Future Impacts on Sediment Flow

Significant: A complete cascade will cause massive decreases in the sediment flow out of China into the LM, with a generally decline down to 5% of natural sediment outflow from the UM to the LM. This in turn will have significant impacts downstream, as the sediment load for the middle and lower reaches of the Mekong will greatly reduced. As Walling (2009) described above, the impacts on sediment flow out of China will decrease with each successive closure of dams. With the Nuozhadu under construction and the Xiaowan recently completed, sediment loads will likely begin to decline noticeably within the next ten years.

Insignificant: As seen in Chen and He 2000; Xinhua 2002b, 2002c; Fu et al 2006; and He et al 2009, it is claimed that China not the main contributor to the Lower Mekong’s sediment load, with the primary source coming from northern Laos. As such, a completed dam cascade will have limited negative impacts on sediment flow and the environment, and may, in fact, be beneficial to navigation and flood water expulsion.

  69   6. Ecological Impacts

The primary concerns for hydropower impacts on the Mekong ecosystem typically revolve around the fish and fish habitats. The Mekong is home to one of the world’s largest inland fisheries, and is the third richest in biodiversity of riverine fish species (Bunn and Arthington 2002). In addition, roughly 60 million people in the LM rely upon the river, its fish, and ecosystem services for their livelihood. Therefore, any detrimental changes would cause significant impacts in the region. Within the scientific literature, there seems little dispute that hydropower development typically only results in negative impacts on biodiversity and ecosystem health. As such the following will

describe more the existing and predicted consequences of development, rather than describe disputes within the literature.

6.1 Data and Method Differences and Problems

Like hydrological and sediment flow impacts, ecological impacts are difficult to tease out from other “interrelated causal mechanisms operating over different temporal and spatial scales, and no one characteristic of the flow is responsible” (Bunn and Arthington 2002). Therefore, determining which attributes of the altered flow regimes and the cause for them are difficult to determine. For example, “is the decline of a fish species due to reduced capacity to migrate under altered peak flows or because of a change in substrate composition of spawning areas or both?” (Bunn and Arthington 2002). That said, there is growing recognition of the importance of flow regimes to ecological processes, e.g., to trigger fish migration and spawing, floodplain rejuvenation, etc. Yet governments and managers typically require specific estimates of the impacts of reduced flow reduction (e.g. what impacts would a reduction of from 10% of natural flow volume to 20% have?). “Our limited ability to predict and quantify the biotic response to flow regulation is a major constraint to achieving ecological sustainability” (Bunn and Arthington 2002). Another difficulty is definitively separating impacts to the ecosystem from changes in the flow regime and land-use changes (e.g. agriculture, aforrestation, etc.) (Bunn and Arthington 2002).

  70   6.2 Primary Ecological Impacts

Bun and Arthington (2002) described four primary principles of the ecological consequences of altered flow regimes on river systems. These principles are confirmed in one way or another throughout much of the literature on the subject in both Chinese and English language sources, and in an interview with a researcher at the AIRC.

Aquatic biodiversity and natural flow regimes

Figure 5: The natural flow regime influences over aquatic biodiversity through four mechanisms laid out by Bunn & Arthington (2002). Principle 1: Relationship between biodiversity and

physical nature of the aquatic habitat primarily driven by large events that influence channel form and shape. Principle 2: Features of the flow regime (seasonality and predictability of flow, droughts and habitat availability, etc.) influence life history. Principal 3: Some flow events create longitudinal dispersal of migratory organisms, while other large events allow access to otherwise disconnected floodplain habitats. Changes to this flow regime negatively impact native biota.

Principal 4: Introduced invasive species or exotic species better adapted to altered flow regime likely to succeed at the expense of native biota.

(Source: Bunn & Arthington 2002, 493) We discuss how the viability of populations of many species of fully aquatic organisms depends on their ability to freely move through the stream hierarchy, or between the river and floodplain wetlands. Loss of longitudinal and lateral connectivity through con-struction of barriers can lead to isolation of popula-tions, failed recruitment and local extinction.

Principle 4: The invasion and success of exotic and introduced species in rivers is facilitated by the alter-ation of flow regimes. Here, we briefly discuss the overall impact of modifying flow regimes on the es-tablishment, spread, and persistence of exotic and introduced species. We also consider interbasin transfers of water as a major mechanism for the spread of exotic and introduced species, as well as disease.

