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© FAO
Climate Change Adaptation in Wetlands Areas
(CAWA)
Hydrological assessment of the Xe Champone and Beung Kiat
Ngong wetlands
Final Report
Guillaume Lacombe, Paul Pavelic, Matthew McCartney,
Khamkieo Phommavong, Mathieu Viossanges
International Water Management Institute
September 2017
1
1 Introduction
1.1 Background
The CAWA project (Climate Change adaptation in Wetlands Areas) aims to reduce the vulnerability of
wetland ecosystems and of their dependent communities to climate change in Laos. The current
understanding of the hydrology of these wetlands is very limited. A good understanding of the hydrology
of the wetlands is a prerequisite for the success of the CAWA project, for four reasons:
• The ecosystem services provided by the wetlands are, to a large extent, dependent on their
hydrological functioning as well as the hydrology of the catchment in which they lie,
• Many of the direct impacts of climate change are expressed and mediated through water (e.g.
changes in rainfall, evapotranspiration, recharge and flows) and consequent changes in hydrology
will have an impact on ecosystem services derived from the wetlands,
• Many possible climate change adaptation strategies (e.g. increased dry season irrigation) will have
an impact on the wetland hydrology and, without good understanding of potential hydrological
implications, can lead to “maladaptation” with negative impacts on local communities (floods,
droughts, water contamination), and ecosystems (e.g. reduction in biodiversity),
• In addition to climate change adaptation strategies, the continued socioeconomic development
and associated utilization of water resources are also altering the wetland hydrology by modifying
surface and groundwater flux between the wetland, the rivers and aquifers.
1.2 Objectives
This study aims to understand and quantify the hydrological functioning of the two wetland RAMSAR sites
in Laos For this aim, three main activities were performed:
- The analyze of historical flow records in the wetlands to identify extreme events and better
understand flow dynamics,
- the quantification of surface and groundwater balances of the wetlands including the
interactions/connectivity between the wetlands and their surrounding water tables to assess how
they are vulnerable to possible environmental changes,
- the calibration of a rainfall-runoff model that predicts flow and water level in the wetland which
can in future be used to investigate how different rainfall projections under climate change
translate into river flow, water levels and flood risks in the wetland,
The level of detail and precision of these analyses vary between the two wetlands because of differences
in the availability of hydro-meteorological data. At the Xe Champone wetland, there are two river flow
gauging stations and rain gauges. At Beung Kiat Ngong, there are no on the ground measurement devices.
In the last section of this report, we provide some recommendations to address key knowledge gaps and
implications for wetland management based on current understanding and knowledge.
The study sites are first described in section 2. Previous modelling efforts in the studied areas are reviewed
in section 3. Our approach (data collection and analytical methods) is described in section 4. Section 5
2
presents and discusses our results. The report ends with recommendations on how to improve data
collection and analyses for improved water management (section 6).
2 Study sites
The project focused on two wetland areas which contain the country’s two designated Ramsar sites: Xe
Champone wetlands in Savannakhet province and Beung Kiat Ngong (BKN) wetlands in Champasak
province.
2-1 Xe Champone wetland The Xe Champone wetland covers an area of 450 km2 including 14 villages with a total population of
around 7,000 people. The wetland consists of a mosaic of perennial and seasonal rivers, freshwater lakes,
ponds, meanders, oxbows, marshes, rice paddy fields and a small area of peat. These various types of
wetlands, as well as evergreen and bamboo forests associated with the wetland, provide habitat for a
number of globally threatened species, including the Siamese crocodile. In recognition of this, 124 km2 of
the wetland are classified as a Ramsar site. The wetlands are fed by the Xe Champone River. At Kengkok,
just upstream of the wetland, this river drains an area of 2,640 km2 (Figure 1) and originates from the
Annamite Mountain Range. There is only around 10m elevation change between the north and south of
the wetland, a distance of about 40 km, resulting in a virtually flat plain (mean slope = 0.02%) crossed by
a slow-flowing river even when the water level is high (Figure 2). The river drains out of the wetlands into
the Xe Xangxoy River and thence into the Xe Banghieng River that ultimately flows into the Mekong River.
Between Kengkok and the confluence of the Xe Champone and Xe Xangxoy rivers, the catchment area of
the Xe Champone River increases by 19.4%, from 2640 to 3153 km2.
The climate is monsoonal and highly seasonal: average annual rainfall is 1,478mm, with strong variation
between the November-May dry season and the May-October wet season (mirrored by a difference
between a minimum low temperature of 13C in January and a maximum high of around 39C in April).
During the wet season, the different wetland types are interconnected, providing important breeding and
feeding habitat and migration pathways for fish. During the dry season, by contrast, falling water levels
mean that many lakes and ponds in the wetland become isolated. Groundwater is found about 4-5 meters
below the surface in the wet season but at 8 meters in the dry season (FAO 2016). A study of the
groundwater resources in the Xe Champone catchment shows that the area is underlain by evaporite beds
and clastic sedimentary rocks of the Mesozoic Khorat Group that are a source of salt found in the
groundwater and surface soils (Wiszniewski et al. 2005; and Figure 3). Salt loads are noted as a threat to
surface water and shallow groundwater resources. Paddy fields around the wetland are subject to salinity
issues (Figure 3). Two artificial reservoirs on the northern side of the wetlands were built some decades
ago to provide water resources for irrigation. Due to water percolation through and/or below the dike of
the Tsui reservoir, paddy fields located downstream of the dike remain saturated with water during a
significant part of the dry season (Figure 4).
3
Figure 1. Land use and catchment of Xe Champone River
Figure 2. Elevation in Xe Champone catchment
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Figure 3. Salt concentration at the soil surface near Kengkok
Figure 4. Tsui Reservoir, north of Xe Champone wetland (Left). Paddy fields located next to the reservoir dike (Right)
2.2. Beung Kiat Ngong wetland The Beung Kiat Ngong (BKN) wetland covers 23.6 km2 and includes 13 villages inhabited by 11,500 people.
This whole area is designated as a Ramsar site (Figure 5). Elevation of the catchment in which the wetland
lies, ranges from 120 to 200m above sea level, partly within the Xe Pian National Protected Area (NPA)
and to the south of Dong Hua Sao NPA which covers the southern slopes of the Boloven Plateau (Figure
6). This catchment extends over 133.64 km2. Both of these NPAs provide the streams feeding the wetland.
Climatic conditions are similar to those in Xe Champone, though with higher mean annual rainfall of
2,000mm (IUCN 2011a).
5
Figure 5. Land uses and catchment of Beung Kiat Ngong
Figure 6. Elevation in Beung Kiat Ngong catchment
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The wetland comprises a large area of freshwater marsh, some permanent, some seasonal, and
interconnected by a complex network of small rivers and streams generally draining water from north to
south. The site comprises two almost separate wetland areas, linked by a narrow corridor. The water in
the northern area is fed by streams from the north and from hills to the west, while the water flowing into
the southern area comes from a larger area to the south.
The wetlands lie in a series of shallow basins filled with peat, forming a complex of marsh, swamps,
perennial and seasonal ponds, and seasonally flooded grasslands and forests, interspersed with islands
covered by shrubs and trees. Along specific margins of the wetland land has been converted to rainfed
rice paddy. Much of the wetland is not open water, but consists of relatively shallow water covered by a
thick layer of decaying grasses with new shoots and emergent weeds, as well as bushes, growing on top.
