Florimond De Smedt

Application of an analytical hierarchical process approach for landslide susceptibility mapping in A Luoi district, Thua Thien Hue Province, Vietnam

A Luoi is a Vietnamese–Laotian border district situated in the western part of Thua Thien Hue province, central Vietnam, where landslides occur frequently and seriously affect local living conditions. This study focuses on the spatial analysis of landslide susceptibility in this 263-km2 area. To analyze landslide manifestation in the study area, causative factor maps are derived of slope angle, weathering, land use, geomorphology, fault density, geology, drainage distance, elevation, and precipitation. The analytical hierarchical process approach is used to combine these maps for landslide susceptibility mapping. A landslide susceptibility zonation map with four landslide susceptibility classes, i.e. low, moderate, high, and very high susceptibility for landsliding, is derived based on the correspondence with an inventory of observed landslides. The final map indicates that about 37% of the area is very highly susceptible for landsliding and about 22% is highly susceptible, which means that more than half of the area should be considered prone to landsliding.

Groundwater recharge and flow in a small mountain catchment in northern Ethiopia

Abstract The hydrodynamic behaviour of a sloped phreatic aquifer in the Tigray Highlands in northern Ethiopia is described. The aquifer is situated in the soils of a plateau on top of a basalt sequence and lies on steep slopes; the latter lead to hydraulic gradients that can cause high discharge fluxes. Distinct wet and dry seasons characterize the climate of the Tigray Highlands and recharge is absent during the dry season. Because of the fertile vertisols that have developed, the plateau is heavily cultivated and thus has great local economic, and hence social, importance. Water for land irrigation is almost exclusively delivered by rainfall, which is largely restricted to the period June—September. During the dry season, the water table drops dramatically and the aquifer drains nearly completely, under the strong gravity-driven, sustained discharges. This study strives to give insights into recharge and discharge mechanisms of the aquifer, in order to improve the effectiveness of the implemented water conservation measures.

Evaluation and comparison of GIS based landslide susceptibility mapping procedures in Kulekhani watershed, Nepal

The goal of this paper is to evaluate and compare the consistency of GIS-based heuristic and bivariate landslide susceptibility mapping techniques in the Himalayan region, taking the Kulekhani watershed of central Nepal as an example. For this purpose, a heuristic and two statistical bivariate landslide susceptibility mapping methods are applied, and three separate landslide susceptibility zonation maps are produced. The maps are compared using three approaches: landslide density analysis, success rate analysis, and agreed area analysis. A comparison of the values obtained from landslide density analysis and the curves of success rate analysis indicate that the two bivariate methods produce almost identical results, whereas the map produced with the heuristic method differs significantly from the others. On the other hand, the agreed area analysis highlights significant spatial differences in the maps obtained from the three methods. Although the three approaches evaluate the consistency of susceptibility maps, only the agreed area analysis is capable of spatially comparing them. Hence, this approach proves to be more suitable for spatially and quantitatively evaluating the consistency of various landslide susceptibility zonation maps.

Evaluation of the consistency of landslide susceptibility mapping: a case study from the Kankai watershed in east Nepal

GIS-based landslide susceptibility maps for the Kankai watershed in east Nepal are developed using the frequency ratio method and the multiple linear regression technique. The maps are derived from comparing observed landslides with possible causative factors: slope angle, slope aspect, slope curvature, relative relief, distance from drainage, land use, geology, distance from faults and mean annual rainfall. The consistency of the maps is evaluated using landslide density analysis, success rate analysis and spatially agreed area approach. The first two analyses produce almost identical quantitative results, whereas the last approach is able to reveal spatial differences between the maps and also to improve predictions in the agreed high landslide-susceptible area.

Validation of soil moisture simulation with a distributed hydrologic model (WetSpa)

The objective of this paper is to test the ability of a spatially distributed hydrologic model (WetSpa) to simulate soil moisture. The test is conducted in the Baron Fork river basin (Oklahoma, USA), where soil moisture has been recorded on a daily basis at the WEST site soil moisture monitoring station of the Oklahoma Mesonet. The model is calibrated by comparing hourly simulated and observed river flows at Eldon gaging station from October 1, 1995 to December 31, 1996. The model performance to predict hourly river flows is verified by comparing model estimates and observations from January 1, 1997 to December 31, 2000. Next, the model predictions of soil moisture are compared with observations of WEST site soil moisture monitoring station for the same validation period. The observations are well reproduced by the model with errors that are within range of the observation accuracy, although the predictions show somewhat more abrupt temporal fluctuations as the whole root zone is considered to react instantaneously to precipitation events. The good performance compared to other studies is especially attributed to the quality of the rainfall data provided by weather radars. It is concluded that the performance of the model to predict soils moisture is promising, although spatial patterns still have to be verified.

