Long-term natural flow regime (spells) analysis for water treatment discharges

Abstract

Conducting mineral extraction activities usually requires obtaining a set of permits for each of the activities planned to be undertaken. This directly concerns water management and discharges associated with any mineral extraction operations. In response to the growing demand for energy resources worldwide, the industry demand for permits relating to the extraction of coal seam (and shale) gas also increased dramatically. This was in turn accompanied by the growing community concerns in regard to fracking and wastewater management practices.

To address these concerns, the state governments in Australia developed a strict framework and guidelines for the permit application process and provided terms of reference for the environmental impact assessments, where required. In accord with the guidelines, a liquefied natural gas mining operator was conducting a research to assess several facets of water releases from Reedy Creek Water Treatment Facility to Yuleba Creek in Queensland. The scope for the research was developed in line with such guidelines and included estimating the downstream extents of flows from several Water Treatment Facility discharge volumes over a period of planned discharges. More specifically, the purpose of the study presented in this paper was to assess flows in Yuleba Creek before and after the proposed releases of treated water from the Reedy Creek Water Treatment Facility, and how the planned change to flow parameters would satisfy the regulatory guidelines. The assessment was based on 41 years of data collected at the Forestry Station gauge.

An analysis of the obtained results suggested that the historical maximum was 25,825 ML/d. An analysis of the median flows suggested that the years 1983, 1999, and 2010-2012 had the highest medians of around 15 ML/d, 10 ML/d, and from 9 ML/d to 12 ML/d respectively. The median flow values would exceed from 0.09 ML/d to 0.69 ML/d flows during the months of February and March only. The lowest 90th percentile flows were obtained for the months from April through to October. The highest flow estimates would be in the months from November through to March. An analysis of the flow duration curves suggested that the annually averaged flow of 0.08 ML/d in the Yuleba Creek would be present for around 48% of the time. Flows predictabilities were calculated; for the baseline flow records, the value of predictability was 0.50, and the constancy/predictability ratio was 0.89. The rates of streamflow rise and fall were estimated and analysed. The results suggested that the rate of streamflow rise varied within a range from 0.0 up to 320.0 ML/d per day. The rates of streamflow fall was up to 15.0 ML/d per day.