Connectivity and Fragmentation; Hydrospatial analysis of dam development in the Mekong river basin

Connectivity and fragmentation Hydrospatial analysis of dam development in the Mekong river basin

Nikolai Sindorf, Bart Wickel September 2011 World Wildlife Fund Conservation Science Program Washington DC

World Wildlife Fund Conservation Science Program Technical report FW2011.1 August 2011

Connectivity and fragmentation Hydrospatial analysis of dam development in the Mekong river basin

Nikolai Sindorf, MSc Bart (A.J.) Wickel, PhD

This report was supported by the generous support of Diversey Inc The ecosystem classification was supported by WWF-GMPO through funding of The Coca Cola Company

Sindorf, N., and Wickel, A.J. (2011). Connectivity and fragmentation: Hydrospatial analysis of dam development in the Mekong river basin. Technical report CSPFW2011.1, August 2011, World Wildlife Fund, Washington DC. 27pp.

1 INTRODUCTION A period of relative regional political stability, rapid economic development and positive investment climate has led to a rapid increase in energy demand in the Mekong region. Along with the Amazon and the Himalayas, the Mekong region can be considered to be one of the hotbeds of hydropower development in the world. Given that hydropower is a largely untapped resource in the region (WWF, 2007), dam building has seen an unprecedented rate of development over the past decade (Hirsch, 2010).

The high pace of dam development has resulted in a situation in which projects are being inadequately planned and dams are being built without adequate accounting for their full impacts on freshwater ecosystems, the river system, and the people that rely on them. For example, poorly planned dams can have devastating impacts on freshwater fisheries, alter delivery of sediments for riparian agriculture, inundate vast amounts of productive land etc. If an environmental impact assessment is performed (see e.g. Baran et al, 2011 or Molle et al, 2009b), it is typically conducted solely at the level of the project site and its direct surroundings, and does not include the broader impacts on connectivity at the sub-basin to basin level.

Our technical study, aims to quantify, evaluate and communicate the potential impacts of cumulative dam development at the basin and sub-basin level. Through two novel analyses it aims to inform decision makers, dam planners and developers on basin-wide connectivity impacts of dam development and improve the understanding of the potential consequences to freshwater ecosystems and their services.

1.1 REGIONAL CONTEXT AND HYDROPOWER DEVELOPMENT The Mekong river basin comprises six countries (China, Burma, Thailand, Vietnam, Laos and Cambodia.

Laos and Cambodia are developing countries, respectively ranking 125th and 127th out of 172 countries on the global list of Human Development Index 2010 (UNDP, 2010)1. According to the World Food Program, every second child under five years of age in rural Laos is chronically malnourished2 while 40 percent of Cambodian children are chronically malnourished3. As a result, both countries are eager to explore development alternatives and regard the development and exportation of hydropower based energy to neighboring emerging economies as a potentially quick and sustainable way to achieve higher standards of living, or, as voiced by a statement of the Lao government on the recently inaugurated Nam Theun 2 hydropower project: “..(the project is) an essential part of the country’s development framework that is likely to provide the first real possibility for Laos to gradually reduce its dependence on Official Development Assistance.” (LaoVoices.com, 2011) In order to capitalize on these development opportunities, a controversial, almost 60 year-old plan has been revived to develop a cascade of 12 dams and associated reservoirs on the lower main stem of the Mekong River (Molle et al, 2009). The market for the energy generated by these projects would be Vietnam and Thailand. This plan is controversial in the sense that it would block and inundate large parts of the lower main stem; a system that sustains the largest known fish migration, both in terms of biodiversity and biomass, as well as the largest inland fishery in the world (Baran et al, 2003). A recent study in the Mekong (Ziv et al, 2012), concluded that:“…hydropower generation, fish production and species conservation have strong and nonlinear trade-offs”, 1

The list is compiled based on country data on life expectancy at birth, mean years of schooling, expected years of schooling, and gross national income per capita and provides a relative insight of a country’s level of development.

Only countries that have reliable information on these indicators are included on this list.

2 www.wfp.org/countries/laos (last accessed September 2011) 3 www.wfp.org/countries/cambodia (last accessed September 2011)

meaning that some projects have a much greater potential to damage fisheries than others, and that many of the dams that are currently planned require no consultation with other Mekong nations, while the impacts could extend well beyond national boundaries.

