The karst water environment in Southeast Asia: characteristics, challenges, and approaches

Abstract

The carbonate areas of Southeast Asia are part of the global set of well-developed tropical-subtropical karst regions and form water-rich aquifers. Due to the strong development of karst features, groundwater in karst conduits flows rapidly and is susceptible to various environmental problems, including rocky desertification and socioeconomic impacts leading to poverty. Karst-related data for the region are scarce and scattered. Based on information contributed by training workshops of the International Research Center on Karst (IRCK) under the auspices of UNESCO, as well as published literature, this study summarizes karst hydrogeological data and water-related environmental issues in Southeast Asia, in an attempt to find commonality, and to form both generally valid and region-specific concepts that can be extended to data-deficient areas, where these concepts may serve as a guide for governments when managing the karst environment. Based on topographic differences, karst terrains in Southeast Asia were classified into four types: karst on plateaux, karst in mountains, karst in plains, and karst on islands. This approach was utilized to compile and classify the surveyed karsts. The examples shared by participants in the IRCK training workshops included karst information from their own countries, most of which have not been published in English. The case studies demonstrate that karst areas in Southeast Asia are widely and repeatedly exposed to droughts and floods, resulting in environmental constraints and development obstacles. These studies also show that environmental problems can be resolved and sustainable development can be achieved if appropriate management measures are taken.

Full text

PAPER
The karst water environment in Southeast Asia: characteristics,
challenges, and approaches
Guanghui Jiang
1,2
&Zhao Chen
3
&Chaiporn Siripornpibul
4
&Eko Haryono
5
&Nam Xuan Nguyen
6
&Thida Oo
7
&
Liza Socorro Juanico Manzano
8
&Sinxay Vongphachanh
9
&Sitha Kong
10
&Fang Guo
1,2
Received: 31 March 2020 / Accepted: 5 November 2020
#Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
The carbonate areas of Southeast Asia are part of the global set of well-developed tropical-subtropical karst regions and form water-rich
aquifers. Due to the strong development of karst features, groundwater in karst conduits flows rapidly and is susceptible to various
environmental problems, including rocky desertification and socioeconomic impacts leading to poverty. Karst-related data for the
region are scarce and scattered. Based on information contributed by training workshops of the International Research Center on Karst
(IRCK) under the auspices of UNESCO, as well as published literature, this study summarizes karst hydrogeological data and water-
related environmental issues in Southeast Asia, in an attempt to find commonality, and to form both generally valid and region-specific
concepts that can be extended to data-deficient areas, where these concepts may serve as a guide for governments when managing the
karst environment. Based on topographic differences, karst terrains in Southeast Asia were classified into four types: karst on plateaux,
karst in mountains, karst in plains, and karst on islands. This approach was utilized to compile and classify the surveyed karsts. The
examples shared by participants in the IRCK training workshops included karst information from their own countries, most of which
have not been published in English. The case studies demonstrate that karst areas in Southeast Asia are widely and repeatedly exposed
to droughts and floods, resulting in environmental constraints and development obstacles. These studies also show that environmental
problems can be resolved and sustainable development can be achieved if appropriate management measures are taken.
Keywords Karst .Southeast Asia .Drought .Flash flooding .Management
Introduction
The World Karst Aquifers Map (WOKAM) shows that karst
is widely distributed in eight of the 11 countries of Southeast
Asia, including Thailand, Indonesia, Vietnam, Laos,
Philippines, Myanmar, Malaysia and Cambodia (Chen et al.
2017; Goldscheider et al. 2020).Karstinthisregionhas
attracted attention since the early twentieth century
(Lehmann 1936;Uhlig1980). About 10% of the total land
surface in Southeast Asia is characterized by karst,
Published in the special issue “Five decades of advances in karst
hydrogeology”
*Guanghui Jiang
bmnxz@126.com
1
Key Laboratory of Karst Dynamics, MNR/GZAR, CAGS, Institute
of Karst Geology, Guilin 541004, People’s Republic of China
2
The International Research Center on Karst under the Auspices of
UNESCO, Guilin 541004, People’s Republic of China
3
Environmental Resources Management, Siemensstr. 9,
63263 Neu-Isenburg, Germany
4
Department of Mineral Resources, Bangkok, Thailand
5
Karst Research Group, Faculty of Geography, Gadjah Mada
University, Djakarta, Indonesia
6
Vietnam Institute of Geoscience and Mineral Resources,
Hanoi, Vietnam
7
Department of Geology, University of Yangon, Yangon, Myanmar
8
Department of Environment and Natural Resources, Mines and
Geosciences Bureau, Metro Manila, Philippines
9
Faculty of Water Resources, National University of Laos,
Vientiane, Laos
10
General Department of Mineral Resources (GDMR), Ministry of
Mines and Energy (MME), Phnom Penh, Cambodia
Hydrogeology Journal
https://doi.org/10.1007/s10040-020-02267-y

