**2. Material and methods**

After the 1995 flood in central eastern Norway, research projects were started in order to document the direct damage of the flood by field experiments at flooded areas. After the direct effects were studied, the effects of different restoration measures were investigated. One of the areas with largest damage after the 1995 flood in the river Glomma was Øksna, north of Elverum in Østerdalen (60°58′ 15″ N, 11°29′ 05″ E). The restoration work took place in the period 1996–1998, and an evaluation of the different measures was done based on studies in a 4 year period, 1999–2002. In total, 11 different measures, including undamaged references, were studied at 26 plots (**Table 1**, **Figure 1**).


#### **Table 1.**

*Flood damage and restoration measures at Øksna, Elverum commune, Norway.*

*Flood Damage on Agricultural Land and Methods for Restoration of Agricultural Soils… DOI: http://dx.doi.org/10.5772/intechopen.109111*

#### **Figure 1.**

*Plots for soil and yield investigations at Øksna, Elverum commune, Norway. Photo from 1998 [7].*

Two different types of sewage sludge were used as soil conditioner, a limed sewage sludge with pH >10 (Plots 10–12), and a sewage sludge where aluminum salts had been used for coagulation for removal of P from wastewater. The amount of sludge used was about 20 Mg dry matter ha−1, which is the permitted amount according to Norwegian regulation on organic fertilizer.

The yield of cereals, spring barley (*Hordeum vulgare*) and oats (*Avena sativa*), was monitored at the plots in the period 1999–2002. Analysis of variance (ANOVA) was performed in order to document if there were significant crop yield differences between the three groups of treatments: eroded topsoil or intact topsoil, leveled areas, and filled erosion craters. As there were unequal sizes of the groups, the Bonferroni method for multiple comparisons was used (p < 0.05).

Soil properties were investigated at plot level, including texture, pH (H20), total organic C, representing the topsoil (Ap-horizon). Readily available plant nutrients were determined according to the AL-method [8]. Intact soil cores (100 cm3 ) were taken for determination of bulk density and total porosity at nine plots with three cores per plot in the topsoil (5–9 cm depth). Total porosity was measured as water content at saturation, while bulk density was determined after drying the soil cores 24 h at 105° C.
