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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa>

2.3.3 Regeneration Water

Technical Description

Use of regeneration water involves the indirect reuse of water that has already been used, primarily in the agricultural sector. In some instances, this water is utilised for urban purposes. The objective of this technology is to augment the available water through reuse.

In irrigation, excess irrigation water applied to the land surface drains via subsurface drains to open channels where it is conveyed away from the fields to prevent waterlogging of the crop roots. Traditionally, such water is discharged to the nearest surface water course, where it is effectively removed from the irrigation system. In contrast, this technology conveys the drainage water to collection areas where it is pumped into reservoirs, mixed with fresh water and reused for irrigation.

Extent of Use

In Zimbabwe, use of regeneration water is currently practised on the sugar estates of Hippo Valley, Chiredzi and Triangle, and in other agricultural areas. For example, the Town of Glendale, Zimbabwe, depends for its water supply on regeneration water emanating from the irrigation of large citrus plantations in the Mazowe Valley.

Operation and Maintenance

Regular inspection, repair and maintenance of pumps and accessories is required.

Level of Involvement

Depending on the scale of the irrigation operations, government, large and small farmers, and other institutions may make use of this technology.

Costs

For irrigation purposes the major cost is pumping. The amounts of money involved depend on the size of the pumps, which, in turn, is dependent on how much water is available. Therefore, cost of this technology is very much a function of the size of irrigation operation. Irrigation pump installation costs in Zimbabwe are about $2 000/ha.

Effectiveness of the Technology

Water from the drains is put to use instead of being "wasted". Additional water for irrigation is made available. With flood irrigation, water collected in the drains accumulates at as much as 3 l/s from a 400 ha section. This water is enough to irrigate an additional 3 ha of cropland. In the case of Glendale, the water requirements of the small town, 32 l/s, are more than covered by the volume of regeneration water recovered through this technology.

Suitability

This technology is appropriate wherever water shortages are experienced. The use of regeneration water may not be appropriate where the regeneration water has a high concentration of dissolved salts.

Advantages

Additional water is made available for many other purposes through the use of this technology. Extra hectares may also be cropped as a result.

Disadvantages

Regeneration water has been found to be extremely saline, having electrical conductivity values greater than 4 million mS/cm at 250C , in some situations. This leads to salinity problems where applications of regeneration water are of high volume and/or prolonged. In cases where the regeneration water is utilised in the area where it is generated, there are usually some increased costs due to the extra pumping required to lift the regenerated water to the head of the irrigation scheme.

Cultural Acceptability

No cultural problems relating to the use of this technology have been recorded.

Information Sources

Hippo Valley Estates, Post Office Box 1, Chiredzi, Zimbabwe, tel. 263-96-2381, fax: 263-96-2554.

Triangle Limited, Private Bag 801, Triangle, Zimbabwe, tel. 263-96-6221, fax: 263-96-6513.

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