Newsletter and Technical Publications
of Alternative Technologies for Freshwater Augumentation in Africa>
1.1.15 Tidal Irrigation
Tidal heights of 1.3 m and 1.0 m exist in the Gambia River at
Jahally and Pacharr, respectively. Special intake structures with gates
were constructed, which, when opened at high tide, allow brackish tidal
water to enter irrigation channels leading to the farms to be irrigated.
The gates are opened for a period of between 3 and 24 hours depending on
the size of the area to be irrigated. Tidal irrigation is coordinated with
pumped irrigation, and is used to irrigate low lying areas along the
Gambia River. Pumped irrigation systems are used for areas at higher
Extent of Use
This technology is used in an on going project in The Gambia, West
Operation and Maintenance
Once installed, this technology can be maintained by locally-trained
artisans with general farm experience.
Level of Involvement
The technology is locally- or community-controlled, although some
expertise is required for the design, siting, construction and maintenance
of the civil structures.
The capital costs of the project, at 1983/84 prices, was $7.5 million.
The current operation and maintenance cost is about $220/ha/year.
Effectiveness of the Technology
The technology has been very successful in paddy rice cultivation. Using
tidal irrigation, double cropping of 167 ha and 850 ha is achieved
annually at Jahally and Pacharr, respectively. Similarly, irrigation of
440 ha and 125 ha is achieved annually at Jahally and Pacharr,
respectively, with pumped irrigation. The annual yield is 9 t/ ha/year at
an annual cost of $70/t/year.
This technology is appropriate in areas where tidal and river conditions
are similar to those at Jahally and Pacharr. Generally, the river is in a
relatively flat basin with an high degree of tidal intrusion. This
technology should only be used with salt-tolerant crops.
There are no known environmental benefits. Drawbacks include a risk of
salination and creation of a barrier to migratory fishes.
The technology is very successful because, once the intake structures
and irrigation channels have been constructed, the operation and
maintenance costs are very low. Maintenance work on the irrigation
channels, and clearing of weeds and bush from the channels and arable
area, can be done by the local farmers.
The major difficulty experienced is the lack of availability of spare
It is accepted by the local community and is seen as an income
Further Development of the Technology
No further development of the technology is necessary.
International Fund for Agricultural Development (IFAD),
African Development Bank (ADB), and the German Government: Fulladu West
District Project, The Gambia.