Recommendations for delta development
Given the present vulnerability of the Mekong delta, a prime focus is given to developing "no/low-regret" and "priority" policy recommendations for the short- (2025) to midterm (2050) that (i) enable the adaptation of land and water use to the short-term climate change impacts, with emphasis on increasing the sustainable land and water use; and (ii) are flexible enough in their structuring of water management and hydrological features to allow for adaptive socio-economic development.
For the mid- to longterm (2100), additional recommendations focus on adapting to the more extreme impacts of climate change. By necessity these are more structural and large-scale in nature, requiring careful valuation, planning and capital outlay and subjected to renewed insights in the actual evolvement of the delta's economy over the next decades, the severity of climate changes, upstream developments, and future developments in water and agriculture technologies.
1. Given the current agricultural state of the delta's economy, and the moderate projected increase of wet season flows due to climate change (10% or even higher increase for high climate change scenario in 2050), the adoption, continuation and implementation of the controlled flooding practices in the Upper Delta is regarded to be a "priority" and "no-regret" measure to be taken in short to mid term (2050).
This measure fits the current state and practices of land and water use in the Upper Delta, although it signifies a clear departure of the triple-rice policies and increasing practices – in particular for the natural flood plain areas of the Long Xuyên Quadrangle and Plain of Reeds. Where this may initially cause a (limited) loss of rice production, a controlled and actively managed (both in space and flood capture/release) controlled flooding practice has additional benefits to offer to offset the losses in rice production: i) post-flood rice crops tend to return higher yields due to soil fertility increases; ii) active silt accumulation in the delta may offset subsidence; iii) it enables diversification (fish and vegetables), modernisation and sustainable agricultural production systems that return higher value products and meet changing food demands of an increasing middle-income urban population (in and outside the delta); iv) smart spatial and controlled flooding strategy may reduce the cost for rural flood protection in the future.
To support this strategy, investments will be needed to support the development of active and purposely controlled flooding production systems that actively retain the flood waters, and adapt and diversify their production system with fresh aquaculture and (irrigated or recession based) vegetable cultivation.
2. Localised urban flood protection and inundation measures (specifically Cần Thơ) are to be considered a "priority" and "no-regret" measure with phased planning to be taken in the short- to mid-term (2050). A dual approach of providing adequate protection against flooding (overflow) and inundation (reversed drainage) through dykes, flap gates and land subsidence control, and provision of temporal (rain) water retention capacity (spatial planning!) within urban centres (urban waterscapes) to allow for low-tide urban water drainage, is proposed. In a wider scope, there is a strong tendency to allow for "overall" (urban and rural) flood protection in the Middle Delta. Creating a system with many and potentially growing number of ring dykes around – expanding – cities first, smaller towns later and then villages may result in an unmanageable length of dykes, requiring ever increasing costs for maintenance and upgrading. Dyking of the area as a whole affects the space that the river needs for lateral storage and flow in a negative sense. Reliable modelling of river flow in different scenarios is a very high priority to find the right strategy for successful spatial management here and avoid negative consequences of a sector or just local approach.
3. The "Major Flood Diversion" is essentially a structural adaptation measure for extreme climate change, which can be postponed to the mid- to long-term plans (2100). However the spatial reservation for these measures is a "priority". The Long Xuyên Quadrangle and Đồng Tháp Mười (Plain of Reeds) already fulfil an important role in flood alleviation for the Upper and Middle Delta.
4. Preliminary studies indicate that morphological changes, due to changes in the river hydrograph (peak and low) and sedimentation loads, may result in a substantial change of the flow division between the Bassac and Mekong branches. This is a process that can be further affected by sea level rise and ensuing changes in the flow gradient of the branches. At present the flow division between the two branches is roughly 50:50, neatly distributing the fresh water supplies over the east and west (Cà Mau) regions of the delta. Preliminary results indicate that changes in morphology are likely to affect the flow division in favour of the East Delta (Mekong branch). As it is primarily the Western Delta (Cà Mau peninsula) that is already feeling the pressures from fresh water shortages in the dry season, this change in flow division between the branches is undesirable. A priority measure for the mid- to long-term (2100) could thus become the restoration of the flow division between the Bassac and Mekong branches in order to secure the fresh water supplies to the Western Delta. This could be achieved with the construction of a Link Canal south of the natural bifurcation of the branches, to divert part of the flow from the Mekong back into the Bassac branch.
Control of land subsidence is an important factor, and requires a radical shift from uncontrolled groundwater extraction for fresh water supply to surface water supply.
5. Under extreme climate change scenarios, and unabated upstream hydrograph impacts, the delta may be subjected to severe reductions in dry season flow in the mid- to long-term (2100). This will severely affect the fresh water supply of the Middle Delta and agriculture (Central Cà Mau and the eastern fruit zone). This is further exacerbated by progressive salinity intrusion in the branches with extreme sea level rise. Measures to deal with this situation are temporary control of the water flow in the estuaries to i) protect the branches against salinity intrusion during the dry low flow season; and ii) provide a fresh water storage capacity within the river branches.