The deepest parts of the wetland remain are 2-3m deep in the dry season. Within the main part of the
wetland, the area of permanent water that remains through the dry season is 3-4 km2, while other
scattered small marshes and pools retain water throughout the year. During the wet season, the whole
area is inundated with water levels rising to 2m above the dry season levels (FAO 2016) (Figure 8).
In geological terms, the area is located on the lower slopes of the Boloven Plateau underlain by Cenozoic
age basaltic lava deposits. Nepheline-olivine basalt is the most common geological unit found within the
study area and underlies the Beung Kiat Ngong wetland. Olivine-pyroxene and pyroxene basalts lie to
areas in the north and east whilst volcanic ash-derived Dacitic welded tuff lies in areas to the south and
west (DGEO & JICA 2008). Drilling logs from monitoring wells drilled by Phommavong (2015) reveal that
the Bolaven basalt layers are less than 20 meters thick and underlain by older Mesozoic sandstone
deposits in the Kiat Ngong village area (Figure 7). The basalt in composed of a permeable weathered layer
of up to 5 meters thickness overlying a less permeable hard basalt layer up to 13 meters thick.
Figure 7. Stratigraphic cross section based on the geological core material recovered from three monitoring wells in the northwestern part of the Beung Kiat Ngong wetland (Source Phommavong, 2015)
These lava flows, which originate from ancient volcanic activity on the Boloven Plateau, formed an
intricate network of depressions that were subsequently filled with alluvial sediments and peats (Meynell
OW1
OW3
OW4
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et al. 2014). The wetland and areas of permanent water now occur in the lowest parts of these
depressions.
The area has no piped water supply and groundwater is the major and often sole source of domestic
supplies. Household and community wells are constructed to depths of up to 50 meters, but typically
much less. For much of the year, water availability for domestic purposes is not an issue. However, in the
late stages of the dry season, water levels can fall to depths of 8 meters or more in several villages (i.e.
Khiet Ngong, Kaelae May, Sanod). For households with shallow wells, this situation leads to water supply
issues as shallow wells may dry out and deeper wells may take considerable time to refill after pumping.
Figure 8. Beung Kiat Ngong wetland (Credit: G. Lacombe/IWMI)
2.3 Importance of groundwater
Groundwater, being an actively replenished part of the hydrologic cycle, is often closely linked to surface
water features such as rivers and wetlands (Winter et al. 1999). Xe Champhone and Beung Kiet Ngong,
wetlands may have dependence on groundwater for wetland functioning, particularly given the extremely
high seasonality of rainfall and limited surface water flows during the drier months of the year. Baseline
studies conducted by the International Union for Conservation of Nature (IUCN) suggests a linkage with
groundwater at both wetland sites (IUCN 2011b, 2011b).
One of the environmental services the wetlands provide is the regulation of climate variability and
hydrology/water flows. The set of studies by IUCN (IUCN 2011a, 2011b, 2012; Meynell et al. 2014) offer
valuable insights about these two wetlands in general, however in terms of groundwater specifically, they
provide limited information and are apparently based on direct observations and/or accounts provided
by local stakeholders. A more detailed assessment of the groundwater – wetland interactions based on
the available data has not been carried out at either wetland. In this report, we provide a preliminary
assessment (section 5.3.2.3) based on groundwater data only available for the Beung Khiat Ngong (BKN)
wetland. Enquiries with authorities in Savannakhet province and a review of the literature suggest an
absence of relevant data for the Xe Champone wetland.
8
3 Review of previous hydrological modelling efforts in the two
study sites
Data are scarce and there is relatively little understanding of the hydrological fluxes and processes
occurring within the Xe Champone and Beung Kiat Ngong wetlands. There have been few previous studies
that have attempted any quantitative analyses.
3.1 Xe Champone
Wiszniewski et al. (2005) developed a groundwater model for a salinized area of the lower Xe Champone
catchment, largely upstream but also incorporating the wetland. The model was developed to investigate
groundwater flow and salt transport in the context of expanding reservoirs for irrigation, with the risks of
increased salinization, as has been observed in neighboring provinces in Thailand. The specific aims of the
project were to investigate major patterns of groundwater flow, identify and quantify the relative
proportion of various recharge and discharge mechanisms, assess which aquifer parameters and
hydrological stresses have the largest influence on groundwater levels at various points in the aquifer
system, and gain information about rates of groundwater flow and solute transport to surface soils. A
conceptual model was developed, based in part on more detailed understanding of geology and
hydrogeological processes in Northeast Thailand. The major groundwater flow path was conceived to be
from the main recharge areas in the weathered and fractured bedrock aquifers along the catchment
boundaries, down the topographic gradient in the shallow and thin alluvial aquifer and finally to discharge
points in natural depressions and the Xe Champone River. Reservoirs in the catchment (upstream of Xe
Champone wetland) were also assumed to recharge the groundwater aquifer through vertical seepage.
Thus, although not stated explicitly, the conceptual model recognized significant lateral movement of
relatively shallow groundwater into the Xe Champone wetland.
Based on the conceptual model, a numerical model was developed using Processing Modflow for
Windows Professional (PMWIN Pro). Initial model parameters were based on values reported for similar
rocks in Northeast Thailand but were calibrated with available hydraulic head observations at five
locations in the study area. The model results suggested that the groundwater system was broadly divided
into two parts: a) relatively fast moving shallow fluxes subject to comparatively high rates of evaporation;
and b) a much slower moving deeper system that picked up salts from rock salt deposits but moved so
slowly that it had little impact on the surface soils. From this it was hypothesized that over short time
scales (100 years), local flow systems are characterized by localized recharge and discharge zones and the
deep groundwater fluxes are minimal. This has important implications for the hydrology of the Xe
Champone wetland, which is most likely a discharge (i.e. not a recharge) point for the shallow lateral
groundwater fluxes.
A water resource assessment of the Xe Banghieng Basin (of which the Xe Champone River is one of the
five major tributaries) was conducted by Phongpachith (2010). This study relied on the ArcSWAT (a
physically-based distributed hydrological model) and the Integrated Quantity and Quality Model (IQQM)
(a water resource planning model) configured for the entire basin. The models were set up to evaluate
possible changes in flow regime arising from the implementation of development projects and climate
change. In addition, hydraulic modelling, using the ISIS model for the period 1985-2008, was conducted
and focused primarily on modelling flood extent between Kengkok and Kengdone, including the Xe
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Champone wetland. The results indicate that i) future irrigation in the Xe Banghieng basin is focused
predominantly on the Xe Champone Basin with likely significant increases in water abstracted and
consumed; ii) hydropower development will occur outside the Xe Champone and will only likely effect
flows downstream of the wetland.
District level flood and drought maps were developed for the Savannakhet province, and specifically for
the Champone district and the Xe Champone catchment, as part of a study into improving the resilience
of the agricultural sector (IRAS) in Lao PDR in anticipation of likely climate change (Phongpachith 2014).
The study used the SWAT model in conjunction with the MRC tool box for analysis (“Impact Assessment
Tools”) for flood and drought mapping in 2040 and 2070. Mapping was based on flows at Kengkok. Flood
frequency and low flows were analyzed. The 2011 flood, which inundated 24,404 ha of the Champone
district (25%) was used as the baseline. This area was anticipated to increase to 30,535 ha (31%) in 2040
and 35,606 ha (36%) in 2070, with an increasing number of affected villagers. Similarly the area at risk of
drought was anticipated to increase from 518.3 ha under baseline, to 1,260 ha in 2040 and 5,371 ha in
2070, again with significant increases in the number of villages and people affected.
