Restriction for navigation by barges and other vessels from the North to Bangkok area using the Nan
and Chao Phraya route is obviously due to the followings:
- The natural navigation channels are not stable. Erosion had caused sand banks in several
reaches.
- The rivers are meandering with several sharp bends.
- Sand dredging in the lower reach of the river has caused sudden changes in river crosssection.
Consequently, the profile of the river is locally reduced to a dangerous level.
During the high water season (September-December) most barges carrying agricultural products from
the North to Bangkok use the Chao Phraya River route which is the shortest route with only one navigation
lock. The size of the lock and lock gate is large enough to accommodate fully loaded barges. But during the
low water season (January-March) about 70 percent of the barge traffic have to use the regulated Suphan
River, Chao Chet Canal and the Noi River route which have several small-sized navigation locks. The
estimated travel speed of a fleet of conventional tug-barge during the high water season using the Chao
Phraya River route is 3.7-7 km/hour downstream and 4.1-4.3 km/hour upstream. While using the alternative
Suphan River-Chao Chet Canal route, the corresponding travel speed would be 2.2-3.0 km/hour and 4.0
km/hour respectively.