Tal's Hill, the massive hill in center field at Minute Maid Park, is being demolished and a 15 million dollar renovation is taking place in Houston. The Astros began construction in center field last week, where they will move the CF fence in from 436 feet to a much more reasonable 409 feet. 436 feet was by far the deepest center field in baseball prior to the renovation.
Last June, the Astros put out some renderings of how the new outfield will look.
The new 409 foot wall will probably add double digit home runs to the ballpark. Last season, there were 24 batted balls hit greater than 409 feet to center field in Minute Maid Park, and only 3 of them were home runs, a 12.5% rate. League wide, batted balls hit to center field greater than 409 feet had a home run rate of 78%. We can probably expect the new dimensions to reasonably add about 15 home runs to Minute Maid Park next season, give or take a few.
Carlos Correa, Jose Altuve, George Springer and Evan Gattis all would have added 1 home run to their 2016 total under the new dimensions, having all lost 1 home run to the hill.
Here's Correa's lost home run: