Utilising a Coffs Harbour 3D physical model to evaluate development strategies in the Southern Precinct

Coffs Harbour is situated on the mid-north coast of New South Wales approximately 600 kilometres north of Sydney. Waves offshore of Coffs Harbor at 80 m depth have been recorded by MHL for a period of over 30 years. Long waves have been simultaneously measured in the harbour over a period of a decade. The government wishes to develop the harbour to enable vessels up to a length 300 m to effectively use the harbour's potential. A 3D undistorted model of scale 1:58 was used in the investigation. Five distinct configurations of breakwaters and berths for development strategies were tested in the model. The model simulated 125 s seiche previously measured in the harbour for over a decade by generating the seiche wave using short wave (13 s and 15 s) Jonswap spectra. The criteria investigated to evaluate development strategies were: a) harbour serviceability - harbour depth, navigation, turning circle, size of ship, berth wave climate which included seiche amplification, recreation for community and reduced frequency of harbour dredging b) boat ramp serviceability and other harbour amenities - improved serviceability of boat ramp, harbour traffic, visibility/aesthetics c) supporting natural processes - beach nourishment potential, provision of long-term sediment input to all beaches north of the harbour d) project revenue - minimising capital expenditure (CAPEX), minimising ongoing or maintenance expenditure (OPEX), berthing revenue, regional growth assessment and increased local growth e) construction/operation impacts. In order to evaluate the options, the shortwave ( 100 s) responses measured during the modelling of the options are presented. This involved constructing a number of structures and additional berths in the existing harbour. Conceptual sediment transport processes obtained from existing literature are discussed. The paper provides the results of a multi-criteria analysis (MCA) of the development options.