Brett Miller

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.

A piecewise regression approach for determining biologically relevant hydraulic thresholds for the protection of fishes at river infrastructure.

A piecewise regression approach was used to objectively quantify barotrauma injury thresholds in two physoclistous species, Murray cod Maccullochella peelii and silver perch Bidyanus bidyanus, following simulated infrastructure passage in a barometric chamber. The probability of injuries such as swimbladder rupture, exophthalmia and haemorrhage, and emphysema in various organs increased as the ratio between the lowest exposure pressure and the acclimation pressure (ratio of pressure change, R(NE:A) ) reduced. The relationship was typically non-linear and piecewise regression was able to quantify thresholds in R(NE:A) that once exceeded resulted in a substantial increase in barotrauma injury. Thresholds differed among injury types and between species but by applying a multispecies precautionary principle, the maintenance of exposure pressures at river infrastructure above 70% of acclimation pressure (R(NE:A) of 0·7) should protect downstream migrating juveniles of these two physoclistous species sufficiently. These findings have important implications for determining the risk posed by current infrastructures and informing the design and operation of new ones.

Evolving role of radiotracers in coastal zone studies

Abstract Recent advances in the off-shore radiotracing program in the Asia Pacific region are described with examples from the Philippines, Thailand, Hong Kong and Australia. Advances are driven by changing requirements from the user community which include: (1) the need to experimentally evaluate the output of numerical models underpinning engineering and environmental investigations; (2) the need to address increasingly sophisticated questions posed by researchers into coastal ecosystems; and (3) the need to respond to pressures from regulators to minimise the level of tracer released to the environment. Four stages in the recent evolution of tracer technology are identified.

APPLICATION OF TMDL AND RISK ASSESSMENT PRINCIPLES FOR PATHOGEN MANAGEMENT AT AN URBAN RECREATIONAL LAKE

Lake Parramatta was a disused water storage located at the bottom of an 8 km2 urbanised watershed in Sydney, Australia in which primary contact recreation had been actively discouraged, because of the perceived risk of infection from waterborne pathogens. However, a recent survey of the Lake showed that safe swimming might be possible during summer dry weather periods, providing high contamination periods (during rain events) could be identified and avoided. To this end we characterized inflow/lake water quality (bacterial indicators, fecal sterols, Cryptosporidium, viruses & turbidity) and hydrology (rainfall, streamflow & Lake depth measurements) to quantify the cycle of lake contamination and water quality recovery. Fecal contamination became noticeable for rainfall inputs > 10 mm in 25 MJ.m-2.d-1, with 10% visible radiation reaching 1 m). None of a range of enteric viruses was detected in the Lake immediately after high stormwater inputs. Fecal sterol analysis indicated that sewage only represented some 0.1% of run-off into the Lake. This data was used to develop a water safety management plan for efficient and timely recreator protection from pathogen-related events, and the Lake was reopened in December, 2006.

First large-scale ecological impact study of desalination outfall reveals trade-offs in effects of hypersalinity and hydrodynamics

Desalination is an increasingly common method of meeting potable water demands, but the associated ecological risks are not well understood. Seawater desalination plants discharge large volumes of hypersaline brine directly into the ocean, raising concerns about potential impacts to marine life. In order to reduce impacts of brine, newer desalination outfalls are often fitted with high-pressure diffusers that discharge brine at high velocity into the water column, increasing the mixing and dilution of brine with ocean water. However, there are few published studies of marine impacts of desalination brine, and no well replicated before-after designs. Here we report a six-year study testing for impacts and subsequent recovery of sessile marine invertebrate recruitment near a desalination outfall with high-pressure diffusers. We used a Multiple Before-After-Control-Impact (MBACI) design to test for impacts and recovery at two distances (30 m and 100 m) from a 250 ML/day plant outfall, as well as a gradient design to test the strength of impacts relative to distance from the outfall. The diffusers achieved the target of less than 1 psμ salinity difference to surrounding ambient waters within 100 m of the discharge outfall, but sessile invertebrates were nonetheless impacted. Polychaetes, bryozoans and sponges reduced in cover as far as 100 m from the outfall, while barnacles showed the opposite pattern and were more abundant near the discharging outfall. Ecological impacts were disproportionate to the relatively minor change in salinity (∼1 psμ), suggesting a mechanism other than salinity. We propose that impacts were primarily driven by changes in hydrodynamics caused by the diffusers, such as higher near-bed flow away from the outfall. This is consistent with flow preferences of various taxonomic groups, which differ due to differences in settlement and feeding abilities. High-pressure diffusers designed to reduce impacts of hypersalinity may inadvertently cause impacts through hydrodynamics, leading to a trade-off in minimizing combined salinity and hydrodynamic stress. This study provides the first before-after test of ecological impacts of desalination brine on sessile marine communities, and rare insight into mechanisms behind impacts of a growing form of human disturbance.

How low can they go when going with the flow? Tolerance of egg and larval fishes to rapid decompression

ABSTRACT Egg and larval fish that drift downstream are likely to encounter river infrastructure and consequently rapid decompression, which may result in significant injury. Pressure-related injury (or barotrauma) has been shown in juvenile fishes when pressure falls sufficiently below that at which the fish has acclimated. There is a presumption that eggs and larvae may be at least as, if not more, susceptible to barotrauma injury because they are far less-developed and more fragile than juveniles, but studies to date report inconsistent results and none have considered the relationship between pressure change and barotrauma over a sufficiently broad range of pressure changes to enable tolerances to be properly determined. To address this, we exposed eggs and larvae of three physoclistic species to rapid decompression in a barometric chamber over a broad range of discrete pressure changes. Eggs, but not larvae, were unaffected by all levels of decompression tested. At exposure pressures below ∼40 kPa, or ∼40% of surface pressure, swim bladder deflation occurred in all species and internal haemorrhage was observed in one species. None of these injuries killed the fish within 24 h, but subsequent mortality cannot be excluded. Consequently, if larval drift is expected where river infrastructure is present, adopting design or operational features which maintain exposure pressures at 40% or more of the pressure to which drifting larvae are acclimated may afford greater protection for resident fishes. Summary: Eggs are extremely tolerant to rapid decompression, although larvae may be injured once pressure falls below 40% of the pressure to which they are acclimated.

Experiences with Physical Scale Basin Modelling Using Mobile Sediments

This paper presents a new modelling paradigm justifying the application of smallscale basin models using mobile bed sediments for predicting medium-term wavegenerated plan form beach response to nearshore structures.