Climate Change Adaptation in Wetlands Areas

33 Pages·2017·2.57 MB·English

by  Guillaume Lacombe

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

© FAO
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
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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 13C in January and a maximum high of around 39C 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).
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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).
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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.
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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
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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.
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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).

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