Assessment of the Jabiluka Project : report of the Supervising Scientist to the World Heritage Committee
Johnston, A.; Prendergast, J. B.; Bridgewater, Peter
E-Publications; E-Books; PublicationNT; Supervising Scientist Report; 138
Alligator Rivers Region
Main report--Appendix 2 of the Main Report. Submission to the Mission of the World Heritage Committee by some Australian Scientists ... --Attachment A. Johnston A. and Needham S. 1999. Protection of the environment near the Ranger uranium mine--Attachment B. Bureau of Meteorology 1999. Hydrometeorological analysis relevant to Jabiluka--Attachment C. Jones, R.N., Hennessy, K.J. and Abbs, D.J. 1999. Climate change analysis relevant to Jabiluka--Attachment D. Chiew, F and Wang, Q.J. 1999. Hydrological anaysis relevant to surface water storage at Jabiluka--Attachment E. Kalf, F. and Dudgeon, C. 1999. Analysis of long term groundwater dispersal of contaminants from proposed Jabiluka mine tailings repositories--Appendix 2 of Attachment E. Simulation of leaching on non-reactive and radionuclide contaminants from proposed Jabiluka silo banks.
Uranium mill tailings - Environmental aspects - Northern Territory - Alligator Rivers Region; Environmental impact analysis - Northern Territory - Jabiluka; Uranium mines and mining - Environmental aspects - Northern Territory - Jabiluka; Jabiluka - Environmental aspects
Supervising Scientist Report; 138
1 volume (various pagings) : illustrations, maps
https://hdl.handle.net/10070/462403; https://hdl.handle.net/10070/462400; https://hdl.handle.net/10070/462405; https://hdl.handle.net/10070/462406; https://hdl.handle.net/10070/462408; https://hdl.handle.net/10070/462409; https://hdl.handle.net/10070/462411
27 Jabiluka project and the scientific information underlying the modelling was based upon previous work of the Supervising Scientist. Despite this, a further investigation of this issue was sought by the Supervising Scientist as part of this review. The University of Melbourne (Chiew & Wang 1999) re-examined the appropriateness of the pan coefficients proposed by Hatton (1997). The average monthly evaporation rates derived using these coefficients were compared with point potential evapotranspiration (PPE) and areal potential evapotranspiration (APE) estimates. The PPE and APE estimates were extracted from the digital maps of evapotranspiration of Australia prepared by the Cooperative Research Centre for Catchment Hydrology. In simple terms, the PPE is the rate of evapotranspiration from a small wet area in an existing environment, while the APE is the rate of evapotranspiration if a large area is well watered. The storage evaporation rate is expected to be somewhere between the PPE and the APE, and closer to APE during the Wet season due to the lower advective energy at this time. On the basis of an assessment against this criterion, Chiew and Wang (1999) concluded that all coefficients except the April and October figures were appropriate and recommended that the Vardavas (1987) values should be used for all months. Figure 3.3.1 shows the evaporation rates calculated using the Vardavas (1987) pan coefficients and these are compared to the APE and PPE values. All of the Vardavas calculations are in agreement with the seasonal pattern of the APE and the PPE. For February and March, the estimated storage evaporation rates are lower than the APE and Chiew and Wang (1999) concluded that this could be due to errors in the recorded pan evaporation (because of the difficulty in accurately estimating pan evaporation when rainfall is high) or errors in the APE estimates. The overall conclusion was, however, that the best estimates of pond evaporation for Jabiluka would be obtained by using the results of Vardavas (1987). The difference in annual pond evaporation arising from the use of the full set of Vardavas coefficients compared to that obtained using the coefficients adopted by ERA in the PER for Jabiluka is about 2%. This difference is clearly very small compared to other uncertainties in the modelling of water management and it can be concluded that there is no significant error in evaporation estimates for the Jabiluka water management system arising from the pan coefficients used by ERA in the PER for Jabiluka. 3.3.2 Inverse relationship between evaporation and rainfall Wasson et al (1998) state that the principal source of error in the evaporation calculations of ERA arises from neglect of the inverse relationship between evaporation and rainfall which arises because solar radiation is lower on cloudy days than on sunny days. They suggest that the adoption of long-term mean values for the pan factors will result in a significant overestimate of evaporation in very wet months and that this effect could exceed 10% during very wet years. Chiew and Wang (1999) investigated the significance of the inverse relationship between evaporation and rainfall using data from a number of meteorological stations in the north of the Northern Territory including Jabiru, Maningrida, Middle Point and Darwin. They found that a linear inverse relationship was statistically significant for both the annual data and the quarterly data at each station and that it was most significant at Jabiru. They concluded that this effect should be taken into account in their modelling of the water management system at Jabiluka and they evaluated the significance of the effect on the required pond volume. The conclusion reached was that the retention pond volume would need to be increased by about 3% as a result of both the inverse relationship and interannual variability in evaporation.