approaching a larger proportion in Laos, Thailand, Indonesia,
Vietnam and the Philippines (Tuyet 1998, Day 2011). The hot
and humid climate contributes to the formation of variable
landscapes in Southeast Asia, including a range of surface
features (dolines, stone forest, tower peaks, cockpits, stream-
sinks, uvala and poljes) and spectacular underground karst
features such as dry caves, active conduits, subterranean lakes
and springs.
Most karst landscapes in the continental Southeast Asia are
formed of Carboniferous-Permian or older carbonates, with
their development dating back to the Tertiary period
(Sweeting 1995a). There are many world-class karst heritage
sites that have been completely preserved. Cave sediments
contain fossils of animals and ancient humans dating back to
the middle Pleistocene (Duringer et al. 2012). Although the
karsts developed in the Cenozoic limestone of the oceanic
island arc are relatively young, the terrain is characterized by
numerous sinkholes, depressions, and cave networks. Most of
the karsts in these regions could be considered mature karst
(Ford and Williams 2007).
Strong karstification in limestone forms underground space
for water flow and habitation. Drainage systems may become
subterranean. Some areas contain large underground river sys-
tems. They usually show highly dynamic hydrological re-
gimes influenced by the monsoon (such as several hydrolog-
ically monitored karst springs in Java in Indonesia). The peaks
in the discharge curve of a karst spring are accompanied by
flooding and a short temporal delay relative to rainfall re-
charge, while if the flow attenuation coefficient is large it
quickly leads to a low water stage. However, the fissures of
ancient and hard rocks, as well as the primary pores of young
and soft limestone, are major storage units in mature karst
aquifers, so that diffuse flow can maintain water resources
during the normal dry season, but not under extreme climatic
conditions.
The well-developed tower karst of Southeast Asia with
steep and rocky slopes may lead to significant environmental
vulnerability and variable interrelated hazards such as
drought, flood, sudden contamination from mining, and de-
sertification. Some such events have already happened in the
karst areas of southern China. In addition, felling of forest
cover because of swidden cultivation, rapid increase in popu-
lation and land development, and climate change all aggravate
environmental degradation (Urich 1993;Kiernan2011),
which not only pose a threat to the karst’s unique ‘ark of
biodiversity’(Clements 2006), but also make it more difficult
to deal with the inherently fragile irrigation, water supply and
disaster prevention measures. In short, karst is so common in
SoutheastAsiathatitisanunavoidabletargetfor
development.
Compared with the karst in neighboring Asia and Oceania,
the karst environments in Southeast Asia have at least the
following characteristics:
&They experience a humid climate, and there are no karsts
like those in the semi-arid regions of Shanxi in northern
China or the arid regions of Nullarbor in Australia.
&They are mostly rugged regions, but all are below the
permanent snow line, and there are no karsts under the
frozen soil of glaciers similar to those of the Tibetan
Plateau.
&They lie in regions of active tectonism, which regularly
rejuvenates the relief, as opposed to the karst of northern
China, which has evolved since the Paleozoic in a conti-
nental shield area. They are similar to karsts in southwest
China, where the crust has experienced geologically re-
cent uplift.
&The areas are densely populated and the anthropogenic
pressure on the natural environment is very high, as op-
posed to the deserts of the Tibetan Plateau, the Mongolian
Plateau and Australia.
The karst areas in Southeast Asia with the aforementioned
characteristics are vulnerable to many kinds of disaster.
Sometimes, a disaster has caused huge long-lasting losses
which are impossible to deal with. In some areas, the risk of
disasters is increasing, but not receiving sufficient attention.
This study summarizes the karst environment in Southeast
Asia and defines the conditions for the occurrence of risks.
The results may be helpful for nations to take effective
countermeasures.
Methodology
The main outcomes of surveys of typical karst sites in
Southeast Asia were compiled and summarized in this study.
A classification scheme was established through the collection
and comparison of case studies and the distribution character-
istics and water environment topics of the different karst types
were summarized. Similarities in the background societal en-
vironments of the various karst sites were identified; further-
more, a wider comparison between continents was used to
distinguish the special characteristics of karst in Southeast
Asia. In addition to the published literature, some data in this
study were adapted from the training workshops of the
International Research Center on Karst (IRCK), under the
auspices of UNESCO, which have been held every year since
2008. A total of 59 trainees from Southeast Asia, comprising
government civil servants, university lecturers, and profes-
sional staff from research institutions, participated in the
workshops from 2015 to 2019. The participants described
the karst conditions of their respective countries in lectures.
A draft of the manuscript was sent to some of them, and their
suggested modifications have been incorporated into this
paper.
Hydrogeol J

Geological and geographical background
Southeast Asia is located between the Pacific Ocean and the
Indian Ocean. It consists of a peninsula resulting from the
southward extension of Tibetan Plateau and Chinese
Yunnan-Guizhou Plateau and long oceanic island arcs, with
high topographic relief in the north and low relief in the south
(Fig. 1). The landscape of Southeast Asia is rugged, contain-
ing plateaux, folded mountains, block faulted mountains,
plains, and volcanic and nonvolcanic islands. In all, 39% of
SoutheastAsiaismountainous(Xiaoetal.2018) and is situ-
ated structurally in the collision zone of the Eurasian Plate, the
Indo-Australian Plate, and the Philippine Plate, as well as
many other plates (Liu et al. 2018). Plateaux and mountains
have been formed by the collision of tectonic plates and are
associated today with frequent geological disturbances such as
volcanic eruptions, earthquakes and tsunamis. Under the
strong influence of the Indian Ocean monsoon and the East
Fig. 1 Karst area of Southeast Asia (revised from Chen et al. 2017, Liu et al. 2018, alpha-2 codes of countries are from https://www.iso.org/obp/ui/#
search/code/)
Hydrogeol J

