Because of their importance, high-head and low-head gates are given special attention in Chapters 3 and 4. In contrast to low-head gates, high-head gates have top seals as they operate under heads larger than their height. Figure 3.1 shows three of the most common types of high-head gates: the cylinder, the Tainter, and the leaf gate. Factors involved in making the selection of a gate or valve for an outlet work have been presented by Kohler (1969). Typical high-head gates, (a) Cylinder gate for 50 m head and (b) Tainter gate for 136 m head according to <xref ref-type="bibr" rid="ref255">Schmausser & Wickert (1987)</xref>; (c) Face-type leaf gate for 87 m head (Grand Coulee dam project) according to US Bureau of Reclamation; (d) Flow visualization by means of Hele-Shaw photograph (<xref ref-type="bibr" rid="ref46">Naudascher, 1957</xref>). https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780203751534/b3a6bdc8-7e49-4f5e-99d8-50556b37ec9f/content/fig3_1.tif"/>