Báo cáo Hydrogeological Characterisation and Groundwater Protection of Tropical Mountainous Karst areas in NW Vietnam

Hydrogeological Characterisation and Groundwater Protection of Tropical Mountainous Karst areas in NW Vietnam by Vu Thi Minh Nguyet Department of Hydrology and Hydraulic Engineering V U B – HYDROLOGIE (48) 2006 i This publication is Nr 48 of the series “V U B – Hydrologie” edited by the Department of Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel Orders should be sent by letter to the Department of Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels c 2006 Dienst Uitgaven VUB Wettelijk depot 1885 This dissertation is dedicated to Mr Thai Duy Ke, our respectful, good-hearted, beloved colleague and great friend, who is always alive in our memory i Acknowledgments This thesis owes much to the help and support of many people, all of whom have contributed in different ways First of all, I would like to express my sincere gratitude and appreciation to my promotors, Prof F De Smedt and Dr N Goldscheider, for their valuable guidance, fruitful discussions and consistent support that made it possible for me to finish this work I am grateful to Dr O Batelaan for his suggestions, practical help and support on my work over many years I would like to thank the Directorial Board of the Research Institute of Geology and Mineral Resources (RIGMR) for the strongly support on my work; to Prof Duong Duc Kiem, Pham Binh, Nguyen Tam, Dang My Cung and many senior researchers and colleagues at RIGRM for the professional advice, supporting data and for their assistance in fieldtrips; to the local people in the Son La and Tam Duong areas who helped me with spring monitoring, tracer sampling and other help during the fieldtrips I am grateful to jury members: Prof J Wastiels, Prof J Vereecken, Prof F De Smedt, Prof W Bauwens, Prof E Keppens, Dr O Batelaan (Vrije Universtiteit Brussel), Dr N Goldscheider (Université de Neuchâtel, Switzerland), Prof R Swennen (Katholieke Universiteit Leuven) and Dr M Dusar (Belgian Geological Survey) for their willing review, valuable and helpful suggestions to improve this thesis I thank to Dr Michael Whitburn for his help on English correction Special thanks to the Belgian Technical Cooperation, the Vietnamese-Belgian Karst Project, and the Swiss Commission for Scholarship for partly provided financial support of my work Thank to Mrs Daphnée Windey, Dr Paul Verle (Belgian Technical Cooperation in Brussels) and all people at the Belgian Technical Cooperation in Hanoi for the willing logistic support A special thanks goes to Dr Koen Van Keer for his fully support and practical help on my work from initial stage and during difficult moments I want to thank the professors and assistants working at the Centre of Hydrogeology, University of Neuchâtel, for giving their knowledge on karst hydrogeology and laboratory i experience to me Thanks to Mariona, Alessandro and many other friends for the unforgettable time we spent together in Switzerland Many thanks to my Vietnamese friends in VUB and other Universities/cities for the pleasant time we spent together to study in Belgium Special thanks to my dear friends, whom I cannot mention here for understanding and support Many thanks to my parents for their patience and give me encouragement during my study Abstract In NW Vietnam, karst areas cover nearly 18% of the land surface and have substantial socioeconomic importance as groundwater resources, as well as zones for forestry, agriculture and tourism In many areas, however, both the karst landforms and the groundwater resources have recently come under pressure in response to urbanisation, economic development and increase of population Karst aquifers are particularly vulnerable to contamination resulting from human activities Karst groundwater consequently requires special protection A sound knowledge of the hydrogeological system is a precondition for any protection strategy Such understanding, however, is presently lacking in Vietnam This work aims at better understanding the hydrogeological characteristics of the tropical karst regions in Vietnam and providing a scientific basis