There was a project to add flood prevention dams in the area but it was blocked for 20 years by the party in power. And it was from their own party's campaign promise. Also, the cleanup of existing dams and rivers was blocked due to environmental reasons. And the EU government was backing all this. At least most of Valencia was spared due to works made over 50 years ago.

I don't believe the mainstream whitewashing of authorities. Administration openly against dams and waterworks, no alerts due to malfunctioning radars, terrible coordination, and lack of appropriate response.

Source: I personally know people from the affected area.