Commentary for Genesis 7:19

והמים גברו, this too is meant to give us additional information. This is why the words מאד מאד have been added, each of these words alerting us to an increasing power of the waters driving the ark. Now the waters were so powerful that they drove the ark far away from where it had stood originally. The second word מאד hints at the ark rising higher than any of the surrounding mountains.

והמים גברו, “and the waters had kept rising and becoming more turbulent;” Verse 18, writing וירבו ויגברו המים, had taught us that when waters increase in volume the Torah describes this in terms of גברו, becoming strong, powerful, turbulent. It is possible, however, to understand the word ויגברו in verse 18 for the word כח also is often referred to as גבורה. In this case the turbulence of the waters uprooted trees, etc.