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A number of investigations have been undertaken by the New South Wales Water Resources Commission to determine the regional and compound effects of large scale extractive industries on the stability of the Hunter River, New South Wales. Sedimentologic studies of bed material suggest that the Hunter River upstream of Denman has an armoured gravel bed that is immobile during regulated releases from Glenbawn Dam but is disrupted by moderate but less than bankfull flows. Annual bedloadyields have been computed by the bedload rating‐flow duration technique for five river gauging stations. Approximate sand and gravel budgets for selected reaches of the Hunter River demonstrate that the present annual extraction rate from temporary sediment storages within the channel greatly exceeds the transport rate upstream of Denman and is approximately equal to the transport rate downstream of Denman. River degradation is imminent if extractive industries continue operating in the channel of the Hunter River

Two species of macrophytes, Baumea articulata and Schoenoplectus mucronatus, were examined for their capacity to remove phosphorus under nutrient-rich conditions. Forty large bucket systems with the two different species growing in two types of substrate received artificial wastewaters for nine months, simulating a constructed wetland (CW) under high loading conditions. Half of the plants growing in the topsoil and gravel substrates were periodically harvested whereas the other half remained intact. Plant tissue and substrate samples were regularly analysed to determine their phosphorus concentrations. With respect to phosphorus uptake and removal, the Schoenoplectus in the topsoil medium performed better than the Baumea. Biomass harvesting enhanced P uptake in the Schoenoplectus, however the effect was not significant enough to make an improvement on the overall P removal, due to the slow recovery of plants and regrowth of biomass after harvesting. From P partitioning, it was found that the topsoil medium was the major P pool, storing most of total P present in the system. Plant parts contributed only minor storage with approximately half of that P stored below ground in the plant roots. The overall net effect of harvesting plant biomass was to only remove less than 5% of total phosphorus present in the system.

Geotechnical aspects of domestic on-site effluent systems (septic tanks) and their impact on groundwaters are discussed and the limited relevant literature is reviewed. While there are few Australian case studies, the early stages of an ongoing study at Dodges Ferry, Tasmania, show a connection between shallow aquifer quality, number of residences and domestic on-site wastewater disposal practices. Of 26 groundwater samples analysed, a number fail to meet established criteria for potable use. Most samples were highly or very highly saline. This renders them unpalatable and has an adverse impact on vegetation if the water is used for irrigation. Several samples had pH less than 6.0 and those taken from shallow wells were discoloured by leached soil organic matter. Elevated nitrate levels, an indicator of contamination by sewage effluents, were found at nine locations and these were usually associated with small clusters of residences. One very high sample was clearly contaminated by effluent from an adjacent on-site wastewater disposal system. One odorous, black organic seep was found at the foot of the dunes backing a bathing beach and this gives cause for concern that failing on-site wastewater disposal systems are contributory to reduced bathing water quality. Faecal coliforms and Escherichia coli were not found, even in samples with the highest nitrate concentrations, suggesting that residence time has been sufficient for bacterial die-off. Contamination of shallow aquifers is greatest where there is a high density of residences with small lots.