Aquifers underlying the 500-sq km onshore part of the Burdekin delta are among the most prolific in Australia. Annual production of groundwater is mainly for irrigation and is in excess of 300 × 10⁶ cu m. Aquifer thickness ranges from zero, where the river crosses a bedrock bar, to 100 m. Mean annual natural recharge has been estimated at 210 × 10⁶ cu m, partly supplied by seasonal rains and partly by the Burdekin River which has a mean annual flow of 10 × 10⁹ cu m and yet is ephemeral. The seasonal pattern of recharge and pronounced variations in recharge year by year cause major fluctuations in the water table. Intensive pumping has accentuated water-level fluctuations and in 1971, at the end of a dry period, the water tab e at one point was 5 m below sea level in an aquifer with a mean transmissivity of the order of 5,000 sq m/d. The short-term problem in the delta is severe fluctuation of groundwater levels and the long-term danger is saline intrusion.

Local water boards have been established to build and operate recharge works--the first such substantive program in Australia. Water is pumped from the river into a system of natural and artificial channels and increasing rates of recharge have been achieved. Pumpage for artificial recharge now is approaching 100 × 10⁶ cu m/a. Suspended clay in the recharge water precludes recharge through bores without expensive pretreatment.

Since commencement of artificial recharge the system has had sharply declining recharge rates particularly in the constructed facilities, and in 1971 the Australian Water Resources Council initiated a group of research projects: (1) numerical modelling of the groundwater system, which will provide a basis for design and management of the expanding artificial-recharge program; (2) detailed study of unsaturated flow below the recharge pits, including the effects of low-permeability layers on and below the floor of the pits; (3) the role of the sediment load in the recharge waters in the reduction of recharge rates; and (4) study of the biota of the warm recharge waters and their effect in limiting recharge.

Other studies are in progress on tritium dating of the groundwater to assist in definition of the flow system and on the heterogeneity of the materials around the recharge pits.

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