Hydrodynamique d'une pessière noire drainée

The depth of the water table was measured before and after the digging of drainage ditches with 20-, 40-, and 60-m spacings in a black spruce wild holly bog. The peat is mesic with the exception of the top 10 cm which is fibric. The hydraulic conductivity of the 20- to 40-cm layer is low in relation with other Quebec sites under study. The extremely low conductivity under the 40-cm depth and the impermeable mineral soil layer at the bottom of the ditches creates the horizontal profile between ditches. The mean water table depths during the 3 years of the study were 42, 29, and 22 cm, respectively, for the 20-, 40-, and 60-m spacings. The corresponding lowering of the water table was in the order of 25, 13, and 6 cm. The water table was maintained 100, 70, and 40% of the time below the 20 cm deep root zone for the 20-, 40-, and 60-m spacings respectively, compared with 23% for the undrained situation (by simulation). The water table is significantly lowered below the 40-cm threshold for the 20-m spacing only.