Some dams are big! They make an obvious impact on the landscape and a case can be made that they are useful: for regulating water supply for rice paddies or tapping the moving water to drive turbines to make electricity. The Shannon Scheme and the dam at Ardnacrusha was as much a political statement about Independence from the Brits, and take her place among the nations of the earth, as it was about servicing the nascent state of Ireland with electricity. The idea for damming the River Tigris North of Mosul had been on the cards since at least 1953. With each change in regime, successive international consultants were called in at international consultant prices as the Tigris Dam got political traction: 1953 Alexander Gibbs; 1956 Kolijan American; 1960 Harza; 1962 Soviet Technoprom; 1965 Amitranvoima; 1972 Geotehnika; 1974 Soletanch; 1978 Swiss Consultants Consortium. If Iraq is anything like Ireland, the fees for the consultants could have built the dam twice.
Actual works didn't start until the 1980s as part of Saddam Hussein's Arabification of the predominantly Kurdish North of the country. Hochtief Aktiengesellschaft, a German/Italian consortium got the go ahead to break ground in 1981. As the bed 'rock' was gypsum which is only harder than talc on the Mohs scale of hardness, and is also water-soluble, the first step was to grout the base of the projected dam. The engineers recommendation was dismissed as too expensive and time consuming and after a slip-slop blanket grouting, construction proper began. The dam was completed by 1984 and is massive: 113m high in the centre and 3500m wide, it is holding 10 billion tonnes of water - that's a reservoir 5000x bigger than Situ Gintung. The dam, however, is more or less of the same earth-core construction. In Indonesia or Wales, you have to be primarily concerned with excessive rainfall over a short period of time; in Northern Iraq the main concern is seasonal snow melt in the mountains of Turkey which is where the Tigris and its tributaries rise.
Going round the news at the moment is a story that the intrinsically under-engineered Mosul Dam is under imminent threat of failure. The US Army Corps of Engineers say it is at "significantly higher risk" of failing than previously thought as more and more untreated voids are becoming apparent in the fabric of the dam or its 'foundations'. Because the job wasn't done properly (or abandoned as futile) at the start, the operators are committed to pour concrete into voids until the end of time or the dam fails. Oh, and there's a war on! ISIL captured the dam in 2014 and the