**1. Introduction**

In recent years, large and catastrophic floods have received much attention. It has been claimed that the large floods occur more often than previously, and the large floods have a more catastrophic pattern. A wilder and wetter climate due to climatic change has been predicted, causing more severe floods with large damage on infrastructure, agricultural soils, loss of lives of animals and humans. In Europe, the number of catastrophic floods was reduced in the period 1870–2016, while the number of humans losing their lives during catastrophic floods increased [1]. A timespan of about 150 years of measurements is too little in order to verify the effects of the largest floods, which may occur once in a millennium or less often. The mechanisms behind the largest floods may be of interest to understand in order to make models for future climatic change.

In many countries, fluvial plains are important agricultural areas with high productivity, but these areas are also the areas that are most exposed to floods. The pattern of Fluvisols [2] with sediments that receive fresh material or have received it in the past and still show stratification indicates areas exposed to floods. Large floods make severe damage on agricultural land by directs damage on crops, erosion, and sedimentation, and different methods for evaluation of flood damage to agriculture have been developed [3]. However, measures for land reclamation and restoration of damaged agricultural areas have sparsely been reported in scientific literature and seem to be absent for areas where combination of snowmelt, melting of glaziers, and heavy precipitation occur.

The aim of this chapter is to show the importance of large floods and the impact on agricultural land both in a historical context and more recent examples with a special focus on restoration and reclamation measures after catastrophic floods in cold regions. The study area is the two largest valleys in Norway; Gudbrandsdalen with the river Gudbrandsdalslågen and Østerdalen with the river Glomma in central eastern Norway, which was severely damaged by a flood in June 1995 [4]. The same area was hit by the largest flood in historical time in July 1789 [5], while the geomorphology of the valleys has been formed by large outburst floods from glacial lakes about 10,000 years before present [6].
