The problem of peat upheaval in finnish artificial reservoirs

Abstract

A substantial disadvantage in connection with most of the artificial reservoirs in Finland and other countries of the same latitude is peat upheaval caused particularly by the liberation of gases during peat humification and summertime warming of the water which contains a large amount of dissolved gas. For instance, in the Lokka Basin, the largest man-made lake in Finland, the most common peat types to float are Carex and Carex-Sphagnum peats. The peat horizons which give rise to the floating mats are more than 2 m thick and the mats themselves are 70 cm thick. The degree of humification is commonly H1–3. The following physical properties have been found critical for upheaval: wet unit weight less than 1 g/cm3, dry unit weight less than 0.110 g/cm3, water content over 88 % of wet weight, porosity over 93 %, degree of humification less than H5, and gas content over 43 litres/m3. Peat upheaval can only be avoided to a certain degree, e.g. by spreading layers of gravel on the peat surface before flooding.