Soil water regimes of the Glendhu experimental catchments

Abstract

The Otago block mountains are important water supply areas with their abundant water yield attributed to conservative water use by narrow-leaved snow tussock (Chionochloa rigida), the dominant vegetation cover of the region. This study looks at three aspects of the soil hydrology of the Glendhu experimental catchments, east Otago, New Zealand: soil water regime changes following afforestation of the tussock grasslands; a comparison of soil water regimes with topographic position in order to identify possible saturated overland flow generation sites; and some characteristics of a peat wetland that is typical of those that occupy gullies in the region. Several sites were set up in the forested and the tussock catchments, and depending on position, contained tensiometer nests, neutron probe access tubes and water table observation wells. Data were collected betw.een 29/3/93 and 19/5/94 and revealed much drier conditions under forest cover, with saturation not occurring in the A horizon throughout the study period. Using tussock catchment sites for topographic comparison, a downslope increase in water content was found on the interfluve, while saturation persisted for longer periods of time at headwall sites where subsurface convergence resulting from the concave planar morphology occurs. Wetland water tables only fluctuated 27.5 cm during the study period, and do not appear to be sustaining the high baseflow that occurs from the catchment.