For example, impacts of the dam on Pak Mun have been widely discussed and evaluated; the construction of the dam blocked connectivity of Thailand’s largest tributary to the rest of the Mekong, and caused considerable collapse of the upstream fishery and significantly reduced upstream freshwater biodiversity (Roberts, 2001 and Foran, 2009): “The problem of Pak Mun Dam and fisheries might be summarized as follows: an artificial and hostile downstream environment (reservoir outflow) and an artificial and hostile upstream environment (reservoir) are connected by artificial and hostile corridors (fish ladder and dam spill-ways). The resulting impact accumulation has devastating over-all effects of fish habitats and fish species. Pak Mun Dam together with its 35-km long reservoir and 4.5 km reservoir outflow is a major biogeographic barrier to all kinds of fish movements between the Mekong and the Mun.” (Roberts, 2001)

1.2 DAM IMPACT ANALYSIS The discussion around dam development brings up a myriad of concerns about energy and socio-economic development, inclusiveness and the environment, and a wide variety of stakeholders seem to have taken strong stances based on such concerns, resulting in a highly polarized debate for and against dam construction (world Commission on Dams, 2000). In order to side-step this polarization, the main step, to be acknowledged by all sides of the divide, is that a river can be classified into ecosystems that are representative of the functions of the river system under consideration. In undertaking this study, we therefore made the following assumptions and simplifications:   

as ecosystems form the foundation of analysis; each unique ecosystem is considered to be of equal importance to over-all river basin functionality. a river system without any dam development maintains full integrity of ecosystem connectivity; natural cascades and rapids are integral part of ecosystems. any dam, regardless of its design or operation, compromises intactness;

These assumptions are made to maintain transparency and prevent any bias in any valuation of planned dams. In reality, there are numerous opportunities to mitigate or maintain ecosystem functionality in dam design. For example, a run-of-the-river dam does leave a different footprint than a dam with a large reservoir. Dams operated with an environmental flow allocation provide a different functionality than hydropower dams that practice ramping of peak flows for maximizing electricity generation. These kinds of considerations are beyond the scope of this study, but definitely need to be evaluated in later stages. In the future, once more insights are gained on the individual ecosystems and their association with specific processes, basin layout and connectivity, impacts can be better geographically quantified.

1.3 HYDROSPATIAL PERSPECTIVE This study lays out a basic framework for analysis of river system fragmentation and ecosystem connectivity, applied to dam development. The study provides new insights into system classifications and explores innovative visualizations of basin information. The study should be considered as an initial insight into what can be done with simple, but powerful analyses, but is part of a larger body of ongoing development.

The quantification and visualization methods used in this study are relatively new approaches to river system network analysis, which primarily became possible through to the recent development of the WWF HydroSHEDS data and tools (Lehner et al, 2008). The almost global coverage by these data means that this kind of hydrospatial analysis can be replicated virtually anywhere in the world at an unprecedented level of consistency and scale.

Although the emphasis of this analysis is on quantification and visualization of upstream-downstream relations and identifying multiple scale linkages between individual tributaries and the entire basin, some of the methods that were employed will allow a user to put virtually any geographic information in a “hydro-spatial� network context.

The novelty of this perspective is that one can evaluate what role a particular tributary plays in respect to the entire river system, and the sub-basin to which it belongs.

The primary objective of this study is a hydro-spatial evaluation of the cumulative impact of existing and future dams on the connectivity between aquatic ecosystems, and to weigh the impact of individual projects in this context. The hydro-spatial analysis concerns three interrelated principles: Topology; defines basic geographic arrangement and layout of the river network.

Subsidiarity; defines the spatial extent of influence of a point based development or a cluster of points (e.g. dam) on the river network and its flow regime.

Connectivity; examines system connections based on ancillary data (e.g. ecosystems, population etc.)

In this study we explore the subsidiarity and connectivity principles by analyzing the size of fragmented systems and free-flowing tributaries, due to dam development and by quantifying the number of connection ecosystems that remain after dam development. It is important to realize that in the current connectivity analysis we only evaluate longitudinal (upstream-downstream) connectivity (REF). The impacts of dam development and their associated reservoirs on lateral connectivity (river to floodplain) due to flow regime alteration and inundation as well as vertical connectivity (infiltration-exfiltration) to groundwater are not included at this point.