Principle 1: Flow Is a Major Determinant of Physical Habitat in Streams, Which in Turn Is a Major Determinant of Biotic Composition

Flow Influences on Habitat

The movement of water across the landscape influ-ences the ecology of rivers across a broad range of spatial and temporal scales (Vannote and others 1980, Junk and others 1989, Poff and Ward 1990, Poff and others 1997, Sparks 1995). The shape and size of river channels, the distribution of riffle and pool habitats, and the stability of the substrate are all largely deter-mined by the interaction between the flow regime and local geology and landform (Frissel and others 1986, Cobb and others 1992, Newbury and Gaboury 1993). In turn this complex interaction between flows and phys-Figure 1. The natural flow regime of a river influences aquatic biodiversity via several interrelated mechanisms that operate over different spatial and temporal scales. The relationship between biodiversity and the physical nature of the aquatic habitat is likely to be driven primarily by large events that influence channel form and shape (principle 1). However, droughts and low-flow events are also likely to play a role by limiting overall habitat availability. Many features of the flow regime influence life history patterns, especially the seasonality and predictability of the overall pattern, but also the timing of particular flow events (principle 2). Some flow events trigger longitudinal dispersal of migratory aquatic organisms and other large events allow access to otherwise disconnected floodplain habitats (principle 3). The native biota have evolved in response to the overall flow regime. Catchment land-use change and associated water resource development inevitably lead to changes in one or more aspects of the flow regime resulting in declines in aquatic biodiversity via these mechanisms. Invasions by introduced or exotic species are more likely to succeed at the expense of native biota if the former are adapted to the modified flow regime (principle 4).

Flow Regimes and Aquatic Biodiversity 493

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Principle 1: Flow is a major determinant of physical habitat in stream, which in turn is a major determinant of biotic composition. River flows determine the shape and size of river channels and stability of substrates, and therefore distribution of habitats.

Specifically, altered flow regimes increase the stability of base flow, while reducing flow variability. This in turn reduces fish and fauna populations and diversity through habitat loss and unstable riverbed substrates (Nilsson and Svedmark 2002). The relationship between flow, habitat structure, and fish are well documented, and so flow modifications affect fish diversity and functional organization. A related impact, described by Roberts (2001), involves channel maintenance and clearance for navigation purposes. This, in turn, leads to the deterioration of fish habitats and water quality, while increasing runoff speed, another determinant of fish species habitats (Roberts 2001; IRN 2002b). Other studies confirm this principle of dam construction negatively influencing the natural distribution of habitats through flow regime alterations (Nilsson & Svedmark 2002; Kang et al 2009a, 2009b, 2013). These changes have been show to lead to a loss of shallow banks and heterogeneous habitats (pools and rapids), and will endanger fish species in the future (Poulsen et al 2002; Kang et al 2009a, 2009b).

Principle 2: Aquatic Species have evolved life history strategies primarily in direct response to the natural flow regimes. This affects the following flow variables: the rates of water level fluctuation, impacting plant life growth rates and seedling survival;

the timing of floods, impacting the stable low flows required for river fish spawning;

changes to the timing of rising flows, losing cues for fish spawning and migration; short-term fluctuations in flows, adversely impacting species with long larval development; and modified temperature regimes below dams, which delays fish spawning, insect

emergence patterns, and eliminates temperature-specific fish species. The species specifically adapted to the reliable flood pulse of the Mekong are likely to be strongly impacted. This principle is frequently confirmed in studies on fish populations. While the pre-Xiaowan cascade held relatively little impact on fish populations, the alterations in flow, depth, dissolved oxygen, light availability, and temperature changes from a complete cascade will strongly influence the migratory cues for fish as well as fragment

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habitats, leading to a decline in biodiversity (Nilsson et al 2005; Kang et al 2009a, 2009b, 2013).

Principle 3: Maintenance of natural patterns of longitudinal and lateral

connectivity is essential to the viability of populations of many riverine species. In other words, an uninterrupted migratory path is necessary for certain species’ survival. Indeed, the disappearance or decline of major migratory fish species frequently follows river impoundment and by obstructing the river (Bunn and Arthington 2002). In addition, the reduced frequency, duration, and area of inundation of floodplain wetlands reduces lateral connectivity (the temporary use of inundated floodplains) and the spawning areas of lowland river fish, decreases water bird species abundance, and causes a decline in wetland vegetation (as confirmed in: He et al 2004; Nilsson et al 2005; Kang et al 2009a, 2009b, 2013)

Principle 4: The invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes. Flow alterations create the following flow variables and biotic responses: loss of wet-dry cycles and increased stability of water levels, reduces growth and survival of native vegetation and increases invasive species’;

reduced variability and increased seasonal stability favors fish species not attuned to the Mekong. Indeed, these changes will likely favor those species that are less reliant upon the flood pulse, and those exotic species that are able to flourish under the new flow regime. Exotic species – along with flow regime alterations from hydropower and

overfishing (Kang et al 2009a) – are considered among the leading causes of biodiversity decline within the Mekong basin (Kang et al 2009a, 2009b).

