Model test study on the formation and development of underground erosion ground fissures in the Kenya Rift Valley

The Kenya Rift Valley is relatively prone to underground erosion ground fissures and associated disasters,which gravely hinder local engineering construction and economic development.In this research,we performed field and experimental studies on ground fissures in the Kenya Rift Valley area,and determined the structural characteristics of underground erosion fissures.Based on a geological survey of the area,we generalized a geological model for typical ground fissures and reproduced the intermediate process of ground fissure propagation using a large-scale physical model test.Further,the development process of underground erosion fissures were categorized into four stages:uniform infiltration,preferential infiltration,cavity expansion,and collapse formation stages.During the development of underground erosion fissures,water content was distributed symmetrically along the fissures,and these fissures acted as the primary infiltration paths of water.When the ground collapsed,the increase in negative pore water pressure was greater,whereas the increase in positive pore water pressure was less in the shallow soil;moreover,in the deep soil,the increase in positive pore water pressure was greater than that of negative pore water pressure.Additionally,the earth pressure increment initially increased and then decreased with the development of erosion.During underground erosion collapse,the water content and pore water pressure appeared to increase and decrease rapidly.These results can be employed to predict the occurrence of underground erosion ground fissures and the resulting soil collapse.

Electrical-hydraulic conductivity model for a weatheredfractured aquifer system of Olbanita, Lower Baringo Basin, Kenya Rift

Groundwater yield in the Kenya Rift is highly unsustainable owing to geological variability.In this study,field hydraulic characterization was performed by using geoelectric approaches.The relations between electrical-hydraulic(eh)conductivities were modeled hypothetically and calibrated empirically.Correlations were based on the stochastic models and field-scale hydraulic parameters were contingent on pore-level parameters.By considering variation in pore-size distributions over eh conduction interval,the relations were scaled-up for use at aquifer-level.Material-level electrical conductivities were determined by using Vertical Electrical Survey and hydraulic conductivities by analyzing aquifer tests of eight boreholes in the Olbanita aquifer located in Kenya rift.VES datasets were inverted by using the computer code IP2Win.The main result is that ln T=0.537(ln Fa)+3.695;the positive gradient indicating eh conduction through pore-surface networks and a proxy of weathered and clayey materials.An inverse(1/F-K)correlation is observed.Hydraulic parameters determined using such approaches may possibly contribute significantly towards sustainable yield management and planning of groundwater resources.

Hydrogeophysical Characterization of a Weathered-Fractured Aquifer System: A Case Study of Olbanita, Lower Baringo Basin, Kenya Rift

Groundwater yields in the Kenya Rift are highly unsustainable owing to geological variability. In this study, field hydraulic characterization was performed by using geo-electric approaches. The relations between electrical–hydraulic (eh) conductivities were modeled hypothetically and calibrated empirically. Correlations were based on the stochastic models and field-scale hydraulic parameters were contingent on pore-level parameters. By considering variation in pore-size distributions over eh conduction interval, the relations were scaled-up for use at aquifer-level. Material-level electrical conductivities were determined by using Vertical Electrical Survey and hydraulic conductivities by analyzing aquifer tests of eight boreholes in the Olbanita aquifer located in Kenya rift. VES datasets were inverted by using the computer code IP2Win. The main result is that InT = 0.537(1nFa) + 3.695, the positive gradient indicating eh conduction through pore-surface networks and a proxy of weathered and clayey materials. An inverse (1/F-K) correlation is observed. Hydraulic parameters determined using such approaches may possibly contribute significantly towards sustainable yield management and planning of groundwater resources.

Enhanced surveillance and cohesive policies needed to tackle Rift Valley fever

Dear editor,There has been an upsurge in Rift Valley fever (RVF) outbreaks in Kenya in the recent past.Even as I write this letter,the country is experiencing an outbreak which was confirmed by the Ministry of Health on 8 June 2018[1].The current outbreak was first reported in Wajir County on 2nd June but has currently spread to other

东非裂谷东支肯尼亚裂谷形成演化

东非裂谷东支肯尼亚裂谷包括5个重点凹陷,除South Lokichar凹陷外,其余凹陷均无发现。肯尼亚裂谷的形成演化及动力机制认识不清是制约油气勘探的关键。通过系统分析肯尼亚裂谷不同凹陷形成年代、裂谷类型和动力机制、构造演化和沉积充填过程,得到以下几点认识:(1)South Lokichar凹陷形成时间早,地层年代老。South Lokichar凹陷主要发育晚渐新世-中中新世地层;Turkana、Kerio及North Lokichar凹陷以中中新世-全新世地层为主;Kerio Valley凹陷主要发育中-晚中新世地层;(2)阿法尔地幔柱和肯尼亚地幔柱的隆升控制肯尼亚裂谷的形成演化。South Lokichar凹陷的形成演化主要受阿法尔地幔柱控制;其余4个凹陷主要受肯尼亚地幔柱控制;(3)不同类型的凹陷构造演化和沉积充填差异较大。South Lokichar凹陷与Kerio Valley凹陷为被动型裂谷,构造演化经历初始裂陷期、主裂陷期和裂陷后期三个阶段,在主裂陷期发育优质烃源岩;Turkana、Kerio及North Lokichar凹陷为主动型裂谷,构造演化包括火山事件活动期和间歇期,以厚层火山岩和粗碎屑沉积为主;(4)肯尼亚裂谷演化分为三期:Ⅰ期裂谷为晚渐新世—中中新世;Ⅱ期裂谷为中—晚中新世;Ⅲ期裂谷为上新世—现今。

肯尼亚裂谷区地裂缝特征及成因分析

肯尼亚裂谷位于东非大裂谷东支中段,现代构造运动以及火山活动强烈,是当今地学研究的热点地区。裂谷区因其独特的地质构造背景、岩土体特性以及气象水文条件,使得地裂缝灾害较为发育。文章以肯尼亚裂谷地裂缝为研究对象,利用资料收集、野外调查、槽探、钻探和室内土工试验等研究手段,对研究区的地质环境背景、地裂缝平剖面结构特征进行研究。裂谷拉张和火山活动等内动力地质作用是该区域地裂缝形成的控制因素,浅表部松散易潜蚀的土体是地裂缝形成的物质基础,强降雨为地裂缝的形成提供了水力条件,“软硬软”的地层结构为水力侵蚀物质提供了有利的堆积场所。将肯尼亚裂谷区地裂缝的形成演化过程分为3个阶段:孕育阶段、扩展阶段和成灾阶段。

肯尼亚内罗毕至马拉巴铁路通道研究

为进一步完善东非铁路网,合理选定内马铁路通道,通过分析内马铁路的功能定位,提出内罗毕—纳罗克—基苏木—马拉巴和内罗毕—纳库鲁—基苏木—马拉巴2条东非大裂谷线路通道方案,针对不同的通道方案,从沿线的经济据点状况及运量、地形地貌、地震裂度、地质构造、地形适应性、运输需求及工程投资等多方面比较分析,得出推荐采用内罗毕—纳罗克—基苏木—马拉巴通道方案的结论,同时内马铁路通道的建设将极大地推动肯尼亚西北部地区旅游业、物流业的发展,从而推动整个国家经济发展。