A Procedure to Assess the Impacts of Drainwater Reuse
The assessment procedure represents a practical management tool that aids selection of the most appropriate strategies and management methods in irrigated agricultural areas that incorporate the reuse of drainage water. It allows systematic evaluation of the likely impacts of drainwater reuse in a given area, so that the best planning and management decisions are made to maximise sustainable agricultural production and minimise negative impacts on soils, crops and the environment.

 Background
In many parts of the world the reuse of agricultural drainage water for irrigation is leading to accumulation of salts and toxins in soils, with detrimental consequences for agricultural production. Salt and toxin build-up in soils promotes plant damage, yield reduction and crop failure, as well as posing a serious threat to soil fertility. The detrimental effects of drainwater reuse can be minimised or even avoided with adoption of appropriate water resource and irrigation management strategies and use of selected cropping regimes and soil management techniques.

The Assessment Procedure
Water resource planners and irrigation managers faced with the prospect of having to utilise water of marginal quality for agriculture have a number of fundamental issues to consider. The main management issues which can be addressed with the Assessment Procedure are:
- Different scenarios of cropping patterns and periods can be analysed and the effects of predicted soil salinity and toxin levels can be assessed
- Utilisation of different sources of water can be considered, and the impacts of alternative mixing ratios evaluated
- The effectiveness of irrigation management and soil management techniques can be assessed.

What it covers
A step-by-step procedure for assessment is presented, which is suitable for use by non-specialists. The procedure is applicable both at project initiation and later on when remedial action is necessary.

Background information on the main hazards associated with drainwater reuse, and potential impacts on soil and crops is included along with a discussion of the management options available to the water resource planner.

  A specification of the data requirements for the procedure and recommendations on water and soil sampling procedures are provided. A useful example application of the Assessment is also included to illustrate the use of the procedure and help the user to apply the technique to their own situation.

With this guide the user should be able to:

  • Identify the main hazards of drainwater reuse in the project area
  • Assess the immediate and long-term impacts on crops and soils
  • Evaluate different scenarios of:
                - water resource planning
                - irrigation management
                - cropping regimes
                - soil management
    and thus make informed planning and management decisions for the project area.

    Contributors
    HR Wallingford Ltd, UK; Water Management Research Institute, National Water Research Centre, Egypt.

    Intended users
    The procedure is intended primarily for use by water resource planners and irrigation managers in agricultural areas that incorporate, or will incorporate, the reuse of drainage water for irrigation. It may also be of use to land development agencies, environmental impact assessors and as an educational tool.

    Abbott, CL and EL Quosy, DED, 1996. A procedure to assess the impacts of drainwater reuse. HR Wallingford, UK. Report no. OD 134.

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