Simulating the post-earthquake morphological response of the lower Rangitaiki River, New Zealand

Abstract

The 1987 Edgecumbe earthquake caused vertical displacements of up to 1.3 m along the Rangitaiki River, New Zealand, creating a morphologic disturbance in the form of a knickpoint in the river. Subsequent river surveys identified migration of this knickpoint upstream and general degradation of the river bed. We attempt to simulate this change using a one-dimensional river morphological model. Bed changes in the model show a pattern of progressive profile-smoothing across the earthquake knickpoint, with degradation upstream and aggradation downstream. However, this did not correspond with the observed progressive river degradation both upstream and downstream of the knickpoint. Some of this discrepancy can be attributed to continued settlement post-earthquake, which will be investigated further.