At the current 534.5′ Lewisville Lake Level, there is 49.5′ clearance.
How did we calculate this? First, we took a look at the NTTA Engineering report, to get the official 52′ clearance above the spillway level, which is at 522′. Then, we subtracted the height of the water above the spillway, 2.5′ (534.5-532).
From NTTA Engineering Report: ” The superstructure consists of 68 spans, each 120 feet in length, and a water craft passage span 360 feet in length. The water craft passage span provides a vertical clearance of 52 feet above the uncontrolled spillway elevation and a 350-foot horizontal clearance between span supports