In Biggles in Borneo, the Limpur River is a river which crossed the Malayan peninsula (today Malaysia) from West to East. Telapur, a sawmill which belonged to a pair of timber merchant brothers, Fee Wong and Ah Wong, stood on the river.
When Biggles freed Fee Wong from Cotabato prison, Fee Wong brought news that an important Japanese convoy of rubber and tin was scheduled to cross the Malaysan peninsula on the Limpur River. It would pass his sawmill and could be attacked. His brother and the workers at Telapur would be available to help.
When Biggles got to Telapur, the convoy, comprising a large number of river barges, had already reached Telapur and was moored there under heavy guard. Unable to sabotage the barges directly, Biggles opted to go upriver and, with the help of Ah Wong's timber working elephants, push teak logs into the river,hoping that the swift currents would turn them into battering rams. Unfortunately, the logs got caught by a fallen tree and created a massive logjam, damming up the river. Kayan, Ah Wong's foreman, freed the logjam at the cost of his life and released a massive flood of water which destroyed the convoy at Telapur and also brought down a pontoon bridge further downstream, drowning a Japanese troop column which was crossing the river at the time.
Following the attack, Biggles was faced with the problem of finding fuel for his Cayman amphibian. He considered siphoning fuel from a number of wrecked river barges but later hijacked a Japanese Kawanishi seaplane for its fuel and was able to fly the Cayman back to Lucky Strike.
The Limpur River is a fictional river and no river crosses the width of the Malaysia peninsula. Being a small detail, it is doubted that Johns would have researched the local geography deeply enough to find a real life analogue to base it on. The closest analogue would be the Pahang River, which flows southeast from its source and then for a large part of its course, traverses the peninsula from west to east. It is the largest river in the Malaysian peninsula and, just like the Limpur in the book, is prone to flooding in the monsoon. Interestingly, the Pahang River was used in ancient times to cross the peninsula from west to east and vice versa. A tributary of the Muar river which flows westwards, comes close to the Serting River which is a tributary of the Pahang River. By using a short portage of about 300 metres, boats were able to connect from one river to the other and thus make a complete journey across the peninsula.