3.2 Beung Kiat Ngong
There have been even fewer studies of the Beung Kiat Ngong wetland than of Xe Champone. The IUCN
Management Plan for the wetland has very little information on the system hydrology but expresses
concern over possible future increases in irrigation projects that may take more water from the wetlands.
The report also proposes that the impacts of future hydropower development on the rivers and streams,
such as the Xe Pian and Xe Kong, feeding the wetlands should be investigated (IUCN 2012).
Meynell et al. (2014) conducted a climate change vulnerability assessment. They described the general
drainage pattern, including the fact that during the rainy season water may back up into the southern part
of the wetland from the Xe Khampo, the tributary into which the wetland drains. A relatively small
catchment (ca. 46 km2) supplies the northern part of the wetland but streams flow in the wet season only.
No attempt was made to quantify the surface or groundwater flows into the wetland and the analyses
comprised an evaluation of the possible impacts of changes in rainfall and evapotranspiration in 2050 for
a single (A1B – considered conservative) climate change scenario. The study concluded that there was
likely to be increased rainfall during the monsoon so that the wetland was likely to expand slightly (on
average 8%) with an increased risk of flooding in high rainfall years. Increased evaporation in the dry
season, due to higher temperatures, was anticipated to cause the wetland to dry up more rapidly with
open water pools becoming shallower. Overall, the Beung Kiat Ngong wetland ecosystem was considered
to be only moderately vulnerable to the climate change scenario investigated, largely because of its
dynamic and resilient character and the fact that dry season evaporation would be “more than
compensated for” by the increased rainfall in the wet season. However, this statement doesn’t indicate
how excess water from the wetter wet season can be stored and used during the drier dry season. It is
also not clear how reliable the climate projection used in this study is, given the wide range of
contradicting rainfall projections available for the lower Mekong Basin (Hasson et al. 2016).
10
4 Method
The method applied in this project included several steps: field visit, data collection, data quality control,
statistical analysis of meteorological records, water balance, hydrological analysis of flow and water level
records, model calibration and simulation.
4.1 Field visit
The objective of the field trip organized in October 2016 was to visit the two wetlands and more
specifically : i/ meet local partners in the two provinces to present our objectives and understand local
problems, ii/ collect data and information on water management and hydrology, iii/ understand local
challenges of the wetlands. A field report was produced and is available upon request (Lacombe 2016).
4.2 Data collection 4.2.1 Surface water
Most of the georeferenced data were collected from the Mekong River Commission. They include the
locations of the hydrological and meteorological stations that have been operated by the Department of
Meteorology and Hydrology of Laos (DMH) over the last 50 years (cf. Figure 10). In addition, we
downloaded HydroSHEDS, a quality-controlled 90-m digital elevation model (Lehner et al. 2006) freely
available at http://hydrosheds.cr.usgs.gov/index.php. Topographic maps were provided by FAO. Daily
time series of hydro-meteorological records (rainfall, river flow, standard evapotranspiration) were
collected from the central- and district-level offices of the Ministry of Agriculture and Forestry (MAF) and
the Ministry of Natural Resources and Environment (MONRE). The actual land surface evapotranspiration
product MODIS 16 (Mu et al. 2011), available at a monthly time step for the period 2000-2009 was
downloaded from http://www.ntsg.umt.edu/project/mod16, and used to compute the water balance of
the two wetlands.
4.2.2 Groundwater
The dataset used in this assessment originates from an activity undertaken as part of a national research
project examining the potential for sustainable expansion of agricultural groundwater use (ACIAR 2016).
This activity began as a one year Master’s thesis research carried out by Mr Khamkieo Phommavong from
NUOL Faculty of Engineering, Laos, to examine the groundwater resources of Kiet Ngong village
(Phommavong 2015). Through a research internship at IWMI in the second and final year, the study area
was broadened to include the wider area including the Beung Kiat Ngong wetland. The aim of this work
was to assess the groundwater resources of an area with good groundwater potential in southern Laos.
Fieldwork was carried out approximately twice per year over the two-year period. Major tasks included:
• drilling of four monitoring wells to depths of 25 metres at Kiet Ngong village, situated adjacent to
the northwestern perimeter of the Beung Kiat Ngong wetland,
• aquifer pump testing of the monitoring wells and some private wells to assess the hydraulic
properties of the shallow aquifer,
• seasonal monitoring of groundwater levels from a network of existing wells over an area of about
200 km2 and covering about 20 villages,
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• household surveys of the levels of groundwater utilization.
4.3 Data quality control of hydro-meteorological time series
Table 1 indicates the availability of data time series for the study areas, collected under this project. Daily
time series of rainfall, river flow, river water level and standard evapotranspiration (ET0) were scrutinized
to identify dubious values. Visual inspection of hydrographs, comparison of records from different years
at the same station or from neighboring stations during the same years allowed the identification of
inconsistencies in data series.
Table 1. Availability of hydro-meteorological data in the study area
River Station Variable Periods of data availability
Xe Champone Kengkok Discharge 1978-2004
Water level 1978-2004; 2010-2014
Donghen Discharge 1995-2004
Water level 1995-2004
Xe Xangxoy Ban Phalane Discharge 1985-2004
Water level 1994-2004
Xe Banghieng Ban Kengdone Discharge 1961-2004
Water level 1995-2004
Mekong Savannakhet Discharge 1950-2015
Water level 1998-2015
Ban Kengdone Rainfall 1992-2003
Ban Donghen 1965-2003
Kengkok 1965-2015
Savannakhet 1965-2015
Seno 1951-2014
Det Udum 1964-1999
Nonghine 1980-2003
Pakse 1960-2015
Pathoumphone 1979-2007
Savannakhet Pan 1981-2015
Seno Evaporation 1962-2014
Pakse 1962-2015
Operating river water level gauges along the Xe Champone and Xe Xangxoy Rivers were visited in October
2016 (Figure 9), revealing two issues: i/ the original stage board in Kengkok is partly destroyed, and has
never been replaced, indicating a lack of maintenance of the measurement devices. Surprisingly, daily
measurements of the river water level are still performed and corresponding records are available in the
flow database, suggesting that observations are made with a decameter or simply estimated without any
device, based on experience; ii/ a few meters downstream of the original measuring scale, a new gauging
station was set-up a couple of years ago by the Japan International Cooperation Agency (JICA). While this
new station is not used yet because of pending approval by relevant authorities, field observations show
that the lower part of the new scale is already buried under sediments.
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Figure 9. Water level gauging station at Kengkok (Xe Champone River). Left: old station, still in operation. Right: new station, not functional yet because of pending approval by local authorities. High rate of sedimentation in the river bed partly buried the lower part of the scale.
Figure 10. Location of hydro-meteorological stations around the two studied wetlands. The catchment of Xe Champone is delineated in black and that of Beung Kiat Ngong is delineated in pink.
Figure 10 shows where the hydro-meteorological stations are located. No flow data are available either
upstream or downstream of Beung Kiat Ngong wetland.
