Infodoc : Sciences, Techniques et Culture

Secondary soil salinization is one major threat to the sustainable development of irrigation scheme in arid or semi-arid region. This study was undertaken to understand the evolution of soil salinity and its relation with irrigation & drainage practices in Hetao Irrigation District, North China. Two parallel approaches were used for this purpose. The first approach was to extract temporal and spatial evolution history of soil salinity and land use by using archive remote sensing images (1973-2006). The second approach was to estimate the salt accumulation at different levels (system, division, irrigated area and root zone) by building a conceptual water and salt balance model and using long historical ground data (1960-2004).
It was found that the developments of artificial drainage[...]

Secondary soil salinization is one major threat to the sustainable development of irrigation scheme in arid or semi-arid region. This study was undertaken to understand the evolution of soil salinity and its relation with irrigation & drainage practices in Hetao Irrigation District, North China. Two parallel approaches were used for this purpose. The first approach was to extract temporal and spatial evolution history of soil salinity and land use by using archive remote sensing images (1973-2006). The second approach was to estimate the salt accumulation at different levels (system, division, irrigated area and root zone) by building a conceptual water and salt balance model and using long historical ground data (1960-2004).
It was found that the developments of artificial drainage system have greatly improved the drainage capacity and taken obvious effect on soil salinity control. The total salt-affected area has decreased from 213,484 ha in 1973 to 124,036 ha in 2006 and the salt-affected irrigated area has decreased trom 67,105 ha in 1973 to 24,853 ha in 2006. Dry drainage was also found to play an important role in sustaining the salt balances of the irrigated area and its root zone in HID. The excess water drained by dry drainage was averagely 11 times as that by artificial drainage. Less than 10% irrigated area were affected by soil salinity, less than 30% salinity occurred in irrigated area but this ratio tended to increase recently with the expanding irrigated area. Besides the groundwater table before ground treeze was found to have a close relationship with soil salinity and be important for soil salinity control. Neither artificial drainage nor dry drainage could meet the drainage requirement for salinity control as long as huge canal seepage is present. The presence of huge canal seepage was the major raison d'etre of dry drainage. To have a successful dry drainage system, three important aspects need to be balanced: the drainage requirement, the transmitting capacity and the dry drainage capacity. Canal seepage is of first importance in the drainage system design of HID and needs to be taken into account in most canal irrigation schemes. Meanwhile, the decrease in water availability, the increase in cropped area and ongoing water saving project caused the decrease in dry drainage capacity and deficiency in leaching, indicating potential soil salinization in HID.