Simplify the following text for a Grade 5 native English-speaking person.
Original: 7 km ( 4 miles ) south of Elmshorn , and 30 km ( 18 miles ) northwest of Hamburg at the small river Pinnau , close to the Elbe river .
Simplified: 7 km ( 4 miles ) south of Elmshorn , and 30 km ( 18 miles ) northwest of Hamburg .