Sustainable Deltas Project researchers focus on importance of deltas across globe. Delta: A place where sediment carried downstream by a river enters the sea, forming a fan of sand or mud. Although deltas make up just 1 percent of the world's land, they're home to more than half a billion people -- and to fertile ecosystems such as mangroves and marshes.
Deltas also serve as economic hotspots, says hydrologist Efi Foufoula-Georgiou of the University of Minnesota. They support much of the world's fisheries, forest products and agriculture, and are food baskets for many nations.
Scientists have found that deltas are disappearing at an alarming rate, however, affecting humans and many other species. Human actions rob deltas of their lifeblood: water and sediment. On a global scale, people have diverted more than 40 percent of river discharges and 26 percent of river sediments into large reservoirs. Losses of wetlands to development, and the erosion that follows, further deplete deltas of sediment. Despite its size, the GBM Delta is foundering.
Photo by Michelle Leinfelder-Miles. Leinfelder-Miles has been studying alfalfa, a crop where the harvested product is its vegetative growth, so any extra energy that it uses to take up water in salty conditions can decrease yields.
Soil salinity can be reduced by periodic leaching — meaning adding more water than the plant needs — but deciding how much excess water a crop needs in any given location can be challenging. To answer this question for alfalfa in the Delta, Leinfelder-Miles worked cooperatively with growers to set up a series of seven field sites that she and colleagues intensively sampled over a number of years.
The work was physically grueling — salinity is often modeled rather than directly sampled because it is physically intensive work. We augered twelve holes in each of our fields, and it took us about six hours to sample a site — if all went well! Sometimes it didn't. Once, we lost the end of a homemade water sampling tool down a foot hole, and we tried so hard to retrieve it but finally had to give up, bury the tool, and remake it.
While alfalfa has been getting a lot of attention as a big water user during the California drought, researchers stress that there are trade-offs involved with all crops. Alfalfa takes about the same amount of water to grow as any crop, but because it is grown year round, its overall water use can be higher. The good news is that it can also be deficit irrigated when needed.
Engineering solutions alone will not stabilize the system, but need to be combined with adaptations of the agricultural production system to increase resilience. Here, the government had installed 10 large sluices to prevent saline water inflow during low-flow periods for an area of , ha, while leaving the large band between a highway and coastal dike for mangrove and marine habitats.
Freshwater from the Mekong is still flowing into the protected area through a dense canal network. These investments enabled many rice farmers to produce two to three rice or upland crops per year, but restricted the supply of saline water required by shrimp producers. As rice prices fell and shrimp prices rose, farmers were no longer able to make a decent profit. The research supported a policy change from an exclusive focus on rice to a broader land and water management policy.
Modeling was used to identify how to operate the sluice gates to supply suitable water for both brackish water shrimp and rice production, including the buffer zone where shrimp and rice are grown in rotation during the dry and wet seasons, respectively. This work set the scene for the WLE research described below. Recently, increasing intrusion of saline water and pollution from overuse of agricultural chemicals have led to deterioration of aquatic resources fish, shrimp, frogs and declining rice yields.
It is a highly regulated system with dams, barrages and extensive embankments on nearly every tributary, diminishing dry season water flow. About million people depend on agriculture and aquaculture for their livelihoods. Climate change is likely to have a serious impact on the reliability and intensity of the southwest monsoon, the intensity of cyclones, and river flows.
River tributaries are often heavily polluted with municipal and industrial wastes. Arsenic in the groundwater is a serious problem. The delta is also threatened by both reduced aggradation and accelerated compaction combined with rising sea levels. The Bangladesh coastal zone is characterized by a vast network of river systems and an ever-dynamic estuary.
Since the late s, polders have been constructed for rice production and to protect people from floods. A polder is a low-lying area between the rivers, protected from tidal flooding and salinity intrusion by an earthen embankment, with internal canals linked to gated outlets in the embankment used to manage water levels within the polder. About 54 polders are located in the Ganges coastal zone of Bangladesh, covering 1. In the more saline regions, polders are used to raise brackish water shrimp and fish both for sale and household use, and in some areas, brackish water shrimp farming is carried out in rotation with rice during the rainy season, as in parts of the Mekong delta.
