M ost areas in Riau are lowland plain, including alluvial islands scattered along coastal line with average elevation less than 200 m above sea level. In mainland region, there are four big rivers, i.e. Rokan river, Siak river, Kampar river and Indragiri river. These rivers spring from Bukit Barisan mountain range stretching along the border Riou Province and West Sumatera Province, and flow down to the Straits of Malacca.

The rivers play an important role as the means of transportation, sources of irrigation, energy, and clean water as well as fishery resources.

Archipelagic region of Riau, on the other hand, is formed of volcanic formation in the form of islands, big and small. The soil is in general of Orga:nosol type (Histosol), containing much organic substance.

Based on their elevation above sea level, areas in Riau can be classified into the following categories: