3D geophysical processing, visualisation and interpretation of rice irrigation impacts

Abstract

The National Centre for Groundwater Management at the University of Technology, Sydney has completed a 3-stage research project at a field site near Griffith NSW, which included an examination of the dynamics of groundwater levels and salinisation adjacent to an irrigated rice paddock. The site had 22 piezometers and was instrumented with 16 dataloggers from October 1999 to September 2001. Ten resistivity imaging and EM34 surveys were conducted during the period October 1998 to June 2001 ? before, during and after irrigation. Some EM31 was also done. This paper will concentrate on the collation and qualitative interpretation of the resistivity imaging data. Each imaging survey comprised 15 lines (during winter) or 10 lines (during irrigation) each of about 200 metres length. The lines were generally 10 metres apart (sometimes 5 m). The results from each survey have been assembled into a movie (using SURFER and SLICER software) which shows the 3-D heterogeneity in resistivity across the site. A couple of movies have been produced showing the variation with time along representative sections. Snapshots of the differential apparent resistivity between surveys before and after irrigation show definite incremental salinisation in the fallow paddock adjacent to the irrigated rice paddock.