Rong Ji

Freshwater shortages in coastal regions are intensifying due to rapid urbanisation, economic growth, and climate variability, particularly in deltaic areas where rivers meet the sea. This study evaluates the feasibility of implementing a Coastal Reservoir (CR) as an innovative solution to increase freshwater availability without relying on desalination. Using the Brisbane River Estuary (BRE), Australia, as a case study, the research examines critical factors such as freshwater inflow, seawater intrusion, and reservoir volume requirements. A three-dimensional hydrodynamic model (MIKE 3) was calibrated and validated using observed data from the 2008 and 2011 flow events. Simulation results indicate that a freshwater discharge of 150 m³/s during a spring-neap tidal cycle effectively pushes saline water out of the estuary. The CR can store 300 GL/year of freshwater with 92% reliability, meeting Southeast Queensland’s (SEQ) annual water demand of 440 GL during drought conditions combined with existing infrastructure. During its initial filling phase, the CR can flush 95% of saltwater within 240 days, using a steady inflow of 150 m³/s. The findings demonstrate the technical feasibility of CRs as a sustainable and practical water management strategy for mitigating freshwater shortages in BRE and other similar coastal regions.

Sediment transport is a geophysical phenomenon characterized by the displacement of sediment particles in both the horizontal and vertical directions due to various forces. Most of the sediment transport equations currently used include only parameters related to the horizontal direction. This study measured both instantaneous longitudinal and vertical parameters, i.e., velocities and forces, and found that the magnitude and direction of the vertical force play an important role in sediment incipient motion. An innovative experimental system was developed to investigate the effect of vertical force on incipient motion in rapidly varying flows. A quadrant analysis of the instantaneous measured forces on the critical shear stress was performed. The research revealed that upward positive vertical forces enhance particle mobility, whereas downward negative vertical forces increase particle stability. Novel equations have been developed to represent the influence of vertical forces on sediment transport. A comprehensive critical Shields stress for sediment transport was proposed, extending the Classic Shields diagram to encompass the incipient motion in highly unsteady flows.

Australia is the driest inhabited continent on earth, and most of its population is concentrated along the coastal line. In recent years, extreme climate events such as floods and droughts have occurred more frequently. Sydney, as the largest city in Australia, requires a reliable water supply. Many solutions have been conducted to secure its water supply. This paper is focused on future water supply for the Greater Sydney area. The analysis supports the concept that in runoff-rich regions like Greater Sydney, there is no water shortage but a lack of water storage. The novel technology, coastal reservoirs, can increase the storage capacity of freshwater in the sea. The average annual discharge at Shoalhaven River mouth is estimated as 1,334 gigalitres. By comparison, the average annual inflow to the Warragamba Dam, which supplies 80% of Sydney's drinking water, is 1,069 gigalitres. This paper discusses how to apply a Coastal Reservoir at the Shoalhaven River mouth to secure additional water supply for ever-growing Greater Sydney. The proposed reservoir with a capacity of 500 gigalitres could supply 1,000 gigalitres of water per year with a reliability of 90%. A preliminary design of the reservoir is demonstrated.