Asian monsoon, Southeast Asia experiences abundant rainfall
and distinct dry and wet seasons, with tropical cyclones bring-
ing a large amount of heavy rain, making Southeast Asia both
a drought-prone and a flood-prone region.
The average annual temperature in the northern plateau
mountains is 20–24 °C, while the average annual temperature
in the southern islands is 22–28 °C. Annual rainfall generally
ranges from 1,000 to 2,000 mm, reaching as much as
3,000 mm in some areas. In short, the warm climate and abun-
dant rainfall in Southeast Asia provide good conditions for
karst development.
Results and discussion
Karst formation in Southeast Asia
The carbonate rocks of the Indochina Peninsula of Southeast
Asia mostly formed in late Paleozoic to early Mesozoic time.
These carbonate strata belong to a number of relatively small
tectonic blocks which separated from Gondwana. They were
not integrated with the Yangtze Plate in the north until the
Triassic era (Stauffer 1983). Since the Oligocene, the Indian
Plate from Gondwana has been colliding with the Eurasian
plate. As a result, the Tethys Ocean disappeared, and the
Tibetan Plateau was uplifted. This uplift marked the beginning
of karst development; therefore, geologically recent karst de-
velopment has been more intense and fully preserved here,
and is younger than that of northern China, but older than that
of the island arcs and Nullarbor area of South Australia.
Under the influence of neotectonic movements, the terrain
has undergone strong uplift and folding, and erosion by rivers
has generated a rugged terrain. In coastal areas, rivers carrying
a high sediment load have formed deltas and coastal plains.
The carbonate rocks in the upper reaches of major rivers in the
north of the Indochina Peninsula have been uplifted to an
elevation of 1,000–2,000 m above sea level (asl). This is lower
than the Tibetan Plateau, which is at about 5,000 m, and the
Yunnan Plateau, which is at about 2,000 m. Fluvial alluvium
covers karst aquifers in delta plains and coastal plains, and
outside southern China these regions become areas of typical
tower karst. In addition, rising sea levels in coastal areas have
turned tower karsts into islands. This marine karst is unique in
the world.
The Malay Archipelago consisting of more than 20,000
islands is the largest archipelago in the world. The Indo-
Australian Plate collided with the Eurasian Plate to form the
Indonesian island arc. And the Philippine Plate collided with
the Eurasian Plate to form the Philippine island arc. Cenozoic
carbonate rocks are widely distributed on the islands with
large exposed areas and strong karst development, forming
large-scale karst landforms, caves and underground rivers.
Karst features are as strongly developed as those in the
Caribbean.
The Indochina Peninsula and Malay Archipelago experi-
ence a tropical monsoon climate and a tropical rain forest
climate. So firstly, rainfall is generally abundant. The karst
areas in Southeast Asia are in a more humid environment than
either that of northern China, or southern Australia. Secondly,
the climate in Southeast Asia is affected by the monsoon, with
an uneven seasonal distribution of rainfall and distinct dry and
wet seasons. It is different from the Caribbean, where rainfall
is abundant and distributed evenly between the seasons—for
example, Bohol Island in the Philippines has an annual rainfall
of 2,000 mm, with a dry season from February to May and a
rainy season from June to December. The annual rainfall in
Gunung Sewu, Java, Indonesia is about 2,000 mm. Here the
rainy season is from October to April, and the dry season is
from June to September. In Inle Lake of Shan state of
Myanmar, 70% of rain falls between July and September.
Thirdly, Rainfall tends to decrease as one goes inland from
the coast, but there are storm centers in the mountains. The
rainfall of the Malay Islands is generally higher than that of the
Indochina peninsula—for example, the annual rainfall in
Sarawak in Borneo is 2,794 mm, while it is 920 mm at Inle
Lake in the Shan Plateau.
The karst environment in Southeast Asia shows much di-
versity. It generally has more negative than positive impacts
on human lives. Uhlig (1980) compared the social develop-
ment of karst areas in Java, Bali and other places, focusing on
the shortage of soil, water resources and food in the polygonal
karst of the highlands. A similar way of life is also found in
southern China (Yuan 1997), northern Laos (Kiernan 2011)
and northern Vietnam. Williams noted that polygonal karst is
found in many regions of the world and in all of them has
similar impacts (Ford and Williams 2007). In southern China,
cultivation and deforestation of slopes of fengcong have
caused soil erosion for hundreds of years and caused serious
rocky desertification (Jiang et al. 2014). Karst areas in
Southeast Asia contain unique ecosystems and important bio-
diversity and may become global biodiversity hotspots and
priority conservation targets (Clements et al. 2006). Forest
degradation and quarries fragment the habitats of
endangered species or even cause them to disappear.
Compared to its importance, the protection of the karst
environment in Southeast Asia is significantly inadequate.
Day (2000) introduced the idea of the development status of
karst reserves in Southeast Asia, emphasizing the diversity of
karst and the considerable differences in their protection be-
tween countries.
Distribution and classification of karst environments
Karsts in Southeast Asia have been studied from the view-
points of hydrogeology, geomorphology, speleology and
Hydrogeol J

biology, and in the view of the general concern of the trainees
of IRCK, a comprehensive study is needed to highlight the
priority issues being faced.
The formation and environment of karst may be character-
ized in a number of ways. Gillieson’s research compared the
geological conditions of karst development, introduced in de-
tail the formation of karst in several important areas, and
pointed out the problems facing karst protection (Gillieson
2005). In the study area topographical features exhibit a clear
trend from north to south. The trend of elevation change in
Southeast Asia is mainly influenced by neotectonic move-
ments, while its influence on climate, hydrology, karst forma-
tion, population and human activities is also clear. According
to the topographical trend, the karst environment in Southeast
Asia can be classified into four types: karst on plateaux, karst
in mountains, karst in plains, and karst on oceanic islands
(Fig. 2). This kind of classification of the karst environment
can be compared with the neighboring karst area in southern
China (Sweeting 1995b).
The northern Southeast Asia mainland, which borders
southern China, is one of the important karst regions. This
region is a continuation of the plateau landform of southwest-
ern China. It has an average elevation of over 1,000 m and is
covered by hard carbonate formed in or before the late
Paleozoic era. There are significant karst areas such as the
Shan Plateau, the Chiang Mai Plateau, Luang Prabang of
northern Laos, Lai Chau and Ha Giang in northwest
Vietnam that border the Yunnan Province of China and Cao
Bang in northern Vietnam adjacent to the Guangxi province of
China. The karst is characterized by fault poljes, river valleys
with tower karsts, deep canyons with extensive fengcong,
small poljes with towers, and big underground rivers.
In continental Southeast Asia, the main mountain systems
parallel to the rivers are also important karst regions. The karst
areas in the Annamite Range extending over the border be-
tween Laos and Vietnam are surrounded by nonkarst areas,
with allogeneic water flowing through the karst areas to form
large caves and underground river systems. In the Karen-
Tenasserim Hills—a mountain chain between Thailand and
Myanmar—karst dolines and valleys are locally developed.
Covered karst plains with towers are developed on river
deltas and coastal plains. They are widely distributed in the
Salween delta, the Mekong Delta, the Red River Delta, the
Chao Phraya River Plain of Thailand, the Phang Nga of
Thailand, the Kinta and Klang valleys of Malaysia, and the
Ninh Bình Province of Vietnam at Trang An, Ha Long Bay
and Cat Ba.
Miocene to Quaternary coral-reef limestones on islands
have been uplifted to form highlands, on which polygonal or
cone karst and big underground rivers may have formed after
millions of years of dissolution. Lots of islands have karst
landforms of different sizes in the coastal zone, as exemplified
by the Gunung Sewu karst area in Java, the karst areas in
northern Sarawak in Borneo, and central and southern
Palawan, Bohol and many other places in the Philippines.
The karst water environment in Southeast Asia
The karsts in Southeast Asia and the karsts in southern
China share similar physical geographies and are even
similar in terms of their impact on society. The two areas
may be regarded as a whole. Together they span a vast
area from the equator to 32° north latitude. The types of
karst in this area are very diverse, and their environment
is very fragile. Some significant examples were revealed
with the help of the IRCK trainees. Some of them are
selected here to demonstrate the characteristics of the four
karst environments (Table 1). There are also some for
which there is only a very basic understanding so far.
Relevant information about these is listed in Table S1of
the electronic supplementary material (ESM).
Fig. 2 Karst distribution and environmental classification in Southeast Asia
Hydrogeol J

