Hydropower-induced land use change in Fincha's watershed, werstern Ethiopia: analysis and impacts

The present article analyzes the land use dynamics caused by hydropower dam construction in 1973 in the Fincha'a watershed (1318 km2), a tributary of the Blue Nile. Aerial photos (1957 and 1980) and an ASTER satellite image of 2001 were used to make 3 land use maps of the watershed using a geographic information system (GIS). The 239-km2 water reservoir inundated 100 km2 of grazing land, 120 km2 of swamp, 18 km2 of cropland, and 1.2 km2 of forestland. In 2001, cropland covered 77% of the land potentially available for community use, indicating that there is hardly any free land available for expansion to accommodate new farmers. Relocated communities operate on relatively small parcels of land situated either on steep slopes or in flood-prone areas. Consequently, they exhaustively utilize the trees available on their holdings, and convert grassland and bush-land to cropland, without applying sufficient soil conservation measures. Farmers resettled at or near bodies of water and swamps, however, are affected by seasonal fluctuations of water levels that very often inundate croplands, grazing land, and homes. The demand for cropland and grazing land is increasing as reservoir and swamp areas expand and new families are created. Soil erosion in steep areas can no longer be reduced in the traditional farming system. These enforced land use changes, combined with a lack of appropriate land management practices, may increase erosion and reservoir sedimentation. This could affect food security and electric power production in the near futur

Wind Erosion in the Sahelian Zone of Niger: Processes, Models, and Control Techniques

In the Sahelian zone of Niger, severe wind erosion occurs mainly in the first half of the rainy season (May - July), when violent winds preceding thunderstorms result in intense sediment transport. Quantification of this wind erosion is difficult due to a high degree of temporal and spatial variability in wind-blown particle mass fluxes. Using improved techniques to collect field data in Niger and developed models revealed that a single wind erosion event may result in severe losses of soil particles and nutrients from unprotected fields. The many technical measures available to reduce wind erosion do not always fit into the Sahelian farming systems. A survey revealed that mulching with crop residues is the main control technique applied by Nigerien farmers, but the quantity of crop residues available for soil conservation is limited, as stover has also other important uses. Field tests with flat pearl millet stalks showed that small quantities can significantly reduce sediment transport during moderate storms. However, sediment transport may actually be intensified by small quantities of mulch during severe storms, because of increased turbulence around the stalks

Evaluating erosion from space: a case study near Uberlândia

Satellites can offer important spatial data for the assessment of soil erosion. This study was conducted to explore how satellite imagery could be used for evaluating erosion in a 10*10 km area in the Brazilian Cerrados. Products obtained from a variety of satellite sensors were analyzed for the purpose of (1) detecting erosion features; and (2) qualitatively mapping erosion risk. Erosion detection was done through visual image interpretation. Optical TerraASTER images allowed for a better detection and delineation of major gullies as ENVISAT ASAR imagery. Gully dynamics could be assessed by jointly interpreting aerial photos of 1979 and a high-resolution QuickBird image of 2003. QuickBird also allowed for the detection of smaller erosion features, like rills. Erosion risk mapping was performed for the complete study area with a simple qualitative method integrating information on slope and vegetation cover. Slope was calculated from the SRTM DEM, and NDVI, being indicative of vegetation cover, was obtained from a wet-season ASTER image. Both factors were automatically classified based on their relative susceptibility to erosion. The erosion risk map was constructed by combining both classifications with the minimum-operator. The accuracyof the map was good (75 %) when compared to field estimates of erosion risk. The method presented therefore allowed for a quick and proper indication of spatial differences of erosion risk in the study area, particularly concerning rill and sheet erosion

Исследование информационных процессов в некоторых повторяющихся играх

Рассматривается неантагонистическая повторяющаяся игра с непрерывным временем. Один раз за всю игру может подействовать возмущающий фактор. Он изменяет существующую ситуацию равновесия на другую. При этом выигрыш второго игрока уменьшается. Найдены равновесные стратегии и оптимальный дискретный режим получения информации. Показано, что наблюдатель оценивает режим получения информации как оптимальный или избыточный в зависимости от модели реальности, которой он пользуется.The non-antagonistic repeated game are considered. The disturbance is able to act once the game. It changes the existing situation of equilibrium for another one. For this the second player gain decreases. The equilibrium strategies and the optimum discrete regime of the information receipt are found. It is shown that observer estimates the regime of the information receipt as the optimum or surplus regime depending on the model of reality which is used by him