Impact of Climate Change on Streamflow and Soil Moisture in the Vermilion Basin, Illinois

AbstractPotential effects of climate change on streamflow and soil moisture in Vermilion basin, Illinois, are investigated using a spatial distributed hydrological model (WetSpa). The model results show good agreement between observed and simulated discharges at the Leonore gauge station and soil moisture at the Stelle soil moisture recording site. Climate scenarios are derived by statistical downscaling of regional climate predictor variables for two climate scenarios and four time periods. The downscaled local climate variables are used as inputs to the WetSpa model. The results of the hydrological simulations show that streamflow in the Vermilion basin may decrease substantially, especially in summer, as a result of less precipitation but primarily due to increased evapotranspiration. Predictions also indicate that reduced precipitation in summer combined with a substantial increase in evaporative demand may lead to soil moisture deficits in the fall, which could have a negative impact on the natural v...

GIS Based Landslide Susceptibility Mapping using a Fuzzy Logic Approach: A Case Study from Ghurmi-Dhad Khola Area, Eastern Nepal

Landslides cause extensive loss of life and property in the Nepal Himalaya. Since the late 1980s, different mathematical models have been developed and applied for landslide susceptibility mapping and hazard assessment in Nepal. The main goal of this paper is to apply fuzzy logic to landslide susceptibility mapping in the Ghurmi-Dhad Khola area, Eastern Nepal. Seven causative factors are considered: slope angle, slope aspect, distance from drainage, land use, geology, distance from faults and folds, soil and rock type. Likelihood ratios are obtained for each class of causative factors by comparison with past landslide occurrences. The ratios are normalized between zero and one to obtain fuzzy membership values. Further, different fuzzy operators are applied to generate landslide susceptibility maps. Comparison with the landslide inventory map reveals that the fuzzy gamma operator with a γ-value of 0.60 yields the best prediction accuracy. Consequently, this operator is used to produce the final landslide susceptibility zonation map.

Impact of climate change and urban development on extreme flows in the Grote Nete watershed, Belgium

This study investigates how extreme flows in the Grote Nete watershed located in the Flanders region of Belgium will respond to climate change and urban growth using the hydrological model WetSpa. Three climate change scenarios (low, mean and high), three urban development scenarios (low, medium and high) and the nine combined climate–urban change scenarios are considered. The results indicate that extreme low flows would decrease noticeably by climate change, while they would be less sensitive to urban development. On the other hand, extreme peak flows are predicted to increase considerably due to both climate change and urban growth. It is concluded that coupling the effects of land use change with climate change may lead to severe increase in the frequency river floods in winter as well as the frequency of extreme river low flows in summer.

