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Jan Nyssen Wim Clymans Katrien Descheemaeker Jean Poesen Ine Vandecasteele Matthias Vanmaercke Amanuel Zenebe Marc Van Camp Mitiku Haile Nigussie Haregeweyn Jan Moeyersons Kristine Martens Tesfamichael Gebreyohannes Jozef Deckers Kristine Walraevens 《水文研究》2010,24(13):1880-1895
Impact studies of catchment management in the developing world rarely include detailed hydrological components. Here, changes in the hydrological response of a 200‐ha catchment in north Ethiopia are investigated. The management included various soil and water conservation measures such as the construction of dry masonry stone bunds and check dams, the abandonment of post‐harvest grazing, and the establishment of woody vegetation. Measurements at the catchment outlet indicated a runoff depth of 5 mm or a runoff coefficient (RC) of 1·6% in the rainy season of 2006. Combined with runoff measurements at plot scale, this allowed calculating the runoff curve number (CN) for various land uses and land management techniques. The pre‐implementation runoff depth was then predicted using the CN values and a ponding adjustment factor, representing the abstraction of runoff induced by the 242 check dams in gullies. Using the 2006 rainfall depths, the runoff depth for the 2000 land management situation was predicted to be 26·5 mm (RC = 8%), in line with current RCs of nearby catchments. Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (ΔT) relative to the water surplus (WS) over the same period increased between 2002–2003 (ΔT/WS = 3·4) and 2006 (ΔT/WS >11·1). Emerging wells and irrigation are other indicators for improved water supply in the managed catchment. Cropped fields in the gullies indicate that farmers are less frightened for the destructive effects of flash floods. Due to increased soil water content, the crop growing period is prolonged. It can be concluded that this catchment management has resulted in a higher infiltration rate and a reduction of direct runoff volume by 81% which has had a positive influence on the catchment water balance. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Policies, measures, and models geared towards flood prevention and managing surface waters benefit from high quality data on the presence and characteristics of drainage ditches. As a cost and labour effective alternative for acquiring such data through field surveys, we propose a method (a) to extract vector data representing ditch drainage networks based on local morphologic features derived from high resolution digital elevation models (DEM) and (b) to identify possible connections in the ditch network by calculating a probability of the connectivity using a logistic regression where the predictor variables are characteristics of the ditch centre lines or derived from the DEM. Using Light Detection and Ranging (LiDAR) derived DEMs with a 1 m resolution, the method was developed and tested for a mixed agricultural residential area in north‐eastern Belgium. The derived ditch segments had an error of omission of 8% and an error of commission of 5%. The original positional accuracy of the centre lines of the extracted ditches was 0.6 m and could be improved to 0.4 m by shifting each vertex to the position of the lowest LiDAR point located within a radius equal to the spatial resolution of the used DEM. About 69% of the false disconnections in the network were identified and corrected leading to a reduction of the unconnected parts of the ditch network by 71%. The extracted and connected network approximated the reference ditch network fairly well. 相似文献
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An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility. 相似文献
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Effect of salinity on heavy metal mobility and availability in intertidal sediments of the Scheldt estuary 总被引：8，自引：0，他引：8
G. Du Laing R. De Vos B. Vandecasteele E. Lesage F.M.G. Tack M.G. Verloo 《Estuarine, Coastal and Shelf Science》2008,77(4):589-602
The effect of the flood water salinity on the mobility of heavy metals was studied for intertidal sediments of the Scheldt estuary (Belgium). Soils and sediments of 4 sampling sites were flooded with water of different salinities (0.5, 2.5, and 5 g NaCl L−1). Metal concentrations were monitored in pore water and surface water. To study the potential effects of flood water salinity on metal bioavailability, duckweed (Lemna minor) was grown in the surface water. The salinity was found to primarily enhance the mobility of Cd and its uptake by duckweed. Cadmium concentrations in pore water of soils and sediments and surrounding surface waters significantly exceeded sanitation thresholds and quality standards during flooding of initially oxidized sediments. Moreover, the effect was observed already at lower salinities of 0.5 g NaCl L−1. This implies that risks related to Cd uptake by organisms and Cd leaching to ground water are relevant when constructing flooding areas in the brackish zones of estuaries. These risks can be reduced by inducing sulphide precipitation because Cd is then immobilised as sulphide and its mobility becomes independent of flood water salinity. This could be achieved by permanently flooding the polluted sediments, because sulphates are sufficiently available in the river water of the brackish part of the estuary. 相似文献
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S. Arickx T. Van Gerven E. Boydens P. L&#x;hoëst B. Blanpain C. Vandecasteele 《Applied Geochemistry》2008,23(12):3642-3650
