Alice Springs town basin, review 2003
Read, R. E.
E-Publications; E-Books; PublicationNT; Report ; no. 42/2003
Made available via the Publications (Legal Deposit) Act 2004 (NT).
Department of Infrastructure, Planning and Environment
Report ; no. 42/2003
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G- 1 DISCUSSION Potentiometric surfaces (Appendix D) and pumping figures from 1996 to the end of 2002 were used to examine the water balance of the basin. Stored volumes were estimated as follows: Grid files of potentiometric surfaces were generated in Surfer for each complete set of monitoring data in the basin. Saturated aquifer volume was then calculated using these files as the upper surface and a grid file for the basement as the lower surface. Stored volume was estimated by multiplying the saturated volume by 0.07. Change in storage was then estimated by subtracting saturated volume of consecutive periods. Figure G- 1 shows change in storage and river flows and rainfall for the period examined. The water balance equation for the aquifer is S= I + Rr +Rd + Rp +Rs + Ri E Os P O Where S is change in storage I is groundwater inflow, about 30 ML/year Rr is river recharge Rd is diffuse recharge Rp is recharge from leaking pipes Rs is recharge from sewers Ri is recharge from irrigation return E is evapotranspiration Os is outflow to sewers P is pumping O is outflow through Heavitree Gap, about 40 ML/year Since P is known, and reasonable estimates exist for I and O. Rr and E vary with weather conditions. The remaining variables can be assumed to be constant with time. Periods with no river flow were selected to attempt to estimate variable terms Rd and E and the aggregate of the other terms. A wide range of values was obtained. Examination of the data for some anomalous increases in storage, as from 4/1997 to 5/1997 showed that the apparent increase was due to a change in the monitoring grid. A contour map of changes in monitoring bores for the same period showed a small decrease. Losses due to evapotranspiration and gains due to rainfall in periods with no river flow were estimated by an iterative process as follows: It was assumed that there is a linear relationship between evaporation as measured from the Class A Pan at Alice Springs Airport and evapotranspiration from the Town Basin. The volume change for each period, corrected for pumping was plotted against total daily evaporation at the airport for the same period.