 It was built as a relief tunnel to mitigate flooding in the town, which had been occasionally severe during the spring runoff.Further on, in the village of Wildegg, the Aabach finally joins the Aare, right after it was joined from the right by its major tributary, the Bünz, just about upstream.Beginning in the second half of the 18th century, the Aabach provided water-power that ran mills that led to the creation of industry in the valley.