2 FRAGMENTATION AND FREE-FLOWING RIVERS The fragmentation assessment is founded on the concept of free-flowing rivers, which so far has primarily been applied in global assessments of large river basins (WWF, 2006). The WWF free-flowing rivers assessment (2006) for example was based on a global analysis of the interruption of the world’s longest rivers (177 rivers with their main stem longer than 1,000 km) and concluded that a mere 35% reaches its outlet into the ocean or inland sea without encountering a dam, weir or barrage on its main stem. This rather grim statistic however masks the fact that there may still be a large conservation potential for many basins especially where relatively few dams have been developed on the main stem or in major tributaries.

When applied to a large river basin like the Mekong for example, the free-flowing assessment will lead to the conclusion that due to the dams on upstream sections of its main stem, it can no longer be considered freeflowing, while a significant part of the river system is currently unimpeded by dams. By acknowledging the remaining free flowing characteristics, important conservation opportunities could be identified.

For the current fragmentation analysis we are proposing a classification scheme that defines where one could expect full free-flowing functionality (e.g. systems without any influence of dams) to remain within a basin, but also sub-basins upstream of main stem dams where regional free flowing functionality remains.

2.1 CLASSIFICATION OF FRAGMENTATION The framework for quantifying free-flowing rivers in this study is focused on fragmentation, and excludes more data intensive evaluation of alterations in the flow regime since this would require much greater knowledge of hydro-climatologic variability and more sophisticated hydrologic models. The method is intended to provide a first insight into the fragmentation status and conservation potential in relation to dam development of river systems in data-sparse settings.

Classification thresholds for free flowing characteristics proposed by Nilsson et al (2005) and Nel et al (2009) were discussed with regional experts and refined for the Mekong river system. For other river systems these thresholds may be different, and will depend on the topology, and other biological considerations that are best captured by consultation with regional experts in the field of hydrology and aquatic ecology.

The four thresholds were defined as: 1.

2.

3.

4.

< 2% of upstream area behind dams â&#x20AC;&#x201C; no significant dam upstream. If the upstream area remains below this threshold, the downstream influence of the dam is thought to be negligible at the basin level.

No dam downstream. Unimpeded rivers that still are in open connection to the main stem outlet. > 100 kilometers of (intact) river length. Sustains free flowing characteristics of regional importance Connected to main stem.

Application of these thresholds in the Mekong basin resulted in two classes of free flowing river types and four levels of fragmentation (Table 1 and Figure 1). Detailed methods on how these criteria were applied can be found in appendix 3.

free-flowing 1: no significant dams upstream and open connectivity to delta/sea free-flowing 2: river system upstream of a dam that supports a river of 100 kilometers length AND without significant dams upstream, AND connected to the main stem compromised 1: river system with a significant dam upstream compromised 1-b: river system with a significant dam in the upstream AND upstream of a dam compromised 2: river system upstream of a dam NOT supporting a river of 100 kilometers length without significant dams upstream compromised 2-b: river system upstream of a dam that supports a river of 100 kilometers length without significant dams upstream TABLE 1

DECISION MATRIX FOR THE FREE-FLOWING RIVER TYPE CLASSIFICATION

Degree of fragmentation Free-flowing type 1 Free-flowing type 2 Compromised type 1 Compromised type 1b Compromised type 2 Compromised type 2b

Code FF-1 FF-2 C-1 C-1b C-2 C-2b

Color (maps)

Conditions fulfilled A B Y Y Y N N Y N N Y N Y N

C Y Y N Y

FF-1 in blue

FF-2 in purple, main stem in black

C-1 in yellow

C-1b in brown

C-2 in red

C-2b in orange

D Y Y N N

FIGURE 1 CLASSIFICATION OF FRAGMENTED AND FREE-FLOWING RIVERS IN A GENERIC EXAMPLE WHERE DAMS ARE REPRESENTED AS YELLOW DOTS

2.2 RESULTS OF FRAGMENTATION ANALYSIS Under current conditions, the Mekong main stem can hardly be considered to be free-flowing (Figure A). At any reach along its length, it has more than two percent of its upstream area behind dams. However, about forty percent of the Mekong Basin can still be considered to be uncompromised and free-flowing, which indicates that the Mekong might be supporting a considerable amount of free-flowing functionality.

