On
March 8, 2013, the training workshop “Coastal Geomorphology, Sediment
Transit and Their Integration into Biodiversity Conservation Planning in
the Mekong Delta” was held in Ben Tre by WWF – Greater Mekong
Programme and Biodiversity Conservation Agency (BCA, MONRE). In the
morning session, Professor Edward J. Anthony[1]
gave lectures on coastal geomorphology and impacts of hydropower dams
on coastal areas (Mekong Delta as a case study). In the afternoon
session, Mr. Ngo Xuan Quy (BCA) gave an overview on biodiversity in the
Mekong Delta and Ms. Tran Thi Mai Huong (WWF Vietnam) gave a brief
introduction to ecosystem-based approaches to climate change. The
workshop ended with the plenary discussion and conclusion.
1. Introduction to coastal geomorphology and coastal evolution
Sediment
sources for coasts are from land (90%, mainly from river catchments),
seabed, from the coast itself (coastal erosion), from marine and
coastal plants and animals (corals, mangroves, salt marshes).
Sediment
types can be boulders, blocks at high energy coasts (brought by
tsunamis, extreme storms), gravel at high-energy-coasts in temperate to
high latitude coasts, and sand or mud at all climate settings, but
dominant in tropical settings due to chemical weathering.
There
are erosional coasts (rocky coasts, cliffed coasts) and
depositional/alluvial coasts (beaches, sandflats, mudflats, salt
marshes, mangroves). Depositional coasts can become erosional in case of
deficient sediment supply.
The
energy sources for coasts are waves, tides, currents, wind flows,
river flows, freshwater – saltwater interactions, exceptional events
(storms, tsunami, earthquakes, landslides, volcanoes, etc) and also
impacts of direct and indirect human interventions.
Longshore
drift is a fundamental coastal process enabling sediment transport
from sources (notably river mouths) to the rest of the coast. Although
longshore sediment drift is essentially due to waves obliquely
approaching the shore, this transport can also be generated by tidal
currents and wind stress, especially where mud is available.
Sediment
gain relates to coastal advance (accumulation, progradation) while
sediment loss relates to coastal retreat (erosion). Sediment losses can
be caused by perturbation of river sediment supply such as forestation,
land use changes, dams, climate change, perturbation of longshore
drift such as ports, coastal defence works, or extreme storms and
tsunamis. Low eroding coasts are likely to be strongly impacted by sea
level rise.
Estuaries are commonly net sediment sinks. High river flow, and ebb-dominated tidal flows, can lead to sediment transport from the estuary to the sea. The supply of sediment to coasts by rivers has, however, been strongly affected by humans through:
- modification
of catchment characteristics such as vegetation cover and soils mainly
related to agriculture, mining, road construction, settlements;
- river
bank and channel engineering works, including waterway diversions,
aimed at stabilizing flow, controlling floods and enhancing navigation;
- and especially through dams and reservoirs for water storage, water control, hydroelectricity, irrigation.
The
sediment input to the floodplains during the annual flood plays a
crucial role in terms of nutrient supply to agriculture. Sedimentation
in floodplain plays a key role for the economic and ecological
sustainability of low lying deltas. Its values can be acknowledged for
nutrient input for agriculture, but also in terms of compensation for
delta subsidence and sea level rise.
The transition from the river to the coast involves complex interactions between sea, coastline and land.
Humans
have increased the sediment transport by global rivers through soil
erosion by 2.3 ± 0.6 billion metric tonnes per year, but yet reduced the
flux of sediment reaching the world's coasts by 1.4 ± 0.3 billion
metric tonnes per year because of retention within reservoirs. Over 100
billion metric tonnes of sediment are now sequestered in reservoirs
constructed largely within the past 50 years, especially in Africa and
Asia (Syvitski et al., 2009).
Large-scale
over-exploitation of riverbed sand, granulates together with dam
construction all over the world have caused significant reduction of
suspended sediment discharge which in turn can result in widespread
coastal retreat. Engineering of delta shoreline for reclamation purposes
can also reduce sediment supply to the coast. Moreover, river flow
declines after dam construction.
Widespread erosion of the Mekong delta shoreline
Existing
and planned mainstream dams in China would have large impacts in terms
of decreasing sediment, given that more than 60% of the Mekong’s
suspended sediment load originates from this part of the river. Models
project that at least 50% of total basin sediment load will be trapped
annually by the Chinese dams. Proposed dams in the lower Mekong would
trap even more sediment, with substantial negative impacts expected in
Cambodia and parts of the Mekong Delta in Vietnam.
Delta
shoreline status shows that erosion dominates with more than 75% of
the Mekong delta shoreline in erosion. Erosion rates of up to 10
m/year. Erosion is severe along the muddy wave-tide-dominated coast
southwest of the delta mouths and most severe along north Ca Mau and
south Bac Lieu provinces. Erosion ‘hot front’ appears to be migrating
southwest.
