Tidal irrigation (Abadan)
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Tidal irrigation is the subsurface irrigation of levee soils in coastal plains with river water under tidal influence. It is applied in (semi)arid zones at the mouth of a large river estuary or delta where a considerable tidal range (some 2 m) is present. The river discharge must be large enough to guarantee a sufficient flow of fresh water into the sea so that no salt water intrusion occurs in the river mouth.
The irrigation is effectuated by digging tidal canals from the river shore into the main land that will guide the river water inland at high tide.
For the irrigation to be effective the soil must have a high infiltration capacity to permit the entry of sufficient water in the soil to cover the evapotranspiration demand of the crop.
At low tide, the canals and the soil drain out again, which promotes the aeration of the soil.
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Interpretations and Explanations
Tidal irrigation at Abadan island, Iran
The Abadan Island in Khūzestān Province is situated between the Bhamanshir and Arvand rivers. The Arvand river (in Arabic: Shatt al-Arab) forms the boundary between Iran and Iraq and collects the waters from the Euphrates and Tigris rivers.
On the island extensive orchards of date palm are found thriving on tidal irrigation in the desert climate, although many date palms were destroyed during the Iraq-Iran war.
Palm tree belt
The palm tree belt stretches along the Arvand River from Abadan south-east over a distance of about 40 km and is bounded in the interior by a road.
The width of the belt varies from 2 to 6 km, and on average it is 4 km. The width is greater in the concave parts of the river bends and smaller in the convex parts. The convex parts have higher river levees and topography.
The total area of the belt is about 16000 ha. The tree spacing is around 6x6 m. There are roughly 300 trees per ha. The maximum yield is about 200 kg/tree and 60 t/ha.
Tidal canals
A sketch of the system of tidal canals [1] is shown in Figure 1. They are 2 to 6 km long depending on the topography and spaced at 50 to 60 m.
The tidal canals cut through and serve the levee soils along the river (Figure 2) and they stop where the basin soils of the backswamps begin.
Between the tidal canals additional lateral ditches have been dug perpendicularly at a spacing of 50 to 60 m to further promote the distribution of the irrigation water.
Field channels originate from the lateral ditches at a spacing of 10 to 12 m and the date palms are planted along these (Figure 3).
Soil properties
The typical properties of the levee soils are shown in Figure 4. There is a well developed topsoil with a thickness of more than 1 m through which the subsurface irrigation water can move in and out with relative ease.
Simulation tidal propagation
The tidal movements are 2 m on average. A simulation of tidal fluctuations in the ditches is shown in Figure 5 for an average and a high river discharge at various distances from the sea. The simulations were made with the Duflow [2] model.
Gallery
 Fig. 2. Longitudinal section of a tidal canal and cross-section through the river levee |
 Fig. 3. The field channels run between the lateral ditches |
 Fig. 4. An impression of soil properties |
 Fig. 5. Simulated tidal movements in canals at different river discharges and at various distances from the sea, assuming a normal tidal range |
Footnotes
- ↑ Consultancy report on the Abadan project. R.J.Oosterbaan, 12 September 2004. Abvarzan Co., Tehran. On line : [1]
- ↑ Duflow model http://www.mx-groep.nl/duflow/model
References
See also
External Resources
Attachments
Abadan.pdf