The main Mekong tributaries in Thailand (Chi and Mun) can no longer be considered free-flowing into the Mekong; this is mainly due to that dam at Pak Mun, which was already shortly discussed in the introduction. Also Vietnam and China have dammed most of their Mekong drainages with several cascades of dams on the tributaries (Vietnam) and the main stem (China) (Figure 2A).

The addition of a dam at the Mekong main stem in Xayabouly, Laos, would deprive another 20% of the entire Mekong of uncompromised free-flowing functionality (FF Type 1; Figure 2B). Some tributaries upstream of the dam however, would still experience a degree of free-flowing functionality, because these systems are large enough for maintaining regional connectivity and remain connectivity to the main stem (FF Type 2).

China

Xayabouly

Pak Mun

Vietnam

A

B

FIGURE 2 A) CLASSIFICATION OF MEKONGâ&#x20AC;&#x2122;S FREE-FLOWING SYSTEMS WITH 50 LARGE DAMS, AND B) THE INFLUENCE OF A PLANNED DAM AT XAYABOULY

Though the maps offer a clear insight into the geography of fragmentation, a more visually detailed systemoriented representation of the fragmentation classes is given in the following river system dashboard, overleaf. By

translating the levels of free-flowing classes into such a decision making dashboard, the impacts of single dams like the Xayabouly can be visualized and compared to other proposed dams (Figure ).

In this case, fragmentation was evaluated across three size classes of streams. This analysis links the hydrospatial principle of subsidiarity (section 1.2) with connectivity and shows that the distribution of fragmentation has different impacts when considered at different scales.

For this analysis on the Mekong, the following levels are identified: entire network; associates to those processes experienced at field level, that have relevant impacts on the river system; e.g. land cover change, erosion and sedimentation, it includes all drainage systems of the basin from upland till main stem , perennial rivers; associates processes that take place inside all rivers and streams, e.g. fish movement, channelization, water levels, large rivers; associates to processes that influence regional level water issues; e.g. flood control, water storage and diversions A dam like the Xayabouly on the Mekong main stem fragments the largest river types most; a comparatively larger part of free-flowing rivers changes to the ‘worst’ classification and gets ‘locked’ in between an upstream dam and Xayabouly. This is not really surprising as it is inherent to any dam on the main stem, though it does add the perspective of subsidiarity.

Additionally, with the dam at Xayabouly, only about 20% of the entire Mekong would remain free-flowing in comparison to pre-project development; with larger rivers relatively worse-off. The classification of free-flowing rivers, both in fragmentation status and in scale, illustrated that dam development shows a certain path of incremental degradation; as opposed to a live-or-let-die approach to river systems under dam development. Such an incremental approach indicates that river basin conservation still makes some sense in river systems under active dam development and operation; though the approach also challenges to which extent a river has to remain free-flowing in order to sustain basin-wide conservation priorities. Therefore, the definitions on which the fragmentation status was based, are (and should always be) under discussion and would have to be adjusted to be applied on different river systems.

The impacts of dam development can be best understood when different scales of river system fragmentation are considered. In this case, the dashboard offers only three scales of analysis, though tools are being explored that would allow seamless scaling between different levels. That would open up more advanced hydrospatial subsidiarity analysis and help to better determine tipping points in all kinds of hydrological analysis.

FIGURE 3 RIVER SYSTEM DASHBOARD ON FRAGMENTATION

3 AQUATIC ECOSYSTEM CONNECTIVITY The fragmentation and free-flowing river analysis provided some insights in how fragmented the Mekong River has become under dam development. The impacts were expressed in the distribution of classes based on system size and relative dam positions. In this section we are introducing an approach to quantify how much ecosystem connectivity still remains in a river basin under active dam development.

For the purpose of conservation planning, aquatic ecosystems are often defined as stream networks that share distinct geomorphology and similar environmental characteristics and processes (e.g. hydrologic, nutrient and temperature regimes; Groves et al., 2002, Higgins et al, 2005; Sowa et al, 2007; Thieme et al, 2007; Heiner et al, 2011). Aquatic ecosystem classifications are a valuable tool for identifying and analyzing large scale aquatic ecosystem characteristics. In most basins around the world freshwater species are systematically under sampled (Millenium Ecosystem Assessment, 2005) which poses as a limitation to any systematic or consistent analysis on freshwater biodiversity. Aquatic ecosystem classification can hence be used as a â&#x20AC;&#x153;coarse-filterâ&#x20AC;? that captures patterns of physical freshwater habitat and ecological processes.

