Hydrological processes inside a hillslope
Biosphere 2 Landscape Evolution Observatory (LEO) consists of three huge landscapes constructed inside an environmentally controlled greenhouse facility. LEO aims to address fundamental “grand challenges” in Earth systems science:
- How will Earth's landscapes change as climate changes?
- How do biological systems (vegetation and microbes) modify landscapes?
- How will terrestrial water resources alter with climate change?
- How do water, energy and carbon move through landscapes?
The purpose of this internship was to gain insight in the hydrological processes inside a hillslope inside LEO. This research consisted of two first experiments for which the closure of the water balance was investigated.
For the first experiment it was intended that a steady state was reached. Artificial rainfall was applied to the hillslope with an intensity of 13 mm/hour, which lasted for 22 hours. During the rainfall event storage change was measured via load cells underneath the hillslope and seepage by tipping buckets. To produce a closing water balance only evaporation needed to be calculated, but an extra term to the water balance was added: overland flow. After 22 hours the precipitation was stopped because overland flow occurred, which was not intended. It was noticed that several sensors were not working properly. Before starting the second experiment these sensors were re-calibrated, re-tested and adjusted. This complicated attempts to close the water budget.
Two sensors which were measuring incorrect values during the first experiment were the MPS2 and 5TM sensors. The soil water retention curve could not be produced and several soil characteristics could not be estimated. Hence, a soil water retention curve experiment was performed in the Soil Physics laboratory at the University of Arizona. For this experiment the same soil as on the hillslope in LEO was used. By fitting the Van Genuchten Model on the measurement results, the parameters of the Van Genuchten model and the porosity could be estimated. The results of the laboratory experiment were compared to the data of the MPS2 and 5TM sensors in the hillslope. The Van Genuchten Model was fitted to the datasets of the MPS2 and 5TM sensors. Results showed that the part, which is most important to predict overland flow part, namely the part where the soil becomes saturated, was not visible in the measurements by the MPS2 and 5TM sensors. Finally the parameters alpha and n of the Van Genuchten model, were compared between the laboratory and hillslope results.
It was concluded that there is a strong dependency between parameters alpha and n in the Van Genuchten model between the different samples. The laboratory and hillslope results showed a similar structure in the dependency between parameters alpha and n. These results can be used to make a better prediction of when overland would occur, thus will help in producing a closed water balance for future experiments inside Biosphere 2 Landscape Evolution Observatory.