for groundwater protection The study focuses on two major mountainous areas that belong to the NW karst belt: Son La and Tam Duong, which mainly consist of thick Middle Triassic carbonate-rock formations An investigation methodology has been applied and adapted to the conditions of the remote areas, for which little information is available The employed methods included tracer tests, hydrodynamic, hydrochemical and microbiological spring monitoring, as well as stable isotope and rare earth elements studies Tracer tests proved underground connections between several swallow holes and springs in the two test site areas The NW-SE and SW-NE faults have a great influence on the underground drainage patterns The flow paths run either across the folds along the SW-NE faults or follow the NW-SE faults; these flow paths coincide with the preferential directions of cave development Groundwater mixing effects can be observed in both areas Hydrochemical data from Son La show a significant difference in the Mg2+ and Ca2+ contents between a swallow hole and a connected spring, which can be explained by mixing effects Stable isotope results further support this observation The high stability of δ18O of karst springs in the Nam La valley (Son La) compared with meteoric water also indicates that this karst system contains well-mixed groundwater The hydrochemical results from the Tam Duong area show a difference in Mg2+ and Ca2+content between a swallow hole and a connected spring, which also can be explained by the mixing effect The little variation in chemical content along the flow path compared to the Son La area may reflect the reduced water–rock interaction in this karst system iii Large karst springs are observed in Son La, while smaller karst springs occur in Tam Duong The results obtained from this study suggest that concentrated recharge prevails in the Tam Duong area, while the recharge processes and groundwater flow in the Son La area appear to be more complicated There is evidence for point recharge and conduit flow on one hand, but also for significant diffuse recharge and flow through small joints and fractures on the other hand Tracer tests in the Son La area gave groundwater flow velocities ranging from 75 to 166 m/h These are typical values for karst aquifers and indicate low-resistance flow paths The flow velocities in the Tam Duong area are up to 700 m/h, which is one of the highest values recorded in the literature The two investigated springs near Tam Duong show a different hydrological and physical-chemical response on precipitation events A dilution effect was observed at one karst spring, while the other spring displayed a piston effect The physical-chemical parameters of all sampled karst water in both areas meet the WHO standards for drinking water The REE concentration levels found in spring water from Tam Duong are higher than those from other karst areas reported in the literature but still safe for the health of the consumers In contrast, the microbial investigation revealed that all karst water contain high levels of thermotolerant coliforms (TTC) The contamination shows high temporal fluctuations and mainly results from untreated domestic wastewaters, agriculture and other human activities In order to protect the valuable groundwater resources in Vietnamese karst areas, a simplified methodology for mapping groundwater vulnerability and contamination risk was developed and first applied in the test sites It is based on a conceptual framework proposed by the European COST Action 620 The vulnerability map takes into account the overlying layers (O) and the flow concentration (C) The risk map is obtained by a combination of the vulnerability map and a simplified hazard assessment The maps provide a basis for land-use planning and groundwater protection zoning Groundwater protection should be a priority in vulnerable zones such as swallow holes and along sinking streams The work gives details and an insight into the understanding of karst hydrogeological characterization in the Son La and Tam Duong areas The methods applied in this work constitute useful tools for the hydrogeological investigation