Irrigated agriculture has made a significant contribution towards world food security. However, water resources for agriculture are often overused and misused. The result has been large-scale waterlogging and salinity. In addition, downstream users have found themselves deprived of sufficient water, and there has been much pollution of freshwater resources with contaminated irrigation return flows and deep percolation losses. Irrigated agriculture needs to expand in order to produce sufficient food for the world's growing population. The productivity of water use in agriculture needs to increase in order both to avoid exacerbating the water crisis and to prevent considerable food shortages. As irrigated agriculture requires drainage, a major challenge is to manage agricultural drainage water in a sustainable manner.
Up until about 20 years ago, there were few or indeed no constraints on the disposal of drainage water from irrigated lands. One of the principle reasons for increased constraints on drainage disposal is to protect the quality of receiving waters for downstream uses and to protect the regional environment and ecology. Many developed and developing countries practise drainage water management. This study has brought together case studies on agricultural drainage water management from the United States of America, Central Asia, Egypt, India and Pakistan in order to learn from their experiences and to enable the formulation of guidelines on drainage water management. From the case studies, it was possible to distinguish four broad groups of drainage water management options: water conservation, drainage water reuse, drainage water disposal and drainage water treatment. Each of these options has certain potential impacts on the hydrology and water quality in an area. Interactions and trade-offs occur when more than one option is applied.
Planners, decision-makers and engineers need a framework in order to help them to select from among the various options and to evaluate their impact and contribution towards development goals. Moreover, technical expertise and guidelines on each of the options are required to enable improved assessment of the impact of the different options and to facilitate the preparation of drainage water management plans and designs. The intention of this publication is to provide guidelines to sustain irrigated agriculture and at the same time to protect water resources from the negative impacts of agricultural drainage water disposal.
This publication consists of two parts. Part I deals with the underlying concepts relating to drainage water management. It discusses the adequate identification and definition of the problem for the selection and application of a combination of management options. It then presents technical considerations and details on the four groups of drainage management options. Part II contains the summaries of the case studies from the United States of America, Central Asia, Egypt, India and Pakistan. These case studies represent a cross-section of approaches to agricultural drainage water management. The factors affecting drainage water management include geomorphology, hydrology, climate conditions and the socio-economic and institutional environment. The full texts of the case studies can be found on the attached CD-ROM.