Ron Cox

Managing Adaptation of Urban Water Systems in a Changing Climate

Current evidence is that climate change is occurring, it is largely manmade and it will have significant implications for human civilisation. Australia is particularly vulnerable to the anticipated effects of climate change, creating major challenges for water resource management and water supply security. Climate change adaptation offers a means by which we can reduce our exposure to future climate change risks, whilst at the same time exploiting any potential benefits that may arise from climatic changes. This review outlines the current major climate change adaptation challenges facing the water supply industry at large, with a particular focus on these challenges in an Australian context. It also aims to highlight the critical knowledge gaps and strategies required to assist in the formulation of adaptation responses to the range of potential impacts on water infrastructure and future water security. A diverse range of management and assessment techniques are used by relevant professions in industry. Here, an adaptive management approach is presented highlighting the important information required for robust assessment.

An overview of numerical modelling of the Sydney deepwater outfall plumes

In order to predict the behaviour of plumes from three deep ocean outfalls for sewage off Sydney, three-dimensional numerical modelling was used. The modelling suite was driven by data generated by an oceanographic monitoring station measuring wind, ocean currents, temperature and wave characteristics. Three different modelling phases are implemented daily, a nearfield model, a hydrodynamic model and a water quality model. Model output can be used by the New South Wales Environment Protection Authority to predict water quality at ocean beaches and inform the community.

Double Walled, Low Reflection Wave Barriers

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

ON THE INFLUENCE OF WAVE GROUPS ON SHOALING AND BREAKING WAVES

1Determining the largest wave height H which can occur in water of depth d without breaking is a fundamental reference quantity for the design of coastal structures. The ratio of breaking height (Hb) to depth (Hb/d), is known as the breaker index and has been the subject of much research over the past 150 years. Current design guidelines are based on investigations which, predominantly used monochromatic waves, thereby neglecting group effects. Groupiness or height modulation in wave trains is inherent to the free propagation of waves in deep water. Whilst our understanding of the formation and propagation of wave groups remains limited, significant progress has recently been made in the prediction of the onset and strength of breaking of wave groups in deep water. Recent two-dimensional laboratory studies have also shown that wave group effects have a marked affect on wave shoaling and breaking, influencing both the position and form of the breaking waves. These studies have used idealised wave spectra to generate modulating wave groups which are repeatable on a characteristic wave group time scale. Some scenarios yielded breaker indices up to 35% systematically above current design guideline values. Due to limitations of conventional wave probes when used near and within the breaking zone, a laser induced fluorescence (LIF) technique has recently been developed at the Water Research Laboratory. The technique yields high spatial and temporal resolution measurements of propagating wave forms from deep water, through the breaking region and inner surf zone. This technique has been verified using conventional capacitance wave probes and high resolution digital video images with resolution of better than 0.05mm obtained giving errors less than ±0.1 mm. Extensive investigations using repeatable wave groups and incorporating the LIF technique have been completed for a uniform bed slope of 10:1 in which the location of a shoaling bed was incrementally adjusted along the wave tank. In this manner, the shoaling and breaking properties of individual waves within the group could be carefully examined. It was observed that, as a wave group encounters a sloping bed, the behavior of the shoaling wave group is critically affected by the spatial phasing of the group relative to the bed. A critical depth between L0/5 > d > L0/8, where L0 is the deepwater wavelength, has emerged as the primary factor delineating two types of group shoaling. When a wave crest is coincident with the group energy maximum at this critical location, wave breaking tends to occur earlier, in deeper water and in a more gentle manner. However, where there is coincidence of a wave trough with the group energy maximum at this depth, delayed shoaling is observed. Notably, delayed shoaling stabilises the waves within the group, delaying the initiation of breaking and can yield Hb/d ratios up to 38% greater than present design guidelines. Our results show that present design guidelines based primarily on monochromatic waves are not conservative when wave group effects are considered.

2D EXPERIMENTAL MODELLING OF HYDRODYNAMIC EFFECTS OF SUBMERGED BREAKWATERS

Laboratory 2D experiments have been carried out in 3 m wide wave flume to investigate wave transmission, wave induced-setup and current over submerged breakwater/reef structures. This paper is aimed at advancing the understanding of overtopping flow across submerged breakwater with different crest widths under different submergences. The experiments have been carried out in a central 1m wide channel so as to minimize/prevent return flow over the structure. Analysis of data shows that flux is most influenced by breakwater crest width rather than other variables. The models provided by Symonds et al. (1995) and Gourlay and Colleter (2005) are investigated for calculating current passing over the breakwater/reef due to wave breaking. With adjustment to the calibration factors and modification of models predictive capabilities are improved.