The reservoirs themselves also cause localized ecological degradation. As was seen with the Manwan reservoir, the filling and releasing of water, along with the construction of the infrastructure around the dam (highways, small irrigation projects, etc) makes the area prone to landslides, sediment concentration behind the dam, and water pollution related issues both in the reservoir and downstream (He et al 2004).

Vegetation typical the area begins to decline as the area becomes permanently inundated.

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The filling of the reservoir contributes to the increased landslides. This in turn displaces the local community, which if not properly relocated may then put ecological and social pressure on the areas surrounding the reservoir (He et al 2004).

Another, more specific impact, will likely occur in the largest fresh water lake in Southeast Asia, the Tonle Sap Lake in Cambodia. The impacts on the lake encompass all of the above principals. Cambodia accounts for 40% of the annual 1 million tons of fish caught in Mekong fisheries, and the Tonle Sap accounts roughly 100,000 tons (Jensen 1996, 2000). Roughly 80% of the animal protein consumed in Cambodia derives from the Tonle Sap (Roberts 2001), with the lake itself directly supporting roughly one million people. In addition, the Mekong main stem accounts from roughly 57% of the lake’s inflow via the Tonle Sap river (52%) and overland flooding (5%) (Kummu and Sarkkula 2008). “The flow in the Mekong River is the principal factor determining the flood pulse of Tonle Sap Lake” (Principal 1) (Kummu and Sarkkula 2008). According to a model of Kummu and Sarkkula (2008), the flood duration would be reduced by 14 days, while the floodplain area, flood volume, and amplitude would be reduced by 7-14%. This is an important impact as a reduced inundation period would lower the floodplain of the lake thus shrinking ecosystem productivity dependent on the pulse (Principal 1-3). In addition, relatively small rises in the dry-season lake water level would permanently inundate large areas of the floodplain, making it impossible for floodplain vegetation and reducing floodplain productivity (Principal 3). In sum, the impacts of flow alterations leads directly to “a decline in every parameter in regard to ecosystem productivity” (Kummu and Sarkkula 2008). In the short term (10-30 years), this will primarily be driven by land-use changes and hydropower development, with climate change becoming more

important later in the century.

6.3 Frameworks

The frameworks surrounding ecosystem impacts from the cascade potentially available to decision-makers are fairly straightforward, as nearly no benefits derive from impacts on the ecosystem services. Rather, ecosystem impacts are frequently the costs with which the benefits must be weighed against.

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Negative impacts on migratory fish: Impacts on migratory fish species, especially those that migrate into the Upper Mekong to spawn, will likely be severely impacted by mainstream dams, as the dams currently constructed or proposed are simply too tall and incompatible with techniques that would allow fish to migrate (e.g. fish ladders, etc.). If the full cascade is built, it will have significant impacts on migrating populations. In addition, an altered flow regime will negatively impact the signals normally used by fish populations to begin migration (flood pulse, temperature differences, etc.)

Decreased biodiversity and fishing yield: As discussed above, the four principals of flow regime alteration (including changes to oxygen levels, temperature, flow rate, etc.), in addition to modified silt flow and channel clearing for navigation purposes, will likely lead to significant decrease in the biodiversity of both riparian animal and plant life. This in turn will severely impact the fishing yield of the Mekong, which is heavily relied upon for sources of protein and on the ecosystem services provided by a healthy ecosystem.

Habitat loss from flow alterations: As shown with the first principal, there will likely be a decrease in fish habitats specifically attuned and reliant upon the consistent flow regime of the Mekong. In addition, those animals and plants reliant on a consistent inundation period in SE Asia will lose the temporary habitats gained by floods of a reliable duration.

