Reproducing runoff initiation in an environment that has dynamic initial abstractions

Hoeksma, J.M. (2015) Reproducing runoff initiation in an environment that has dynamic initial abstractions.

Abstract:In this research the Wasa and Dicasm models are validated concerning runoff initiation in the Caatinga biome. Runoff initiation for the model outcomes is calculated as runoff above zero millimetres per event. The Aiuaba Experimental Basin (11.5 km2) is the study site of this research. Research has shown that runoff initiation in the basin is dynamic and seasonal. Runoff initiation is considered as dynamic because tree roots shrink during dry periods. After that, precipitation will fill the pores that arise after that dry period whereby less or no runoff will occur. When the pores are saturated, precipitation will run off in almost all cases. Next to that the root depth in the Caatinga biome is about 15% smaller in dry season compared with the rainy season. The aim for this research is to identify a way to simulate runoff initiation in the AEB. Since field measurements show the aforementioned dynamic behaviour, the models should be able to simulate that similar behaviour. Several hydrological models will be run for 116 runoff events in the period from 2005 until 2014. All these events will be run after initial conditions of the models. The main objective of this research is described as: “to assess the specific validity of Wasa and Dicasm for application, by analysing their ability to explain runoff initiation at the event scale in the Caatinga biome”. The results of this research show that both models give show a smooth relationship between precipitation and runoff depths or cumulative initiation. Measurements conducted in the AEB show higher deviations. Furthermore both models are overestimating runoff initiation. Wasa produces for every event within the AEB runoff in case of precipitation higher than 15 mm. Dicasm produces runoff even for events with low rainfall magnitudes. In Dicasm the base percentage is used instead of the infiltration and water store mechanisms. This formula is not suitable to show any dynamics and cannot distinguish runoff initiation since there will be always runoff for each precipitation. This might be caused by the short run time of just one day, whereby the more extensive systems that are used by Dicasm are not considered. The contingency table in the results shows that for all events Wasa agrees in 37% of the cases. For events up to 31 mm 38 out of 78 (roughly 50%) of the runoff initiation is predicted correctly. It can be concluded that the used models do not consider the aforesaid dynamic behaviour. In general, the higher the precipitation, the more intense runoff. Therefore no similar rainfall events result in different runoff and vice versa.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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