Salween Dams: a study-part 2

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Evaporation of water would increase.
 
Temperatures in the upstream end, and in the upper reaches of the 
reservoir would increase.
 
Due to the combined influence of temperature, sediment and other 
chemical constituents, the water in the reservoir would become 
stratified or not evenly mixed. As a result of this parts of the reservoir 
would become deoxygenated and fish would not be able to survive.
 
As water seeped into the dry land, as the reservoir level fluctuated, 
the reservoir shoreline would begin to erode.
 
Stratification in the reservoir could cause chemicals attached to 
bottom sediments to be released into the reservoir, leading to water 
quality problems and potential impacts on the aquatic food base.
 
Biological Changes
 
As the reservoir fills, the flooding of land and vegetation would 
release nutrients and organic matter into the water. The increase in 
nutrients combined with the increased light penetration in the 
reservoir would cause the plankton to multiply rapidly. As the 
plankton food base responded to the new conditions, zoo plankton 
and macro invertebrates would respond in much the same way, 
resulting in an overall short term increase in the productivity of the 
reservoir ecosystems. But once the nutrients from the flooded soils 
were depleted, the plankton population might either decrease or 
increase depending on the inflow of nutrients to the reservoir.
 
The fish presently found in the Salween have evolved in a riverine 
system. If the river were to be transformed into a reservoir, the native 
fish species would, in all likelihood, be unable to maintain themselves. 
They would attempt to move upstream to more favourable waters or 
seek other refuges.
 
In the long term whether or not fish populations -- either native or 
introduced -- could be sustained in their new environment would be 
determined primarily by the rate of flow through the reservoir and the 
amount of fluctuation in flows per year.
 
The decline of native fisheries in reservoirs is well documented for 
reservoirs in the United States, the former Soviet Union, and has been 
witnessed by fishing communities throughout Thailand.
 
For example, in the Colorado River (USA) and its tributaries which 
have been extensively dammed over the past several decades, native 
fish species are threatened with extinction.
 
Reservoirs Spread Water-Borne Disease
 
When a river is dammed and a deep lake is created, those forms of life 
which were adapted to the riverine ecosystems are likely to disappear. 
In their place, other species emerge. Some will thrive in the new, deep 
lake along the shoreline that fluctuates with daily operation of the 
dam to produce hydroelectricity.
 
As such, the permanent submergence of riverine ecosystems can lead 
to serious water quality problems and public health hazards. Dam 
reservoirs in tropical countries are responsible for the spread of 
serious diseases such as schistosomiasis and malaria.
 
Schistosomiasis is caused by parasitic flatworms known as 
schistosomes. The larvae of the schistosomes develop within the 
bodies of freshwater snails. When people swim or wade in water 
contaminated by infected snails the larvae bore through their skin and 
enter their blood stream. From there they move to the liver where they 
mature in a few weeks and mate. The eggs then leave the human body 
via urine or faeces but also tend to spread to various organs while in 
the body. Reservoirs provide ideal habitat for fresh water snails and 
the schistosome parasite.
 
Swamps, marshes and stagnant pools of water are ideal breeding 
grounds for malarial mosquitoes. Large reservoirs have created 
permanent and extended habitat for mosquitoes.
 
Reservoir Water Quality and Disease
 
Decaying organic matter, can create eutrophic conditions in the 
reservoir leading to algal blooms, oxygen depletion and massive fish 
kills. Water from the reservoir and directly downstream of the 
reservoir is often unfit for human or animal consumption years after 
the project is completed.
 
(Poor quality water also corrodes the turbines and dissolve concrete, 
affecting dam safety and operation.)
 
PART II:  DOWNSTREAM ENVIRONMENTAL EFFECTS
 
The Salween river, like all rivers, is an ecological system: what 
happens upstream has an impact on what happens downstream; some 
impacts are immediate while others are more gradual. Many of the 
environmental problems associated with major rivers and estuaries of 
the world can be attributed largely to dam construction and the 
creation of large man-made reservoirs.
 
2.1  Fisheries Destroyed
 
The loss of fish and other aquatic life throughout the river basin once 
the river is dammed can be equal or even exceed the temporary 
benefits from fisheries in the dam's reservoir.
 
Dams tend to reduce the catch of fish from the river because fish 
cannot reach their spawning and feeding grounds. Even without the 
physical obstruction of the river, regulation of the river flow and the 
changed patterns of erosion and siltation in the river can destroy fish 
food and habitat.
 
Dams reduce the flow of rivers which means less habitat, nutrients 
and increased stress on aquatic life downstreams of the dam.
 
