The Gal Oya hills and the Central mountains are the main uplands , while the Mahaweli ( Sinhalese : great-sandy ) and Menik ( Sinhalese : gemstone ) rivers and the huge Senanayake Samudraya and Maduru Oya Reservoirs are the major waterways .
The Mahaweli and Menik rivers and the huge Senanayake Samudraya and Maduru Oya Reservoirs are the major waterways .