Some hydrological effects of peatland drainage in Alberta's boreal forest

Abstract

Ninety hectares in a treed fen in north central Alberta were drained to improve growth of stagnant black spruce (Piceamariana (Mill.) B.S.P.) and tamarack (Larixlaricina (Du Roi) K. Koch) stands. Installation of 30-, 40-, 50-, and 60-m ditch spacings resulted in a lowering of the average water table by 79, 66, 56, and 73 cm, respectively. The results and the groundwater level criteria used (drainage norm, 40 cm; flood duration limit, 14 days) indicated that the 50-m ditch spacing was hydrologically the most appropriate one for this area. Given the relatively high hydraulic conductivity of the area, it is believed the 30-m spacing was too narrow and resulted in an excessively low average water table. The 60-m spacing was also overeffective, but in this case, overeffectiveness was attributed more to "edge effects" i.e., to site factors such as the proximity to uplands and the small size of upstream source areas, than to the distance between ditches. The results illustrate the importance, for ditch network design purposes, of taking into account hydrologic conditions both within and well beyond the boundaries of an area proposed to be drained. Peat subsidence after drainage appeared to be related to the average drop in water table level and amounted to about 5 cm•a−1.