ديدگاه هاي نو در زهكشي

The New Approaches on Drainage

Poor irrigation water management combined with inadequate drainage infrastructure renders irrigated areas at risk of becoming waterlogged and gradual build up of salt concentration leading to soil degradation in arid and semi-arid regions. The objective of this review article is to recognize two main and new subjects in drainage issues: Integrated approach and impacts of climatc change. The drivers for a change towards an integrated approach to drainage are: increasing complexity of water control systems; conflicts of interest in many water management systems; re-prioritization of land and water management objectives because of changing social values; and declining luster of drainage as a professional sector and the need for the professional drainage community to rethink its position. On ihc basis of this analysis of the present situation with regard to drainage, a new and broader definition of drainage, less exclusively focused on agricultural productivity, can be formulated as a first step towards an integrated approach: "Drainage is land and water management through the processes of removing excess surface water and managing shallow water tables - by retaining and removing watcr-with the aim of achieving an optimal mix of economic and social benefits while safeguarding key ecological functions". Moreover, drainage systems were designed for a long life, on the assumption that climatic conditions would not change in the future. This will not be so in the years to come, due to the global warming and the greenhouse effect. Although an anthropogenic ally-induced climate change is expected to have significant impacts 011 drainage systems, the range of uncertainty as to how these climate impacts, at the geographic scales of interest, affect the drainage development process is still great. Moreover, the absence of a uniform understanding makes it difficult to assess the adequacy of existing planning principles and design criteria, in the light of these potential changes. Therefore, planners, designers, researchers and decision makers need to review the strengths and weaknesses of current trends in drainage development and rethink technology, institutional and financial patterns, research thrust and manpower policy, so that service level and system efficiency can be improved in a sustainable manner. At present, the challenge is to identify short-term strategies to face long-term uncertainties