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4.4 Data selection
Based on the assessed reliability of the inspected time series and their geographic relevance, a set of
stations with good quality data and near the Xe Champone wetland, was selected for the modelling. It
includes daily rainfall and river flow at Kengkok and pan evaporation at Seno and Savannakhet stations
for the period April 1991 – March 2004, and daily river water level at Kengkok for the period 1978-2004.
It should be noted that the zero of the gauge elevation is 129.98 m above mean sea level (MRC 1980). For
the long-term rainfall analyses, rainfall gauging stations at Savannakhet and Pakse were found to be the
only rain gauges with data of sufficient quality and covering time periods long enough.
4.5 Hydrological modelling 4.5.1 GR2M model
Many types of hydrological models exist with various levels of complexity and data requirements. For our
case study, given the overall scarcity of good hydro-meteorological data, we opted for a 2-parameter
monthly lumped conceptual rainfall-runoff model “GR2M” to simulate streamflow of the Xe Champone
River at Kengkok located upstream of the wetland. The catchment area is 2,640 km2. The advantage of
this model is that it does not require any land-use or soil data. The rainfall-runoff relationship is captured
by a set of mathematical relationships parameterized using time series of observed flow and rainfall.
GR2M was empirically developed by Mouelhi et al. (2006) using a sample of 410 basins worldwide under
a wide range of climate conditions. GR2M includes a production store and a routing store. The model
estimates monthly streamflow from monthly areal rainfall and monthly ET0. The two parameters of the
model determine the capacity of the production store and the flow of underground water exchange.
Compared with several widely used models, GR2M ranks amongst the most reliable and robust monthly
lumped water balance models (Mouelhi et al., 2006). For this analysis, like in most hydrological analyses
performed in the Mekong Basin, each hydrological year (n) starts in April of calendar year (n) and ends in
March of the following calendar year (n+1).
4.5.2 Model parameterization
Daily time series of rainfall, river flow and ET0 were first aggregated into monthly time series. Inter-annual
mean monthly values, rather than temporally varying time series of ET0 derived from pan evaporation
measured in Savannakhet, were used as input to calibrate the models because of several data gaps in the
time series (Oudin et al. 2005). The parameters of the model were adjusted to maximize the Nash and
Sutcliffe (1970) coefficient (NS). A constraint of less than 10% bias on annual streamflow over each year
was applied to all calibrations. Because of the lack of the initial conditions (i.e. water levels in the model
reservoirs), the period April 1991-March 1992 was used to initialize the model. Adopting a split-sample
approach, the model was calibrated over the period April 1992 – March 1998 and validated over the
period April 1998 – March 2004, yielding NS coefficients of 90% and 75%, respectively. In order to assess
the stability of the catchment’s hydrological behaviour over the adjustment period, the calibration and
validation periods were permuted. The new NS coefficients (75% in both calibration and validation)
indicate that the hydrological behaviour was slightly different between the two periods. Possible causes
are numerous and include change in land use, reservoir operation in the catchment, and inaccuracies in
the data set used to calibrate the model.
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5 Results 5.1 Rainfall
Figure 11 shows annual rainfall time series at Pakse, Savannakhet and Kengkok gauging stations which are
the stations with the longest and error-free time series of data, although 7 years had to be discarded from
the analysis in Kengkok because rainfall data gaps. These time series were tested for long-term trend with
the Mann-Kendall trend detection test (Mann 1945; Kendall 1975). Both visual inspection and statistical
test show no significant trends at 95% significance level in the tested time series over the period 1960-
2015. However, a highly significant downward trend is observed in Kengkok over the period 2001-2015.
Similar downward trend, though with a lower statistical significance (p-value > 0.1), is observed over the
same period in Savannakhet. Strikingly, the years 2014 and 2015 are the driest years recorded in Kengkok
since 1965, totaling 862 mm/year and 815 mm/year, respectively, while the inter-annual average at this
station is 1447mm. These two extremely dry years are likely attributed to an extreme El Nino event (FAO
2015), that extended until 2016 (Thirumalai et al. 2017). Consistently, annual rainfall recorded in Pakse
and Savannakhet in 2015 is among the lowest on records while more heterogeneities are observed in
2014. These records are in agreement with the statements of the provincial office of the ministry of
natural resource and environment in Savannakhet, who reported that many marshes of the Xe Champone
wetland completely dried out in the last couple of years, which never happened over the last 50 years.
Other contributing factors that could have exacerbated this drought include climate change, the on-going
sedimentation of the wetland and the increasing irrigation water demand.
Despite the absence of long-term rainfall trend in Pakse, much greater inter-annual variability is observed
at this station with a coefficient of variation (standard deviation/mean annual rainfall), 19%, exceeding
that in Savannakhet: 16%.
Figure 11. Annual rainfall (mm/year) at Pakse and Savannakhet gauging stations
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5.2 Analysis of actual water level and flow data in Xe Champone
Figure 12. Recorded water level of the Xe Champone River at Kengkok.
Figure 12 illustrates the temporal variability of the actual daily water level of the Xe Champone River at
Kengkok. Each year, the red, green and blue curves indicate the value of the lowest, median and highest
daily water levels in the river, respectively. The Mann-Kendall trend detection test (Mann 1945; Kendall
1975) indicates that there is a rising trend in the lowest water level from 1978 to 2004, statistically
significant at the 99.9% confidence level (p-value = 0.001). This trend means that there is possibly a
tendency for higher low flow during the dry season in the Xe Champone wetland. This rising trend is also
reflected in the median water level of the river, though with a slightly lower statistical significance (p-
value =0.1). This result is consistent with the varying NS coefficients observed when switching the
calibration and validation periods of GR2M model (cf. section 4.5.2). Possible causes of increasing low
flow include land-use changes in the upstream catchment, involving greater infiltration and groundwater
recharge resulting in enhanced river base-flow (e.g. deforestation, cf. Calder, 2007). Another possible
cause is the development of storage structures (e.g. dams) releasing water during the dry season. The
only two reservoirs identified (Tsui and Bak Reservoirs) (Figure 4), located on the right bank of the Xe
Champone River could have enhanced low flow. Their cumulated storage capacity is 63 million m3.
Assuming that they release constant flow over the 6 months of the dry season and become half empty at
the end of the dry season, the emptying discharge would approximate about 2 m3.s-1. According to the
rating curve displayed in Figure 21, this additional flow could raise the river water level by about 0.5-1
meter during the dry season. This change is comparable to the magnitude of the water-level rise observed
in Figure 12. Therefore, it is possible that the two reservoirs explain this hydrological change. Under this
assumption, the gradual dry season water level increase observed in Figure 12 could correspond to a
gradual increase in the permeability of the reservoir dikes, in relation with temporal deterioration.
Another possible explanation for the rise in the gauged water level during the dry season is the
sedimentation of the riverbed, observed during the field trip in October 2016 (cf. Figure 9), leading to a
rise in the water level over years, while the average river flow remains the same. It should be noted that
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16
annual rainfall (cf. Figure 11) and dry season rainfall remained stable during the study period and thus
cannot be the cause of this rise in low flow water level.