The water environment of karst on plateaux
The northern Southeast Asian countries of Myanmar,
Thailand, Laos, and Vietnam are adjacent to China’s
Yunnan-Guizhou Plateau, and feature borderland, rugged ter-
rain, remote transportation access and underdeveloped econ-
omies. The part of the plateau with plains is populated and
cultivated. The development of water resources has surged
and brought about eutrophication. In the mountainous parts,
peak-cluster depression areas still contain small villages. The
local ethnic minorities are traditionally engaged in rotational
swidden agriculture, hampered by frequent droughts and
waterlogging. Moreover, intensified swiddening systems
using irrigation, which leads to groundwater extraction, are
increasing as road networks expand into the mountains
(Schreinemachers 2013).
The Shan Plateau, including Shan State, Kaya State, Kayin
State and Mon State, has a wide distribution of carbonate
rocks which formed in the Permo-Triassic period (Oo et al.
2002). The area of carbonate rocks is 57,500 km
2
. The pure
carbonate rocks are limestone and dolomite faulted against
Devonian silici-carbonates, with a total thickness of more than
1,000 m. This area is considered to be rich in karst, but there is
little related research (Mouret 1997). According to the IRCK
trainers’reports and some brief field work by IRCK staff in
2017, the karst landforms are mainly large-scale structural
poljes, with the surrounding mountainous areas containing
classic karst features such as towers, dolines, caves, spring
pools and underground rivers.
The Inle basin which contains lakes in the heart of the Shan
Plateau is thought to be a kind of polje. Similar in formation to
the hundreds of faulted basins in the Yunnan Plateau, the
basin’s creation is related to neotectonic movements caused
by plate subduction and collision. Today active faults generate
earthquakes in Myanmar (Crosetto et al. 2018). The Shan
Plateau is underlain by thick carbonates of Paleozoic to
Permo-Triassic age. Locally, marine clastics, carbonates and
continental red beds are found above the Permo-Triassic lime-
stone (Crosetto et al. 2018).
Inle Lake is the second largest freshwater lake in Myanmar,
with an elevation of 884 m and a water depth of less than 3 m;
it drains an area of 5,612 km
2
. Hydrochemically, the lake
water is Mg (Ca)-HCO
3
with an average pH value of 8.27,
indicating that carbonate equilibrium dominates its
hydrochemistry. In addition to being recharged by the sur-
rounding rivers, the lake is fed by groundwater and hot springs
from deep faults (Re 2018). Tourism and agricultural activities
in the form of floating gardens are developing fast. They cause
silting-up, eutrophication, and atrophy of the lake. Recharge
from the karst aquifer is critical for maintaining a
hydrochemical equilibrium to prevent the accumulation of
nutrients.
The Shan Plateau, known as the karst plateau, may be very
rich in water resources because of the large area of exposed
karst and underlying synclinal structures. Groundwater in
these karst areas mainly discharges into rivers and supplies
lakes by means of flow through deep faults, while the dis-
charge by karst springs is not predominant. Here, groundwater
supports agriculture, centralized urban water supplies
(Nyaungshwe, Taunggyi City), and the ecological health of
lakes. However, as water consumed by irrigation and urban
water supplies increases, the volume of groundwater flowing
into lakes is bound to be reduced, which may accelerate eu-
trophication. Such disasters have occurred in many similar
lakes of the Yunnan Plateau (Ni et al. 2011). Research on karst
water resources of the plateau should at least give priority to
solving the following problems. What are the main aquifers in
the plateau? Where is the recharge region of groundwater in
the karst area? And where is the interface between groundwa-
ter and surface water?
Table 1 Significant examples illustrating karst environmental characteristics in Southeast Asia
Country Environment Significant examples Published or unpublished sources
Vietnam Plateau Dong Van Geopark Nguyet and Goldscheider 2006; Ender et al. 2018
Mountain Son La Blind Valley Tam et al. 2004
Mountain Phong Nha –Ke Bang Limbert et al. 2020;
Laos Mountain Hin Nam No Mouret et al. 1997; Ponta and Aharon 2014
Thailand Plateau Ang Khang Siripornpibul et al. IRCK training courses, Unpublished reports 2011, 2016, 2019
Mountain Sai Yok National Park
Plain Ban Subthakain
Myanmar Plateau Inle Lake Re et al. 2018;Thinetal.2020
Malaysia Coastal plain Klang Valley and Kinta Valley Muhammad and Alkouri 2009;Gillieson2005
Indonesia Island Gunung Sewu Adji et al. 2012,2017, Adji and Bahtiar 2016; Nurkholis et al. 2019
Philippines Island Bohol Urich 1993, Urich et al. 2010; Restificar et al. 2006
Hydrogeol J

