The technology needed to employ artificial irrigation techniques is only effective if there is a constant water source. Other agricultural innovations used in Sumer were dams and sluice gates. On higher ground, diversion dams were built over secondary waterways to restrict the flow of water and allow it to accumulate in large quantities. These reservoirs supplied the canals and plains with water during droughts and slowed the flow of water during flood seasons. Many of the canals and dams along the Tigris and Euphrates Rivers were also controlled by sluice gates which regulated the direction, rate, and flow of water.
Figure 9. Click here: Image of Dams and Sluice Gates. University of Toronto Atlas of the Ancient Near East, c. 3000-300 BCE.
 Richard Cowen, “Chapter 17: Ancient Irrigation.” Exploring the Earth. Accessed January 7, 2018. http://mygeologypage.ucdavis.edu/cowen/~gel115/index.html