In this analysis we specifically approach the ecosystem classification as an important input to evaluate the layout of bundled ecosystem processes they represent. Following that approach an ecosystem becomes less static (than a proxy of habitat) and depends more on the types and bundles of ecosystem processes that it needs to represent.

In this assessment we tried to capture processes that are of importance to triggering medium- to long-distance fish migration, which includes considerations of flow pulse, seasonality, intermittency, proxies of water temperature, etcetera. This is the main reason why WWFâ&#x20AC;&#x2122;s 2005 habitat classification was used as the starting point, with new insights added, mainly of relevance to connectivity. In future, any new classification will probably lead to a better perspective and alternative insights.

3.1 AQUATIC ECOSYSTEM CLASSIFICATION The aquatic ecosystem classification used in this study is based on a combination of GIS-data and expert input. The premise of this approach is that by conserving representative ecosystems and the eco-hydrological processes that maintain freshwater habitats, common species and communities and the environments in which species evolve are conserved (Jenkins et al 1976, Hunter 1988). The approach is not intended to capture species-level nuances, but aims to capture the specifically relevant characteristics that shape the integrity of river system as a whole (see figure 4).

FIGURE 4 FACTORS THAT SHAPE AQUATIC ECOSYSTEMS INTEGRITY (AFTER KARR ET AL, 1986)

The aquatic ecosystem classification of the Mekong in this study (preceded by an earlier habitat classification of the Mekong by Lehner et al. (2005) is used to inform and construct scientific arguments for the conservation of hydrological connectivity and river system integrity, and to identify particular sections within the system where dam development is thought to be most harmful to processes that sustain the ecosystem.

The dominant factors that shape freshwater systems and their diversity in the Mekong basin were identified by regional multi-disciplinary experts4 through interactive consultation, are: terrain elevation, as a proxy for the temperature regime of the stream, and primarily the occurrence of frost conditions or tidal influences slope, as a proxy for white water/flow rate conditions and the potential presence of cascades and natural breaks in connectivity limestone geology, as a proxy for the presence or absence of karst phenomena which often result in greater probability of endemism (Williams, 2008) river length, as a proxy of discharge and system size.

Elevation, slope, and river length were defined using HydroSHEDS dataset at a scale of 15s. The presence or absence of limestone geology or karst was defined using the World Map of Carbonate Rock Outcrops, version 3.0 (Williams & Ford, 2006). Reference temperatures were derived from the 30 arc second climate surfaces of Hijmans et al (2005) and cross validated with elevation.

The classification thresholds for each variable are summarized in Table 1 and thresholds are discussed in the following section.

TABLE 2 ECOSYSTEM CLASSIFICATION VARIABLES

4

Personal communication: Professor Ian Baird (University of Wisconsin-Madison), Professor Yu Xuezhong (China Institute of Water Resources and Hydropower Research), Dr. Dokrak Marod (Kasetsart University, Bangkok)

Variable

Associated with:

elevation

temperature, climate, geography, plateau, upstream / downstream relations, ice / snow, delta / tidal influences Classes: 0-100m; 100-3000m; >3000m

slope

elevation drop in rivers, stream gradient, erosion / sediment rates, temperature, cascades / rapids, local runoff, vegetation Classes: 0-10%; >10%

karst geology

chemistry, caves, endemism Classes: Karst formation present/absent

river length

scale, seasonality, discharge, floodplains / wetlands, riverlandscape interaction Classes: < 250km; 250-1000km; >1000km

Careful consideration of geographical hierarchies and combination of the master variables summarized in Table 2 (elevation, slope, river length and karst) led to a classification with 13 distinct ecosystem types (Figure 5). For example, cross correlation of the classification layers revealed a strong correlation between elevation and temperature (figure 5a) , as might be expected, while elevation and slope revealed some level of positive correlation at lower altitude (up to 1750m) while correlation at higher altitudes seems to be non-linear (Figure b).

It is important to reiterate that this classification is a mere interpretation of what are thought to be variables based on expert opinion. It should also be noted that the final classification is never all encompassing and that the master variables of importance are basin specific. The full classification process is described in annex 1.