The magnitude of the annual highest daily water level exhibits high inter-annual variability (standard
deviation = 1.17 meter). The three highest water levels on records occurred on 16 August 1978 (11.3
meters), 5 August 1990 (11.0 meters) and 24 September 1996 (10.1 meters). Figure 12 shows that the
occurrence of the highest water level is centered on August 19th, with inter-annual variations comprised
between June 21st and October 10th (standard deviation = 27 days), thus highlighting the difficulty of
anticipating when the flood peak will occur each year. The absence of temporal trend in the magnitude
of the annual highest water level suggests that land-use change is not a driver of low flow change observed
in Figure 12. Indeed, any land-use change would typically alter both high and low flows as observed by
Lacombe et al. (2016) in Laos and Vietnam.
Figure 13. Return period of annual highest river water level of Xe Champone River at Kengkok
Figure 13 provides the return period of the annual highest daily water levels of the Xe Champone River at
Kengkok. This relationship was calculated using the historical records displayed in Figure 12, assuming
that they follow a distribution of Gumbel (1954). A fitting corresponding to R2=91.9% was obtained using
the maximum likelihood method. Figure 13 shows that annual maximum water levels from 10 to 11
meters have a return period varying between 12 and 30 years, respectively. According to the director of
the provincial office of the Ministry of Natural Resources and Environment in Savannakhet, the flood
warming level of the river at Kengkok is 8 meters. Based on Figure 13, this level is reached by the river
every other year, indicating that flood risks are high in this wetland.
Based on the elevation of the gauging station (zero of the water level scale located at 129.98 meters above
mean sea level), it is possible to assess the flood extent for any water level. Using the DEM Hydroshed,
Figure 14a displays the spatial extent of a static flood corresponding to a river water level of 10 meters at
Kengkok. Figure 14b displays the actual spatial extent of the flood in September-October 2000, based on
satellite observations. The similarities in flood extent derived from DEM or satellite observations suggests
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that the maximum daily water level at Kengkok in 2000 was close to 10 meters. Using Figure 14a, it is
possible to approximate the flooded area when the river water level at Kengkok reaches the warning
threshold of 8 meters. This flooded area corresponds to areas in Figure 14a where flood depth is greater
than 2.
Figure 14. Flood in the Xe Champone wetland. A: flood extent and depth computed with DEM, assuming a 10-meter river water level at Kengkok. This assessment is static and assumes no spatial variation in water levels caused by flow velocity. B: actual flood area derived from satellite observations in 2000.
Figure 15. Daily records of river water level (illustrated in meter above mean sea level) and possible backwater effects in the Xe Champone wetland
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By comparing the daily water level variations at Kengkok and Ban Kengdone, Figure 15 illustrates a
possible influence of the Xe Banghieng River on water levels in the Xe Champone wetland. Although there
is a difference in elevation of river gauging stations greater than 20 meters between Kengkok and Ban
Kengdone, the difference between river water levels at the two stations nears zero during floods (e.g. in
November 1999), especially during the peak flood events that were recorded along the Xe Banghieng River
(Figure 15). Figure 15 indicates that the flood water level at Kengkok in 2000 reached 138.3 m above mean
sea level (14 September 2000), equivalent to a local water level of 138.3 – 129.98 = 8.32 meters. This
water level is lower than the level of the flood mapped in Figure 14a (i.e. 10 meters), suggesting that the
flood mapped in Figure 14b is partly caused by downstream backwater that may occur, as evidenced in
Figure 15 where absolute water levels (i.e. water level above mean sea level) at the stations Kengkok and
Ban Kengdone can become very similar, despite differences in topography. This back water effect,
exacerbating the magnitude of river floods, confirms that the Xe Champone wetland is a flood-prone area.
5.3 Water budget 5.3.1 Xe Champone
Mean annual river discharge measured at Kengkok (1668 106m3) is equivalent to 632 mm for the entire
river basin area. It represents 42% of mean annual rainfall (1509mm). According to MODIS 16, actual land
surface evapotranspiration in the Xe Champhone catchment averaged over the period 2000-2009 is
1046mm.
Depth (mm) Volume (106 m3)
Rainfall 1509 mm 3983
Runoff -632 mm -1668
Actual ET -1046 mm -2761
Lateral groundwater flux 1046+632-1509=169mm 446
This simple water balance of the catchment of Xe Champone River at Kengkok indicates that there is an
inflow of groundwater into the catchment. However, this result should be interpreted with caution, given
that the different terms of the water balance were computed over different periods because of
constraints in data availability.
Between Kengkok and the confluence of the Xe Champone and Xe Xangxoy rivers, the catchment area of
the Xe Champone River increases by 19.4%, from 2640 to 3153 km2. The total area of the wetland itself is
about 400 km2. Assuming an average water depth of 0.5 meter over this area, the total water volume is
200 million m3, equivalent to 12% of the mean annual flow. This indicates a significant capacity to regulate
the river flow.
5.3.2 Beung Kiat Ngong
5.3.2.1 Surface water balance
There is no river gauging station in this wetland. River flow is estimated using relationships between
geomorphological and climate characteristics of the catchment, and flow metrics. According to Lacombe
et al. (2014), mean annual streamflow Qmean (m3.s-1) can be estimated at any point along ungauged rivers
of the Lower Mekong Basin using the following equation: Qmean = 5.6647×10-9 × Rain2.543 × Area0.883 ×
19
Drai1.089 where Rain is the mean annual rainfall over the studied catchment derived from the gridded
rainfall product Aphrodite (Yatagai et al. 2012), Area (km2) is the drainage area of the catchment and Drai
(=drainage density in km-1) is the cumulative length of all streams within the catchment, normalized by
Area. Here, a stream is considered as such when it drains an area of at least 40 km2 (Lacombe et al. 2014;
cf. Figure 5). Area and Drai were derived from HydroSHEDS using ArcMap 10.3 considering the outlet point
depicted in Figure 5. Resulting values are: Rain = 1,837 mm.year-1, Area = 133.64 km2. Drai = 0.0823 km-1.
Based on these values, Qmean = 5.62 m3.s-1, equivalent to 1,327 mm.year-1. According to MODIS 16
(http://www.ntsg.umt.edu/project/mod16), actual evapotranspiration is greater than 1000 mm.year.-1.
The terms of this water balance are reported in the following table:
Depth (mm) Volume (106 m3)
Rainfall 1837 mm 245.5
Runoff -1327 mm -177.3
Actual ET -1000 mm -133.6
Lateral groundwater flux 1327+1000-1837=490 65.4
This water balance suggests that 65.4 million m3 of goundwater are entering the catchment annually and
draining into the river that flows into the wetland. Following the method proposed by Lacombe et al.
(2018), it is possible to assess the baseflow QB in the catchment of Beung Kiat Ngong, using estimates of
Rain, ET0 (annual standard evapotranspiration), the geographic coordinates of the centroid of the
catchment, and the catchment area. The resulting value, 2.75 m3.s-1 is equivalent to 86.7 million m3. This
value is greater than the estimated lateral groundwater inflow to the catchment because of additional
groundwater recharge inside the catchment, equivalent to 86.7 106 m3 – 65.4 106 m3 = 21.3 106 m3 or 160
mm, representing less than 10% of rainfall.
