Year

1994

Degree Name

Master of Science (Hons.)

Department

Department of Geography

Abstract

Rainfall patterns were related to watertable fluctuations over an eight month monitoring period, as a basis for understanding acid drainage development at Jasper's Brush, on the lower Shoalhaven floodplain. The watertable was shown to fall quickly on the floodplain very shortly after rainfall. As the height of groundwater dropped, groundwater acidity increased rapidly and sulphate, iron and aluminium rose to extreme levels. Watertable fluctuations were analysed in a backswamp section, across a large main flood mitigation drain, to understand groundwater movements and the resulting severity of acid drainage in the drain. The severity of acid drainage was also analysed in a small mole drain which was fed by a particularly strongly oxidising environment. Water quality was analysed along the length of the main drain studied; recurrent drainage of the drain water, through the floodgate upon low tides, allowing more saline creek waters into the drain was shown to have an effect of buffering the acid drainage severity. Water quality in Broughton Creek was analysed for a month after a minor flood event, with results (mainly lowered pH and elevated aluminium levels) highlighting the movement of acid drainage from the floodplain into the creek. The severe adverse effects on fish were documented. Management options are given. The main option involves proposing a rise in the watertable by increasing drain water depth (how this may be achieved is explained) to achieve a reduction in pyritic oxidation, and the likely reduction in acid drainage severity is estimated.

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