New study explores win-win approach that could boost agricultural production and contribute to flood control on the Chao Phraya River.
 Storing excess water beneath the ground could alleviate a recurring cycle of floods and droughts |
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The monsoon season experienced by Thailand one year ago brought with it one of the worst floods in the nation’s history. Having inundated provinces of Northern, Northeastern and Central Thailand from July, the floodwaters entered the capital city of Bangkok in October. By January 2012, 65 of the country’s 77 provinces had been declared as flood disaster zones. The waters submerged 20,000 square kilometres of farmland and claimed the lives of more than 800 people. As well as causing damage to domestic properties, several manufacturing facilities were inundated, disrupting global supplies of some products in the automobile and computing industries. The World Bank ranked the floods as the fourth most costliest disaster ever.
In the aftermath of the destructive monsoon, plans were put forward for various flood-prevention schemes across Bangkok. These ranged from building dams and reservoirs to developing huge new artificial waterways. The owners of one flooded industrial estate began building a 77km concrete wall around the factories, to help keep out future floodwaters. Now, a new idea has been put forward that seeks to harness natural processes to turn the menace of floodwater into an opportunity. Less costly to implement that some of the grand schemes outlined thus far, it could nonetheless save billions of dollars. It involves providing incentives to farmers to allow parts of their land to percolate floodwaters and storing that water below ground for times of drought.
 Balancing-out floods and droughts: Opportunities to utilize floodwater harvesting and groundwater storage for agricultural development in Thailand |
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“This approach has the potential to solve two problems in one go but has not been applied in this way before” explained Paul Pavelic, a groundwater hydrologist with the International Water Management Institute (IWMI), a CGIAR consortium center, based in Lao PDR. “Downstream-focused engineering solutions that are being used to protect the built environment of the Chao Phraya flood plain (which includes Bangkok) are vital, but do not necessarily capture the potential for agricultural intensification when floodwater is recognized as a valuable resource. Our aim is to divert water underground in upstream areas in very wet years and thereby turn it into an opportunity by enabling farmers to pump it out for irrigation of high-value crops in the dry season, when drought often causes crops to fail.”
With its economy still largely based on agriculture and rural poor comprising 40% of its population, Thailand frequently suffers badly when floods and droughts strike. The cumulative cost of damage from drought between 1989 and 2003 was around Baht 4474.4 million (US$122 million). Meanwhile the five major floods that occurred between 1983 and 2006 in the lower Chao Phraya river basin alone caused Baht 22,472 million of damage. The cost of damage by the inundation in 2011 was estimated by the World Bank to be around US$ 45 billion. The scientists believe that integrating how water excesses and shortages are managed at a river-basin scale could better balance water supplies for upstream and downstream users across monsoon and dry seasons.
Published this month in the Journal of Hydrology, the article: Balancing-out floods and droughts: Opportunities to utilize floodwater harvesting and groundwater storage for agricultural development in Thailand , suggests this vicious cycle of too much and too little water could be ameliorated by a strategically targeted program of managed aquifer recharge (MAR). MAR is typically used to store wet-season flows in dry climates but has not been systematically employed to capture floodwaters to protect urban infrastructure in the tropics. The collaboration of around a dozen scientists and postgraduate students from the Thailand Department of Groundwater Resources, Groundwater Research Centre of Khon Kaen University, Hydrogeosci and IWMI conducted field, laboratory and modelling studies to establish the techno-economic feasibility of recharging surplus canal water in one of the sub-basins of the Chao Phraya. The experts also analyzed the timing of actual flood events from data gathered between 1965 and 2009 which revealed that during this time there were 11 major floods.
The researchers estimated that, if harvesting only took place in flood years when the monthly wet season flow exceeded 5 billion m³ per month, the amount of surplus water available would equate to a depth of just 5 millimeters if distributed across the basin. The actual volume of surplus water that could be harvested averaged just over 800 million m³ per year and peaked at 6 billion m³ per year. This volume is third in size when considering the major existing water storage facilities in the river basin (only the Bhimibol and Sirikit dams are greater).
The volume of water outlined above represents 28% of the Chao Phraya’s average total annual discharge. At present, this water eventually discharges into the Gulf of Thailand. It was therefore important for the scientists to consider what impacts retaining such a large volume of water during flood years might have on the coastal environment. Fresh water and the nutrients carried by it into the Gulf are of vital importance for maintaining marine ecosystems, which in turn support industries such as fisheries and tourism. A minimum discharge is also important to ensure saltwater does not intrude upstream into areas where farmers pump out freshwater to irrigate their crops.
The scientists found that the levels of particulates, nutrients and other contaminants transported by the river today are higher than before the 1970s when major land-use changes began occurring in the basin. Therefore reducing nutrient volumes is unlikely to have a detrimental effect on the environment and could even benefit coastal ecosystems because of the associated reduction in pollutants from sewage and industrial outflows. Diverting wet-season flows in any particular year was unlikely to have a major effect on flows during the subsequent dry season. The trial of managed aquifer recharge under way in the Lower Yom River sub-basin of the Chao Phraya, meanwhile, has yielded recharge rates that are encouraging, and comparable to those encountered in similar systems around the world.
The livelihoods of farmers relying on rainfall to water their crops could be significantly improved if they had greater access to water in the dry season. In upland areas of Thailand, farmers tend to grow sugar cane, maize, cassava and orchards, while in the lowlands, rice, soybean and vegetable crops are prevalent. The approach to putting the system in place could range from installing small-scale equipment on private smallholdings through to larger-scale infrastructure on commercial farms or government land. However, the authors stress the need for careful governance to underpin the system’s success. For example, farmers would need to be encouraged to forego land for recharge and become “stewards” who manage infrastructure for the benefit of downstream communities.
An economic analysis undertaken by the scientists shows that the system has the potential to recover its investment in 14 years, if moderate performance is achieved. It would generate around US$250 million annually in export earnings while helping to alleviate poverty. The researchers suggest that further work is required to test the system’s viability. This would include: identifying and assessing areas with the greatest opportunity for floodwater harvesting; investigations to assess site suitability; engagement between farmers and the water resources sectors; and development of demonstration sites to illustrate feasibility. If the concept could be proven for the Chao Phraya basin, it could also be relevant for other river basins that discharge to the sea in Thailand and across Asia.
“This important study shows that surplus wet-season waters, could be used to lessen the damaging and costly impacts of floods and droughts while alleviating poverty and maintaining vital coastal ecosystems,” said Jeremy Bird, Director General of IWMI. “Bringing the study to reality will require detailed investigations to determine areas where environmental conditions are suitable for aquifer recharge. However, provided a participatory approach is taken that unites farmers with water resources managers and flood protection authorities, this innovative idea could seed flood alleviation successes on the ground across Asia.”
So far, the 2012 monsoon season has not brought to Thailand the destructive level of flooding experienced a year ago but it is only a matter of time before another damaging deluge strikes the nation. In light of the high cost of the 2011 disaster, efforts to increase resilience to floods need to come quickly. As well as putting long-term water management projects worth more than $9bn up for tender to Thai and multinational companies, the government has proposed creating new flood-retention zones. Under the plan, huge areas of low-lying land, upstream and around Bangkok, would be allowed to flood in years of excessive rain. If this latter plan can be combined with rainwater harvesting and managed aquifer recharge schemes, Thai farmers might, in future, help protect urban areas from flooding while saving their crops from failure during the dry spells that are destined to follow in the wake of the monsoon.