Estimation of groundwater recharge and assessment of groundwater quality in urban landscapes : a case study of the Wattle Grove area

United Nations Population Fund estimated that half of the world’s population lived in urban areas in 2008 and projected that by the year 2050, the population living in towns and cities would be up by 68%. Furthermore, half of the world’s urban population depends on groundwater as the main source of water supply which puts pressure on groundwater as the urban population grows. The main aim of this research is to estimate the groundwater recharge within urban centres with water table fluctuation (WTF) method and to evaluate physico-chemical quality of groundwater using Wattle Grove area, Sydney, Australia as a case study. The groundwater table depths were continuously monitored on an hourly basis over one year with data loggers installed in the four newly developed boreholes. The groundwater samples were collected on a monthly basis and taken to the university environmental laboratory for physico-chemical analysis. The concept of rainfall-induced groundwater recharge is taken as groundwater recharge caused solely by rainfall while total groundwater recharge is caused by all other factors including rainfall. Both were estimated by considering the wet and dry periods in the year. On average, during the rainy periods, BH1 had the highest recharge per day of 1.67 mm/day while BH4 with 0.28 mm/day was the least. The variation of recharge estimates across the four sites could be attributed to different surface topography, presence of water bodies and underground water movement. In spring and summer season, the groundwater-level response to rainfall shows that BH4 recorded the shortest lag time of 3 days while BH2 recorded the longest time of 14 days. The fastest time is as a result of fissure flow while the longest time is attributed to slow matrix flow. The combined analysis of spring and summer also shows that BH4 has the shortest response time and rainfall has a direct impact on groundwater level fluctuations. For all the four boreholes pH, calcium and potassium concentrations in groundwater were within Australian Drinking Water Guideline (ADWG) and World Health Organisation (WHO) standards. Only BH1 has a high sodium concentration of over 4000 mg/L and a magnesium concentration of 500 mg/L and both exceed the aforementioned guidelines value of (50 – 300 mg/L). Too, the TDS value of BH1 exceeds EPA’s guideline value of 1500 – 2600 mg/L and that makes the groundwater unsuitable for irrigation. This indicates that the groundwater may be contaminated by the salt. The source for the salt, at this stage, is unknown. The groundwater from the four boreholes exceeds the turbidity limit of 5 NTU and it cannot be used directly for drinking

Assessment of urban land use and cover on groundwater recharge and quality

This study focusses on a method for estimating the urban recharge and evaluating the ground water quality for drinking and irrigation purposes. The study was carried out in the Liverpool Local Government Area of New South Wales, Australia, and it included year-long monitoring of four boreholes for the water table depth and water quality. Average depth of water table was in the range of 1 to 4 m from the land surface. The pattern of variations in the water table depth (WTD) varied across the four boreholes. The WTD variations between borehole 2 (BH2) and borehole 3 (BH3) were similar, but significantly different variations were exhibited in BH1 and BH 4, with BH1 showing a quicker response to rainfall events. The presence of lake appears to have influenced the recharge pattern in the adjacent area as reflected in the WTD variations in BH3 and BH4. The recharge rates for BH3 and BH4 was about 2 to 5 times higher than those observed for BH1 and BH2, which are located at a relatively greater distance from the lake. This indicates that the presence of urban lakes can influence recharge rate in the area. Water quality analysis indicated higher salt and turbidity levels, which may be attributed to the local geology (the Wianamatta group) present in the study area and/or possible saltwater intrusion. This has implications for the treatment cost associated with the supply of the groundwater for drinking and irrigation purposes. Pearson’s analysis indicated a significant correlation between EC, TDS, Turbidity and pH. The turbidity of groundwater varied between 33 and 530 NTU, indicating that the turbidity may have been affected by the dissolution of salt deposits via colloidal particles. Significant variations in groundwater quality during rainy periods, also, indicated the existence of groundwater recharge in the study area. This study highlights the issues associated with the groundwater recharge and quality management in urban landscapes and provides a basis for further research

Creating livable subdivisions using stormwater, recycled water and groundwater

Integration of green infrastructure (comprising urban lakes, wetlands and parklands) within an urban centre subdivision can significantly improve its livability. Stormwater generated within the urban centre, which is often considered as water carrying significant amounts of pollutants, can be used to create green infrastructure within the subdivision. In addition, recently, “sewer mining” is being used to supplement the non-potable water for urban centres. This source of recycled water is primarily used to satisfy the water required to maintain healthy green infrastructure. Extensive research conducted in recent years have also led to the plan of utilizing constructed lakes and wetlands, as part of green infrastructures, for storing and improving stormwater quality. Furthermore, they serve as significant water features within an urban centre increasing property values. In this work, we present a case study of a local government area (LGA) in Western Sydney, to provide some insights on how using urban lakes (which besides serving as stormwater purifying system) can greatly add to recreational value to a subdivision. City Councils in Western Sydney have successfully created parklands and physical exercise amenities around these constructed wetlands and lakes. These areas attract a large number of visitors throughout the year. The beneficial value of the urban lakes is demonstrated by the increasing values of the properties which are located around these lakes. We conclude that by employing best practices for managing stormwater runoff provide both socioeconomic and environmental benefits to urban centres, and cansignificantly increase the economic value of the region