Saltation transport on a silt loam soil in northeast Spain

16 Pags., 4 Tabls., 4 Figs. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-145XThe Ebro River valley in Northeast Spain experiences regularly strong west-northwest winds that are locally known as cierzo. When the cierzo blows, wind erosion may potentially occur on unprotected agricultural lands. In this paper the first results of field measurements of soil characteristics and saltation transport in the Ebro River valley near Zaragoza are presented. An experiment was conducted on a silt loam soil in the summers of 1996 and 1997. Two plots of 135×180 m were both equipped with a meteorology tower, three saltiphones (acoustic sediment sensors) and ten sediment catchers. The plots were different with respect to tillage practices. One plot received mouldboard ploughing followed by a pass of a compacting roller (conventional tillage—CT), whereas the other plot only received chisel ploughing (reduced tillage—RT). Soil characterizations indicated that soil erodibility was significantly higher in the CT plots than in the RT plots. Consequently, no significant saltation transport was observed in the RT plots during both seasons. In the CT plot, four saltation events were recorded during the 1996 season and nine events during the 1997 season. Most events were preceded by rainfall during the previous one or two days, which reduced saltation transport significantly. It is concluded that the occurrence of wind erosion in the Ebro River valley depends on the timing and type of tillage, distribution of rainfall and soil-surface crusting.The WELSONS project is funded by the European Union under Contract No. ENV4‐CT95‐0182. Peer reviewe

Effect of hydraulic parameters on sediment transport capacity in overland flow over erodible beds

Sediment transport is an important component of the soil erosion process, which depends on several hydraulic parameters like unit discharge, mean flow velocity, and slope gradient. In most of the previous studies, the impact of these hydraulic parameters on transport capacity was studied for non-erodible bed conditions. Hence, this study aimed to examine the influence of unit discharge, mean flow velocity and slope gradient on sediment transport capacity for erodible beds and also to investigate the relationship between transport capacity and composite force predictors, i.e. shear stress, stream power, unit stream power and effective stream power. In order to accomplish the objectives, experiments were carried out in a 3.0 m long and 0.5 m wide flume using four well sorted sands (0.230, 0.536, 0.719, 1.022 mm). Unit discharges ranging from 0.07 to 2.07 × 10<sup>−3</sup> m<sup>2</sup> s<sup>−1</sup> were simulated inside the flume at four slopes (5.2, 8.7, 13.2 and 17.6%) to analyze their impact on sediment transport rate. The sediment transport rate measured at the bottom end of the flume by taking water and sediment samples was considered equal to sediment transport capacity, because the selected flume length of 3.0 m was found sufficient to reach the transport capacity. The experimental result reveals that the slope gradient has a stronger impact on transport capacity than unit discharge and mean flow velocity due to the fact that the tangential component of gravity force increases with slope gradient. Our results show that unit stream power is an optimal composite force predictor for estimating transport capacity. Stream power and effective stream power can also be successfully related to the transport capacity, however the relations are strongly dependent on grain size. Shear stress showed poor performance, because part of shear stress is dissipated by bed irregularities, bed form evolution and sediment detachment. An empirical transport capacity equation was derived, which illustrates that transport capacity can be predicted from median grain size, total discharge and slope gradient

Sonic anemometers in aeolian sediment transport research

Fast-response wind and turbulence instruments, including sonic anemometers, are used more and more in aeolian sediment transport research. These instruments give information on mean wind, but also on fluctuations and turbulent statistics, such as the uw covariance, which is a direct measure of Reynolds' stress (RS) and friction velocity. This paper discusses the interpretation of sonic anemometer data, the transformations needed to get proper results and turbulence spectra, and how they are influenced by instrument size, sampling frequency, and measurement height. Turbulence spectra characterize how much the different frequencies in the turbulent signals contribute to the variance of wind speed, or to the covariance of horizontal and vertical wind speed. They are important in determining the measurement strategy when working with fast-response instruments, such as sonic anemometers, and are useful for interpreting the measurement results. Choices on the type of sonic anemometer, observation height, sampling period, sampling frequency, and filtering can be made on the basis of expected high and low-frequency losses in turbulent signals, which are affected by those variables, as well as wind speed and atmospheric stability. Friction velocity and RS, important variables in aeolian sediment transport research, are very sensitive to tilt or slope errors. During a field experiment, the slope sensitivity of the RS was established as 9% per degree of slope, which is 1.5 times the value reported in literature on the basis of theoretical considerations. An important reason for the difference probably is the large influence of streamline curvature on turbulence statistics and thereby on the slope sensitivity of the RS. An error of 9% per degree of slope in the RS will translate into an error of approximately 4% per degree of slope in the calculated friction velocity. Space-time correlation of the horizontal wind speed is much larger than that of the vertical wind speed and the instantaneous RS. This largely explains why, in previous studies, a poor correlation was found between instantaneous RS measured at 3 in height and saltation flux near the surface, whereas the correlation between wind speed at some height and saltation flux was much better. Therefore, the poor correlation between RS away from the surface and saltation flux does not contradict that saltation flux is caused by RS. (C) 2003 Elsevier B.V. All rights reserved