A COMPARATIVE STUDY OF LANDSLIDES AND GEOHAZARD MITIGATION IN NORTHERN AND CENTRAL MALAWI By Golden Gadinala Ashan Chizimba Msilimba Thesis Submitted for the Degree Doctor of Philosophy, Faculty of Agricultural and Natural Sciences, Department of Geography, University of the Free State November, 2007 Promoter: Professor Peter J. Holmes i FRONTISPIECE Landslides play a major role in the development of hill slopes. They cause habitat degradation, derange drainage systems, alter drainage path ways, destroy riparian vegetation, bank erosion, accelerate meander development and loss of scenic beauty of mountain environments. Landslides threaten people, their property and livelihood sources. Degraded marginal lands are clearly observed as can be seen in this photograph, taken at the Ntchenachena study area in the Rumphi District of Northern Malawi. ii DECLARATION I declare that this thesis is a product of my own independent work and has not previously been submitted for the award of a similar or related degree in any other university. All sources of information used have been correctly referenced, and any other assistance rendered has been fully acknowledged. I furthermore cede copyright of the thesis in favour of the University of the Free State Signature: Author : ………………………………………….. Date: ………………………… Golden Gadinala Ashan Chizimba Msilimba iii ABSTRACT In 2003, a number of landslides occurred in the Ntchenachena and the Chiweta Areas of the Rumphi District in Northern Malawi, and in the Livilivi/Mvai Catchments of Ntcheu District in Central Malawi. The landslide events caused significant damage to crops, farmland, livestock and infrastructure. Worse still, they caused the death of four people. The high density of landslides occurrences suggested instability of the slopes of these areas. In light of these landslides, this study set out to assess the slope stability status of the areas. The study addressed landslide mapping and classification of observed events; assessment of the causes and contributing factors; assessment of the socio-economic and environmental impacts of the events; exploration of traditional knowledge, beliefs and peoples perceptions surrounding landslides; determination of the coping strategies; and development of mitigations to landslides as geo-hazards. This study involved a landslide inventory of all observed events. The physical characteristics of the terrain influencing slope instability were measured. The characteristics recorded included slope length, angles, aspect and altitude, and channel dimensions. Landslides were classified based on the type of movement, degree of stabilisation, and age, and materials involved in the movement. Soil samples were collected, using core and clod sampling methods and were tested for plastic limit, liquid limit, plasticity index, bulk density, hydraulic conductivity, aggregate stability, and particle sizes. Structural rock weaknesses were also measured. Vegetation data was collected, using the quadrant method and was analysed for average diameters at stump and breast height, canopy cover, and height. Questionnaires/surveys were used to assess local knowledge and perceptions towards landslides. A SPSS statistical package was used to analyse both social and physical data. iv It was found that 131 landslides had occurred of which 98 were in the Rumphi District, Northern Malawi and 33 occurred in the Ntcheu District, Central Malawi. The variations were observed to be due to the degree of disturbance of the physical environment. The Ntchenachena Area, with the highest density (88), was under cultivation and the afro-montane vegetation had been completely destroyed. The deepest channels were observed in the Ntchenachena Area, partly because of the deep chemical weathering of the basement. In contrast, the rest of the areas had thin soils. Slope aspect and type were found to be of little significance in the occurrence and spatial distribution of the events. The analysis of data suggested that the events were caused by liquefaction of sand and silt fractions due to high and prolonged precipitation. The evidence from the Chiweta and the Mvai Areas suggests that high cleft water pressure between rock and soil masses might have caused some failures. However, destruction of vegetation, cultivation on marginal lands, high slope angle, weathering of the basement, and slope cutting contributed to the instability. The study also noted that the Ntchenachena, the Mvai and the Livilivi Areas largely require soft solutions to the landslide problem. These include afforestation, proper siting of houses, and restricting settlement activities in danger-prone areas. Income generating activities to reduce poverty, community participation in natural resources management and public