RESUMEN
Application of suitable methods to generate landslide susceptibility maps (LSM) can play a key role in risk management. Rwanda, located in centre-eastern Africa experiences frequent and intense landslides which cause substantial impacts. The main aim of the current study was to effectively generate susceptibility maps through exploring and comparing different statistical and probabilistic models. These included weights of evidence (WoE), logistic regression (LR), frequency ratio (FR) and statistical index (SI). Experiments were conducted in Rwanda as a study area. Past landslide locations have been identified through extensive field surveys and historical records. Totally, 692 landslide points were collected and prepared to produce the inventory map. This was applied to calibrate and validate the models. Fourteen maps of conditioning factors were produced for landslide susceptibility modeling, namely: elevation, slope degree, topographic wetness index (TWI), curvature, aspect, distance from rivers and streams, distance to main roads, lithology, soil texture, soil depth, topographic factor (LS), land use/land cover (LULC), precipitation and normalized difference vegetation index (NDVI). Thus, the produced susceptibility maps were validated using the receiver operating characteristic curves (ROC/AUC). The findings from this study disclosed that prediction rates were 92.7%, 86.9%, 81.2% and 79.5% respectively for WoE, FR, LR and SI models. The WoE achieved the highest AUC value (92.7%) while the SI produced a lowest AUC value (79.5%). Additionally, 20.42% of Rwanda (5048.07â¯km2) was modeled as highly susceptible to landslides with the western part the highly susceptible comparing to other parts of the country. Conclusively, the comparison of produced maps revealed that all applied models are promising approaches for landslide susceptibility studying in Rwanda. The results of the present study may be useful for landslide risk mitigation in the study area and in other areas with similar terrain and geomorphological conditions. More studies should be performed to include other important conditioning factors that exacerbate increases in susceptibility especially anthropogenic factors.
RESUMEN
Groundwater is the main source of water for domestic use in Nigeria because it is perceived to be clean. The presence of geogenic contaminants (arsenic and fluoride), and the level of awareness of their presence in groundwater in Ibadan, Nigeria was examined in this study. A total of one hundred and twenty groundwater samples were collected from hand dug wells which tap into shallow aquifers and their location taken with the aid of a GPS. The concentration of arsenic was determined by Atomic Absorption Spectrophotometry (AAS) while concentration of fluoride was determined by single beam spectrophotometer. Three hundred and fifty semi structured questionnaires were also administered within the study area to determine the level of awareness of contamination problem. Simple summary statistics including mean (m) standard deviation (s) and minimum-maximum values of the hydro-chemical data was used in the data analyses, while spatial concentrations were mapped using ArcGIS. The results showed arsenic concentration exceeding the WHO (2011) recommended concentration for drinking water in 98% and 100% of the dry and wet season samples. Concentration of Fluoride exceeded the recommended limits in 13% and 100% of the dry and wet season samples. Questionnaire analyses revealed that 85% of respondents have never tested their wells, 55% have no knowledge of geogenic contamination, while 92% never heard of arsenic or fluoride (52%). The study recommends enlightenment on geogenic contamination and testing of wells for remediation purposes.