Hydrologic behaviour and hydraulic properties of a patterned fen in Saskatchewan

Abstract

A patterned, partially-treed, fen in the mid-boreal region of central Saskatchewan was the site of renewed hydrological research from 2002 to 2004. Hydraulic conductivity, transmissivity, and storativity were determined through use of a surface loading test, pumping tests, and an enclosed field drainage test. None of these field tests have been previously described in the literature as having been used in peat environments. The combined results of field and laboratory drainage tests were used to obtain a general storativity with water table depth relationship in the upper peat layer. The hydraulic conductivity, measured with slug tests, the loading test, and pumping tests, is high near the surface, declining greatly with depth. These previously untested field methods have the advantage of representing volumes of peat from tenths of a meter to cubic meters. Characterization of the hydrology of the peatland involved year round observations of water table, piezometric head, peat surface elevations, frost depth and peat temperatures. Fluctuations of the water table, and soil moisture changes produce changes in effective stress that lead to volume change in the highly compressible peat. This is particularly important for sites with thick peat deposits. Independent compressibility estimates were as high as 10-5 N/m2 in the upper peat. At three fen sites, changes in peat thickness were estimated from monthly estimates of effective stress change, using year round hydrological observations, and compared to measured annual peat thickness changes. Water table changes causing soil moisture changes, and freeze-thaw processes, explained the majority of peat surface movements.