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Examing the geomorphic effects of the Canterbury earthquakes on the Hororata River.

Pezij, Michiel (2013) Examing the geomorphic effects of the Canterbury earthquakes on the Hororata River.

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Abstract:Due to a large earthquake in September 2010, part of the river bed of the Hororata River locally dropped. This caused a flood because the water could not continue its way through the original channel. A farmer enlarged the original channel to encourage the water back into the river. The National Institute of Water and Atmospheric Research (NIWA) in Christchurch, New Zealand, wants to know how the river has adjusted in the period since the 2010 earthquake. Also, they want to test their morphological model GRATE, “Gravel Routing and Bed Textural Evolution model”. This model will simulate the river for the period 2010-2013 and try to reproduce the adjustments. The predicted adjustments are calibrated and validated by means of fieldwork material. There are two main research objectives: 1. Measure how the Hororata River responded to the September 2010 earthquake and subsequent human channel modifications. 2. Test NIWA’s 1-D model (GRATE) to see how well it predicts the measured response from goal 1. The main research question in this project is: How has the Hororata River adjusted in response to the effects from the Canterbury earthquakes and can this response be properly simulated? The following sub questions will underpin the main question: 1. What were the direct effects of the 2010 earthquake with respect to the Hororata River? 2. What morphological changes are predicted by the model GRATE for the period 2010-2013? 3. What is the morphology of the river in 2013 and which adjustments did take place? 4. How well does the GRATE model predict the measured water levels and changes between 2010 and 2013? Around 300 meters of river bed has dropped 1.5 meters down due to an oblique down slip of the Greendale fault. This resulted locally in an increase of river bed slope of 2.3 times the average slope. According to the simulation of GRATE, only adjustments occur around the meandering bend. Validation data proved the correctness of the simulation and indeed, only changes were visible near the meandering bend. After three years, both the model run and the 2013 survey data showed that the slopes of the reach around the fault line have evened. In the humanly enlarged channel are almost no adjustments visible. The GRATE simulation is predicting erosion and deposition in an accurate way. The simulation calculates the vertical adjustments of the river with an average deviation of 0.20 meter. There are no horizontal changes possible in GRATE (bank erosion processes are currently not well represented in this model). However, GRATE may be predicting the degree of adjustments adequately, but not the nature of the adjustment. Generally, GRATE can predict the adjustment of the river very well. In the future the river slope will eventually be restored to levels before the earthquake. However, the speed of these adjustments and restoration depends on the farmer. Bank protection may encourage bed erosion if there is excess energy in the river that need to be dissipated. This will lead to a quicker restore of slope. If not, the river will probably continue to erode his banks and deposit sediment right after the drop in order to restore the slope of the river.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
Link to this item:http://purl.utwente.nl/essays/63864
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