He is an active researcher with an international reputation in the field of fluvial sediment transport. His expertise encompasses most aspects of water resources engineering, including hydraulic, hydrological, river, environmental and hydro-electric engineering. He is a founding member of the Centre for Infrastructure Research and is Associate-Editor of the (ASCE) Journal of Hydraulic Engineering, has served on local and international research committees, and has been a member of many tribunals for water consent hearings. He has supervised more than 30 PhD students and published over 100 refereed journal papers. He received the 2002 ASCE Hydraulic Structures Medal, in recognition of his contributions in the field and was elected to fellowship of the Royal Society of New Zealand in 2006. In 2007, he received the R.J. Scott Medal from RSNZ for his research contributions and in 2012 he received the Dobson Supreme Technical Award in Transportation Infrastructure. In 2011, he was promoted to Distinguished Fellowship of IPENZ and was awarded a Hood Travelling Fellowship. He received the Henderson Oration Award in 2014.