University of Twente Student Theses


Estimating the root-zone storage capacity to predict discharges in the river Moselle

Berge, A.A. ten (2021) Estimating the root-zone storage capacity to predict discharges in the river Moselle.

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Abstract:This study evaluates the differences between two methods to estimate the root-zone storage capacity in the hydrological wflow_sbm model of the Moselle, in order to obtain more reliable hydrological predictions. The first method for estimating the root-zone storage capacity is currently used in the wflow_sbm model and relies on look-up tables that relate rooting depth to land-use. As this approach is rather uncertain and static, a more dynamic method was used to estimate the rootzone storage capacity. This second method is the water balance approach, in which climate data is used, and has as main assumption that vegetation adapts its root-zone storage capacity to overcome dry periods. The differences between the two methods were evaluated by comparing the predictive power of both versions of the wflow_sbm model. The sensitivity of the wflow_sbm model of the Moselle to a change in root-zone storage capacity was assessed by creating different scenarios for the rooting depth. The root-zone storage capacity has substantial influence on both annual and event time scale, as a higher root-zone storage capacity leads to an increase in evaporation and thus a decrease in discharge. In the estimation of the root-zone storage capacity using the water-balance approach, four different return periods were used. For a return period of 10 years, this resulted in an average root-zone storage capacity of 171 mm. The root-zone storage capacity was translated to a rooting depth in order to implement the new estimations in the wflow_sbm model, using estimates of the saturated and residual water contents. The resulting average rooting depth for a return period of 10 years (635mm) was 99.7% higher than the current average rooting depth in the wflow_sbm model of the Moselle. The predictive power of both versions of the wflow_sbm model was compared using different metrics at different locations. The annual average run-off coefficient at Cochem simulated with the version in which the water balance approach was used, deviated 1.4% from the observed run-off coefficient, while this deviation was 11.7% for the current version of the model. This makes the water balance approach for estimating the root-zone storage capacity recommended for application in water management planning. For application in operational water management, the water balance approach is recommended as well, as the height of peaks in wet periods of wet years were simulated closer to the observations when using the root-zone storage capacity values derived with the water balance approach, even without any further calibration of the model.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Programme:Civil Engineering BSc (56952)
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