a problem for runoff detection. However, the difference between successive time pictures permits to distinguish flow paths easily. In conclusion, thermography stands as a good alternative for connectivity study. It’s obviously a preliminary study which gives some indications of the possible use of thermography. At present, we are testing real rainfalls (different types) with different camera’s positions and different land use (different vegetation density). [less ▲]

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See detailEfficiency of thermography in the study of hydrological connectivity
Cantreul, Vincent ULiege; Burgeon, Victor ULiege; Triquet, Johan ULiege et al

Poster (2016, March)

Hydrologic connectivity is an emerging concept which permits deeper understanding of catchments behavior. However, the measurements of functional connectivity is complex and still needs new developments ... [more ▼]

Hydrologic connectivity is an emerging concept which permits deeper understanding of catchments behavior. However, the measurements of functional connectivity is complex and still needs new developments in order to approach the « dynamic » part of the story. This study aims at assessing the efficiency of thermography to analyze hydrologic connectivity in an agricultural catchment in Belgium (loamy soils). Tests have been performed on experimental tubs at first and on field at second. Under controlled conditions, hot milk was spread on an experimental tub with bare soil and grass. The hot milk permits to compare color tracer with thermic one. The results are quite good. The binarization of pictures from usual camera and from thermic one gives similar percentage of runoff coverage at same locations. The mean difference is about 8% for bare soils and 10% for planted grass. There is a slight overestimation with thermic camera because of time delay of soil cooling after milk passing. In the same time in the planted grass, there are some runoff pixels which are hidden by vegetation. On field, blue colored water was used to simulate a rainfall on a field covered with mustard and on the same field without any coverage. Where runoff flows, the soil appears warmer because of heat extracted by water in the soil. The results comparing visual and thermic pictures are more nuanced. The mean difference reaches 30% on bare soil. Indeed, (i) the rainfall drops seem to hide the runoff during the rain; (ii) the vegetation density (mustard) is quite a problem for runoff detection. However, the difference between successive time pictures permits to distinguish flow paths easily. In conclusion, thermography stands as a good alternative for connectivity study. It’s obviously a preliminary study which gives some indications of the possible use of thermography. At present, we are testing real rainfalls (different types) with different camera’s positions and different land use (different vegetation density). [less ▲]

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See detailHow to measure connectivity?
Cantreul, Vincent ULiege; Pineux, Nathalie ULiege; Swerts, Gilles ULiege et al

Poster (2015, September)

Erosion is a major threat to European soil. Consequences can be very important both on-site and off-site. Belgian loamy soils are highly vulnerable to this threat because of their natural sensitivity to ... [more ▼]

Erosion is a major threat to European soil. Consequences can be very important both on-site and off-site. Belgian loamy soils are highly vulnerable to this threat because of their natural sensitivity to erosion on the one hand, and because the land is mainly used for intensive agricultural practices on the other hand. Over the last few decades, rising erosion has even been observed in our regions. This shows the importance of a deeper understanding of the coupled phenomena of runoff and erosion in order to manage soils at catchment scale. Plenty of research have already studied this but all agree to say that it seems to have a non-linear relationship between rainfall and discharge, as well as between rainfall and erosion. For that reason, a new concept has been developed a few years ago: the hydrological connectivity. Several research have focused on connectivity but up to now, each there are as much definition as papers. In this thesis, it will be important firstly to resume all these definitions to clarify this concept. Secondly, a methodology using various transects on the watershed and some pertinent field measurements will be used. These measurements include spatial distribution of particle size, surface states and perhaps soil moisture. A new approach of photogrammetry using an UAV will be used to observe erosion and deposition zones on the watershed. In addition to that, infrared camera will be installed on different positions in the catchment. This permits to detect when and where variably saturated areas are active and so when connectivity is active between hillslopes and stream. In this framework, several time scales will be studied from the event scale to the annual scale passing by monthly and seasonal scales. All this will serve to progress toward a better understanding of the concept of hydrological connectivity in order to study erosion at catchment scale. The final goal of this study is to describe hydrologically each different part of the catchment and to generalize these behaviors to other catchments with similar properties if possible. Afterwards, this research will be integrated in an existing (or not) model to improve the modelling of discharge and erosion in the catchment. Thanks to that, a scenario of hydraulic mitigation measures could be proposed in order to reduce runoff and erosion in the catchment. This scenario will include hydraulic, hydrologic but also ecological, landscape and economical points of view. [less ▲]

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See detailCan spatial study of hydrological connectivity explain some non-linear behaviors of catchments?
Cantreul, Vincent ULiege; Pineux, Nathalie ULiege; Swerts, Gilles ULiege et al

Poster (2015, April)

Erosion is a major threat to European soil. Consequences can be very important both on-site and off-site. Belgian loamy soils are highly vulnerable to this threat because of their natural sensitivity to ... [more ▼]

