Maiduguri metropolis Nigeria, lies on a relatively flat terrain of about 350 meters above sea level and is part of the undulating Borno Plain that slopes towards the Lake Chad. The rapid physical expansion of the metr...Maiduguri metropolis Nigeria, lies on a relatively flat terrain of about 350 meters above sea level and is part of the undulating Borno Plain that slopes towards the Lake Chad. The rapid physical expansion of the metropolis and the annual recurrent flash flooding and inundation problems within the city continues to impact devastating socioeconomic effects on the livelihood of residents sometimes leading to loss of lives and property. It is important therefore to understand the spatial pattern of floods and terrain characteristics in Maiduguri for planning purposes. The paper examined the spatial pattern of urban flash floods and inundations, and the terrain characteristics in Maiduguri metropolis. Digital Terrain Model (DTM) generated from the Shuttle Raddar Topography Mission was used to provide the basis for the terrain analysis to generate hydrological parameters such as elevation, flow accumulation and direction, drainage network and slope angle as well as classified elevation images and terrain wetness index to map out potential flood risk areas. The DTM identified potential areas liable to flash flood and inundation. The 3D Digital Terrain Model (DTM) of the area showed where potential floods or traps were located in the metropolis. The findings further revealed that Maiduguri was generally characterized by low lying locations with slope angles of less than 5 degrees covering an area of 144.4 km<sup>2</sup> out of 148 km<sup>2</sup> making it extremely difficult to drain. The processed flow accumulation of the study area showed a high flow accumulation pixel value of 19,972 that drained into outlet, suggesting that a large proportion of the study area was getting flooded during a rainstorm. Even though the calculated drainage density of 0.73 for the study area indicated a very good drainage system, this was also undermined by the flat terrain and urbanization. The study recommends for improved land use planning;raising awareness of the residents, provision of more drainages and continued vulnerability mapping improved the functionality of bodies responsible for flood management among others for sustainable flood management in the study area.展开更多
黄河上游青藏高原东北边缘的自然环境具有高度的敏感性和脆弱性,其对全球变化的响应受到国内外学术界的广泛关注。特别是关于官亭盆地喇家遗址及其周边区域的史前灾害与形成机制问题,国内外地学与考古学界存在激烈的学术争论。通过多年...黄河上游青藏高原东北边缘的自然环境具有高度的敏感性和脆弱性,其对全球变化的响应受到国内外学术界的广泛关注。特别是关于官亭盆地喇家遗址及其周边区域的史前灾害与形成机制问题,国内外地学与考古学界存在激烈的学术争论。通过多年对官亭盆地黄河北岸古洪积扇前沿和第二级阶地及吕家沟、岗沟、马家沟等区域细致的野外考察,在该区域选取4个天然沉积剖面,对其进行高分辨率的系统性采样,并分析测定磁化率、粒度成分和砂级颗粒。结果表明:晚更新世晚期到全新世早期官亭盆地黄河北岸古洪积扇前沿和黄河第二级阶地区域沉积了风成黄土(L1-1和Lt),全新世中期形成了黑垆土古土壤(S0)。该区域沉积剖面结构普遍的特征是,全新世中期黑垆土古土壤被山洪泥流层和山洪砂土层分隔为多个层段,这是发生在OSL年龄3960~3650 a,对应14C年龄3850~3600 a B.P.期间的大规模暴雨山洪泥流灾害事件造成的结果。这期间官亭盆地发生了两场多次大地震,并且伴随短时段高强度暴雨诱发的大规模山洪泥流,其在古洪积扇前沿溢出沟槽,扩散到黄河第二级阶地沉积下来,淹没农田和聚落,以喇家遗址为代表的大型齐家文化聚落由此而毁灭。通过与全球气候变化对比分析,发现这个山洪泥流盛行期发生在全球气候变化的转折阶段。气候恶化造成青藏高原边缘大气环流不稳定,对流旺盛,极端性暴雨频发。在史前人类土地开发利用与多次大地震造成的坡面失稳背景条件之下,暴雨诱发大规模山洪和泥流、泥石流等灾害性地表过程,毁灭了喇家遗址的齐家文化聚落。这个研究结果对于深入理解黄河上游史前气候环境变化、自然灾害和人地关系演变具有重要科学价值。展开更多
