Spatiotemporal evolution of the constructed Hühnerwasser catchment (“Chicken Creek”)

Abstract:

The Huehnerwasser ('Chicken Creek') Catchment was constructed from quaternary sandy sediments (2 to 4 m thick) lined by clay materials at the bottom on an area of 6 ha. The subsurface topography of the clay liner consisted of a subsurface dam, that allowed the catchment to develop a groundwater body. Below the subsurface dam, an alluvial fan developed by receiving sediment form the upper catchment. Below the alluvial fan area, a pond collects the surface and subsurface discharge from the upper catchment. Commencing from 2005 a monitoring program was established that recorded rainfall, runoff at various parts of the catchment, groundwater levels, pond levels, as well discharge from the pond in to the stream. Those data were complemented with soil moisture as well as tensiometer observations at various location within the catchment. Besides hydrological monitoring, detailed vegetation surveys were carried out every year that captured species distribution in space which was further complemented by aerial photographies capturing vegetation coverage.

While the initial phase was dominated by runoff and erosion processes, generating an extensive surface drainage network in the upper part of the catchment, the subsequent phases where dominated by the formation of biological soil crusts and plant establishment. As vegetation established itself within rills and gullies as well as the interrill areas, the runoff dynamics changed to the point that the erosional regime changed to a regime of subsurface and surface flow discharging into the pond. The transition of those regimes occurred very rapidly. The high correlation of pond and groundwater levels during the last few years, indicate strong coupling and a significant subsurface flow component into the pond. With the growing vegetation, the hydrological response is currently moving towards a regime with a very strong evapotranspiration component, leading to lowering of the ground water table. This presentation will evaluate how vegetation pattern during the establishment phase contribute to changes in hydrological regimes.