Context Sedimentation in the rivers and on the coasts of Timor-Leste has increased since deforestation, affecting floods and probably living aquatic resources.

Aims To provide scientifically based estimates of long-term and short-term erosion rates to assess the apparent role of deforestation, a topic that has not received sufficient quantitative attention in the Coral Triangle.

Methods Short-term erosion rates have been estimated from regional relationships between river sediment yield and catchment areas and cosmogenic nuclides for long-term rates. An attempt has also been made to estimate changes in rates of delta progradation to determine whether recent increases have occurred following deforestation.

Key results The major scientific finding is that reduction in vegetation cover for agriculture and timber harvesting, particularly in the mountains, increased sediment yield by factors up to 120, mainly by landsliding. And there has been a large amount of sediment exported to the delta and offshore from river-channel change.

Implications Impacts on living resources are likely both in rivers and on the coast, but require assessment. Revegetation of hillslopes is likely to reduce these impacts and improve the livelihoods of local people.