Irrigation

Many modern methods of agriculture require some form of irrigation in order to meet the needs of an increasing population.

One method is Channel Irrigation where large trenches are dug and lined with concrete to channel the water from dams. This water is then siphoned off into the fields using smaller concrete-lined channels and ultimately small channels hand-dug by farmers. These trenches can be highly destructive to the sites they pass through, and can also result in chemical leaching from the concrete, which can affect artefacts that are still buried in the soil.

In 1980, construction began on a large civil infrastructure programme, the Saddam Dam (now called the Eski Mosul Dam) on the Tigris River (Figure 1). The plans called for the construction of an extensive network of canals, pipelines, feeder roads, agricultural complexes, new settlements, and massive mechanical irrigators that would cover an initial 400 km2 and eventually 750 km2. These developments, together with the ensuing multi-irrigated cropping, would drastically alter the face of the landscape.

Figure 1 (left): The Eski Mosul dam, Tigris river, Iraq. Source: ESRI digi-globe imagery, 2015

Figure 2 (below) shows the archaeological sites in the area around the site of Tell al-Hawa, in the Jazira in Iraq, which was affected by the infrastructural developments following on from the development of the Eski Mosul dam. The Iraqi State Antiquities Board designated the area a rescue zone and foreign archaeological teams were invited to participate in a program of rescue work, recording the sites before they were destroyed. The first satellite image shows the sites and ancient routes around Tell-al-Hawa (marked in red and green respectively) on a CORONA satellite image from December 1967 (courtesy of the CORONA Atlas of the Middle East). When the area is viewed on a DigitalGlobe image on Google Earth from October 2010, the large number of canals, and the effect of this development on the archaeological sites (and the wider landscape), can be seen.

Another method is called centre pivot irrigation. Water is pumped from a depth of up to 1km to the surface and distributed via a large centre pivot irrigation feed (Figure 1). The large circular fields can vary from a few hundred metres to as much as 3km in diameter. In order for them to function, the terrain needs to be reasonably flat, so archaeological sites are usually cleared to make way for the plants.  DigitalGlobe satellite images, viewed on Google Earth, show the increase in the centre pivot irrigated fields of Saudi Arabia between January 2000 and February 2015. The number of irrigated areas has more than doubled.

The threat posed to archaeological sites can be seen in Figure 2 (below) of a desert kite (marked in red) near Azraq (the stone walls radiating from the oval structure on the right) in October 2003 and June 2013. Kites are long dry-stone walls converging on a neck that opens into a confined space, and are used for hunting wild animals. There are a number of other small circular enclosures around the kite that are not marked.

 

Figure 1 (left): Centre pivot irrigation at Jubbah Oasis, southern Nefud, Saudi Arabia. Copyright Richard Jennings, Palaeodeserts Project.

Figure 2 (below): Encroachment of centre pivot irrigation upon deserts kits near Azraq, Saudi Arabia. See also NASA’s recent image of the day – crop circles in the desert  –  for other examples see here.