Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in ...Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in structure and species composition, are dominant along these river banks: Aquatic vegetation, Wetbanks, Palmiet, Scrub, Forest and Shrubland(Fynbos). The study aims to correlate the vegetation patterns to flooding patterns, in particular the inundation frequency and stream power. A problem arises: because these catchments are ungauged, like most mountain catchments, with the only weirs at the downstream end of the catchment. Discharge data at the weirs are extrapolated to the sites upstream by multiplication with a factor based on the size of the subcatchment that drains through a sample site. In this way, recurrence intervals for floods in mountain streams are derived. Discharges at sites are also calculated using bed roughness(Manning's n) and slope in straight sections with uniform flow conditions. Stream power is derived from the discharges calculated in this manner. The combination of stream power and recurrence intervals explains the occurrence of most vegetation types occurring on the banks, except for one type: Afromontane Forest. This type is probably more dependent on other factors, such as protection from fire and the depth of the groundwater table.展开更多
The stream and rain data acquisition system presented in this paper makes the mapping of hydro potentials in the region or of the country economically and practically possible. Moreover, it can also serve as a flood w...The stream and rain data acquisition system presented in this paper makes the mapping of hydro potentials in the region or of the country economically and practically possible. Moreover, it can also serve as a flood warning system.展开更多
Based on the flood area hydrodynamic model, this paper backs the analysis of the risk warning point of the Mayang Stream in the typical flood process, to determine the disaster-caused critical precipitation and the co...Based on the flood area hydrodynamic model, this paper backs the analysis of the risk warning point of the Mayang Stream in the typical flood process, to determine the disaster-caused critical precipitation and the corresponding flood risk map at different depths of submergence. The result is used as the mountain torrent disaster monitoring and warning indicators and risk assessment of the Mayang Stream. Then based on the flood risk warning service system of small and middle rivers of Fujian Province, the risk warning service of mountain torrent disaster is developed during the impact time of Meranti in 2016. After the process of typhoon, the mountain torrent caused by Meranti was back analyzed by using the decided flood area model, then compared with the results of filed investigation to verify the accuracy of the disaster-caused critical precipitation forecast and the effect of monitoring and early warning services. The result shows that the cause of Mayang Stream’s mountain torrent disaster of the typhoon Meranti is the heavy rainfall and the strong wind. The highest mountain torrent disaster was forecasted by the refine precipitation based on the disaster-caused critical rainfall of the Mayang Stream. The simulated flood scenarios and the field trip’s results were basically matched in upstream and not matched in the downstream. The post-mountain simulation assessment also showed that the flood inundation range basically matched with reality, but the flood process was biased. The reason was that in addition to the differences between the surface rainfall forecast and the real situation, many actual situations cannot be ignored. For example, Meranti caused serious damage to trees, increased river blockages, resulting in changes in flood inundation time and depth, affecting the flood process. It showed the tourism development would cause the river way blocking and increase the risk of flood. In order to prevent and reduce the flood disasters accurately and effectively, the flood risk forecast and the disaster-caused facts should be considered at the same time.展开更多
Since the 1990s flood water hazards have recurrently created reason vexing moments on the Cameroonian urban folk of major and minor towns by inflicting fatality toll beating-off manned efforts to mitigate the ugliness...Since the 1990s flood water hazards have recurrently created reason vexing moments on the Cameroonian urban folk of major and minor towns by inflicting fatality toll beating-off manned efforts to mitigate the ugliness unleashed. Flood catastrophe in frequency and toll in towns sited on more inland highland towns like Bamenda has given birth to dynamic survival strategies since impacts change in space and time. Northern Bamenda has emerged as haven for ravaging River Mezam with rising forms of flood havoc on humans and their investments. Primary and secondary data collected from related stakeholders (government and municipal officials concerned with abating the flood occurrence and managing its aftermath as well as individuals who consciously or not trigger the floods). The aim of this study was to relativize flood water bearing on urban population reactions in the wake of the rising calamity. Results reveal that flood trends are advancing yearly in the like of fatalities that systematically make nonsense of urban setup human endeavours to tame floods. This study considers that an urgent urban flood hazard perception revolution must be engaged for this unplanned urban front that is developing where the topography presents a funnelling effect to stream water and so obviously has no respect for the existing flood countering socio-economic and engineering adaptations. Such flood disrespect for urban humans call for man-centred innovative and comprehensive paradigms should there be any hope for less hazardous sustainable city growth in Cameroon.展开更多