of remote and mountainous tropical karst areas in Vietnam and made it possible to provide a scientific basis for sustainable groundwater management iv Table of contents Acknowledgments .i Abstract iii Table of contents v List of figures ix List of tables xiii Introduction 1.1 Karst in tropical regions 1.2 Karst hydrogeological research in Vietnam 1.2.1 Overview of karst in Vietnam 1.2.2 Importance of karst hydrogeology study 1.3 Objectives and structure of the study .4 1.4 Research collaboration Study area-the NW karst belt 2.1 2.1.1 Location and topography 2.1.2 Climate .7 2.1.3 Social and economic conditions 2.2 Geography The geology of the NW karst belt 2.2.1 Overview of geological setting 2.2.2 Tectonics 10 2.3 Principles of hydrogeological characterization of karst aquifers 11 2.4 Karst landform .14 2.4.1 Definition of tropical karst landforms 14 2.4.2 Karst landscapes in NW Vietnam 15 Methods and techniques 19 3.1 Tracing experiment 19 3.1.1 Tracing in karst study .19 v 3.1.2 Tracer breakthrough curve 20 3.1.3 Traci95 Programme 22 3.1.4 Tracing tests in Son La and Tam Duong areas 23 3.2 3.2.1 Overview 24 3.2.2 Hydrochemical investigation in the test sites 25 3.3 Microbiological investigation 26 3.4 Stable isotope study 27 3.5 Rare earth elements study 29 Hydrogeology of the Son La karst area 31 4.1 Location, landscape and climate 31 4.2 Overview of previous studies 32 4.3 Geology 33 4.3.1 Geological framework and stratigraphy 33 4.3.2 Stratigraphy 34 4.3.3 Tectonics 36 4.3.4 Hydrogeology, spring and surface water 38 4.4 Tracer tests 41 4.4.1 Tracer tests 41 4.4.2 Tracer sampling and analysis 43 4.4.3 Results 43 4.4.4 Discussion 47 4.5 Hydrochemistry 50 4.5.1 Hydrochemistry and karst water quality 50 4.5.2 Oxygen isotope 53 4.6 vi Hydrochemical investigation 24 Conclusion 57 4.6.1 Hydrogeology and underground flow paths 57 4.6.2 Hydraulic properties and groundwater quality 57 4.6.3 Groundwater mixing 58 Chapter For the Tam Duong area, further investigation is recommended such as: • Tracer experiments carried out in the central part of the area (Tam Duong town or Nam Loong village) would be useful There is still no information about the regional groundwater flow system and catchment area of the big karst springs further to the NW (Nam So River) and SE (Ban Giang village) Future work should make it possible to characterize the karst flow system on a regional scale • Further hydrogeological investigation in the area will provide more detailed information about the geology and hydrogeology of the karst system Land-use practices are also rapidly changing in urbanization areas like the Tam Duong The vulnerability, hazard and risk maps 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for the Protection of Carbonate (Karst) Aquifer, final report COST Action 620 EUR 20912 European Commission, Directorate-General for Research Luxemburg 132 LIST OF PUBLICATIONS IN THE SERIES "VUB-HYDROLOGY" EDITED BY THE DEPARTMENT OF HYDROLOGY AND HYDRAULIC ENGINEERING Nr 30 Nr 31 Nr 32 Nr 33 Nr 34 Nr 35 Nr 36 Nr 37 Nr 38 Nr 39 Nr 40 Nr 41 Nr 42 STOCHASTIC PREDICTION OF SUMMER RAINFALL AMOUNTS OVER THE NORTHEAST AFRICAN HIGHLANDS AND OVER INDIA by Y Seleshi, 351 pp (1995) Price: 18.6 Euro CONCEPTUAL STOCHASTIC STREAMFLOW MODELS FOR MONTE CARLO SIMULATION AND FORECASTING by Zhong-Min Wang, 291 pp (1996) Price 13.6 Euro MODELLING OF TOXIC POLLUTANTS TRANSPORT IN AN ESTUARINE ENVIRONMENT by F Mwanuzi, 211 pp (1998) Price: 13.6 Euro CONCEPTUAL RAINFALL - RUNOFF MODELS FOR DIFFERENT TIME STEPS by F Moreda, 229 pp (1999) Price: 13.6 Euro WATER QUALITY MANAGEMENT OF RIVER BASINS AND EVALUATION OF THE IMPACT OF COMBINED SEWER OVERFLOWS USING AN INTEGRATED MODELLING APPROACH by C Fronteau, 252 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PROTECTION OF TROPICAL MOUNTAINOUS KARST AREAS IN NW VIETNAM by Vu Thi Minh Nguyet, 132pp (2006) Price: 16 Euro Dienst Uitgaven VUB Wettelijk Depot 1885 To be ordered at Department of Hydrology and Hydraulic Engineering, VUB, Pleinlaan 2, B-1050 Brussels fax +32-2-6293022, e-mail: hydr@vub.ac.be http://twws6.vub.ac.be/hydr/default.htm Your order will be followed by an invoice which must be paid prior to the dispatching of the publication [...]