Flood-Based Livelihood Systems (FBLS) are systems that make use of temporarily predictable flood water to support farming, fishery, (agro)forestry, grazing grounds, recharge and groundwater storage. FBLS can be found all across the globe but can be mainly seen in the Middle East, North Africa, West Asia, East Africa and parts of Latin America. An estimated area of 30 million ha worldwide is under FBLS of which over 15 million ha in arid and semi-arid regions in Sub-Saharan Africa (SSA). FBLS are very risk-prone. The uncertainty comes both from the unpredictable nature of the floods and frequent changes to the river beds that carry these floods. FBLS are often left out between rain-fed and conventional irrigated agriculture and much of its potential is still unharnessed. It is often the poorest segments of the rural population whose livelihood and food security depends on floods. Substantial local wisdom has developed in organizing FBLS and managing both the flood water and the heavy sediment loads that go along with it. Investing in FBLS could lift 700-800 million people out of poverty and into prosperity.
Water availability is increasingly under pressure as a result of population growth, environmental degradation and climate change. More than ever, the potential offered by seasonal floods needs to be harnessed; to strengthen agricultural livelihoods, to improve social equity and to increase the ecosystem integrity. Harnessing floods is a quintessential method to allow rural communities in vulnerable areas to adapt to climate change. For many farmer communities who depend on agriculture and fisheries, floods are not a hazard but rather an asset.
FBLS can be divided into different categories:
Sedimentation is an important feature of FBLS and FBLS are as much about managing water as it is about managing sedimentation. Flood waters are usually laden with sediment. Scour and siltation are part and parcel of FBLS. Rivers carrying flood water lift and deposit huge quantities of sediment. As a result there is constant change in bed levels, resulting in changes in bed levels and water distribution. The impact of these processes differs between the various systems. It depends on the amount and composition of the sediment load that a river carries, which depends on the rainfall pattern and the characteristics of the catchment area; its geology, morphology and vegetation cover. Farmers are usually able to identify the origin of a flood by the type of sediment that is transported by it. The degree of siltation and scour also depends on the local topography and the type of material. In FBLS areas with low gradients, as are found on the plains, a river is always in danger of choking itself with its own silt deposits and finding another way. Moreover, in the fine sandy deposits of the plains, the scouring of the riverbed is a larger danger than it is in the armuoured river beds of the highlands. As a result, the lowland flood irrigation systems are particularly dynamic.
Farmers however, are not passive actors in these scour and siltation processes. They actively manipulate the scour and sedimentation processes. They may deepen the headreach of a flood channel, in order to attract a larger flood that will further scour out the channel. If a flood river breaks its banks, farmers may close the breaches. If it deflects water away from their land or on other occasions, they will leave the breaches intact so that these will act as escapes, creaming off the peaks of the very high floods and maintaining the flow at their own system at a manageable level. In other cases, farmers will manipulate the siltation process to force the river bed to purposely silt up. The latter is in practice where the river has become uncontrollable, because its bed may has become to deep or to steep. The remedy is to built a strong permanent bund across the river and force the river to deposit its sediment load upstream of the bund.
As a testimony of the diversity in development in the world, FBLS are on the decline in rich areas such as Saudi Arabia, but is on the increase in low income countries such as Ethiopia and Eritrea. Generally FBLS are associated with low returns per labour, great variability in income between good and bad years and a high degree of social organisation to maintain the systems. Where more rewarding sources of income come up, where a period of long droughts force people to abandon their area or where the local organisation is undermined FBLS may disappear.
Another important change in several areas, that are traditionally spate irrigated is the introduction of groundwater irrigation. In many FBLS areas groundwater resources are relatively rich due to long periods of recharge. With the availability of relatively inexpensive pumpsets groundwater has become an important source of irrigation, for instance in spate areas in Dera Ghazi Khan (Pakistan), Tunesia or Yemen. This has resulted in a neglect of the spate infrastructure and a change towards perennial cropping.
The number of public programs to support FBLS have been relatively limited. One reason has been the difficulty to justify investments in civil engineering works on systems, dominated with low value farming. The second reason has been that it has been hard to identify successful interventions in FBLS, because these systems are often hydraulically and socially generally very complex.
An alternate approach to support FBLS has been the subsidization of mechanical traction. This approach has been followed with a relative high degree of success in Pakistan and Tunesia. Bulldozer programs have put a very useful resource at the hand of local FBLS farmers – who have remained in charge of the design and implementation. The cost effectiveness of bulldozer has been relatively high, moreover.