A Kasetsart University geotechnical engineer says Nan's repeated floods come from its valley geography and short distance between communities and steep slopes, so water arrives fast. He argues dikes raise flood severity by encouraging building in risky low areas, and that the main tools are local building-control and earth-filling rules, which local authorities (provincial, Tambon or city administrations) can enforce more strictly. If you run a business in flood-prone northern areas, check whether your site sits in a water channel and whether local rules on construction and fill could affect your premises.