Regional groundwater flow modeling of the Geba basin, northern Ethiopia

The Geba basin is one of the most food-insecure areas of the Tigray regional state in northern Ethiopia due to recurrent drought resulting from erratic distribution of rainfall. Since the beginning of the 1990s, rain-fed agriculture has been supported through small-scale irrigation schemes mainly by surface-water harvesting, but success has been limited. Hence, use of groundwater for irrigation purposes has gained considerable attention. The main purpose of this study is to assess groundwater resources in the Geba basin by means of a MODFLOW modeling approach. The model is calibrated using observed groundwater levels, yielding a clear insight into the groundwater flow systems and reserves. Results show that none of the hydrogeological formations can be considered as aquifers that can be exploited for large-scale groundwater exploitation. However, aquitards can be identified that can support small-scale groundwater abstraction for irrigation needs in regions that are either designated as groundwater discharge areas or where groundwater levels are shallow and can be tapped by hand-dug wells or shallow boreholes.RésuméLe bassin de Geba est l’une des régions les plus touchées par l’insécurité alimentaire de l’état régional de Tigray dans le nord de l’Ethiopie en raison de sécheresse récurrente résultant d’une répartition erratique des précipitations. Depuis le début des années 1990, l’agriculture pluviale a été soutenue par des projets d’irrigation à petite échelle, principalement par la collecte des eaux de surface, mais le succès a été limité. Par conséquent, l’utilisation des eaux souterraines pour l’irrigation a attiré une attention considérable. Le but principal de cette étude est d’évaluer les ressources en eau souterraine dans le bassin de Geba au moyen d’une modélisation MODFLOW. Le modèle est calibré en utilisant les niveaux d’eau souterraine observés, conduisant à une idée précise concernant les systèmes d’écoulement des eaux souterraines et les réserves. Les résultats montrent qu’aucune des formations hydrogéologiques ne peut être considérées en tant qu’aquifères permettant une exploitation des eaux souterraines à grande échelle. Cependant, des aquitards capables de supporter des prélèvements d’eaux souterraines à petite échelle pour les besoins de l’irrigation peuvent être identifiées soit dans les régions qui sont désignées comme des zones de décharge des eaux souterraines ou des zones où les niveaux d’eau souterraine sont peu profonds et peuvent être captés par des puits creusés à la main ou des forages peu profonds.ResumenLa cuenca de Geba es una de las zonas con mayor inseguridad alimentaria del estado regional de Tigray en el norte de Etiopía debido a las recurrentes sequías resultantes de la distribución irregular de las lluvias. Desde comienzos de los años noventa, la agricultura de secano ha sido apoyada mediante regímenes de riego a pequeña escala, principalmente mediante la recolección de aguas superficiales, pero el éxito ha sido limitado. Por lo tanto, el uso de agua subterránea para fines de riego ha ganado considerable atención. El propósito principal de este estudio es evaluar los recursos de agua subterránea en la cuenca de Geba mediante un enfoque de modelado MODFLOW. El modelo se calibra usando los niveles observados de agua subterránea, lo que da una idea clara de los sistemas de flujo de agua subterránea y reservas. Los resultados muestran que ninguna de las formaciones hidrogeológicas puede ser considerada como acuíferos que pueden explotarse en una explotación de agua subterránea a gran escala. Sin embargo, se pueden identificar acuitardos que pueden apoyar la extracción de agua subterránea a pequeña escala para las necesidades de riego en regiones designadas como áreas de descarga de aguas subterráneas o donde los niveles de aguas subterráneas son superficiales y pueden ser aprovechados por pozos excavados a mano o pozos poco profundos.摘要由于降雨分布极度不均从而造成周期性的干旱,致使Geba流域是埃塞俄比亚北部Tigray州粮食最得不到保障的地区之一。自从20世纪90年代开始,旱作农业主要通过地表水收集而进行的小规模灌溉计划得到支持,但成就有限。因此,使用地下水用于灌溉受到了人们的极大关注。本研究的主要目的就是通过MODFLOW模拟方法评价Geba流域的地下水资源。采用观测的地下水位校正模型,深入了解了地下水流系统和地下水储量。结果显示,没有一个水文地质层可以作为含水层进行大规模地下水的开采。然而,发现一些弱透水层,这些弱透水层在地下水排泄区或地下水位浅的地方可以进行地下水开采以满足灌溉所需,可以通过手工挖掘井或者浅的机井抽取。ResumoA bacia de Geba é uma das áreas de maior insegurança alimentar no estado regional de Tigray, Norte da Etiópia, devido às secas recorrentes resultantes da distribuição errática da precipitação. Desde o inicio da década de 1990, a agricultura dependente da chuva vem sendo mantida por sistemas de irrigação de pequena escala, majoritariamente utilizando águas superficiais, mas o êxito tem sido limitado. Desse modo, a utilização de águas subterrâneas para irrigação ganhou uma atenção considerável. O principal propósito desse estudo é avaliar os recursos hídricos subterrâneos na bacia de Geba por meio de modelagem utilizando o MODFLOW. O modelo é calibrado utilizando níveis freáticos observados, fornecendo uma visão clara sobre o sistema de fluxo e reservas de água subterrânea. Os resultados demonstram que nenhuma das formações hidrogeológicas podem ser consideradas como aquíferos que permitem a extração de água subterrânea em larga escala. Entretanto, podem ser identificados aquitardos que podem apoiar a captação de águas subterrâneas em pequena escala para utilização na irrigação em regiões que são tanto designadas como áreas de descarga como onde os níveis freáticos são rasos e podem ser captados por poços escavados a mão ou poços rasos.

Characterization of a cavern conduit system in vietnam by time series correlation, cross-spectrum and wavelet analyses

Abstract Abstract Time series analyses are applied to characterize the transient flow regimes of the Nam La cavern conduit, northwest Vietnam. The conduit transforms the input signal to an output signal, and the degree of transformation provides information on the nature of the flow system. The input for the analysis is net precipitation and the flow hydrograph at the cave entrance, while the output series is the flow hydrograph at the resurgence. Cross-correlation and cross-spectrum analysis are used to investigate the stationarity and linearity of the input–output transformation of the system, resulting in hydrodynamic properties such as system memory, response time, and mean delay between input and output. It is shown that during high flow periods, the flow in the conduit is pressurized. Consequently, the linear input–output assumption holds only for low flows. To highlight the hydrodynamics of the cavern conduit for the high flow periods, wavelet spectrum and wavelet cross-spectrum analyses are applied.