Sino-Dutch team develops Yellow River plan
Conflicting demands on water resources for urban and agricultural uses, combined with a variable rainfall pattern, is seriously impacting on livelihoods and the environment in the central part of the Yellow River basin in north-east China. Robert Smit and Koen Roest of Wageningen University & Research Centre (WUR), in The Netherlands, report on a Dutch-Chinese partnership project that is investigating options for groundwater and surface water management in the region.
Agriculture in the Yellow River basin was historically concentrated in the river valleys. However, the population now stands at more than 80 million inhabitants, which has led to widespread deforestation and cultivation of lands on the central loess plateau where soil erosion is high.
In the central part of the Yellow River Basin, average annual rainfall amounts to some 400mm (range 150-850mm) with great annual variation. In the river valleys, agriculture is often supported by irrigation, enabling the cultivation of two crops per year.
Although irrigated agriculture covers only 10% of the total area, it consumes 95% of the water resources. As a consequence, downstream agriculture and ecosystems suffer from water shortages.
Low discharges in the Yellow River, combined with increased pollution loads, have also resulted in poor water quality, affecting agriculture in the downstream provinces Henan and Hebei and the coastal wetlands. The Dutch government has supported the project Improvement of Water Management in North China, which investigated stress factors in crop production and measures related to regional water management in agriculture in the Taiyuan Basin and in particular the Fenhe Irrigation District.
The district is centrally located in the basin along the river Fen, a tributary of the Yellow River. It was found that:
- Yields of (irrigated) winter wheat are well below their potential, primarily caused by water stress
- Demand for high-value crops, such as vegetables and fruits, is on the rise, but associated water requirements are difficult to meet with the erratically distributed rainfall in summertime and old-fashioned, rigid irrigation systems only capable of delivering large quantities of water on a limited number of occasions
- The district is relatively water-rich for crop production, compared with neighbouring districts, due to its direct access to a large upstream reservoir.
Flexibility for farmers
Local and regional solutions have been sought through groundwater extraction, water transfer, and demand-management measures. Research also established that abandoning the outdated irrigation system, in favour of a groundwater-driven system, would be an option.
It was established that the proposed groundwater system, accompanied by artificial infiltration of surface water from the reservoir, measures to improve rainfall harvesting and the existing water transfer from the Yellow River, would meet municipal and industrial demands from Taiyuan City. It would also offer farmers operational flexibility to meet their water requirements, while providing an inter-annual buffer against dry years.
However, given the limited water resources in the basin and the steadily increasing demands due to rapid economic developments, it seems unlikely that restoration of the old Fen discharges is feasible. Although water management could be improved in irrigated agriculture, wetlands and agriculture in the downstream parts of the Yellow River will continue to suffer from water shortages.
Potentials for real water savings probably lie in the most northern stretch of the Yellow River, where large-scale irrigation is practiced in Inner-Mongolia, a desert region with very high evaporation.
Water use and conflicts
The Taiyuan Basin, which is approximately 16,000km2, lies in the upper shed of the Fen River, in the middle of Shanxi Province in north-east China. Taiyuan, the province’s capital, is situated in the northern part of the basin. The alluvial plain is largely in use as irrigated croplands and divided into irrigation districts, the total area of which is estimated at 3500km2.
At 1400km2, Fenhe Irrigation District (FID), located along the river, is the largest and receives its water from a large reservoir in the Fen River upstream of the basin. Average annual rainfall amounts to some 480mm and is concentrated in the summer season.
The average supply from the reservoir added some 200 million m3 available for irrigated agriculture in the past, but has decreased to a mere 140 million m3 in the 1990s due to drought spells in the upper shed. Until recently public and industrial water supply were secured by groundwater, but economic developments, largely concentrated around Taiyuan City, have caused an unsustainable lowering of water tables of several hundreds of meters.
The use of groundwater is now gradually being replaced by water piped directly from the Yellow River. Agriculture in the region is plagued by water shortages. Typically, wheat is grown during winter and spring and supplied with 2-3 water gifts. Maize and vegetables are cultivated in summer, sometimes supplemented by irrigation depending on need and water availability.
Low wheat yields in FID, an average of 4500kg per ha, could clearly be attributed to water shortages, and field and model experiments indicated the potential for grain yields of about 5800kg per ha. The yield gap for maize is even larger, at 40%, caused by erratic rainfall and insufficient irrigation water.
Due to heavy silt loads of the Fen waters, irrigation is infrequent, with large volumes to prevent sedimentation.
A rapid rise in the standard of living is causing a shift in crop cultivation from wheat and maize to more remunerative, but water-intensive crops such as fruit and vegetables, and animal products. However, the present irrigation system is unable to cope with more frequent but smaller water gifts and farmers are increasingly turning to groundwater to meet demand.
The new water transfer from the Yellow River to Taiyuan City will only ease the conflicting demand between municipal and industrial water supply and cash-crop irrigation in the distant future, because groundwater restoration will take some time. Solutions also have to be found for wastewater discharges into the surface water and groundwater systems.
Wastewater treatment is only partly implemented in the main cities and not at all in the minor cities and villages. In the countryside, farmers still collect night soils and use them to fertilise their fields. The (partly) treated wastewater contaminates the irrigation water and poses a danger to health.
New systems for wastewater treatment are needed that leave the valuable nutrients in the water, but remove pathogens dangerous for health. Winter storage of treated wastewater during the winter period, when the soil is frozen, is a special problem that needs solving.
However, more importantly for the agricultural reuse of wastewater, it is essential to separate industrial and municipal wastewater. Industrial wastewater needs specific purification to remove heavy metals and toxins.
In order to evaluate alternative water management systems in the Taiyuan basin, two scenarios were compared to a ‘business as usual’ reference situation:
- Irrigation modernisation – the irrigation system in Fenhe Irrigation District is modernised in such a way that it serves as an on-demand pressurised system. Considering available resources and zero losses, sufficient water would be available to optimally serve wheat and vegetables, while maize and other crops remain under a rain-fed regime.
- Well-irrigation and recharge starts from a groundwater-driven supply again for wheat and vegetables, where the annually available amount of water from the reservoir is artificially infiltrated into the aquifer. Irrigating other crops would violate sustainability as aquifers should not be depleted.
These scenarios were tested with Hydrosplash, a grid-based 3D-hydrological model covering processes at the soil surface, the unsaturated zone and aquifer. It was established that implementation of either scenario would further reduce discharges at the basin outlet and hence ecological flows.
The lower discharge of the second scenario is the result of higher open water evaporation, stemming from the ponds necessary for artificial infiltration. Considering costs for investments and operation and maintenance, the second scenario appears the most attractive.
Use of the aquifer would also provide a buffer against occasional droughts in the basin. Capturing flash floods through rainfall harvesting can further contribute to this buffer.
Prerequisite though is well-licensing for farmers and routine monitoring of groundwater tables to prevent unauthorised extraction. From an operational perspective existing authorities for surface water and groundwater should be brought under unified management.
Solutions for the multitude of problems facing the region can only be tackled by integrated approaches, going beyond the technical disciplines. To combine the water cycles on different spatial scales, from field plot to the whole Taiyuan Basin, is challenging, but provides scope for innovative solutions. However, the success of these solutions will only be achieved if sustainability is truly addressed.