Many debris flow hazards were triggered in Earthquake area after the Wenchuan Earthquake. On 13 Aug.2010, a catastrophic debris flows were triggered by heavy rainfall in Bayi Gully, Dujiangyan county, southwestern china. This debris flows originating shortly after a rainstorm with an intensity of 75 mm/h transported a total volume of more than 116.5×104 m3. Our primary objective for this study was to analyze the characteristics of the triggering rainfall and the debris supply conditions, and to estimate debris flow volume, mean velocity, and discharge. The debris flow destroyed the most downstream dam in the catchment during a heavy rain storm. The debris flow with a peak discharge of 1082 m3/s, a total volume of 1.16 million cubic meter, a density of 1.88g·cm－3 and a yield stress of 6700 Pa caused 2 persons were missing, 1 persons were injured and 140 houses buried. After three rainy seasons, Only 30% sediment of debris deposition was taken away by 4 large-scale debris flow events. New debris flow will be triggered by rainfall in Bayi Gully in the future. It will be a long term work to prevent the debris flows in Bayi Gully.
The disposal of waste materials by burial is the oldest form of solid waste disposal. A major concern with the usage of traditional dump sites is the potential of polluting groundwater. The pollution could be metals, microbes or other substances. This problem of groundwater contamination from refuse disposal especially those located uphill are worsened when communities that rely on dump site disposal system also depend on private wells for drinking water. Wastewater often makes its way into other water bodies. Water runoff from rain may wash contaminants into the surface waters. A more significant hazard is when pollutants from the drain field move quickly through the soil and potentially into the groundwater making the supposed potable water unusable. The application of methods involving identification of anisotropic behavior and heterogeneities in rocks has become increasingly acceptable because these methods provide adequate knowledge about the presence of fractures and their directions. Observed changes in apparent resistivity with azimuth are typically used for such interpretation which indicates fracture anisotropy. Due to repeated cases of groundwater pollution in the area, this study researches into the application of surface geophysical methods to detect bedrock fractures and to estimate hydraulic properties of the fractured bedrock in order to determine the direction of wastewater flow from a dump site located uphill into a public borehole. Azimuthal Square array was used to detect fractures in bedrock in parts of Owo area in Ondo State, Nigeria. Apparent resistivities measured at four locations near the dumpsite changed with the orientation of the array. Scattered plots and Graphical interpretation of the technique indicate that a dominant fracture set is oriented NW/SE. Hydrochemical analysis of water samples collected from three hand dug wells around the dump revealed presence of leachates. The presence and interconnectivity of fracture zones in almost all the sampled points even at the over burden in the study area provide pathway for easy movement of the waste water.
Flooding is one significant process that contributes to the movement of sediment and metals. With higher velocities of water, flooding can take contamination downstream. The soil samples were collected from three floodplains of Owena river, Ogbese river and Ala river in Ondo State were analyzed for their physico-chemical characteristics. The study also investigated the chemical speciation of Cd, Cu, Ni and Zn and total concentration in the soil samples. The concentration of the heavy metals in the selected floodplains were orderly as Zn > Cu > Ni > Cd. Investigating the speciation showed that contribution to the total metal content of the alluvial soil was from both geogenic and anthropogenic sources. Pollution/Contamination index evaluation showed that the alluvial soils had very slight metal contamination for all the metals except for Cd being found in the range of very severe contamination to slight contamination in Owena and Ala floodplains. The enrichment factor of the heavy metals had a general trend of Ni = Cu < Zn < Cd. The geo-accumulation index also had a general trend of Ni < Cu < Zn < Cd. The pollution index had highest value in Ala.
Prominent locations in the Nigerian basement complex are known to harbor precious rocks and gemstones, in addition to the basement rocks being quarried for engineering construction. However, reserve estimates of these rocks and mineral deposits are largely unknown. Geophysical investigations have been undertaken at Olode-Gbayo village in Ibadan, southwestern, Nigeria. The primary objectives are to estimate overburden thickness and extend results to estimate probable gross basement tonnage and probable reserve of mineralized pegmatite in the basement rock. The Olode-Gbayo pegmatite has been found to be mineralized in aquamarine at depths. A total of seventeen vertical electrical soundings (VES) were carried out. Data acquisition involved the use of Schlumberger electrode configuration. Interpretation of the geoelectrical data involved the use of curve matching technique and computer iteration. Geoelectrical cross sections and isopach maps were constructed based on lateral combination of inverted soundings from the VES surveys. Existing mining pits were logged and rock samples were collected to estimate basement rock distribution and determine specific rock gravity. The VES result showed a three to four geo-electric layers, the top soil, weathered layer, partially weathered layer and fresh or partially fractured basement. Overburden thickness varied from about 2.6 to about 7.7 m. The thickest overburden is observed in the southern part whereas thinner overburden is observed in the northern part of the area. Using an exploitable basement rock thickness of 50 m, gross basement rock tonnage was estimated as 1.95 x 108 tons, with pegmatite being estimated to constitute about 0.5% of the basement rock volume. Generally, the basement rock is considered economically viable for mining and engineering construction, whereas the pegmatite rocks could be economically minable as host rock for gemstone.
Scarcity of water within and around Northern Nigeria is no longer a wieldy issue. There is an over reliance on groundwater, and this has led to an increase in the number of bore-holes drilled in order to augment the water needs within the study area. Unfortunately the failure of many installed bore-holes has been rampant in this area. This is due to absence of or improper groundwater investigation and interpretation of site suitability. In this study, a remote sensing approach was employed to delineate and classify groundwater potentials of the Sokoto basin. GIS-based groundwater potential map of Sokoto Basin was modelled by producing and subsequently combining thematic maps. The data set includes; drainage, lineament, soil, lithology, elevation, slope and rainfall. Thematic maps of each data set were produced as distinct layers first before combining them together. For each layer, weighting for different classes was performed. The ground water potential map was then reclassified into five classes; very good, good, moderate to good, moderate and poor class. Results from the maps produced show that areas mapped indicating zones of very-good groundwater potential covers approximately 2.2% (1432.66 km2); zones mapped indicating good groundwater potential covers approximately 7.79% (5071.5237 km2); zones mapped indicating moderate to good groundwater potential covers approximately 27.5% (17577.8 Km2); zones mapped indicating moderate groundwater potential covers approximate 49.2% (32030.676 km2) and zones mapped indicating poor groundwater potential covers approximately 13.1% (8528.493 Km2) of the study area. The study further revealed that the southern part of the study area has a better water potential than the northern part of the study area. There is a close agreement between the groundwater potential map produced and field pump test data obtained previously within the Sokoto Basin according by previous authors.