The anniversary of the 2012 flood approaches. What protected much of Duluth 10 years ago? 435 miles. 8,439 football fields. The length of Minn., from North to South. That’s how far the drainage tunnels flow below Duluth’s hollow streets. “100-year-old brick arches” to brand new iron and metal grates. According to the project coordinator of Minnesota Power, Chris Kleist, the materials used to construct the…