The incident took place at 10pm on Tuesday July 30 and the police attended the scene at the river crossing near the Memorial Garden.
It is alleged that the victim was repeatedly assaulted by a man who is believed to be known to her. The suspect, aged 26 and from the Tonbridge area, was arrested at the scene.
Officers are keen to speak to a man and a woman who are said to have interacted with both the suspect and victim as the assault was taking place.
The attack follows two other incidents in the town where a woman on a mobility scooter was alleged to have been bullied by youths, and a man on a park bench was kicked.
To provide information, call the West Kent appeals line on 01622 604100, quoting reference 46/147038/19.
Alternatively, contact the independent charity Crimestoppers anonymously by calling 0800 555111 or using the anonymous online form at Crimestoppers-uk.org