awareness and outreach programmes are highly recommended. The Chiweta Area requires urgent major engineering works such as construction of embankments, cable nets, wire meshes, improving drainage and plugging. Stabilisation and rehabilitation of river banks is also recommended to minimize bank collapse and flooding. Integration of traditional knowledge into the existing scientific body knowledge is critical to a better understanding of the mechanisms that generate landslides Further work needs to be carried out in areas of willingness to relocate to safer ground; change in production system; geological analysis of the Chiweta beds; v hydro-geological assessment of the areas; development of landslides predictive models for Malawi; and the development of a landslide early warning system. Msilimba Golden G.C University of the Free State November, 2007 Keywords Malawi; Landslides; Geohazard; Mitigation; Assessment; Traditional Knowledge; Gender; Rockfalls; Debris flows; Rotational; Translational. vi OPSOMMING In 2003 het ‘n aantal grondstortings voorgekom in die Ntchenachena en Chiweta gebiede van die Rumphi distrik in noord Malawi, en in die Livilivi/Mvai opvanggebiede van die Ntcheu distrik in sentraal Malawi. Die grondstortings het merkbare skade aan gewasse, landbougrond, lewende hawe en infrastruktuur aangerig. Erger nog, dit het die dood van vier persone veroorsaak. Die hoë digtheid van die voorkoms van grondstortings dui op die onstabiliteit van hange in hierdie gebeide aan. In die lig van hierdie grondstortings is hierdie studie daarop gerig om die stabiliteit van die hange in die gebiede te bepaal. In die studie word grondstortings gekarteer en waargenome gebeurtenisse geklassifiseer; oorsake en bydraende faktore word evalueer; sosio-ekonomiese en omgewingsimpakte van die gebeure word evalueer; tradisionele kennis, gelowe en mense se persepsies aangaande grondstortings word ondersoek; hanteringstrategieë word bepaal en versagting van grondstortings as gevare word ontwikkel. Hierdie studie sluit ‘n inventaris van alle waargenome grondstortings in. Die terrein se fisiese eienskappe wat hang onstabiliteit beïnvloed het, is gemeet. Die eienskappe wat aangeteken is, sluit in hanglengte, helling, aspekte en hoogte, en kanaal dimensies. Grondstortings is geklassifiseer op grond van die tipe beweging, die graad van stabilisering, ouderdom en die materiaal betrokke in die storting. Grondmonsters is versamel deur van kern- en kluitmonster metodes gebruik te maak en is getoets vir plastisiteitsgrens, vloeigrens, plastisiteitsindeks, bulkdigtheid, hidrouliese geleidingsvermoë, aggregaatstabiliteit en partikelgrootte. Strukturele rotsswakhede is ook gemeet. Plantegroeidata is versamel deur gebruik te maak van die kwadrant metode. Dit is ontleed vir gemiddelde deursnitte vii op stomp- en borshoogte, kroonbedekking en -hoogte. Vraeslyste/opnames is gebruik om plaaslike kennis en opvattings oor grondstortings te bepaal. ‘n SPSS statistiese pakket is gebruik om beide die sosiale en fisiese data te verwerk. Daar is bevind dat 131 grondstortings plaasgevind het, waarvan 98 in die Rumphi distrik, noord Malawi, en 33 in die Ntcheu distrik, sentraal Malawi, plaasgevind het. Die variasies word toegeskryf aan die graad van versteuring van die fisiese ongewing. Die Ntchenachena area, met die hoogste digtheid (88), was onder verbouiing en die afro-montane plantegroei is totaal vernietig. Die diepste slote is in die Ntchenachena area waargeneem, deels as gevolg van die diep chemiese verwering van die bodem. In teenstelling daarmee het die res van die gebied dun grond gehad. Daar is bevind dat hange en hulle aard weinig bydra tot die voorkoms en ruimtelike verspreiding van insidente. Die analise van data het aangedui dat die insidente veroorsaak is deur die vloeibaarmaking van sand en silt fraksies as gevolg van hoë en langdurige neerslae. Die aanduiding uit die Chiweta en die Mvai areas is dat hoë kloofwaterdruk tussen rots- en grondmassas sommige grondstortings kon veroorsaak het. Nietemin, die vernietiging van plantegroei, verbouiing op marginale landerye, hoë hangehllings, verwering van die basis en hellinginsnyding het tot onstabiliteit bygedra. Tydens die studie is ook opgemerk dat die Ntchenachena, die Mvai en die Livilivi areas grotendeels haalbare oplossings vir die grondstortingsprobleem vereis. Dit sluit in bosaanplanting, behoorlike plasing van huise en ‘n verbod op nedersettingsaktiwiteite in moontlike gevaarsones. Inkomste-genererende aktiwiteite om armoede te viii verminder, gemeenskapsdeelname in natuurlike hulpbronbestuur en openbare bewustheids- en uitreikprogramme word sterk aanbeveel. Die Chiweta gebied benodig dringende grootskaalse ingenieurswerke soos die konstruksie van walle, kabelnette, draad netwerk, verbetering