China’s southern provinces of Yunnan and Guangxi, bor-
dering Southeast Asia, have karst areas of 110,900 and
98,700 km
2
respectively. The karst terrain mostly shows bare
rock, called peak forest or peak cluster, distributed on an ero-
sion surface on both sides of deeply incised rivers. These areas
not only suffer serious ecological degradation, but are also
mired in poverty. The problem of a symbiosis between the
fragile karst environment of the plateau and poverty also ex-
tends into Southeast Asia.
The Vietnamese province of Ha Giang lies in the northwest
of the country. Here the Dong Van Global Geopark was
established in 2012 with an area of 2,300 km
2
. Karst plateau
accounts for 80% of the total park area, and is distributed
along the banks of the Hong River and its tributaries, with
the incision depth of the canyon reaching 400 m. The karst
developed in carbonates from middle Devonian to Permian
time with a total thickness of more than 700 m, forming peak
clusters and deep depressions due to crustal uplift (Do 1998).
In the absence of aquitards, groundwater partly discharges
into poljes but at the same time continues to move downwards
to adapt to the base level.
This region has a population of 250,000 and more than 20
ethnic minorities live there, who are engaged in the farming of
maize and other cereal crops, as well as potatoes. Due to water
shortages, the agricultural yields are almost completely deter-
mined by the weather, leading to a low ability to withstand
natural disasters, and worse, an unreliable drinking water sup-
ply (Nguyen et al. 2013a; Nguyen et al. 2013b). The farmers
rely on expanding the cropped area to increase production,
which has led to severe damage to the land and forests on
steep slopes. In short, long-term farming has caused soil and
water loss, leading to rocky desertification.
Comparing karsts in northern Vietnam with southern
China, it could be concluded that the wide areal distribution
of thick carbonate rocks creates special hydrogeological con-
ditions and a fragile environment. A total of 540,000 km
2
of
the karst of southern China has 2,836 underground rivers, but
tens of millions of people depend on them without access to
reliable drinking water, let alone irrigation. In addition, the
safety of these underground rivers is seriously threatened by
pollution(Guoetal.2013; Nguyet and Goldscheider 2006;
Ender et al. 2018).Asaresult,apolicyofecologicalmigration
has been adopted. In southern China the number of eco-
migrants from the extremely bare karst areas in Yunnan,
Guizhou and Guangxi exceeds 3 million.
The water environment of karst in mountains
The fold and fault structures and magmatic activity in moun-
tainous areas often cause the carbonate rocks to have linear
outcrops bounded by other lithologies, which give rise to
water-blocking structures and allogeneic recharge conditions.
The outcrops are conducive to the development of landforms
such as poljes, blind valleys, marginal depressions, long caves
and big subterranean rivers. Cave exploration has gone on for
decades because of the huge cave complexes. It is also true in
southern China that the biggest subterranean rivers are not
under the plateaux but in the surrounding mountainous area
such as Leye-Fengshan Geopark in Guangxi (Chen et al.
2020). Here the vast cave system provides a unique habitat
for many rare species. Moreover, the hydrological function of
segments of underground rivers becomes critical for the
mountainous karst environment. However, soil and water loss
from the non-karst area leads to blockage of ponors, and there-
by waterlogging, which may have serious consequences (Guo
et al. 2013).
The examples used in this section exhibit different land use
patterns, namely urban and rainforest—the example from
Guangxi province in southern China is provided to prove that
karst hydrogeological features in mountainous areas can be
compared on a larger scale. Their karst hydrogeological char-
acteristics are compiled in Table 2. The data were collected
from the publications of Mouret and Brouquisse 1997;Mouret
et al. 1997; Tam et al. 2004; Ponta and Aharon 2014;Limbert
et al. 2020; and Huang 2014.
The Son La Valley in northwestern Vietnam is a densely
populated area of urban and agricultural production. The val-
ley has an elevation of 600 m, and the nearby Da River has an
elevation of 120 m; thus, the river is 480 m below the valley.
The Nam La River, which rises in the Son La Valley, has an
average flow of 5.43 m
3
/s. After going through an urban area,
it flows underground through a ponor at the end of a blind
valley, thereby becoming an underground river which re-
surges 5 km downstream. The cultivation of coffee, mango
and longan on the upstream mountain slopes along the river
has resulted in soil loss and excessive surface runoff, which in
turn makes the river water highly turbid. In addition, in the
urban area, a large amount of plastic waste is washed away by
river waters after heavy rain, finally accumulating in the
ponor, which seriously affects the flood discharge capacity
of the underground river. In 1991, the valley was flooded
and there were fatalities (Tuyet 1998).
To solve the flooding problem, the government built a 1-
km-long tunnel and a 4-km-long drainage pipeline in 2009.
Further, sluices were erected at the entrance to the under-
ground river and upstream of the ponor to filter out the debris,
and a power station was built at the resurgence point of the
underground river. However, neither the problem of upstream
soil and water loss nor the urban garbage generation has been
alleviated during the operation of the power station, resulting
in a need to constantly clean up the waste intercepted on the
sluices and the sludge in the river. The turbine has also been
damaged several times by gravel.
A large area (1,800 km
2
) of late-Paleozoic carbonates of is
exposed in the Annamite Range between Laos and Vietnam.
Large caves and underground rivers have attracted diving
Hydrogeol J