基金supported by funding from the National Research Foundation to C. Boucher and the VSB Funds (the Netherlands) to E. Siebenadditional funding from the Water Research Commission
文摘Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in structure and species composition, are dominant along these river banks: Aquatic vegetation, Wetbanks, Palmiet, Scrub, Forest and Shrubland(Fynbos). The study aims to correlate the vegetation patterns to flooding patterns, in particular the inundation frequency and stream power. A problem arises: because these catchments are ungauged, like most mountain catchments, with the only weirs at the downstream end of the catchment. Discharge data at the weirs are extrapolated to the sites upstream by multiplication with a factor based on the size of the subcatchment that drains through a sample site. In this way, recurrence intervals for floods in mountain streams are derived. Discharges at sites are also calculated using bed roughness(Manning's n) and slope in straight sections with uniform flow conditions. Stream power is derived from the discharges calculated in this manner. The combination of stream power and recurrence intervals explains the occurrence of most vegetation types occurring on the banks, except for one type: Afromontane Forest. This type is probably more dependent on other factors, such as protection from fire and the depth of the groundwater table.
文摘The stream and rain data acquisition system presented in this paper makes the mapping of hydro potentials in the region or of the country economically and practically possible. Moreover, it can also serve as a flood warning system.
文摘Based on the flood area hydrodynamic model, this paper backs the analysis of the risk warning point of the Mayang Stream in the typical flood process, to determine the disaster-caused critical precipitation and the corresponding flood risk map at different depths of submergence. The result is used as the mountain torrent disaster monitoring and warning indicators and risk assessment of the Mayang Stream. Then based on the flood risk warning service system of small and middle rivers of Fujian Province, the risk warning service of mountain torrent disaster is developed during the impact time of Meranti in 2016. After the process of typhoon, the mountain torrent caused by Meranti was back analyzed by using the decided flood area model, then compared with the results of filed investigation to verify the accuracy of the disaster-caused critical precipitation forecast and the effect of monitoring and early warning services. The result shows that the cause of Mayang Stream’s mountain torrent disaster of the typhoon Meranti is the heavy rainfall and the strong wind. The highest mountain torrent disaster was forecasted by the refine precipitation based on the disaster-caused critical rainfall of the Mayang Stream. The simulated flood scenarios and the field trip’s results were basically matched in upstream and not matched in the downstream. The post-mountain simulation assessment also showed that the flood inundation range basically matched with reality, but the flood process was biased. The reason was that in addition to the differences between the surface rainfall forecast and the real situation, many actual situations cannot be ignored. For example, Meranti caused serious damage to trees, increased river blockages, resulting in changes in flood inundation time and depth, affecting the flood process. It showed the tourism development would cause the river way blocking and increase the risk of flood. In order to prevent and reduce the flood disasters accurately and effectively, the flood risk forecast and the disaster-caused facts should be considered at the same time.
文摘Since the 1990s flood water hazards have recurrently created reason vexing moments on the Cameroonian urban folk of major and minor towns by inflicting fatality toll beating-off manned efforts to mitigate the ugliness unleashed. Flood catastrophe in frequency and toll in towns sited on more inland highland towns like Bamenda has given birth to dynamic survival strategies since impacts change in space and time. Northern Bamenda has emerged as haven for ravaging River Mezam with rising forms of flood havoc on humans and their investments. Primary and secondary data collected from related stakeholders (government and municipal officials concerned with abating the flood occurrence and managing its aftermath as well as individuals who consciously or not trigger the floods). The aim of this study was to relativize flood water bearing on urban population reactions in the wake of the rising calamity. Results reveal that flood trends are advancing yearly in the like of fatalities that systematically make nonsense of urban setup human endeavours to tame floods. This study considers that an urgent urban flood hazard perception revolution must be engaged for this unplanned urban front that is developing where the topography presents a funnelling effect to stream water and so obviously has no respect for the existing flood countering socio-economic and engineering adaptations. Such flood disrespect for urban humans call for man-centred innovative and comprehensive paradigms should there be any hope for less hazardous sustainable city growth in Cameroon.
