Water flow in a hummocky landscape in central Saskatchewan, Canada, III. Unsaturated flow in relation to topography and land use

Abstract

The importance of unsaturated flow in groundwater recharge and soil development in the Interior Plains region of North America is poorly understood. The purpose of this study was to obtain quantitative estimates of unsaturated water flow rates in a hummocky upland area and to relate the flow rates to topography and land use. The sites consisted of closed drainage basins, 80–150 m across, surrounding individual temporary sloughs in the Black soil zone in central Saskatchewan and were instrumented with tensiometers and neutron access tubes. The sites were divided into lower slope, upper slope and saddle positions on the basis of landscape surface foam. The magnitude of the unsaturated flux was commonly 10 −8 ms −1 in the lower slope positions, 10 −9 to 10 −8 ms −1 in the saddle positions, 10 −10–10 −9ms −1 in the upper slope positions following summer-following and 10 −10ms −1 or less in the upper slope positions following three consecutive years of cropping. Downward flow was of similar magnitude to upward flow inthe lower slope positions and two- to five-fold higher than upward flow in the upper slope and saddle positions. In a year with 30% above average rainfall, up to 25 mm of downward flow and 5 mm upward flow occurre across the bottom of the root zone in the saddle positions. The unsaturated downward flux penetrated to greater than 2.5 m depth and was sufficiently large to be of importance to soil development and crop growth. Deep drainage was greater in saddle then in upper slope positions, greater following summer-fallow than following three years of cropping, and least under native vegetation.