Subbasin classifications

A: Mean annual temperature shows a rather straight linear correlation with elevation

B: Elevation shows clear non-linear correlation with landscape slopes

FIGURE 5 CORRELATIONS BETWEEN DIFFERENT CLASSIFICATION ATTRIBUTES FOR THE MEKONG SUBBASINS

The 3,000 m threshold was chosen since it coincides with the frontier of what is considered to be an important indication of snow/rainfall interaction; the seasonal temperature threshold of mean monthly temperature (WorldClim) at least three months below 2oC (Le Quesne et al, 2011). The local influence of karst formations was upscaled by applying a 10% threshold of karst coverage at 500 km2 sub-basin resolution; any sub-basin with more than 10% of karst coverage was flagged as karst. The distinction between the lower plateau (Cambodian Eastern Plains - Srepok, Sesan, Sekong-, Tonle Sap) and the Khorat plateau (Chi, Mun and Southern Laos counterparts) is important since it is thought to capture some of the ecosystem functions that support long distance fish migration (MRC, 2002). Though that distinction is made by a simple elevation threshold at 100 MSL, this might be significant at a global scale, since the freshwater ecoregions of the world (Abell et al, 2008) show that same distinction between the two plateaus. The threshold of 10% slope-proxy was informed by the geographical distribution of that threshold (figure 6) so that it effectively captured relevant mountain ranges, plateaus (e.g. Bolaven in South Laos) and the upland slopes.

A Elevation classes with 100 amsl and 3,000 amsl thresholds

B Slope-proxy classes 10 % slope threshold

E

C River length classes 250 km and1,000 km treshold

D Location formations

of

karst

F

FIGURE 6 KEY ATTRIBUTES OF THE MEKONG CLASSIFICATION (A-D), THE FINAL AQUATIC ECOSYSTEM CLASSIFICATION MAP WITH 13 FRESHWATER ECOSYSTEMS (E) AND THE RIVER ECOSYSTEM CONNECTIVITY TREE (F)

Our characterization of aquatic ecosystem types and their connectivity with one another allow for the following insights: 

 

the upstream is characterized by relative short tributaries that join a long mainstem and that are under the strong influence of seasonal snow and glacial processes of the Tibetan plateau, (from the top of the connectivity tree down to Nam Loi) the middle parts of the basin are characterized by karst influences and more complex tributaries, fed by the uplands slopes (from Nam Loi down to Nam Loei); and the lower tributaries are larger and more complex, drain the several different plateaus (Mun, Chi, Srepok, Sesan, Sekong, and Tonle Sap), and have their headwaters in surrounding mountain ranges (Figures 6E and 6F).

The connectivity tree (figure 6F) is a powerful visualization that stretches each tributary into a collection of straight lines. To many people this provides improved insight on how tributary systems are comprised of different sequences of ecosystems, and how this shapes a tributary with regard to other tributaries, and their inter-linkages.

The next session will go into more detail about this kind of visualization of connectivity.

3.2 ECOSYSTEM CONNECTIVITY METRIC We defined ecosystem connectivity to be a function of the number of ecosystems that remain connected upstream or downstream of a dam combined with the length of river network upstream or downstream of a dam.

Using the assumptions outlined above, we completed a rapid analysis of how future constellations of dams influence a river ecosystem layout. The data inputs were a) an accurate database on current and planned dam locations, and b) a basin-wide freshwater ecosystem classification. In practice, it does not matter how many different ecosystems are identified for a river system; the approach evaluates ecosystem layouts, increasing or decreasing the number of ecosystems does not automatically increase the sensitivity of connectivity to dam development.

Our first step is to come up with a basic network formula that calculates the number of possible connections between a given number of ecosystems. For a system with 13 ecosystems; the number of unique connections among the ecosystems amounts to 78; or:

With n being the number of ecosystems.

A river basin with 13 ecosystems, and with full integrity, would capture 100% connectivity. A river like the Mekong already shows a degree of lost connectivity; see figures 8 and 9. Now the assumption that every single ecosystem provides equal functional connectivity to the any of the other ecosystems, allows us to lump those parts of the Mekongâ&#x20AC;&#x2122;s river network that offer connectivity by the amount of ecosystems, and attribute this by network length.

