Glomma
The Glomma, or Glåma, is Norway's longest and most voluminous river. With a total length of , it has a drainage basin that covers fully 13% of Norway's surface area, all in the southern part of the country. Geography At its fullest length, the river runs from the lake Aursund near Røros in Trøndelag and runs into the Oslofjord at Fredrikstad. Major tributaries include the Vorma River, which drains Lake Mjøsa, joining the Glomma River at Årnes in Nes. The Lågen drains into Lake Mjøsa, collecting drainage from the large Gudbrandsdalen and significantly increasing the Glomma's flow. Because it flows through some of the richest forest districts, it has historically been Norway's leading log-floating river. The combination of raw materials, water power, and easy transport has over the centuries encouraged industry along the Glomma. Some of the country's largest manufacturing and processing concerns are found around its mouth, where supplies of timber and hydropower have been backed by excellent port facilities. The upper limit of the Glomma valley farms is variable, but typically runs about in Østerdalen, slightly lower than in the Gudbrandsdalen, which reflects the colder climate. The treeline, with a light birch forest, rises to about in Østerdalen.