To develop and publish recommendations on safe use of drainwater for irrigation.

To field-test an effective method of reclaiming salt affected clays, and publish recommendations, in collaboration with IIDS, Southampton University.

(1) Use of marginal quality water (Drainwater Reuse)

Macro-study: A reconnaissance survey was carried out over an 18 month period in which the basic long-term variation of the soil salinity profile was evaluated in three areas of the Nile Delta in which Drainwater Reuse for irrigation had been practised for several years. Called the macro-study, the survey used soil-sampling techniques to investigate the temporal variation of total salts and specific salts over the cycle of the Egyptian agricultural year. The investigations compared salinity profiles between areas where irrigation was (i) free from drainwater, (ii) partially drainwater and (iii) completely drainwater. The comparisons were completed for representative areas selected in the western, eastern and central sections of the delta.

Micro-study: A detailed study was carried out at one particular area, the Noubaria Area in the western part of the Nile Delta. The study comprised day-by-day intensive monitoring of the water and salt balance on an instrumented field. The results from this intensive examination as well as substantiating the macro-study soil-sampling surveys, gave data with which the guidelines developed in the next stage of this project could be tested.

Guide-lines: Based on an extensive consideration of the widely distributed information about the effects of salinity in water, soils and crops, a procedure was developed for assessing the impact of salinity in areas where drainwater reuse has been utilised or is being contemplated

(2) Reclamation of salt-affected clay soils (Horizontal Leaching Technique) This study, which was carried out in conjunction with IIDS, Southampton, followed on from a series of three earlier studies in which the reclamation of salty clay soils had been investigated. These earlier studies comprised:

(i) the Zawia Study, Egypt, in which the difficulty of removing salt held in the monolithic clay structure had been identified,

(ii) laboratory studies in the UK in which the general principles of the HLT were developed and

(iii) field studies in Turkey in which the general feasibility of the technique was established.

A series of full-scale investigations were carried out to develop and optimise the technique up to the point where it could be utilised by other organisations such as land reclamation agencies. The work was carried out on salt-affected clay soils on a sugar estate in Jamaica, The work consisted of a series of trials both (linear one- and two-dimensional, and one- and two-way flow, to identify optimal land treatment, dimensioning of reclamation areas and water application.

A manual detailing the recommendations based on the results has been published and disseminated.

(1) Use of marginal quality water (Drainwater Reuse)

The macro-study indicated that salinity variation is occurring in areas such as the Nile Delta and that drain water reuse is making a significant contribution to the process. Local farmers had a good appreciation of how to deal with the salinity effects effecting their land. The variation of salinity with type of irrigation regime for each area, are detailed in the report. It also contains an analysis of the statistical validity of the soil sampling methods used.

The micro-study showed that the seasonal increases in soil salinity were not due to a simple process. The salt profile was found to build up during the summer due to irrigation with the marginal quality water supply. This salt is removed from the profile during the months leading into winter, with the net effect that over a year the salinity profile stays constant. This is a positive result since it indicates that irrigation with reused drainwater appears to be sustainable in areas such as Noubaria.

The assessment procedure developed for drainwater reuse was tested using the information gained from Noubaria. This showed that the procedure could be used to assess current and proposed procedures and could develop recommendations for operating procedures for the irrigation of such areas.

(2) Reclamation of salt-affected clay soils (Horizontal Leaching Technique)

Tests using the Horizontal Leaching Technique showed that over 60% of the soil's salt content was removed within 20 to 25 days of water application. Most occurred during the first 10 days. This was achievable on field plots 45m long and 30m wide. On land where the slope is less than 1%, a two-way flow arrangement can be used with no loss of removal efficiency and with better coverage.

(1) Use of marginal quality water (Drainwater Reuse)

Extensive field studies in the Nile Delta, combined with intensive water and salt balance studies at Noubaria, have shown how soil salinity levels vary under typical cultivation regimes. As well as indicating the circumstances under which farmers have been able to use marginal quality water in a sustainable way, the studies have enabled an effective assessment procedure and guidelines to be developed.

(2) Reclamation of salt-affected clay soils (Horizontal Leaching Technique)

Field trials showed that the HLT is a feasible and viable technique for reclaiming saline clay soils.

C Abbot and D El Quosy (1996) Soil salinity processes under drainwater reuse in the Nile Delta, HR Report OD/133

C Abbot and D El Quosy (1996) A procedure to assess the impacts of drainwater reuse, HR Report OD/134

C Abbott, D El Quosy, G Pearce, M Bayoumi (1996) Soil salinity levels due to drainwater reuse in the Nile Delta Proc. 6th ICID Intl. Drainage Workshop (Slovenia, April 1996)

C Abbott, D El Quosy, G Pearce (1996) A management tool for drainwater reuse Proc. 16th ICID Congress on Sustainability of Irrigated Agriculture (Cairo, September 1996)

Safe use of marginal quality water in irrigation - development of management tools (May 1996) WATER#2

A Armstrong, E Hughes, D Rycroft, T Tanton, G Pearce, C Abbott (1996) Manual for the Horizontal Leaching Technique - Reclamation of saline clay soils HR Report Reclamation of saline clay soils (November 1995) WATER#1

Both sets of outputs are now ready to be applied to saline soil situations in developing countries. Discussions have been carried out with respect to utilising the DWR guidelines in countries such as Egypt, Pakistan and India. Discussions have also been initiated with respect to introducing the HLT into Egypt. Further work has been carried out by IIDS Southampton on how to develop the HLT so that it can be used for soils which also have sodicity problems. This principally involved the incorporation of chemical amendment techniques such as gypsum addition.

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Email: dfid-kar-water@hrwallingford.co.uk