On the Death Railway, you’ll be in the floodplain of the Mae Klong, in the greater Chao Phraya floodplain, which is where most of Thailand lives for better or worse.
Once every 2 or 3 years when the river floods over onto the floodplain, a large amount of fine sediment called alluvium is deposited onto the floodplain. The finer and lighter alluvium such as clay and silt drifts further away from the river out into the plains during a flood, and this regular deposit of alluvium is what makes these areas so fertile and suitable for rice cropping.
The larger, heavier, and coarser alluvium such as gravel and sand is deposited closer to the river. This means that After many flood events, raised areas of land, called levees, build up on the river banks. This is what is often preventing you from seeing the Chao Phraya itself, or its tributaries, from the train.
To a large extent, you could consider Thailand a Kingdom defined by the Chao Phraya river system. Its agricultural richness is due to this flooding cycle. Thailand’s borders are in the mountains that skirt its basin. The early trade that made the Ayutthaya kingdom powerful was built on the river’s navigability, and the canals that spread from it helped to transport its levers of power to the neighbouring chiefdoms and kingdoms.
Flooding is a normal and necessary part of life in a floodplains. Yet severe flooding of this floodplain has also been the scourge of modern and developed Thailand. For example, the 2011 monsoon season innundated over 20,000 square kilometers, left Bangkok flooded for around 6 months – killing 815 people and further affecting 13.6 million with almost 50 billion dollars of damage, particularly in the industrial estates on the outskirts of Bangkok. Disrupted supply chains led to a global shortage of hard disk drives, and automobile parts.