Dams trap silt which previously would flow downstream. That silt or 
sediment contains nutrients which are vital to the survival of fisheries 
in the lower reaches of the river, in the estuary and in the sea beyond.
 
2.2  Middle and Lower Reaches
 
INFORMATION NEEDED AT LOCAL, NATIONAL, 
INTERNATIONAL LEVELS
 
Population living downstream?
General description?
Salween estuary?
Farming and fishing communities?
Commercial fishing industry?
Wildlife & Habitat?
 
The impact of damming the Salween river on downstream areas 
depends not only on the size and operation of the dam and reservoir 
but also on the hydroelectrical characteristics governing the river 
system such as the volume, timing, and duration of water flows. 
Second only to these factors is the transport, erosion and deposition 
of the river's sediment in determining the basic character of the 
aquatic environment immediately downstream of the dam to the 
estuary hundreds of kilometres away.
 
The extent to which the Salween river influences water levels 
downstream of the dam depends on a number of factors:  flood flows 
from the upper reaches, timing of regional monsoon precipitation, and 
tributary flood patterns. Certainly, operation of the dam to serve peak 
power demand in Thailand would cause fluctuations of water levels in 
the middle and lower reaches of the Salween.
 
During the rainy season, the flow downstream would be reduced and 
in the dry season, water levels could fluctuate widely on an hourly 
and daily basis.
 
In short, the way in which the dam disrupts the river's flow of water 
and sediment influences the fate of downstream fisheries, farming, 
water quality and supplies, wildlife, estuarine and coastal marine life.
 
2.3  Downstream Channel Degradation
 
Once the river loses its sediment to the reservoir, it gains more power 
to erode its channel and banks downstream and may eventually shift 
is course and cause disastrous flooding as a result. Aggravating the 
situation is the mining of sand and gravel for dam construction and 
road building.
 
As the sediment-free water released from reservoir tends to erode 
river bed and bank material -- river banks may cave in -- the water 
surface elevation of the river can drop dramatically.
 
The degradation of the channel bed can extend hundreds of 
kilometres downstream, stranding irrigation and water supply intakes, 
undermining bridge piers and any structures on the riverbanks. 
Embankments designed to control flooding are undermined. 
Degradation of the main river can then in turn affect the tributary 
channels.
 
2.4  Salween Estuary, Wetlands and Coastal/Marine Areas
 
The Salween river is the principal source of beach sands and estuary 
silt and mud flats which provide nutrients for estuary and coastal 
fisheries. Dams would block the flow of the vital materials, depriving 
fisheries of nutrients, causing shoreline erosion and loss of wetlands. 
Coastal areas would become more vulnerable to greater flooding 
during storms.
 
A significant percentage of the Salween's annual sediment load is 
deposited in the estuary or is carried out to the ocean. Depending on 
tidal influence and the seasonal flows of the Salween, the river and 
estuary waters can be fresh, brackish or salt water.
 
The Salween estuary provides a rich food source for birds, as well as 
feeding, spawning and nursing grounds for aquatic life, for example, 
herring, anchovies, eel, crab and shrimp.
 
Salween Estuary
 
A combination of drought, diversion of water from behind the dam 
into river basins in Thailand and conflicting demands on the reservoir 
(store vs. release of water), can severely reduce the flow of the river 
downstream. In some cases, reduced flow caused by dam operation 
has caused sea water to intrude inland, further than under natural 
conditions, thereby damaging crops, soils and water supplies 
(example:  Srinagarind Dam, Thailand, 1980). In some river basins, for 
example in Bangladesh and Vietnam, sea water will intrude up to 100 
kilometres every dry season when the rivers are at their lowest levels. 
Dams on the Ganges and Brahmaputra rivers have worsened the 
situation every dry season.
 
If dams were constructed on the Salween, the demand for water from 
the reservoirs would likely exceed the available flow of the rivers -- 
particularly in the dry season. The delta would be most vulnerable to 
the effects of development upstream as it is at the tail end of the water 
supply.
 
Farming and fishing communities in the Salween delta would suffer 
the most because of the reduced flow in the river and a subsequent 
decline in the quality of water. Less flow means the river would have 
less capacity to flush out pollution and keep saltwater at bay.
 
Info required to inform local, national and international action:
 
Details of towns, villages, populations upstream/downstream; use of 
land closest to rivers.
Hydrological, bioregional features of the Salween river basin
Himalayan river, length, silt load, annual volume of flow?
General layout of the river basin.
Length of border defined by the Moei river, Salween river?
Percentage of the Salween watershed in Thailand?