Hydrologie : recherche actuelle

Quantification of Land Use Land Cover (LULC) change influence river basin on hydrology will enable local government and policy makers to formulate and implement effective and appropriate strategies to minimize the effect of future LULC change. In this research Soil and Water Assessment Tool (SWAT) with Sequential Uncertainty Fitting Intervals (SUFI-2) was used for analyzing the LULC changes on the Water balance of Katar and Meki River Basins, in the Rift Valley of Ethiopia. LULC map of 1996 and 2014 was used for the change analysis and the results revealed that the reduction of Forest and expansion of Agriculture and Built-up areas have an influence on the surface water spatial distribution and the water balance components. During the land use change periods, the increment of annual surface runoff from 67.54 mm to 129.14 mm has resulted from Katar river basin and 40.64 mm to 59.56 mm has resulted from Meki river basins. This result has revealed that the above land use changes are the main contributors to the increment of surface runoff on both river basins. With this regard, major changes from the Forested region on both river basins have resulted in runoff depth increment. Forexample, runoff depth increment of 4-53 mm to 10-65 mm on Katar river basin and 2-34 mm to 23-60 mm range from Meki river basin mainly from forested regions resulted. Therefore, LULC change is becoming a serious threat to Katar and Meki river basin, hence appropriate measures should have to be taken for the stabilization of the land cover change with the regional development plan. Furthermore, the outcome of this study serves for policymakers as a valuable information for the planning of best land management strategies and priorities for the region.

This paper illustrates the potential of Sentinel-1 and -2 for flood detection, mapping and characterization with the aim of establishing policies and procedures that need to be followed in order to lower the impact of future floods. The study area is located in Ras Baalbeck, where highlands meet vast plain area. As it relatively contains poor infrastructures and where income is mainly based on agriculture, flood prevention and mitigation initiatives are much needed. Multiple field visits were conducted to identify the affected areas. Based on the later and while computing thresholds, we did classify multiple satellite imageries into damaged and un-damaged areas. The results achieved were produced under Geographical Information System (GIS)-based software. The adopted methodology is described followed by an analysis of future perspectives. The flooded areas extended 5.08 km2 and over two major villages. While Sentinel-2 generated acceptable results, Sentinel-1 did not show any difference between affected and non-affected area in term of soil water content. Still, with their high spatial and temporal resolutions, these two satellites, particularly when coupled, could have the potential to identify the affected areas and to deliver compensations based on it.

Drought is one of the most complexes and least understood natural disaster that causes loss of life and property destruction. The objective of this study was to analyze meteorological drought using Standardized Precipitation Index (SPI) and climate variability (ENSO) in North Shewa Zone, Amhara Regional State. Spatiotemporal variability or trends of rainfall, and temperature were also analyzed. For the seasonal trend analysis of rainfall, maximum and minimum temperatures the MK test was applied and there have been significant increasing trend in maximum, minimum temperature, mostly in semi-arid district. The rainfall of three agro-ecological zones showed strong variability with negative Sen’s slope indicated decreasing signal mostly for Belg season and semi-arid district. The Belg season rainfall showed high variability. Ataye station Belg season (April and May) dry events occurred in 1999, 2000, 2008, and 2011, while the wet events occurred in 1990, and 1993. In the same station, the kiremt season (June and July) wet years occurred in 1990 and 2010, whereas extreme dry events occurred in 1994, 2000, 2008 and 2011. The Kiremt season dry events years were also much higher in Ataye (semi-arid) district as compred to other district, whereas the wet events years were higher in debre berhan (cool, humid, highlands) district. The major El Nino years were in 1982, 1987, 1997 and 2015, whereas the major La Niña years occurred in 1988, 1999, and 2000. In Ataye station the correlation between Kiremt rainfall and Niño 3.4 was -0.43, while in the Belg season it was 0.53. In most of the years the La Nina was associated with rainfall deficiency in Belg season but increase rainfall in Kiremt season. The contrary was true for El Nino events.

Modeling Surface runoff and sediment loading provides important planning tools that can be used in management of land and water resources which can be used in the understanding of dynamic processes and prediction of the existing processes which have advance implication in the understanding of physical and biological processes of watershed.The objective of the study is to model runoff-sediment yield for Guder Catchment, characterizes the runoff from catchment and associated sediment yield, to evaluate spatial distribution of sediment source areas and identify hot spot areas, to assess the impact of different catchment management interventions on runoff and sediment yield and finally develop appropriate management options to control soil erosion and sedimentation problems in Guder watershed by using physical based SWAT model. SWAT model were calibrated and validated at Guder gauging station for both stream flow and sediment yield yielding reasonable results in monthly time step. The 17 years simulation result indicates that the simulated annual average suspended sediment yield by SWAT model was 4,842,000 ton/yr, which is 7.5 t/ ha /yr. The model prediction verified that about 9% of the watershed is erosion potential area contributing high sediment yield exceeding the tolerance limit (soil formation rate) in the study area and about 25% of the watershed area has high potential for soil erosion which produces above 10 ton/ha/yr sediment yield of the watershed. The simulation results showed that applying filter strips and parallel terrace/stone bunds scenarios reduced the current sediment yields by 48% and 53% respectively from the existing condition scenario both at the sub basins and the basin outlets i.e. sediment yield reduced to 3.908 t/ha/yr and 3.54 t/ha/yr by using filter strip scenario and conservation structure scenario respectively. Generally, studies like this in quantifying the total volume of runoff and sediment yields are urgently required for better land and water resources planning and management purposes.

The North-West Upper Tana River (NWUT) Basin is one of Kenya’s most important basins as it provides water for urban-rural water supplies, hydro-electric power (HEP) generation and irrigation. This study therefore investigated the influence of rainfall variability on the river discharge and sediment yield in the basin. The study relied on data archived by Water Resources Authority (WRA) and Kenya Meteorological Department (KMD) for the period 2010-2012. The methods applied in the study included the use of time series, double mass curve and the use of other statistical methods. The study established that there is a significant relationship between river discharge and rainfall in the basin. The variations in stream flow can largely be explained by variations in rainfall in the basin. There is however evidence of shift in rainfall patterns so that rainfall during the short rainy season seems to be more dominant than that experienced during the long rainy season. There is also a significant relationship between sediment yield and stream flow. The basin generally experiences high rates of sediment production due to inappropriate land use practices and lack of application of soil and water conservation measures on cultivated lands. Mathioya, Saba Saba, Thika and Maragua sub-basins exhibited high rates of sediment production rates due to high rates of soil erosion in these sub-basins. The high sediment yield in the basin has potential of reducing the benefits associated with Masinga Dam in terms of water supply, irrigation, flood control and HEP generation. The study recommends implementation of enhanced programmed for land and water conservation in the basin, including implementation of payment for Ecosystem Services (PES).