Water quality assessment in the Hawkesbury Nepean River system, New South Wales

Abstract

Surface waters are the most vulnerable to pollution due to their easy accessibility for disposal of wastewaters. Both the natural processes as well as the anthropogenic influences together determine the quality of surface water. The Hawkesbury Nepean River system (HNRS) is an icon of Australia's largest city, Sydney, with important ecological, social and economic values. Since European settlement, the reliance on this river system has steadily increased to meet the drinking water requirements of the population, and it now provides 97% of fresh drinking water to more than 4.8 million people living in and around Sydney. HNRS has been placed under increasing pressure and the environmental health of the river system has suffered due to the increasing development and population growth over time. The river regulation has resulted in large volumes of water being extracted for drinking water, irrigation and industrial uses. There are a number of sewage treatment plants (STPs) located in the catchment, and stormwater runoff from agricultural and urban areas can also carry pollutants into the river system. Algal and introduced macrophyte blooms have commonly occurred in the past and are likely to continue to occur in the future unless serious intervention is made by the NSW Government. Identifying the deteriorated section of a river and actual sources of pollution along different parts of the river helps to make suitable pollution prevention activities. Therefore, this study attempts to investigate the state of the HNRS, using water quality data from the past 20 years. Therefore, the following objectives are primarily emphasized in this thesis: Assess the water quality in the HNRS; Assess the trend of water quality in the HNRS; Develop prediction equations to predict water quality from surrogate water quality parameters; Assess the impact of land use on the water quality of the HNRS; Develop a water quality index for the river in order to conduct an overall evaluation of the water quality of the river. This thesis consists of a series of experimental and numerical studies. They include exploratory analysis, trend analysis, principal component analysis, factor analysis, regression analysis, and application of water quality index method to make an overall water quality assessment of the HNRS. This study has found that the concentrations of total phosphorus, nitrogen oxides and chlorophyll along the HNRS are higher than those recommended by the Australian and New Zealand Environment and Conservation Council (ANZECC) guidelines. An increasing trend for turbidity, chlorophyll-a, alkalinity, dissolved organic carbon, total iron, total aluminium, total manganese and reactive silicate has also been detected for majority of the monitoring stations. Application of the Canadian Water Quality Index (WQI) method shows that the water quality at 9 stations fall under either the poor or marginal category. Stations N14 and N35 were found to be the most polluted stations in the HNRS among the 9 stations. There are many sewage treatment plants discharging treated wastewater to upstream of N35. Also, the dominant land use in this part of the catchment includes rural, grazing, commercial gardening, intensive agriculture and urban and industrial activities. These land uses can be attributed to the low WQI at N35. Water quality at station N14 should be improved due to dilution by high quality inflows from the Colo River and the undisturbed upstream catchment. The high pollutant levels at N14 need to be investigated to find the possible reasons and to devise controlling measures. Although an improvement in water quality can be seen at some stations downstream of the undisturbed parts of the catchment, there has been an overall water quality deterioration in the HNRS during the last decade. The HNRS is a very important river system of Australia .The findings of this study would provide an important basis for better land use planning in the catchment of the HNRS, which would improve the overall state of the river water quality.

Date of Award	2016
Original language	English