Other areas, like in the Tonle Sap, may become permanently inundated

7. Social Impacts

Social impact research in the Chinese literature generally covers the extent of the dams influence on domestic groups, rather than examinations of downstream social impacts in Southeast Asia. Transnational impacts are more commonly addressed in research pertaining to sediment flow (i.e. and its impacts on the Tonle Sap lake) and hydrological changes. Typically within Chinese literature, social impacts are described as a factor dependent largely on the socioeconomic status of a given region, and therefore

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the impacts of the cascade are both highly variable and highly dependent on local situations downstream, which are both fair and valid points.

However, a basic overview of the status social impact science is in order, and is perhaps more fully addressed in the next chapter as social impacts are much more intertwined with the activism of civil-society organizations (CSOs) as described by Magee (2006a), or as they are typically referred to, NGOs.

In other case studies of relocations after evidence surrounding the Three Gorges Dam indicates that displaced populations in China are vulnerable to landlessness, joblessness, homelessness, food insecurity, community disarticulation, increased morbidity, loss of community resources, and depression among displaced residents (Brown et al 2008). Overall, research around the world studying the social impacts of dam-induced resettlement suggests that only very rarely do conditions for resettled communities improve, with most conditions getting worse (WCD 2000; Cernea 2003;

Galipeau et al 2013). Some go even farther saying that there is not a single case in which dam-induced displacement resulted in improved livelihoods for local people (Scudder 2005). Specific studies on the social impacts of the upper and lower Mekong seem to be relatively sparse, compared to other projects like the Three Gorges Dam. The Upper Mekong (Lancang) cascade, with its multiple development projects spreads out the impact of resettlement among a culturally heterogeneous region of a number of minority nationality groups, in areas that are frequently less populated relative to other large hydropower projects.

7.1 Dam Specific Impacts

In a number of the articles reviewed by the author, locals typically supported or at least believed in the importance of the hydropower projects as a means of improving China’s economy, yet had near unanimous agreement that resettlement was bad for households, communities, and local culture (Galipeau et al 2013).

Currently, China has roughly 86,000 dams, with a number of them having relocation issues of local populations. Of the issues already addressed in this chapter, relocation issues are something the central government has been actively dealing with

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since the 1980s (Yu & Jia, n.d.). The Central Government Leading Group for Poverty Alleviation claimed that of the 10.2 million people displaced domestically, 7 million are living in poverty-stricken conditions. The Ministry of Water Resources allocated 1.9 billion RMB to 46 resettlement projects to help roughly 5 million resettled people (Yu and Jia, n.d.). As described by Yu and Jia, typically in these projects insufficient attention was paid to social impacts, and as such the short-term and long-term needs of resettled populations are often overlooked. Compensation for displacement and resettlement does rest with locals, but rather the local government. Compensation funds are given to village and township-level governments, as technically all land is collectively owned (Galipeau et al 2013). As such, while local officials may claim they want to do right by their constituents, how resettlement compensation is distributed depends on higher-level officials.

In addition, in cases like the Nuozhadu dam, reallocation of land to relocated villagers left them with smaller portions of agricultural and forest land than that they lost, thus worsening livelihoods for already marginalized groups (Galipeau et al 2013). Wang et al (2013) in a study of impact on resettled communities, delineated wealth types into three categories: material wealth (land holdings, crops, money, etc.), embodied wealth (agricultural skills, etc.) and relational wealth (social connections and physical

infrastructure, hospitals, roads, etc.). Generally speaking, compensation does not

explicitly cover losses of embodied wealth, i.e. a loss of application of agricultural skills by reduced and/or lower-grade farmland, forcing the farmer to go into manual labor.

Relational wealth also is frequently ignored by decision-makers (as seen below), despite its long-lasting impacts on the society of the community. That said, in some resettlement cases the quality of life did sometimes improve, and steadily improved with each

consecutive project from the Manwan to the Nuozhadu dams as compensation laws and policies gradually improved.

7.1.1 Manwan & Dachaoshan

The resettlement of the Manwan remains a controversial case of poorly and inadequately compensated populations. Officially displacing 3208 people, the Manwan

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reservoir forced many off their land through land degradation from landslides (Wang et al 2013). As is true with a number of other studies, those villages displaced near to their original location suffered significant losses of farmland, with insufficient funding to build new housing (Wang et al 2013). Others gained slightly from the influx of professionals constructing the dam, allowing some locals to supplement their income through

reservoir forced many off their land through land degradation from landslides (Wang et al 2013). As is true with a number of other studies, those villages displaced near to their original location suffered significant losses of farmland, with insufficient funding to build new housing (Wang et al 2013). Others gained slightly from the influx of professionals constructing the dam, allowing some locals to supplement their income through