expeditions in the past decades. The Phong Nha-Ke Bang
National Park in Vietnam came under UNESCO protection
in 2003 as a World Natural Heritage Site. It has two relatively
separated subterranean drainage systems, Phong Nha and
Nuoc Mooc. The Son Doong Cave in the upstream part of
Phong Nha has caves over 200 m high and 175 m wide in
the 9.4-km-long explored segment (Limbert et al. 2020).
There are many other caves of a similar size.
The center of the heritage site is densely forested and
sparsely populated, and is classified as a principal protected
area; however, some marginal valleys in the buffer zone of the
protected area are inhabited. The rivers in these valleys serve
as important allogeneic upstream water sources for the envi-
ronment in the heart of the protection zone. Poor living con-
ditions with regular flash floods make protection difficult to
implement.
On the west side of the mountains of the Phong Nha-Ke
Bang National Park is the Hin Nam No Biodiversity Reserve
in Khammouane Province, Laos. Streams from the surround-
ing mountains merge in the karst areas to form many isolated
poljes, and their only access to the outside world is via long
underground rivers. Significant stream caves, among them Xe
Bang Fai and Nam Hinboun, are listed in Table 2. The karst
environment in the wilderness land with numerous caves and
underground rivers should be thought of as a priority conser-
vation area for species diversity. However, the inhabitants are
hoping to attract more tourists to improve the living conditions
of the locals. Tourism must be carefully developed.
Environmental monitoring is necessary to assess the impact
of tourism (Trinh et al. 2018).
The water environment of karst in plains
All Southeast Asian countries except Laos have long coast-
lines, and the coastline of the Indochina Peninsula is
17,000 km long. Karst areas are widely distributed in the
coastal zone. They have not only formed the unique offshore
tower karst such as Ha Long Bay and Phang Nga Bay, but
have also generated widely distributed towers in the plain
areas such as Salween Delta in Moulmein, Mekong Delta in
Campot (Kiernan 2010), as well as sediment covered karst
aquifers. The utilization of underground spaces and ground-
water by urbanization causes land subsidence and sinkhole
collapse. Similar disasters occur in economically developed
regions such as Sue city, the Kuala Lumpur Valley and
Singapore, as well as in the highly populated and urbanized
Pearl River Delta.
Karst in the plain areas is covered by fluvial unconsolidated
sediments. Dolines and dissolution depressions are rare, al-
though there are still sinkholes in places with a thin soil cover.
The secondary porosity generated by the expansion of rock
fissures or the formation of cavities significantly increases the
potential volume of water stored in the aquifer. The water
content of the rocks is not uniform, however, necessitating
the use of hydrogeological surveys to determine the distribu-
tion of groundwater.
Agricultural activities and human population are concen-
trated in the plain areas, where improvements to the quality of
life and the development of agriculture depend on water re-
sources, with the rich reserves of the karst having a great
potential for exploitation. The demand for water resources in
Ban Subthakain of the Chao Phraya River Plain in Thailand
has increased due to economic development. The Thai gov-
ernment has focused on karst water as a development target in
its commitment tofulfilling the rising demand for water. Karst
hydrogeological maps have been compiled to reflect the spa-
tial variation of water richness in the aquifers and to provide a
basis for developing water resources. The government sup-
ports the preparation of large-scale hydrogeological maps that
highlight characteristic karst manifestations such as caves,
Table 2 Hydrogeological characteristics of underground rivers in mountainous areas of Southeast Asia and southern China
Underground
river
Rock age Carbonate content
(%)
Host mountains, elevation
(m asl)
Stream cave, length
(m)
Springs
Elevation (m
asl)
Discharge
(m
3
/s)
Nam La Devonian-Carboniferous
-Permian-Triassic
–1,700 5 150 4
Phong Nha Devonian-Carboniferous
-Permian-Jurassic-Cretaceous
–1,624 92 11 10
Nuoc Mooc Devonian-Carboniferous
-Permian-Jurassic-Cretaceous
–1,492 33 25 10
Xe Bang Fai Devonian-Carboniferous
-Permian-Jurassic-Cretaceous
63 1,578 6.4 155 2.2
Nam Hinboun Devonian-Carboniferous
-Permian-Jurassic-Cretaceous
62 1,592 7.5 174 0.36
Poxin Devonian-Carboniferous
-Permian-Triassic
52 1,190 37 476 6.6
Hydrogeol J

groundwater seepage sites, and exposure sites. The
hydrogeological maps are used in conjunction with borehole
pumping tests, which help to generate distribution maps of the
potential exploitation of groundwater resources.
The Malaysian capital city of Kuala Lumpur is built in a
sediment covered karst area. Drilling surveys performed while
investigating the foundations of buildings have revealed that
pinnacle karst has formed at the soil–rock interface. Before the
1990s, the excavation of tin mines led to the removal of the
overburden, revealing that the height of the stone ‘teeth’be-
low the overburden or the depth of the karrens reached 6 m.
Caves formed below the uneven rock surface, which serve as
channels for the loss of the overlying soil are high-risk loca-
tions for the development of sinkholes (Zabidi and Freitas
2013). The local people in Malaysia are accustomed to using
rainwater, but the annual precipitation totals are variable due
to climate change, thus making the future exploitation of
groundwater more likely. The disturbance of aquifers by the
withdrawal of groundwater may be a primary factor for trig-
gering sinkholes. Sinkholes in urban areas may cause serious
damage.
The water environment of karst on islands
The carbonates exposed on the Southeast Asian islands devel-
oped from relatively young coral-reef limestones of
Quaternary to Tertiary age, which were uplifted due to crustal
or volcanic activity and exposed above the ocean surface,
forming the islands. Water shortages because of subterranean
drainage systems as well as the monsoon climate are a prob-
lem that faces island communities. The need for protection of
karst landscapes has been highlighted by nations and interna-
tional organizations (Day 2011).
The Gunung Sewu (“Thousand Mountains”) karst area in
Java, Indonesia, developed in Miocene-Pleistocene limestone.
The limestone plateau has an elevation of 600 m and an area of
1,300 km
2
, and its surface contains karst hills and depressions
(Haryono et al. 2017). The density of the karst hills is 30/km
2
,
while their heights only range from 30 to 80 m. A surface-
water system is lacking in the karst. Hundreds of sinkholes
convert surface runoff into underground rivers, which flow
into the sea under 100-m-high coastal cliffs, indicating that it
is logistically difficult to access the groundwater. Despite wa-
ter shortages, the karst plateau is densely populated and the
local residents have been engaged in agriculture for a long
time, using long-run slope cultivation which results in rocky
desertification. Deforestation has taken place over the last
500 years (Hartmann et al. 2013). A low-permeability clay
at the bottom of depressions inhibits water drainage, leading
to the conversion of the depressions into temporary ponds
during the rainy season and thus providing drinking water.
However, during the dry season, rainfall is low and the ponds
evaporate, causing the residents to suffer-water shortages.
Now the water supply to the area depends on pumping water
from karst springs and underground rivers. Water is obtained
from the Bribin, Seropan, and Baron underground rivers. The
water is pumped up from an underground river at a depth of
100 m and distributed under gravity to the local population
(Kudella et al. 2016). During the rainy season the water con-
tains high amounts of E-coli bacteria and suspended sediment
from the surrounding agricultural land. There are still major
technical and financial gaps to fill in order to solve the
drinking-water supply and ecological restoration problems.
Bohol Island in the Philippines consists of Miocene to
Pleistocene limestone and exhibits numerous conical hills.
The local residents refer to the cone-shaped mountain peaks
as the Chocolate Hills and have been engaged in rice cultiva-
tion for hundreds of years. Although the plateau has the same
elevation of 600 m and the same strong karst development as
the limestone plateau in the Gunung Sewu karst area of Java,
the limestone in Bohol Island contain a clay bed, whose im-
permeability leads to the formation of springs in the karst
valleys. The associated streams become a source of water for
agricultural irrigation, eventually disappearing in sinkholes
after flowing a few kilometers through the valley (Urich
1993). Groundwater resources are fully utilized.
Population pressure and forest destruction have imposed a
heavy burden on water resources. In addition, due to extreme
weather conditions, the water sources derived from unreliable
karst water are more prone to depletion. The recent 7.2 Mw
earthquake altered the karst landscape and underground water
flow. The intense ground shaking resultedin the subsidence of
hillocks and other surface subsidence which exposed numer-
ous cavities and sinkholes. It also caused the uplift of a reef
flat off the southwestern coast to about 2 m asl, and as a result,
the shoreline receded 50–100 m (Kobayashi 2014). The im-
pact of earthquakes in the island arc area on the karst environ-
ment and groundwater movements is rarely discussed. More
observations and investigations are required to evaluate the
impact of seismic events on spring discharges or flow direc-
tions, and possible disasterrisks; related work has been carried
out in central Italy (Nanni et al. 2020).
This paper attempts to express the characteristics of the
karst environment in a visual way (Fig. 3), although it must
be realized that the formation of karst is affected by many
factors, and the environment is very diverse, so the limitation
of this form of expression is obvious. The example of poljes in
the Yunnan Plateau was chosen to show the basic causes of
environmental problems, meaning that cultivated land is lo-
cated in poljes, while water resources are most often available
deeply buried in an underground river (Yuan and Cai 1988).
The karst area in the middle part of the Annamite range was
chosen as an example of how abundant allogeneic water forms
large caves and underground rivers, and also causes flash
flooding and thick sediment deposition. The hydrological pro-
cesses of ponors have a vital impact on changes in the water
Hydrogeol J

