Resources About Trail Design and Maintenance
The Ice Age Trail Alliance has published a rucksack load of informational booklets on trail building and maintenance, specific to the Ice Age Trail. You can find links to many of them here. These are PDF's, and clicking the link will download them for your own library. Toward the end are other references from the NPS, DNR, and USFS.
Introduction to Rigging for Trails
NPS Resources: Trail Development and Management Standards
Wisconsin DNR: Runoff Standards for Public Trails Near Waterways and Wetlands
US Forest Service: Trail Construction and Maintenance Notebook