Simplify the following text for a Grade 8 native English-speaking person.
Original: In November 1828 , Hume journeyed with Charles Sturt into western New South Wales , where they discovered the Darling River , the Murray River 's longest tributary .
Simplified: In November 1828 , Hume journeyed with Charles Sturt into western New South Wales , where they discovered the Darling River .