environment. The Niah National Park in Sarawak was chosen
to show that the uplift is intermittent, leaving multiple layers
of caves in the towers of the peak forest plain (Dodge-Wan
et al. 2017). The water table corresponding to the modern base
level of erosion is shallow and easily leads to karst collapse
and pollution. Gunung Sewu in Java was introduced to show
that the uplifted relatively young karst highlands can also de-
velop into dolines and poljes. In these circumstances, the
groundwater is deep without aquitards, and the environment
here is drought prone.
The management of the karst environment
The demand for karst water resources in Southeast Asia is
rising, making the investigation, protection, and development
of water resources a very competitive research and develop-
ment field. In response to the stress on karst-related water
resources, drought, and waterlogging, as well as the resulting
losses of soil and water, forest degradation, and even rocky
desertification, the nations of Southeast Asia have taken many
effective countermeasures.
The Thai government has strengthened the investigation
and monitoring of karst resources in order to assess the state
of its current karst resources. The Department of Groundwater
Resources and the Department of Mineral Resources of
Thailand organized geological heritage surveys in the three
karst areas of Mae Hong Son Province in northern Thailand,
Kanchanaburi Province in central Thailand, and Phang-Nga
Bay in southern Thailand. The surveys included cave investi-
gations and mapping, investigations of karst water sinkholes
and resurgences, and investigations of karst collapse in the
southern coastal plains, collecting data on cave morphology,
cave sediments, and cave biology, as well as the development
and utilization of karst water resources. A more detailed sur-
vey has been conducted of the geoparks. The survey results
will provide strong support for responding to emergencies
Fig. 3 Conceptual models of karst water environments in Southeast Asia.
(1) Plateau polje model, based on the Yunnan plateau (Yuan and Cai
1988); (2) Mountain model, based on Guangxi (Yuan 1997); (3) Plain
model, based on the Niah National Park (Dodge-Wan et al. 2017); (4)
Island model, based on Gunung Sewu (Urushibara-Yoshini 1991). a
Polje; bSubterranean river; cCave; dDoline
Hydrogeol J

