Sumatera Island, which has a total area of 409,000 sq.km, has been devided into 30 river basins, as follow: 1. Krueng Aceh 2. Meureudu - Ureun 3. Pase - Peusangan 4. Jambu - Aye 5. Tamiyang - Langsa 6. Wolya - Lembesi 7. Singkulat - Tripa 8. Singkil 9. Wampu 10. Belawan 11. Bahbolon 12. Asahan 13. Barumun - Kualuh 14. Batang Toru - Batang Gadis - Natal 15. Rokan 16. Siak 17. Kampar 18. Indragiri 19. Silaut 20. Anal - Sualang 21. Batanghari 22. Sugihan 23. Baturusa - Cerucut 24. Mual 25. Mesuji - Tulang Bawang 26. Seputih - Sekampung 27. Semangka 28. Kanal - Alas - Talo 29. Lais - Bintuhan - Ketahun 30. Ibuh - Manjunto - Teramang Average annual rainfall for the whole Sumatera island is estimated as 2,600 mm.
by F.J. Putuhena