... hydrogeology in tropical regions is generally less common in comparison to other karst zones Many previous karst studies in tropical regions have focused more on origin and evolution of karst towers and on karstifiable rocks than on karst 1 Chapter 1 hydrogeology To date, the number of publications on karst hydrogeology, karst groundwater, and karst modelling as well as karst groundwater protection in tropical. .. understand karst hydrogeology in order to protect the spectacular karst landscape and its sustainable development in tropical regions 1.2 Karst hydrogeological research in Vietnam 1.2.1 Overview of karst in Vietnam Karst is a widespread phenomenon in Southeast Asia This region contains some of the most spectacular surface karst in the world The countries of Myanmar, Thailand, Laos, Cambodia, Malaysia and. .. factors influencing the nature of karst landscape and development The first factor is the rocks in which karst landforms are formed, the second factor is climate, and the third factor is the drainage system or base-flow of the area Areas of differing climate produce different landforms or karst topography: e.g., Caribbean karst, temperate karst and tropical karst (Ford and Williams, 1989) Karst landforms... considered Information on water quality at karst springs, which are used for drinking water, is still missing Groundwater flow on karst and fluctuations in quantity and quality of groundwater resources, as well as contamination sources have not been investigated A karst groundwater protection scheme is still not established and applied in any of studies Vietnamese karst areas Hence, through building knowledge... in karst systems • To develop and apply an approach for karst groundwater vulnerability mapping in remote mountainous areas The study deals with two major areas that belong to the NW karst belt: Tam Duong and Son La (Fig 1.1) The economic development, urbanisation and increase of population in those areas has recently put more and more direct and/ or indirect pressure on karst groundwater demand, groundwater. .. carbonate hills, and peak forest or peak cluster for the karst landform features in this study 2.4.2 Karst landscapes in NW Vietnam The karst landscape in Southeast Asia, particular in Vietnam, is one of the most notable and spectacular landscapes in the world (Mouret, 2004; Waltham and Hamilton-Smith, 2004) The NW Vietnamese karst belt is closely related to the karst belt of southern China, but also... and Vietnam all have important limestone karst areas Large areas of sandstone and buried evaporite karst are also present in this region The total karst areas cover about 10 % of the region, around 215, 000 km2 (Mouret, 2004) In Vietnam, karst areas cover approximately 18% of the land surface or about 60,000 km2 (Dao Trong Nang, 1979) Figure 1.1 shows the occurrence of karst areas in Vietnam The areas. .. specifically characteristic of tropical karst The tower karst occurs in Papua New Guinea, Australia, Honduras, Cuba, Jamaica, Puerto Rica and Southeast Asia including Malaysia, Indonesia, Thailand and Vietnam (Gunn, 2004) The tower karst in Guilin of southern China is regarded as one of the most spectacular landform in the world The group of karstifiable rocks are not restricted to evaporites and carbonates, which... is 875 mm, and this evaporation increases with decreasing altitude 2.1.3 Social and economic conditions Various ethnic minority groups are living in the NW area, mainly including the Thai, H’Mong, Kinh, Dao, Muong, and Tay ethnic groups The H’Mong and Dao often inhabit the high mountains above 1000 m, while the Thai and Tay often settle along the rivers, valleys, and the lowland areas The Kinh lives... cone karst, kegel karst, tower karst, fengcong and fengling are usually used in order to describe variant morphology of residual hills of tropical karst land form Because the tropical karst terms are used as synonyms in different areas or countries, it is therefore useful to explain the origin of above terms: • Cockpit karst is a Jamaican term that is used to describe tropical karst topography containing