Polders are extremely vulnerable to flooding, largely due to high rainfall during the rainy season, lack of separation between low and high lands internally, poor drainage management and cyclones. Saline water intrusion occurs sporadically in patches during cyclonic storm surges or because of damaged or missing sluice gates and poor management of the gates. Agricultural production is much lower than in the rest of Bangladesh, and food and nutrition insecurity and poverty rates are higher.
Polder 30 has a population of 38, people and covers 6, ha with a net cultivable area of 4, ha. There are multiple drainage and flushing sluices and six inlets to the area. Internal drainage congestion and external siltation had made some land unsuitable for crop production.
In both deltas, a great deal of technical research and modeling has been done starting with DFID-supported research projects and subsequent CPWF research.
The results demonstrate that achieving sustainable agricultural intensification in such complex systems requires a multi-scale, whole-systems, landscape or agroecological approach.
Thaibaan is a participatory research method that is led by the farmers, not the scientists—a form of citizen science. From conception to dissemination, villagers themselves are the principal researchers. Local officials are also involved to ensure their buy-in. An innovation has been the combination of photovoice and Thaibaan methods, in which the village people—especially women—are trained to use photographic techniques and storytelling.
This research has helped community members understand their own role in managing water resources, notably on how pesticide use and rubbish disposal can affect their livelihoods. Special efforts have been made to ensure women and ethnic minorities participate in the research. Farmers have already adapted their livelihood strategies to include extensive shrimp farming, which uses brackish water and has minimum impact on the environment. Farmers grow rice when freshwater flows through the channels and change to shrimp farming when the seawater arrives.
The results support those of recent research in Ben Tre, another Mekong coastal province. It concluded that the option currently favored by policy makers, i. The alternative is to offer farmers more freedom of choice in how they adapt, and support their efforts to find solutions, for example, by diversifying their agroecosystem.
Collectively, the results suggest there is now sufficient research-based evidence to support scaling up more flexible institutions and policies for land-use planning and agricultural production in the Mekong delta. Previous CPWF research had shown that the path to shifting to high-yielding rice varieties, sustainable intensification and crop diversification in the polders was improving water management—especially drainage during and immediately after the rainy season.
The CPWF research demonstrated the potential benefits of creating small community water management units within the polder, based on the hydrology of the landscape and the common aspirations of farmers.
A recent WLE project built on these results by implementing a pilot project in three villages in Katakhali sub-polder of Polder This is a Dutch and Bangladesh government effort to strengthen value chains and WMOs, and rehabilitate and upgrade water infrastructure.
The research confirmed the importance of organizing the community around hydrological units within sluice gate catchments and of synchronized cropping within these units. To address this question, we used a computer model to project changes in the flows of sediment to almost 50 major deltas worldwide.
We used the model to explore the impact of various environmental changes, including climate change, population growth, increases in wealth and the construction of dams. Our results are published in the journal Environmental Research Letters. Our results suggest that many deltas — already significantly stressed — will become sediment starved, further compounding the risks of rising relative sea levels.
This is particularly concerning because these deltas are among the largest and most densely populated in the world. We found that climate change will generally drive a small increase in the flows of sediments as, among other factors, warmer temperatures lead to increased precipitation and more soil is washed into rivers. But in many deltas this modest uptick will be more than offset by dams which trap river sediments and improved soil conservation practices as societies become wealthier.
International cooperation will be essential in deltas such as the Mekong and Ganges which are supplied by large rivers that drain many countries.
For dams specifically, comprehensive environmental risk assessments that fully cost the consequences for downstream regions are required so that plans can be changed or scrapped. For those dams that are to be built in the coming decades, their design must accommodate transport of sediment downstream. For authorities within deltas, faced with managing a dwindling supply of river sediment, new approaches are needed to better manage this precious declining resource.
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