5.3.2.2 Water infrastructure interventions
The provincial head of the Water Resources Department of the Ministry of Natural Resource and
Environment in Pakse indicated that one priority for local authorities is to build a dike between the two
main pools of the wetlands of Beung Kiat Ngong wetland, in order to keep water in the upstream pool
during the dry season for biodiversity conservation. Figure 16 maps the inundated areas corresponding to
dikes of one and two meters, using the DEM Hydroshed (Lehner et al. 2006). This inundated area would
extend over 7.1 km2 (dark blue colour in right panel) and 10.1 km2 (dark+light blue colour), with dikes of
1 and 2 meters, respectively. Most of the additional inundated area (light blue colour corresponding to
the additional area inundated when the dike height increases from 1 to 2 meters) is located in the
northern part of the wetland. Field topographic measurements would have to be performed to verify that
this extension is actually filled by water and not naturally blocked by local relief preventing inundation in
places.
20
Figure 16. Flooded area created by two dikes indicated in the right panel. Dark blue: inundated area with one-meter dike (164 meter above mean sea level). Light blue: additional inundated area with two-meter dike (165 meter above mean sea level)
5.3.2.3 Ground water balance
Groundwater fluctuations and trends
Monitoring well data from Khiat Ngong village over a two-year duration shows the seasonal pattern in
groundwater level. Groundwater levels reach their peak at around 1 to 2 meters below the surface in the
latter stages of the wet season (typically between September and November) and are at their deepest
level, around 4 to 5 meters below surface, at the end of the dry season (around May). There is a clear
correlation between the groundwater levels and the magnitude and timing of rainfall (Figure 17).
Increases in groundwater levels during the wet season reflect the occurrence of recharge events that
occur almost entirely during the wet season. The lag between rainfall events and recharge to groundwater
is very short due to the shallow depth to groundwater and thin top soils in the area. Declining levels during
the dry season are thought to reflect discharge from pumping, evapotranspiration and baseflow to open
water bodies within the wetland complex.
The groundwater table behaviour measured at Khiet Ngong aligns well with observations made by
Meynell et al. (2014). These authors suggested that groundwater levels in the freshwater marshes of the
wetland rise to the surface, with seasonal ponding occurring if rainfall is sufficiently high and flooding
prolonged. In the subsequent dry season the high evaporative demand brought about by higher
temperatures, in conjunction with limited rainfall causes groundwater levels to fall, leading to drying out
of some marshes.
21
Figure 17. Seasonal pattern of groundwater depth of three monitoring wells in Khiet Ngong village (a) and monthly rainfall for Pakse station (b) (Sources of data: IWMI, DMH). Location of monitoring wells is shown in Figure 7.
Interactions between groundwater and Beung Kiat Ngong wetland
A groundwater level contour map (with heights above mean sea level) derived from groundwater levels
measured in 80 wells in November 2015, shows that the direction of groundwater flow is generally from
north to south during both the wet and dry seasons (Figure 18). Groundwater level trends largely follow
the surface drainage pattern. Groundwater outflow from the study area coincides closely with the surface
water outlet of the watershed. The maps clearly shows that the Beung Kiat Ngong wetland is fed by
groundwater originating from the surrounding areas to the north. The wetland intercepts groundwater
flows from across most of the area except for the eastern portion which bypasses the wetland. It is
interesting to note that the wetland does not act as a termination feature for all groundwater discharge,
with some groundwater flow taking place beyond the Ramsar site boundary approximately towards the
south.
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Figure 18. Groundwater contour map for the study area in November 2015 (late in the wet season). Grey dotted arrows indicate the approximate groundwater flow paths. (Source of data: IWMI)
Conceptual groundwater model and groundwater balance
Based on our current understanding, a groundwater balance for the Beung Kiat Ngong wetland Ramsar
site (2,360 ha), represented by the white area in Figure 18, can be defined as follows:
Total Recharge (QR) + Lateral Groundwater Inflows (QI) = Groundwater Evapotranspiration (QET) + Lateral
Groundwater Outflows (QO) + Wetland/Groundwater boundary exchanges (QWB) (1)
The main aim of this water balance is to estimate the water exchanges (QWB) between the open water
body of the wetland and the surrounding aquifer. Such an assessment is a prerequisite to understanding
the potential contribution of groundwater to the overall water budget of the wetland. The inputs and
outputs of groundwater represented in this equation can be more easily visualized through the schematic
representation given in Figure 19. The groundwater balance includes two main components:
(i) groundwater with a short residence time (age) regenerated annually within the Beung Kiat Ngong
wetland via rainfall-recharge and returned to the atmosphere via evapotranspiration around the wetland,
(ii) groundwater of a longer age generated also by rainfall-recharge from areas beyond the wetland
that enters the site (also found in depths greater than seasonal fluctuations within the wetland site).
It should be noted that the source of the ‘open water’ (in the wetland) shown in Figure 19 may be from
precipitation intercepted by the pools, by surface water inflows, or by groundwater discharges.
Groundwater pumping by the local community (for domestic purpose) is not considered to be of
significance within the Beung Kiat Ngong wetland site because return flow from domestic usages partly
compensate extracted volumes.
GW flow path
23
Figure 19. Conceptual representation of the groundwater-wetland interactions within the Beung Kiat Ngong Ramsar wetland site boundary. Here, the water balance is applied to the water table comprised between the bottom of the diagram and its surface that vertically oscillates between the wet and the dry seasons, as indicated in the figure.
The approach used to estimate each of the groundwater balance components is as follows:
Vertical downward groundwater recharge from rainfall (QR) is assumed to be 1000 mm/year (i.e. 50
percent of annual rainfall) across the entire wetland area of 2,360 hectares except for the 400 hectare of
permanent open water where groundwater recharge or discharge is already accounted in the term QWB
(cf. below). The remaining 50 percent of rainfall is assumed to contribute to surface water flows through
runoff and surface evapotranspiration. The recharge estimation used here (1000 mm/year) is higher than
the groundwater recharge estimated by Phommavong (2015) (700 mm/year) over the wider region
because the shallow water-table conditions in the wetland site would promote higher rates of recharge.
Evapotranspiration (QET) from groundwater around the open water body is assumed to be at the potential
rate of 1600 mm/year around the entire wetland area. The shallow water-table conditions would be
anticipated to provide high soil moisture conditions year-round, mobilized by the roots of wetland
vegetation.
Lateral groundwater inflows and outflows (QI and QO, respectively) are calculated by Darcy’s Law based on
estimates of aquifer hydraulic conductivity, cross-sectional area of the aquifer and annual average
groundwater hydraulic gradient. The groundwater level contour trends in Figure 18 indicate that at the
upstream, the cross sectional length of the aquifer that feeds the wetland is large (9 kilometers) whereas
in the downstream, the aquifer length is considerably narrower (2 kilometers) due to the funneling effect
induced by the wetland and the geomorphology. An average uniform saturated aquifer thickness of 25
meters is assumed at across the area which reflects the typical aquifer thickness of the wells used to
determined groundwater flow map.
Perhaps one of the greatest source of uncertainty in the water balance lies in the aquifer hydraulic
conductivity value, which in basaltic aquifers can vary by three or more orders of magnitude. Water
balance scenarios reported in Table 2 were developed based on two sets of values; the lower bound value
of 4 m/day based on the highest calculated pumping test value, and the upper bound of 100 m/day
considered plausible for the site conditions (Freeze and Cherry 1979). There is also uncertainty concerning
QRQET
QR
QET
QIQO
QWB QWB
open water
QR
24
the hydraulic properties of soil layers which may also transmit lateral flows under high water-table
conditions which have not been taken into account.
