To indigenous Australians Isabel and George Coe, the hills near a 280-foot-tall dam here are part of a sacred landscape that is dotted with burials and ceremonial sites. Now, new plans by the government to raise the wall of the dam could flood many of those areas. “We’ve already had enough of our countryside being destroyed,” said Isabel Coe, 34 years old, as she surveyed the rocks and barren trees by the man-made lake behind Wyangala Dam, about 130 miles west of Sydney. “Our whole landscape is significant:…