A

B

FIGURE 9 A) 13 FRESHWATER ECOSYSTEMS AND THE LOCATION OF THE 50 EXISTING DAMS IN THE MEKONG BASIN B) NUMBER OF REMAINING CONNECTED FRESHWATER ECOSYSTEMS

A: Current status

B: With Xayabouly dam

FIGURE 10 A) DISTRIBUTION OF ECOSYSTEM CONNECTIVITY, EXPRESSED IN NUMBER OF CONNECTED ECOSYSTEMS RELATIVE TO THE TOTAL LENGTH OF THE STREAM NETWORK AND B) THE IMPACT OF THE PLANNED ON MAIN STEM XAYABOULY DAM . IN AN INTACT SYSTEM, 100 % OF RIVER LENGTH (HORIZONTAL AXIS) WOULD BE CONNECTED TO 13 TYPES OF ECOSYSTEMS (VERTICAL AXIS).

The functional connectivity of a river system can therefore be quantified by summing the total number of connected ecosystems upstream of each dam and incorporating the total length of the flow network upstream of each dam relative to the total number of ecosystems and total network length:

This ratio quantifies how much of a river ecosystem layout is still connected and functional instead of providing a mere index of negative impacts. One caveat, that needs to be explored further however, is that in this quantification all dams and all ecosystems are treated equally in their functionality and impacts on connectivity.

This is exactly where the further development of the connectivity analysis is focused on; how to qualify and quantify the importance of different ecosystems and their associated processes.

3.3 RESULTS OF ECOSYSTEM CONNECTIVITY ANALYSIS There are 50 large dams that are located throughout the Mekong Basin (9A) Connectivity of ecosystem types is highest lower in the basin, both due to a higher level of ecosystem diversity in the lower Mekong, the more complex layout of its tributaries there, and the location of dams in the basin (9B) Yet, no part of the Mekong connects all thirteen ecosystems (Figure 10A).

Interestingly, a substantial part (60%; figure 10A) of the system still maintains connectivity between eleven out of thirteen ecosystems; with the two cold highland systems in China being locked behind the dam cascade in the Chinese upper main stem; while six ecosystems remain connected upstream of that cascade. It is possible that this loss of connectivity has certain impact on downstream seasonal water temperature and flow regimes. However, if Xayabouly Dam were built more downstream, only 40% of the system would maintain connectivity among eleven ecosystems (Figure 10B).

Applying the formula; about 45.9% of the Mekongâ&#x20AC;&#x2122;s functional ecosystem connectivity is conserved, while the single addition of the Xayabouly dam reduces this, by 4.9%, to 41.0%. In order to illustrate how this network function works, we calculated what would happen if connectivity to the sea is also considered (which is a very viable consideration). The current connectivity between ecosystems would amount to 46.8%, whereas adding the Xayabouly dam would reduce connectivity to 40.2%. This specifically illustrates that the connectivity formula is a network-layout function, and by no means a linear function.

4 DISCUSSION 4.1 DAM DEVELOPMENT IN THE MEKONG The freshwater ecosystem classification and its connectivity and fragmentation analysis provide unprecedented insights into the layout of the Mekong river system, and its potential interaction with incremental dam development.

We found that the Xayabouly dam on the Mekong main stem would result in a large loss of free-flowing functionality and ecosystem connectivity throughout the basin. The additional eleven planned dams on the lower Mekong main stem (and many more on the tributaries) could benefit from a similar assessment of impacts on freeflowing functionality and ecosystem connectivity. Our analysis provides a cursory evaluation of impacts. We recommend that an in depth evaluation of the cumulative impacts on ecosystems, services, biodiversity, ecosystem connectivity and fragmentation for all planned dams in the basin. The strength of our approach is that it provides a system-wide view of impacts beyond an environmental impact statement of a single dam, such that multiple configurations can be considered simultaneously and thus, use this for planning to minimize loss of connectivity.

The analyses performed as part of this study build the foundation for decision making on which parts of the main stem and which tributaries would be better left without dams. The emphasis here is on â&#x20AC;&#x2DC;betterâ&#x20AC;&#x2122;, since current development paths (in the Mekong and elsewhere) tend to prioritize hydroelectric development as a central strategy for regional development; often disregarding opportunities for alternative development and conservation, or failing to properly incorporate multi-purpose design standards (such as effective flood management or environmental flow requirements)(Molle et al, 2009b).

The approach being discussed here is still under active development, but already provides essential insights on what connectivity would remain after the dams are in place on the Mekong river system. No analysis of the exact function of each system has been made however, which could mean that e.g. systems of a particular importance to fish migration (e.g. spawning sites) could be cut off (or remain connected). An assessment of critical linkages for migratory fish species would require more detailed information on fish biology, but should be explored in future studies.

