JultikaUniversity of Oulu repository

Hydraulic conductivity is one of key parameters needed in wetland hydrogeological and landform development models such as greenhouse gas models. It also helps in determining nutrient transport and runoff characteristics in peatlands and is an important factor with regards to water table management as a means of checking peat mineralisation. However, the complex nature of peat soils makes estimation of hydraulic conductivity in peat soils a difficult task since most of the theories associated with hydraulic conductivity measurements were developed using mineral soils. This study was done with the aim of evaluating different methods of measuring hydraulic conductivity in drained peat soils and establishing the most suitable method among the methods evaluated. All the sites used in the study were all drained peatlands with different land uses (agriculture, forestry, and peat harvesting). Three different methods of measuring hydraulic conductivity which have been applied in previous studies were evaluated based on their consistency in replicating results and the closeness of the hydraulic conductivity values they produced to the hydraulic conductivity values predicted using DRAINMOD model of the groundwater table in one of the site (peat harvesting site). The DRAINMOD simulation produced an acceptable agreement between the calibration model and the validation model with coefficient of determination (R2) of 0.79 for the calibration model and 0.74 for the validation model. The coefficient of efficiency achieved in both models falls within the acceptable range (>0.4 to >0.75) for validation of model. The hydraulic conductivity values achieved with the two in-situ methods used fall within 10 E– 7 to 10 E– 9 m/s at both layers studied while the laboratory method produced values within the range of 10 E– 9 to 10 E– 10 m/s at the top layer and 10 E– 10 to 10 E– 11 m/s at the lower layer. Comparing the results with the model predicted values of hydraulic conductivity (10 E– 6 m/s in both layers), the laboratory method yielded the highest deviation from the modelled value compared to the two in-situ methods while the slug test method produced the least deviation and the closest range of hydraulic conductivity values (10 E– 7 to 10 E– 8 m/s) to the modelled value. The closeness of the range of hydraulic conductivity values obtained using the in-situ methods to the model predicted values of hydraulic conductivity suggests that the in-situ methods presents the best option when it comes to measuring hydraulic conductivity in peat soils.