Erosion is a major threat to European soil. Consequences can be very important both on-site and off-site. Belgian loamy soils are highly vulnerable to this threat because of their natural sensitivity to erosion on the one hand, and because the land is mainly used for intensive agricultural practices on the other hand. Over the last few decades, rising erosion has even been observed in our regions. This shows the importance of a deeper understanding of the coupled phenomena of runoff and erosion in order to manage soils at catchment scale. Plenty of research have already studied this but all agree to say that it seems to have a non-linear relationship between rainfall and discharge, as well as between rainfall and erosion. For that reason, a new concept has been developed a few years ago: the hydrological connectivity. Several research have focused on connectivity but up to now, each there are as much definition as papers. In this thesis, it will be important firstly to resume all these definitions to clarify this concept. Secondly, a methodology using various transects on the watershed and some pertinent field measurements will be used. These measurements include spatial distribution of particle size, surface states and soil moisture. A new approach of photogrammetry using an UAV will be used to observe erosion and deposition zones on the watershed. In this framework, several time scales will be studied from the event scale to the annual scale passing by monthly and seasonal scales. All this will serve to progress toward a better understanding of the concept of hydrological connectivity in order to study erosion at catchment scale. The final goal of this study is to describe hydrologically each different part of the catchment and to generalize these behaviors to other catchments with similar properties if possible. Afterwards, this research will be integrated in an existing (or not) model to improve the modelling of discharge and erosion in the catchment. Thanks to that, a scenario of hydraulic mitigation measures could be proposed in order to reduce runoff and erosion in the catchment. This scenario will include hydraulic, hydrologic but also ecological, landscape and economical points of view. [less ▲]

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See detailANALYSE COMBINEE DE L’HYDROLOGIE ET DES PERTES EN SOL DANS LES TETES DE BASSIN VERSANT AGRICOLE – MESURE ET MODELISATION DANS LE BASSIN D’HEVILLERS (CHASTRE)
Cantreul, Vincent ULiege

Master's dissertation (2014)

Le phénomène d’érosion est la plus grande menace pesant sur le sol européen. Les conséquences peuvent être importantes aussi bien sur le site érodé qu’en aval de celui-ci. Les sols loessiques belges sont ... [more ▼]

Le phénomène d’érosion est la plus grande menace pesant sur le sol européen. Les conséquences peuvent être importantes aussi bien sur le site érodé qu’en aval de celui-ci. Les sols loessiques belges sont particulièrement vulnérables à ce phénomène à cause de leur sensibilité naturelle à l’érosion mais aussi à cause de l’occupation du sol majoritairement agricole de ces terres. Depuis quelques décennies, il a même été observé une augmentation de l’érosion dans nos régions pour plusieurs causes. Ceci montre l’importance d’approfondir la compréhension des phénomènes couplés de ruissellement et d’érosion afin de gérer de manière raisonnée et intégrée les sols au niveau du bassin versant. Le travail modélise à l’aide du logiciel STREAM les volumes ruisselés et les quantités de terre érodée en analysant différents pas de temps et en étudiant l’impact de la pédologie et de l’occupation du sol dans ces phénomènes. Les résultats montrent globalement une sous-estimation des événements hivernaux, une surestimation des événements estivaux et une estimation plus nuancée des événements considérés comme particuliers. Le pas de temps le mieux adapté aux modélisations est celui de 30 minutes. L’analyse montre également une influence prépondérante de l’occupation du sol sur le ruissellement et l’érosion même si la pédologie joue un rôle non négligeable avec notamment un effet modérateur des phénomènes érosifs pour les plages pédologiques à texture sablo-limoneuse, limono-sableuse et pour la plage pédologique Abp. [less ▲]

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See detailEstimation of the fascine efficiency in terms of runoff infiltration and sediments deposition
Degré, Aurore ULiege; Pineux, Nathalie ULiege; Cantreul, Vincent ULiege et al

in Geophysical Research Abstracts (2013), 15

Runoff inundations and mudflows are more and more frequent phenomena. In 2011, Belgium had a lot of its municipalities affected by this problematic. Since then, mitigation measures are more and more set ... [more ▼]

Runoff inundations and mudflows are more and more frequent phenomena. In 2011, Belgium had a lot of its municipalities affected by this problematic. Since then, mitigation measures are more and more set up in agricultural watersheds. The fascines are one of these measures which allow to protect the public and private infrastructures and in the same way, which don’t reduce the famers productivity. They consist in branches faggots piled up between two rows of stakes. These linear constructions are mainly put in place across concentrated runoff axis in order to slow down the water and to filter the mud. Only few quantifications of their effectiveness (in terms of flow and concentration water reduction) exist and are however needed to better recommend these types of mitigation measures. Our experiment aims at measuring discharge and mud concentration reduction due to the fascines in a completely defined context. The tests were realised through fascines planted in field border. A watertight surface of 2,45m to 0,80m carries the water to the fascines. Three types of fascines were tested (willow wood fascine, straw fascine, straw compacted fascine), three different water flows were applied (0,5L/s, 3L/s and 6L/s) and three water concentration in dry soil (13g/L, 26g/L, 38g/L) were used. The different factor combinations were tested. The results show that we can expect a reduction of 60% of the flow for the biggest water flows (proportional efficiency with the water flow). The factor interaction study doesn’t allow to see a difference between the type. About the sediment water concentration, the filtration can reach 50%, the fascine with wood faggots showing a better efficiency. Finally, the difference between the fascine type show that straw fascine can support a biggest watershed (25 hectares) than the wood faggot fascine can (5-10 hectares) but during a smaller return period (one year against five years). [less ▲]

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