Future
stability of the Mekong delta shoreline and assurance of the
continuity of its ecosystem services will strongly depend on dam
effects on the sediment balance, in a context of exacerbated
vulnerability from sea-level rise and delta sinking.
2. Biodiversity conservation in the Mekong Delta
The national policy for adaptation to climate change requires assessment
of climate change impacts to related aspects, including biodiversity.
The draft national strategy on biodiversity conservation recognises
climate change as one of the threats to biodiversity and suggests
actions for biodiversity conservation in the context of climate change.
Planning
is considered as a useful tool to conserve and identify priority zones
for conservation, particularly relevant in the context of climate
change. Among 12 provinces in the Mekong Delta, Soc Trang, Ben Tre and
Ca Mau have developed their biodiversity conservation planning.
3. Introduction to ecosystem based approaches to climate change
An
ecosystem approach is a strategy for the integrated management of land,
water and living resources that promotes conservation and sustainable
use in an equitable way. Mainstreaming an ecosystem based approach to
biodiversity conservation plan is crucial.
Ecosystems
provide a variety of services to people and economies that range from
provisionary services such as water and food to regulatory services
such as regulating local climate. Ecosystem-based approaches
address the crucial links between climate change, biodiversity,
ecosystem services and sustainable resource management which have the
potential to simultaneously contribute to the avoidance and reduction
of greenhouse gas emissions while maintain and increase resilience,
reduce vulnerability of ecosystems and people, help to adapt to climate
change impacts, improve biodiversity conservation and livelihood
opportunities and provide health and recreational benefits.
Ecosystem-based adaptation (EbA)
is the use of biodiversity and ecosystem services as part of an
overall adaptation strategy to help people to adapt to the adverse
effects of climate change.
Ecosystem based mitigation (EbM) is the use of natural ecosystems as the major carbon stores and sinks to mitigate the causes of climate change (mitigating and reducing GHG emissions from energy production or land use changes).
Final
decision of using one approach instead of the other one needs to be
carefully weighted, considering local situations and scientific
evidences, since in many cases the best strategy might be the
combination of the two. It may be appropriate to combine EBA and
infrastructure solutions in some cases.
In the tentative
agenda, the half-day fieldtrip on March 9 was supposed to visit the
erosion site in Ben Tre. However, since they could not get permission
for the two foreign experts (Prof. Edward Anthony and Dr. Marc Goichot,
senior adviser of WWF), the plan was changed to visit Vam Ho Bird
Sanctuary and the Ba Lai sluice gate.
Vam Ho has long
become a favourite destination for many animals, especially birds. Vam
Ho Bird Sanctuary is home to thousands of storks, herons and other types
of bird. We arrived at the entry to Vam Ho Bird Sanctuary but could not
move deeper inside the forest. Again unfortunately, the visit to Vam Ho
Bird Sanctuary had to cancell for safety reason because of huge amount
of mosquitos and because people were not well prepared (wearing shorts).
On the way back,
we had a quick look at the Ba Lai sluice gate, which was built in 2000
and has been operated since 2002. The aim of this Ba Lai sluice gate
construction is to serve for salinisation prevention, freshwater
retention, flooding drainage and soil reclamation. However, currently
salinization, reduction of sediment, erosion at the two banks of the
estuary are some problems in the area.
Some key remarks at the plenary discussion
· Dams
construction and overexploitation of sand cause sediment deficits
which in turn affects significantly to coastal stability because this
creates more erosion downstream.
· Reduction
of sediment is just one legacy of dams construction, there are many
more negative consequences, including the reduction of fish resources.
· Mekong Delta are facing risks of erosion, shrinking and sinking.
· Putting
coastal barriers can affect downstream, especially for muddy coast.
Therefore, we need to see the whole picture, looking the whole coast as a
system.
· “Hard”
solutions or structural measures such as sea dyke are costly and only
create temporary sense of safety. After some years it can be collapsed
and washed away out to the sea. Moreover building sea dyke can block
the water exchange which is needed for mangroves (as mangroves also
need freshwater), resulting in mangrove death.
· Ecosystem based approaches or “soft” measures are environmental friendly and can bring multiple benefits at the same time.
· Restoration
of coastal mangroves can facilitate rehabilitation of biodiversity
through creating habitats for aquatic resources and other animals,
birds.
A
video clip in Vietnamese made by VTV Can Tho about building
wavebreaker in Vam Ray, Hon Dat, Kien Giang province to reduce wave
energy (reduce 63% wave energy) and stimulate sedimentation (deposition
rate of 20 cm sediment/year) for mangrove planting was shown. Results after 3
years of implementation this model (2010-2013) show that no more
erosion, increasing deposition, decreasing of salinization, restoration
of habitat with more aquatic resources, birds returning to the area.
*****
My friend Cam Nhung, she is working for WWF.
Me at the Ba Lai sluice gate