In Flanders, recycling of bottom ash is mainly inhibited by the high leaching of Cu. Although it has been proved that dissolved organic C plays a major role in the Cu leaching, the possible role of inorganic Cu mineral speciation has never been experimentally examined. In this study the speciation of Cu is investigated using a combination of optical microscopy and electron microprobe –WDX/EDX. Several Cu species were determined. Metallic Cu (with or without an oxide shell), CuO and Cu2O were the most abundant. These particles were most likely present in wire-like structures. Copper also occurred as alloy (brass, bronze, zamak), and was found frequently together with typical elements such as Ca, Cl and S. Finally, small metallic Cu particles seemed to be trapped in or precipitated on oxides and silicates. Based on this Cu speciation study, pure Cu minerals were selected and leached as a function of time. The solubility after equilibrium of all studied Cu minerals never exceeded 20 μg/L (which equals 10% of the total Cu leaching).The effect of heating (2 h at 400 °C) on the speciation of Cu was investigated using the same combination of techniques. Results show that metallic Cu seemed to be converted to Cu oxide (mostly CuO) and that the particles were more porous after heating. These conclusions were verified by XRD analysis of the heated pure Cu minerals. After heating, the Cu minerals were also leached as a function of time, to study the impact on Cu leaching. Results indicate that their leaching had slightly increased in comparison with the non-heated Cu minerals. However, the major decrease in Cu leaching in heated bottom ash, more than neutralizes this effect and thus can be attributed to the destruction of organic matter and not to the (small) change in Cu speciation. 相似文献
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Ine Vandecasteele Jan Nyssen Wim Clymans Jan Moeyersons Kristine Martens Marc Van Camp Tesfamichael Gebreyohannes Florimond Desmedt Jozef Deckers Kristine Walraevens 《Hydrogeology Journal》2011,19(3):641-650
A hydrogeological study was undertaken in the Zenako-Argaka catchment, near Hagere Selam in Tigray, northern Ethiopia, during the rainy season of 2006. A geological map was produced through geophysical measurements and field observations, and a fracture zone identified in the north west of the catchment. A perched water table was found within the Trap Basalt series above the laterized upper Aram Aradam Sandstones. A map of this water table was compiled. Water-level variation during the measurement period was at least 4.5?m. Variation in basal flow for the whole catchment for the measurement period was between 12 and 276?m3/day. A groundwater flow model was produced using Visual MODFLOW, indicating the general direction of flow to be towards the south, and illustrating that the waterways have only a limited influence on groundwater flow. The soil water budget was calculated for the period 1995?C2006, which showed the important influence of the distribution of rainfall in time. Although Hagere Selam received some 724?mm of rainfall per year over this period, the strong seasonal variation in rainfall meant there was a water deficit for on average 10?months per year. 相似文献
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Jan Nyssen Wim Clymans Jean Poesen Ine Vandecasteele Sarah De Baets Nigussie Haregeweyn Jozef Naudts Amanuel Hadera Jan Moeyersons Mitiku Haile Jozef Deckers 《地球表面变化过程与地形》2009,34(9):1216-1233
An overall approach to assess the effectiveness of soil conservation measures at catchment scale is the comparison of sediment budgets before and after implementation of a catchment management programme. In the May Zeg‐zeg catchment (187 ha) in Tigray, north Ethiopia, integrated catchment management has been implemented since 2004: stone bunds were built in the whole catchment, vegetation was allowed to re‐grow on steep slopes and other marginal land, stubble grazing abandoned, and check dams built in gullies. Land use and management were mapped and analysed for 2000 and 2006, whereby particular attention was given to the quantification of changes in soil loss due to the abandonment of stubble grazing. Sediment yield was also measured at the catchment's outlet. A combination of decreased soil loss (from 14·3 t ha–1 y–1 in 2000 to 9·0 t ha–1 y–1 in 2006) and increased sediment deposition (from 5·8 to 7·1 t ha–1 y–1) has led to strongly decreased sediment yield (from 8·5 to 1·9 t ha–1 y–1) and sediment delivery ratio (from 0·6 to 0·21). This diachronic comparison of sediment budgets revealed that integrated catchment management is most effective and efficient and is the advisable and desirable way to combat land degradation in Tigray and other tropical mountains. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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J. Moeyersons Ph. Trefois L. Nahimana L. Ilunga I. Vandecasteele V. Byizigiro S. Sadiki 《Natural Hazards》2010,53(2):291-311
Uvira occupies a series of narrow alluvial fans squeezed between the NW corner of Lake Tanganyika (±710 m asl) and the W-shoulder
of the Tanganyika rift, the Itombwe–Mitumba Plateau (±3,000 m asl). In 50 years, the fans progressed into the lake over distances
up to some hundreds of metres. This happened during a few catastrophic flash floods issued from the torrents which cascade
from the rift shoulder with a mean longitudinal gradient of 0.2 m m−1. The last event in 2002 led to the destruction of parts of the town and to some 50 casualties. Landslides occurred in the
hills. On the base of stereoscopic interpretation of aerial photographs from 1959, complemented with data from 2000 ETM and
2004 IKONOS imagery, a geographical inventory has been made of strongly incising (10−1 to 0 m in 43–45 years) river sections, of all types of landslides and of all tectonic structures, visible in the rugged hinterland
of the fans. Traces of active N–S as well as E–W trending faults are present. Some of these faults and some surfaces, interpreted
as degraded fault facets dip at angles of 40° or less and are probably remnants of formerly active lystric extension faults,
originally at a depth of some 2 km, but now at the surface as a result of posterior uplift and erosion. Sixty landslides could
be identified. Six slides fall far below the topographic threshold envelope, where the slope at the incision head is expressed
as a function of drained surface. Therefore, they are considered to be seismic in origin. Most of the other landslides are
located along strongly incising river sections. Temporary landslide barriers contribute to irregular river hydrographs. It
is concluded that Uvira is threatened by landsliding, potentially massive (>18 × 106 m3 debris), in the case of heavy seismicity. It is further discussed that the regularisation of the river regime depends on
soil and water conservation strategies, to be developed in the headwaters of the torrents Kavimvira, Mulongwe and Kalimabenge. 相似文献
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