Water boundary exchanges (QWB) between the surface water body of the wetland and the aquifer are
determined by difference according to the balance between the other estimated components. Negative
values suggest groundwater inputs to the open water bodies within the wetland whereas positive values
suggest that surface water inputs are needed to sustain the groundwater storage.
Table 2. Groundwater balance estimates for the Beung Kiat Ngong wetland RAMSAR site under high and low groundwater flow scenarios
Component
Volume (x103 m3/year)
Percent [1]
Low groundwater flow scenario:
GW Inflows (QI) 986 + 4.8
Recharge (QR) 19600 + 95.2
GW Outflows (QO) 110 - 0.5
GW Evapotranspiration (QET) 31360 - 152.3
Wetland/Groundwater boundary exchanges (QWB) 10884 + 52.8
High groundwater flow scenario:
GW Inflows (QI) 24638 + 55.7
Recharge (QR) 19600 + 44.3
GW Outflows (QO) 2738 - 6.2
GW Evapotranspiration (QET) 31360 - 70.9
Wetland/Groundwater boundary exchanges (QWB) 10140 - 22.9 [1] the percentages given are relative to the total groundwater inputs (QR + QI). Positive values reflect inputs to
groundwater (GW) system; negative values reflect outputs. The overall sum of inputs and outputs is zero.
The groundwater balance estimates given in Table 2 indicates that the Beung Kiat Ngong groundwater
system is replenished to a large extent by diffuse rainfall recharge each year (19,600 x 103 m3/year).
Evapotranspiration is a major output from the groundwater system (31,360 x 103 m3/year), and
significantly higher than recharge within the Ramsar area. Both QR and QET values are unchanged between
the two scenarios. Lateral groundwater inflows exceed outflows by around one order of magnitude in
both scenarios: 986 x 103 m3/year and 110 x 103 m3/year, respectively, for the low flow scenario, and
24,638 x 103 m3/year and 2,378 x 103 m3/year, respectively for the high flow scenario. For the low flow
scenario, lateral inputs are not a significant input (4.8 percent) whereas for the high flow scenario this is
significant (55.7 percent), and in fact, exceeds the magnitude of diffuse recharge.
For the low lateral flow scenario, the inputs from recharge and lateral inflow are less than outputs from
evapotranspiration and lateral outflow. In this scenario a contribution of 10,884 x 103 m3/year would be
needed from surface water. For high flow scenario the groundwater sustains baseflow into the wetland
(10,140 x 103 m3/year) with no surface water contribution necessary. This second value is consistent with
the surface water balance and baseflow estimations for the whole catchment of the wetland described in
section 5.3.2.1. Indeed, the larger base flow value obtained for the whole catchment (86,700 103 m3/year)
accounts for groundwater drainage into the river stream as well. Consistently the ratio (Wetland
25
area/catchment area) (17.6%) is of the same order of magnitude as that of the ratio (QWB of scenario
2/total catchment baseflow): 11.7%.
This groundwater balance demonstrates the overall great uncertainties due to the lack of reliable data,
though it exhibits some consistencies between the surface and groundwater balances. This suggests that
more data needs to be collected for a more precise surface water balance assessment of the wetland that
is required for a proper management.
5.4 Hydrological modelling results for Xe Champhone
Figure 20. Performance of GR2M in the Xe Champone catchment at Kengkok
Figure 20 illustrates the performance of GR2M between 1991 and 2004. Note the good match between
observed and simulated flow during the dry season, while simulation of high flow is less precise.
Figure 21. Discharge-water level rating curve for the Xe Champone River at Kengkok
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Figure 21 provides the equations of the rating curves for the Xe Champone River at Kengkok. These rating
curves were obtained by plotting time series of river discharge against time series of water level for the
period 2000-2004. The relationship between water level and discharge is not stable over years, possibly
reflecting instability of the river cross section (e.g. caused by sedimentation) and dubious values in the
time series. These two equations can be used to convert the output of the GR2M model (river discharge)
into water level (m) in order to estimate flooded areas for a given return period. This rainfall-runoff model,
calibrated for the Xe Champone catchment, can be used to assess how the magnitude of floods, with given
return periods, will evolve under a changing climate. This model is available as an Excel Spreadsheet and
can be easily used by staff non-familiar with hydrology.
6 Recommendations 6.1 Improving data
This analysis, that aimed to characterize the hydrological functioning and determine a preliminary water
balance of the two wetland RAMSAR sites in Laos, demonstrates the paramount importance of having
access to sufficient good quality hydro-meteorological data. The review of available data reported in
sections 4.2 and 4.3 showed that the data required to complete this study are extremely limited.
The existing state of knowledge on the eco-hydrology of the Xe Champone and Beung Kiat Ngong wetland
site is at a very basic level and needs to be greatly enhanced to provide a more reliable foundation for
decision-making. Areas that clearly need to be improved include:
• the delineation of the aquifer structure/properties and shallow surface and subsurface water
fluxes in and around the wetland,
• the delineation of flooded areas in the wetlands, and the variability of their extent between
seasons and years,
• evapotranspiration rates and dynamics from both surface water and groundwater as these are
controlled by a complex distribution of very site-specific factors such as soil properties, vegetation
type and water levels.
In order to enable effective water management in the wetland, the first step is a good understanding of
the water balance that should inform understanding of water resource availability and its variability over
time, as well as the processes influencing the variability of this water resource: influence of land use,
water infrastructures, climate change and climate variability on water flow, sediments and nutrients,
interactions of the groundwater that will control how wetlands will respond to environmental
perturbations. For example, once rainfall data for the whole year 2016 becomes publicly available at the
department of meteorology and hydrology for the stations of Kengkok, Savannakhet and Pakse, one
priority will be to verify if the declining rainfall trend identified in Figure 11 persists in that year.
Instead of relying on pre-existing data to conduct such assessment, given the overall data scarcity,
particularly in the Beung Kiat Ngong wetland, we suggest to first equip the site with a relevant set of
stations to measure river flow (upstream and downstream of the wetland), rainfall with rain-gauges set
up at different elevations, evapotranspiration, piezometers to measures variations in groundwater levels,
the use of tracers or electrical conductivity to determine the groundwater flow contribution to surface
flow. The department of Water Resources together with line agencies at the provincial (PoNRE) and
district (DoNRE) have a mandate that would align well and are an obvious candidate to undertake such
27
activities. As groundwater monitoring is not routinely carried out in southern Laos, the technical capacity
of staff in these agencies would need to be enhanced for successful implementation. Strategic
coordination with other projects aiming at rehabilitating agro-meteorological monitoring networks in Laos
could facilitate such implementation by including these wetlands in the priority sites for interventions.
An alternative solution to ground measurements relies in the interpretation of remote sensing data for
identifying spatio-temporal patterns of inundation and vegetation distribution. Time series of remote
sensing data, supported by field observations to validate land classifications, are increasingly seen as an
important and useful source of information for the management of wetlands. In addition, bathymetric
maps of wetland areas can help improve their management. Long waveband radar data can be used to
detect water beneath dense wetland vegetation and trees, as observed in the Xe Champone wetland. In
addition, C-band radar data derived from shorter wavelength can help identifying different wetland
vegetation types. These radar data should be used in combination with optical data (e.g. Landsat) to
produce more accurate results in terms of characterizing wetland vegetation and habitats, as well as
inundation dynamics. For instance, “water accounting +” provides a methodology for determining all
elements of water budget from space and was successfully applied in other basins
(http://wateraccounting.org/). This water accounting should be combined to water audits to account for
existing and planned water uses in the catchment to enable a better understanding of the potential
implications for the wetland in the policy, political and financial contexts (Batchelor et al., 2016). Other
complementary methods and techniques include drone technologies and Eddy covariance methods.