Any future next steps in the development of the methodology have to focus more on the processes associated with the freshwater ecosystems. This can be achieved by highlighting the connectivity from the perspective of an individual -or bundled- freshwater ecosystems process, which does not necessarily require the holistic basin perspective (as was followed in this study). Another recommendation would be to challenge the current finding by applying different kinds of ecosystem classifications; e.g. how does the perspective and outcomes of the analysis change if a different set of relevant ecosystems is applied? How would the classification change if it were to be based on climate change vulnerability of food security, compared to vulnerability of freshwater biodiversity?

Gaining these insights will help to establish a better understanding of how ecosystem processes in a river basin are influenced by incremental dam development, which can again be tested by reconstructing the chronology of dam development inside the basin.

In the current methodology, each ecosystem and each dam design was considered to be of equal relevance throughout the entire basin. In the future, once more insights are gained on the individual ecosystems and their association with specific processes, basin layout and connectivity, impacts can be better geographically quantified.

These next steps are of special importance to conservation of freshwater biodiversity and ecosystems as they would provide essential information on expected impacts, opportunities, and river system tipping points; past and future.

4.2 IMPACT OF THE XAYABOULY DAM By evaluating the planned Xayabouly dam project in the DPR of Laos, this study showed that the dam at Xayabouly will have significant impacts on the Mekong as a whole. The proposed dam would ‘degrade’ the fragmentation status of over twenty percent of the entire Mekong, with a relative worse impact on larger river types, while the dam would reduce at least 5% of the Mekong’s total ecosystem connectivity. An earlier application of the analysis (Sindorf et al, 2011) calculated that Xayabouly dam would result in disproportionately greater amount of damage to the Mekong’s ecosystem connectivity in comparison to tributary dams of the same generating capacity (e.g. the Nam Theun 2 in Laos and the Sesan cascade in Vietnam).

In a review of the dam’s feasibility and its Environmental Impact Assessment, Baran et al (2011) argue: “The coverage by the Xayaburi EIA of the study area and of operation rules is insufficient, as well as the assessment of the project impacts on hydrology, on water quality, on fish habitats on fish migrations, on fish species life stages and on fish abundance is actually not done in this EIA.” The assessment of dam impacts on connectivity and fragmentation, while lacking detailed insights the missing components of the EIA as outlined above, does show that the impact of Xayabouly dam on the Mekong’s entire river (eco)system is quantifiable. Even with the lack of more detailed information, large projects like these can be evaluated on a much broader basin-wide scale than just local level impacts. The analysis presented in this report provides an initial setup on how to integrate ecosystem connectivity and fragmentation in dam planning exercises.

5 CONCLUSIONS This report sets a precedent in providing a science-based system-wide environmental assessment of dam development impacts beyond individual dam assessments. This approach and associated methodology is under development and this report provides the first pilot assessment. The types of analysis introduced here are replicable in any river system, worldwide, and the results provide environmental insights to all sectors involved in water resource management (ranging from hydropower to conservation). Whereas the initial analysis on the Mekong took weeks to complete; the workflows outlined in this report will enable the replication of similar analyses on other river basins in a matter of days. Currently, the workflow is still being improved and new steps are being explored which could improve time of completion to hours.

Once the analysis can be run that efficient, it would allow to â&#x20AC;&#x2DC;openâ&#x20AC;&#x2122; up and challenge some of the rather rigid assumptions on dams, fragmentation, and ecosystem connectivity that formed the basic assumptions of this report. Then, focus can be aimed at specific processes (such as fish migration, climate change), dam design and operation (such as flood protection, environmental flows, or hydropower potential) and quantifying issues of scale (as in river conservation, ecosystem services).

The analysis should never be considered as stand-alone or on its own; as it does not cover socio-economic impacts, nor fully represent the spectrum of environmental impacts. It does however present a new framework to effectively integrate ecosystem connectivity and free-flowing functionality into dam planning, and adds a basinwide perspective to conventional environmental impact assessments.

6 ACKNOWLEDGMENTS We would like to acknowledge the essential insights and valuable contributions that were provided to this work by Trang Dangthuy of WWF-GMPO, Michele Thieme and Sarah Freeman of WWF-US.

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