Bart Schultz
The main branch in the delta is the Shatt al-Arab River. This river also forms the border between Iraq and Iran. On the Iranian side, along the Shatt al-Arab lies the isle of Abadan. This is an elongated isle between two river branches in the delta. Most of the isle has an elevation of no more than two metres above mean sea level.
Date palms are widespread along the river branches. Because the area is very arid, with annual rainfall of less than 200 millimetres, irrigation is essential. Traditionally, date palms were irrigated through a system of canals controlled by the tides from the Persian Gulf. At high tide, these canals transported river water to the plots, where it infiltrated in the soil. This is still the case in some areas. In a few others, more modern irrigation systems have been installed. In a few other areas, irrigation is no longer feasible due to the encroachment of saline water from the Persian Gulf. Consequently, some areas have been abandoned.
Three types of areas are distinguished. In the upstream part of the date palm belt, tidal water almost never floods the land. In the middle section, there is a transitional situation. In the downstream part, the land was more frequently flooded and the water was salty. Due to their low elevation, especially near rivers, the lands are protected from tidal flooding by dikes, and farms are often situated on artificial mounds. The reclaimed areas have an elevation close to the average water level of the Persian Gulf.
A 2004 advisory report by R.J. Oosterbaan contains information on tidal fluctuations in the rivers. The fluctuations are greatest in the estuaries and gradually decrease upstream. At the estuary, in the lowest-lying areas near the coast, the tidal fluctuation varied between 1.7 and 1.9 metres. Upstream, in the middle section, the fluctuation ranged from 1.5 to 1.7 metres, and in the upstream area, the tidal range became increasingly smaller. In winter and spring, the river discharge was higher, the slope in the water level was steeper, and the water level rose. Although the tidal surge did not reach as far upstream during high discharges, this was fully compensated for by the higher river water levels.
Oosterbaan further describes that in the lower part of the palm belt, the canals, which ran more or less perpendicularly from the river into the land, were relatively wide and deep. Even in canals six kilometres long, the decrease in tidal amplitude was therefore limited, and on the inner side of the canals, the fluctuation could still be 1.3 to 1.5 metres. In the upper part, the canals were shorter, shallower, and narrower. The tidal fluctuation at a distance of two kilometres from the river would be 1.1 to 1.3 metres here, if the canal beds were at the level of the low tide. In reality, the bed level was often higher, resulting in a smaller amplitude. In poorly maintained canals, the fluctuation was even smaller.
In recent decades, several dams have been built in the upper reaches of the Euphrates and Tigris rivers for irrigation and hydropower generation. This has significantly reduced the river discharge. For the date palm areas, this not only resulted in a much smaller discharge of freshwater, but also in salt water intrusion from the Persian Gulf, especially during the dry season, which can extend further upstream, preventing the water from being suitable for irrigation. This poses a particular risk to the polder areas closest to the coast. Google Earth shows that while date palm polders still exist in the polder area along the Shatt al-Arab, they have almost completely disappeared on the other side of the isle. The situation is unlikely to improve much in the future, and the date palm polders are facing difficult times.