6. Investing in the sustainability and productivity of the brackish aquaculture based coastal zones and restoring of the dynamic shoreline reinforcement is to be considered an absolute "priority" and "noregret" measure for the short- to mid-term (2050). The establishment of a sustainable brackish coastal environment is critical for the hydrological scenario of the delta in the short- to long-term (adapting to saline water intrusion and dry season reductions in fresh water supply), as well as sustaining and enabling a high-value agro-based economic (export) sector. The current coastal erosion has reached a critical stage. Restoration of the active and dynamic sedimentation and expansion of the delta's shorelines could minimise the investment costs for sea-defence structures (dykes) against sea level rise in the mid- to long-term.
This coastal strategy comprises a set of comprehensive measures that aligns the brackish aquaculture with environment and coastal reinforcement in an integrated manner. The present monoculture based brackish aquaculture practices are prone to water quality problems, disease and yield failure, which undermine the physical and economic sustainability as well as the export viability of the sector. This needs to be turned around by transforming the mono-based shrimp cultivation into a modern polyculture based aquaculture system of multiple fish and shrimp species that thrive on each other’s water discharge. This proven method has the capacity to sustainably improve the brackish water quality, reduce disease occurrences and yield losses, and diversify income. In addition it meets international certification standards of sustainability and quality, which enables producers to enter higher value markets.
7. A critical issue (2050) arising in the Coastal Zone of the delta is the depletion of the phreatic ancient deep groundwater resources. Intensification of its exploitation has risen starkly over the last decade, driven by the widespread diversification of shrimp farmers into horticulture and, to a lesser extent, salinity control in shrimp farming. This is an unsustainable practice that needs to be halted. This scarce fresh water resource should for the short- to long-term be reserved for drinking water supply only. Its unabated use in agri- and aquaculture will lead to depletion of this scarce resource, as well as induce undesirable land subsidence. In the short- to mid-term a successful transformation of the brackish aquaculture sector should lead a reduced pressure on this resources base, as diversification and sustainability is thought within brackish aquaculture, rather than next to aquaculture.
In the mid- to long-term (2100) a saline agriculture practice for the Coastal Zone may become feasible, that is specialised and geared towards the production and processing of food, cosmetic and medical derivatives (half products), or even energy, that can be successfully and sustainably farmed within a brackish environment (e.g. saline environment plants, sea-weeds, algae). Though still in its early research and development stage, this type of 'new'-species based agriculture is promising for its capacity to target high-value, half-product, international market base. This strategy would enable the Coastal Zone to further lessen its dependency on fresh water and diversify its saline productivity base.
For the coastal higher elevated sandy areas, investments and efforts need to be made to develop physical and economically feasible fresh water storage facilities (rainwater harvest / wet season surplus), to enable limited cultivation of high-value horticulture and fruits. This needs to be done in the short to mid term (2050) to decrease the dependency on limited groundwater supplies.
8. The Dual Zone Coastal Management strategy will not be feasible to apply along the entire shoreline of the delta. For those areas that have no or limited capacity to accommodate a Dual Zone Coastal Management strategy (e.g. north-west shore line), the coastal defence infrastructure will have to keep pace with sea level rise. In particular for the mid- to long-term (2100) under extreme climate change, this may require major investments that need to be put in place timely. At these coastlines and along the major river estuaries, an active and green outer line should be kept in place as long as possible, so as to co-opt the natural sedimentation dynamics in shoreline and embankment reinforcement. At many if not most places the sea dykes have been constructed too close to the actual shoreline. Large areas of mangroves have either been directly impacted and disappeared or their nutritional tidal plains have been affected to the extent of slow mangrove deterioration. Land use behind the dykes and the roads on the dykes impair a sustainable approach of rerouting of the coastal defence line. Uncoupling of the road and dyke system and good natural coast (mangrove) management are therefore important measures to achieve an affordable and sustainable coastal defence.
9. In all scenarios industrialisation will benefit from a better logistic system. Good inland waterways and good harbour facilities near the coast are essential for competitiveness. Some studies have already been carried out for a harbour near the Trần Đề estuary of the Bassac/Hậu river. Phasing, layout of the harbour, its facilities and its business case still requires significant research and cooperation between the provinces of the Mekong Delta. In the Dual Node Industrialisation scenario an industrial area west of Cần Thơ could need a port at the West Sea Coast. The feasibility of a bigger port here is yet difficult, since the – muddy – condition of this coast does not easily allow for deeper ships. Dredging of the river to allow ships with a bigger draught up the river to Cần Thơ or possibly further needs to be part of the system. Inland waterways improvement, creation of waterways with few or no ship locks and a range of coastal or river feeder ports need consistent development in which combined forces of the provinces are essential to create a sufficiently large economic market. The link by road between Cần Thơ and Hồ Chí Minh City is already being upgraded, the waterway connection requires upgrading in relation to a possible Cần Thơ – Trần Đề route. In view of the vision and strategy of this Mekong Delta Plan it is recommended that planning of this type of infrastructure should be intensified and integrated in the strategy for the Mekong Delta.
10. Joint fact finding, coherent data collection and open sources, coherent research to develop programmes and plans for decision within the framework of an integrated development of the delta is of utmost important to make the right decisions for delta management.
11. Integration of socio-economic aspects, land and water management as a sound base for sustained economic development, the planning and construction of other infrastructure, services, finances etcetera is of great importance to achieve prosperity in the delta.
12. Upstream developments do not only affect the hydraulic behaviour of the river system, but also determine the possibilities for import and export of goods, water quality, fishery, water transport and other infrastructure. A dedicated foreign policy may contribute to a favourable economic development and sustainable river management.