 Many waterfalls are little known and most are not measured yet, it is possible that there are waterfalls in excess of 300 m tall.Drainage throughout most of Guyana is poor and river flow sluggish because the average gradient of the main rivers is only one meter every five kilometers.Swamps and areas of periodic flooding are found in all but the mountainous regions, and all new land projects require extensive drainage networks before they are suitable for agricultural use.