Anyway as far as I know (I live nearby) there are no settlements Sinhalese/Tamil/Muslim* within the National Park. In the case of the letter in Colombo Telegraph the accusation is that there are Sinhalese settlements in Veratenna, Bogaswewa, Namalgama, Senaleenigama, Nandamitragama. I am sure there are settlements in these villages, but also equally sure that these villages are not within the Wilpattu National Park.
One Example: Bogaswewa. Thats about 70 km from Wilpattu near Rambewa. Thats the blue ballon in the map. The location of Bogaswewa is 8° 28' 0" North, 80° 30' 0" East.
Another quote: Along the Wilpattu Reserve on the Welioya Road. Maybe there is a Weli Oya in this area. But as far as I know Weli Oya is on the East of Sri Lanka.