Multiple choice general knowledge science & technology Base level is: the level associated with the base of a river channel the normal elevation of a reservoir the level above which flood waters will not rise the level below which streams will not erode Reveal answer Fill a bubble to check yourself D Correct answer Explanation Base level is the lowest elevation to which a stream can erode - typically sea level or a local reservoir level. Streams cannot erode below this point, making it the fundamental control on valley depth.