Water table levels at different drainage intensities on deep peat in Northern Norway

Abstract

This report comprises a 10-year study on the effects of ditching-systems on water table levels in deep peat. The following factors have been tested: ditch depth, ditch distance, vegetation type, surface fall, permeability of peat, air temperature, evaporation and rainfall. Correlation and multiple regression analyses showed that mean water table level midway between ditches for the growing season (June—September) could be predicted with good precision ( R = 0.74 – 0.87) by: ditch depth, logarithm (e = 2.7183) of ditch distance, rainfall, permeability and initial water table level on 1 June (autocorrelation factor). Multiple regression tests on orthogonalized variables showed that ditch depth is very important. On unfurrowed peatland this factor reduced total variation in the annual mean water table levels from 1 June to 30 September by 26.2%. On furrowed peatland, logarithm of ditch distance, ditch depth and rainfall each accounted for between 15.1 and 17.2% of the variance. Proper drainage for afforestation in Northern Norway could be attained by an effective ditch depth of 0.8 m and ditch distances from 9 to 25 m. This rather broad range depends on regional variation in mire types, permeability of surface peat layers and rainfall.