Despite the large data gaps, some preliminary results emerge from our analyses. The Beung Kiat Ngong
wetland is potentially dependent on long residence time groundwater (groundwater with slow lateral flux
below 10 meters/year) moving slowly from upstream areas to the north if the basaltic aquifer is
sufficiently permeable. There is insufficient understanding to establish, with a degree of confidence, which
of the two scenarios presented in Table 2 is the most likely but it is clear that in either cases, lateral
groundwater inflows are an important component of the wetland water balance. This suggests that
careful management of the groundwater resources in the catchment of the wetland is required to avoid
detrimental effects on the wetland integrity. Proposed land or water resources developments that can
lead to increased groundwater abstraction or affect the balance between recharge and discharge should
be carefully evaluated prior to implementation. This groundwater assessment should also be compared
with surface water flux in order to understand the relative importance of surface and groundwater
resource development and their effects on the wetland.
There is no surface water monitoring station and the groundwater monitoring ‘network’ used here was
comprised of existing household wells that were not designed or intended for scientific purposes. The
geological strata in which they intersect water is largely unknown, and their regular usage confounds the
ability to obtain reliable water levels unless due care is taken.
It was beyond the scope of this study to consider water quality aspects. Whilst the groundwater quality
around the Beung Kiat Ngong wetland is generally suited to domestic supplies, levels of arsenic are known
to be an issue in some cases (Meynell et al. 2014). Monitoring of groundwater supplies from boreholes
and dug wells in Khiat Ngong village shows arsenic concentrations in some wells are as high as 0.09
mg/L, nearly double the national standard for drinking water of 0.05 mg/L (Phommavong 2015). Any
continuation of groundwater monitoring should also include periodic assessments of water quality
28
linked with the implementation of risk mitigation measure if required (e.g. water filtering, selection
of alternative drinking water resources).
Field observation in the catchment of Xe Champone and within its wetland have shown issues of
salinity affecting crop yields, high sedimentation rates threatening the different parts of the wetland
by silting its various natural reservoirs. In order to identify the source of sediments and salinity, and
minimize erosion processes in these locations, water and sediment sampling along the course of the
river and across its alluvial plain are required. Causal links with land use and land management in the
wetland and the upper catchment need to be identified.
6.2 Management implications
The Beung Kiat Ngong and Xe Champone wetlands lie in an area exposed to shortfalls in rainfall and
periodic droughts that cause crop failure. A series of generic adaptation options have been proposed
within the agricultural sector to address such issues (DMCC 2013). Improvement in water efficiency and
potential for introducing new water management interventions (rainwater harvesting, small–scale
irrigation, etc.) are amongst those that are proposed. Most surface water bodies (e.g. small rivers,
wetland, ponds) in the area tend to partly dry up over the dry season whereas groundwater generally
offers a perennial source of supply. Assuming that groundwater uses develop in the coming years, in
response to greater water demand for agriculture, the potential impacts on the Beung Kiat Ngong and Xe
Champone wetlands, and associated trade-offs would need to be recognized and accounted for. The
socioeconomic benefits from expanding irrigation production for food security and income must be
weighed up against the other benefits derived from sustaining a healthy and bio diversity rich wetland for
food and nutritional security, maintaining fisheries, medically important plant species and supporting the
tourism sector. Groundwater utilization for domestic purposes represents a small component of the
replenishable resource. Whilst this most likely does not present a major threat to the wetland ecosystem,
major development for agriculture could impact on the domestic supplies.
In contrast to droughts, floods, particularly in the flood-prone wetland of Xe Champone, require different
techniques for mitigation and adaptation. An improved management of land uses across the whole
watershed of Xe Champone should aim to reduce surface runoff production and associated erosion. Any
land conversions, driven by market opportunities in most of the cases (e.g. replacement of secondary
forest by tree plantations), should be performed in a way that does not expose soils to greater erosion,
i.e. by ensuring that understoreys and hillslopes remained covered by protective vegetation layers. While
such techniques can significantly reduce overland flow and soil losses by promoting local rainfall
infiltration in the soil, their effectiveness is moderate in the case of extreme rainfall events. It is therefore
important to improve flood-preparedness of exposed populations and ensure that warning systems are
operating well. For that aim, one prerequisite is the need to ensure functional hydro-meteorological
monitoring devices with real time telemetry), operational forecasting systems involving the conversion of
hydro-meteorological data into forecasts and hazard maps using models, and operational chain of action
from forecast to persons responsible for action.
Even relatively small changes in either surface or groundwater flows (e.g. as a consequence of human
interventions or climate change) could significantly influence its hydrological functioning and hence the
wetland ecology. With this in mind, there is a need for greater recognition at all levels of policy, planning
and management of two key points:
29
i) any new major development of surface and groundwater (particularly to the north) may impact upon
the wetland, as well as domestic supplies. For example, the proposed construction of the dikes between
the two pools of the Beung Kiat Ngong wetland would result in greater water levels during the dry season
in the upper pool.
ii) effective management of surface and groundwater resources at the catchment scale will help to
maintain the health and functioning of the two wetlands that can, in turn, naturally regulate river flow,
thus providing an ecosystem service for climate change adaptation.
To control soil salinization in this context where salinity naturally originates from the geologic substratum,
surface salt contamination can be mitigated by applying irrigation to reverse upward capillary rise of saline
groundwater. However, this is subject to availability of irrigation water and environmental impact
assessments.
7 Acknowledgements
This report was prepared for the project on Climate Change Adaptation in Wetlands Areas (CAWA) led by
the Food and Agriculture Organization of the United Nation in Vientiane, Laos. We are grateful to Stephen
Rudgard, FAO Representative in Lao PDR, who supported this work, to Xavier Bouan, FAO Chief Technical
Advisor for the CAWA project who managed the overall project, ensured the coordination among the
project partners, and provided significant help in the field, together with Khonesavanh Louangraj, director
of Environmental Technology division of the Ministry of Natural Resources and environment (MONRE), to
organize meetings with national partners in the provinces and districts. We acknowledge Louise Whiting,
Senior Water Management Expert at FAO’s Regional Office for the Asia Pacific, and Xavier Bouan, for their
review and comments on a previous version of this report, which resulted in this improved version. We
thank Mr Noukane Inthapangna, deputy head of the department of Natural Resources and Environment
(DONRE) in Savannakhet, Mr Bouala, deputy head of the department of Hydrology and Meteorology
(DMH) in Savannakhet, Miss Keoudone, deputy head of the district office of MONRE in Champone, Mr
Sengsoulivanh Inthachak, head of the water resources department in Pakse, Mr Somboun Oudomsine,
deputy head of irrigation sector in Pakse, and Mr Viengsai Manivong, head of planning and cooperation
division of DMH in Vientiane, for the informative discussions on the wetlands, and for the provision of
hydro-meteorological data. We are grateful to Mr Oudomxay Thongsavath, IUCN field coordinator in
Savannakhet Province, for his guidance in the field and for his translation support.
30
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