The Tongola groundwater pumping/re-use project: A pilot study for groundwater table control in the Shepparton region in northern Victoria

Abstract

Rising saline watertables and associated increasing soil salinity problems are threatening agricultural production in Northern Victoria. Groundwater pumping from shallow aquifers is now generally accepted as the most feasible strategy to control watertable levels. Disposal into the River Murray system is not acceptable because of downstream water users, both urban and agricultural. As most of the water is of a reasonable quality (average about 1500 mg 1 −1 TDS) it can be used for irrigation after shandying to appropriate levels. The Tongala project is a pilot scheme to investigate the strategy to integrate groundwater pumping for salinity control with on-farm use of the water. This paper reports on the results after 5 years of project operation. The project was initiated in May 1980 and became operational in 1981. Eleven major dairy farms (>20ha), one orchard and 8 smaller properties are included in the project area which covers 610ha. Seventeen groundwater pumps are now operational. All but one are privately installed and operated. Two units are licenced to outfall into the surface drainage system, all other units re-use the pumped ground-water for on-farm irrigation. The project monitors watertable levels, piezometric levels, soil salinities, watertable salinities, rainfall, evaporation, pumped volumes, pumped water qualities and irrigation water use. After 5 years of operation it has been shown that the project farmers pump enough groundwater to keep watertables at > 1m below surface. Even during the relative wet season of 1983/84, 1100 ML was pumped or 1.8 ML ha −1. This compares favourably with the estimated watertable accessions in the area which are thought to be between 1 and 2 ML per year. Soil salinities in the project area decreased in response to the groundwater pumping. Farm productivity was monitored on one farm in the pilot area from 1978 (two years before pumping started) to 1985 (5 years after pumping started). During this period butter fat production increased from about 300 to 390 kg/ha in productive land. This was attributed to the combined effect of a reduction in average soil salinity in the top 60 cm of the profile from 2400 to 1200 mg TDS per kg dry soil and an increase in irrigation water use from less than 10 ML/ha before to nearly 12 ML/ha after pumping started. The groundwater pumping/re-use management system offers only a temporary solution to the problem of increasing salinity. In the long term, aquifer salinisation is llikely to occur as salts are both washed down from the overburden into the aquifer and laterlly drawn in from surrounding areas. Salt balance, both on a regional and on a farm scale, is a pre requisite for a long term sustainable agricultural system.