Complex sentence: The exodus started in September 1969 when the then Portuguese Electricity Company (Compania Portuguesa de Electricidade) started to pay out the indemnisation fees til October 1970 when notices were posted throughout the village that the dam was about to be filled.
Split into simpler sentences: The exodus started in September 1969, when the then Portuguese Electricity Company (Compania Portuguesa de Electricidade) started to pay out the indemnity fees. In October 1970, notices were posted throughout the village stating that the reservoir was about to be filled.