similar to the mishap that led to the Tham Luang Cave rescue
(Colzato 2018). The Department of Groundwater Resources
of Thailand has signed a cooperative agreement with the
China Geological Survey, and the two parties have built hy-
drological and hydrochemical observation stations at the karst
springs in Sai Yok Park in Kanchanaburi Province, which is
one of the 654 groundwater observation stations in Thailand.
By conducting proper measures, it is possible to make good
use of the karst in order to compensate for the deficiency of
water resources. Chiang Mai Province in northern Thailand
has launched the Doi Ang Khang Royal Agriculture Project,
which aims to prevent local opium cultivation through
supporting local people to grow flowers and develop garden-
ing and tourism. This region is a karst polje at elevations of
1,400–1,800 m, where half of the landforms are peak-cluster
depressions with Permian limestones and half are clastic rock
mountains formed in the Carboniferous period. Precipitation
and streams leak underground through ponors and resurge at
an elevation of 800 m. Some mountain ponds have been con-
structed in the polje for drinking and irrigation purposes, but
these mountain ponds experience a severe annual drought
during the 4-month dry season from February to May.
Engineers believe that the exploitation of karst groundwater
resources faces great technical difficulties, and therefore all
boreholes are being drilled in the sandstone area. Boreholes
drilled in the karst zone failed to provide a water supply be-
cause of their small discharge, while 14 wells drilled to a depth
of 60–150 m in the fractured aquifer jointly provide a daily
flow of up to 1,800 m
3
.
Governments have identified best practice for utilizing
karst resources, namely establishing Global Geoparks or na-
tional parks in order to protect karst landscapes. A set of eco-
tourism guidelines pertaining to caves in the Philippines have
been put in place. DENR Administrative Order No. 2013–19
provides a set of guidelines on the planning and management
of ecotourism in protected areas including caves found therein
(BMB-DENR 2015,2016).
Although some areas have not previously been protected
and therefore have experienced ecological degradation, it is
not too late to improve the situation. The Gunung Sewu karst
area in Java is an economically underdeveloped region suffer-
ing from water shortages and long-term ecological degrada-
tion. The government of Indonesia had established a small
hydropower development project with cooperation with
Karlsruhe Institute of Technology for the underground rivers
in order to alleviate both water and energy shortages (Kudella
et al. 2016). Moreover, the Indonesian government has ap-
plied to establish a Global Geopark in the Gunung Sewu area.
The geological park presents a complete range of karst land-
scapes such as cone-shaped karst landforms, caves, and sink-
holes, as well as local ethnic culture. The Global Geopark of
Ha Giang Province, Vietnam is another successful example of
taking protective measures after severe ecological damage has
occurred. This Global Geopark was established in an area that
was one of the most remote and socioeconomically backward
areas of Vietnam and had experienced extreme ecological
degradation. The Geopark not only attracts tourists, but also
significantly improves local living conditions due to govern-
ment investment in the construction of infrastructure.
Conclusions
Southeast Asia contains various types of karst that are widely
distributed and well developed, although in many regions
there is a lack of data on karst hydrogeology and water re-
sources. This study relied on the training workshops of IRCK
to collect and organize surveys of 62 typical karst sites in
Vietnam, Laos, Thailand, Myanmar, Malaysia, Indonesia,
Philippines and Cambodia. This paper compiles the main out-
comes of the surveys and provides an overview of the distri-
bution and characteristics of karst areas as well as their envi-
ronmental problems. The karst water issues and environmen-
tal challenges were addressed for four types of karst—karst on
plateaux, karst in mountains, karst in plains, and karst on
islands. The water environment in each subregion was de-
scribed with respect to water utilization, drought, floods, and
related ecological degradation, with the hope of providing a
benchmark for governments where they wish to formulate and
implement policies for water resources and environmental
management.
In general, high-grade karst development and strongly
climate-influenced hydrological dynamics together determine
that the karst areas in Southeast Asia are highly vulnerable and
have a significant risk of a range of disasters. In particular, the
plateau areas have a high risk of water shortage and
waterlogging, and face stresses caused by population growth,
poverty alleviation, and the development of tourism, resulting
in a large demand-supply gap of water resources. Moreover,
coping with this gap problem involves overcoming significant
technical difficulties.
The karst resources in mountainous areas are focused on
distribution and protection in various forms despite the low
level of anthropogenic disturbance. It is still necessary to meet
the need for water, reduce disasters, and promote the harmo-
nious development of protected areas. The karst water re-
sources in the plain areas have development potential and
may be used to meet the needs of large-scale agricultural irri-
gation and urban water use, although it is necessary to quan-
titatively specify the limits on water exploitation in order to
prevent natural disasters. The development of water resources
on karst islands should be conducted in conjunction with for-
est restoration. In addition, it is necessary to reconcile the
conflicts between agricultural water use, drinking water use,
and ecological water use through ecological management.
Hydrogeol J

Supplementary Information The online version contains supplementary
material available at https://doi.org/10.1007/s10040-020-02267-y.
Acknowledgements The authors appreciate the presentations and discus-
sions of the following IRCK members: Dawruang Dechaop, Mahippong
Worakul, Narongrit Boonchaiwong, Warintra Thepju, Kadsarin Siri,
Naramase Teerarungsigul, Pakkapong Sribuatong, Patsakron Assiri,
Saranya Mongkhonvoravibul, Pranee Raksaboon, Pronusa Udomsilpa,
Umapon Charoenkhunnatham, Rungroj Benjakul, Russarint
Siripattarapureenon (Thailand); Emilya Nurjani, Hendy Fatchurohman,
M. Widyastuti, Pipit Wijayanti, Tommy Andryan Tivianton, Tri Astuti
Nuraini, Matur Nuwun (Indonesia); NguyễnĐại Trung, Nguyen Thac
Cuong, Quang Viet Nguyen, Ho Tien Chung, Do Van Thang, Hoang
Ngo Tu Do, Dang Tran Nhu Thuy, Nguyen Minh Quang, Vu Thi Minh
Nguyet, Do Quang Thien, Tran Thanh Le (Vietnam); Nurzaidi Abdullah,
Mazatul Akmar Aros, Azrul Normi Idris, Othman Bin Kangsar, Hasnida
Zabidi (Malaysia); Ounakone Xayviliya, Aekkalak Xayadeth, Laochou
Sotouky, Sengkham Douangsavay, Phimmatha Phothisan, Somphone
khongsab (Laos); Terry Bolger; Ross Dominic D. Agot Madonna Feliz
B. Madrigal, Roberto Soriano, Jose Marcel S. Laud Marcko San E.
Miguel (Philippines); Meas Panha, IM Sim, Kim Seng, Keat Lenarith,
Men Ratana (Cambodia); Thiha Soee, Kyaw Kyaw Ohn, HanThet Aung,
Myo Min Thant, Kay Khine Oo, Myo Swe Ei (Myanmar). Countries and
names are arranged in random order. The authors thank Prof. Paul W
Williams and Prof. Daoxian Yuan for providing comments in the prepa-
ration of this paper. The authors wish to thank the reviewers for their
constructive comments. The authors thank Fan Liu for revising the
figures.
Funding This study was funded by the Key projects of Guangxi Natural
Science Foundation (2020GXNSFDA238013), National Natural Science
Foundation of China (41772269 and 41977168), and the Key Research
and Development Program of Guangxi (Guike AB18221093).
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