文摘Maiduguri metropolis Nigeria, lies on a relatively flat terrain of about 350 meters above sea level and is part of the undulating Borno Plain that slopes towards the Lake Chad. The rapid physical expansion of the metropolis and the annual recurrent flash flooding and inundation problems within the city continues to impact devastating socioeconomic effects on the livelihood of residents sometimes leading to loss of lives and property. It is important therefore to understand the spatial pattern of floods and terrain characteristics in Maiduguri for planning purposes. The paper examined the spatial pattern of urban flash floods and inundations, and the terrain characteristics in Maiduguri metropolis. Digital Terrain Model (DTM) generated from the Shuttle Raddar Topography Mission was used to provide the basis for the terrain analysis to generate hydrological parameters such as elevation, flow accumulation and direction, drainage network and slope angle as well as classified elevation images and terrain wetness index to map out potential flood risk areas. The DTM identified potential areas liable to flash flood and inundation. The 3D Digital Terrain Model (DTM) of the area showed where potential floods or traps were located in the metropolis. The findings further revealed that Maiduguri was generally characterized by low lying locations with slope angles of less than 5 degrees covering an area of 144.4 km<sup>2</sup> out of 148 km<sup>2</sup> making it extremely difficult to drain. The processed flow accumulation of the study area showed a high flow accumulation pixel value of 19,972 that drained into outlet, suggesting that a large proportion of the study area was getting flooded during a rainstorm. Even though the calculated drainage density of 0.73 for the study area indicated a very good drainage system, this was also undermined by the flat terrain and urbanization. The study recommends for improved land use planning;raising awareness of the residents, provision of more drainages and continued vulnerability mapping improved the functionality of bodies responsible for flood management among others for sustainable flood management in the study area.
文摘黄河上游青藏高原东北边缘的自然环境具有高度的敏感性和脆弱性,其对全球变化的响应受到国内外学术界的广泛关注。特别是关于官亭盆地喇家遗址及其周边区域的史前灾害与形成机制问题,国内外地学与考古学界存在激烈的学术争论。通过多年对官亭盆地黄河北岸古洪积扇前沿和第二级阶地及吕家沟、岗沟、马家沟等区域细致的野外考察,在该区域选取4个天然沉积剖面,对其进行高分辨率的系统性采样,并分析测定磁化率、粒度成分和砂级颗粒。结果表明:晚更新世晚期到全新世早期官亭盆地黄河北岸古洪积扇前沿和黄河第二级阶地区域沉积了风成黄土(L1-1和Lt),全新世中期形成了黑垆土古土壤(S0)。该区域沉积剖面结构普遍的特征是,全新世中期黑垆土古土壤被山洪泥流层和山洪砂土层分隔为多个层段,这是发生在OSL年龄3960~3650 a,对应14C年龄3850~3600 a B.P.期间的大规模暴雨山洪泥流灾害事件造成的结果。这期间官亭盆地发生了两场多次大地震,并且伴随短时段高强度暴雨诱发的大规模山洪泥流,其在古洪积扇前沿溢出沟槽,扩散到黄河第二级阶地沉积下来,淹没农田和聚落,以喇家遗址为代表的大型齐家文化聚落由此而毁灭。通过与全球气候变化对比分析,发现这个山洪泥流盛行期发生在全球气候变化的转折阶段。气候恶化造成青藏高原边缘大气环流不稳定,对流旺盛,极端性暴雨频发。在史前人类土地开发利用与多次大地震造成的坡面失稳背景条件之下,暴雨诱发大规模山洪和泥流、泥石流等灾害性地表过程,毁灭了喇家遗址的齐家文化聚落。这个研究结果对于深入理解黄河上游史前气候环境变化、自然灾害和人地关系演变具有重要科学价值。
