In Orchids for Biggles, the Rio Jurara was a river on which stood the Peruvian town of Cruzuado on the tripoint border of Peru, Brazil and Bolivia. Also on the river was the town of Puerto Vecho, 20 miles downstream of Cruzuado. In the story, the Jurara was a tributary of the Rio Madiera which is itself a tributary of the Amazon, meeting near Manaus. Biggles, flying the Gadfly amphibian, landed on the Jurara several times, first, when searching for Cruzuado and later when pursuing Bogosoff from Cruzuado to Puerto Vecho.
The Jurara is a fictional river. The actual river which forms the border between Peru and Brazil and whose waters flow over the tripoint border is the Rio Acre. And the Acre is not a tributary of the Madiera (an actual river) but the Purus, another tributary of the Amazon.