bigquery sql to find max value in an event

need some quick help with analysis GA data in bigquery. One pageviews on our side we trigger scroll event to understand how far a user has scrolled. I need to analyze the longest scroll depth per per per session. So if a users scroll first 3 pages of product page like /jeans we would trigger a scroll event 3 times with value of the scroll depth (1,2,3) and in this case but i only want to capture 3 in this case. if the same users then visits /jackets pages and scroll only pages I should capture 2. Similarly for all the sessions onsite.