Measurements of evaporation from a mine void lake and testing of modelling approaches

McJannet, David; Hawdon, Aaron; Niel, Tom Van; Boadle, David; Baker, B.; Trefry, M. G.; Rea, Iain

doi:10.1016/j.jhydrol.2017.10.064

Cited by 31 publications

(27 citation statements)

References 40 publications

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“…Evaporation from the pit lake is generally assumed to be lower than evaporation from a water body at natural surface due to the depth of the pit lake surface below natural surface (McJannet et al 2017). A pan factor is applied to the daily pan evaporation to account for this reduction in evaporation from the pit lake.…”

Section: Pan Factor Sensitivity Analysis Methodologymentioning

confidence: 99%

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Simplified method to predict final void water levels

Morgan¹,

Hocking²,

Henderson³

2019

Proceedings of the International Conference on Mine Closure

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At the completion of open cut coal mining, the open cut pit may remain, becoming a final void. In the majority of cases, the BHP final voids will collect water until they reach an equilibrium level where net inflows equal net outflows. BHP currently has over 100 open cut coal mine pits across Queensland and New South Wales coal operations, some of which may be final voids at closure. A decision framework is being developed by BHP to facilitate more efficient and consistent decisions about rehabilitation of final voids. Within this framework, an understanding of the pit lake equilibrium water level is needed to assess the interaction with groundwater aquifers (whether the void will be a groundwater sink or a source of groundwater recharge) and the likelihood of discharges (overflowing) to surface waters. At present, the most common method for predicting the final void pit lake level is to use a daily time step water balance model (WBM), often derived from complex WBMs developed for site operations. Considering the number of pits BHP needs to assess at various stages of mine planning, with frequent mine plan changes in the decades prior to closure, developing and continuously updating complex WBMs for each pit would result in inefficient closure planning. Consequently, BHP recognised the benefit in developing a simple and efficient screening method to predict the long-term pit lake water level. To facilitate the development, a suite of daily time step WBMs were developed based on the current methodology BHP adopts to assess final voids. The aim of the WBMs was to evaluate the typical behaviour of the pit lake using a range of representative final void configurations from a representative sample of seven BHP operations. Recognising the uncertainty in the key parameters adopted in the BHP operational WBMs, a sensitivity analyses of four key parameters associated with runoff, evaporation, groundwater and spoil storage were undertaken. The results were used to guide the development of the screening method by identifying which parameters have the most influence and should therefore be accounted for in predicting the behaviour of pit lakes. A 'pit lake prediction tool' has been developed and benchmarked to the WBM results to show confidence in the screening method. A risk assessment was included to allow effective communication of the pit lakes' risk of interacting with groundwater or spilling to the receiving environment. This pit lake prediction tool forms part of the BHP final void decision framework, which facilitates more efficient and consistent decisions about rehabilitation of final voids.

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Section: Pan Factor Sensitivity Analysis Methodologymentioning

confidence: 99%

“…The pan factor is assumed to be constant for all water levels. Some studies suggest that this simple approach may not be accurate (Mulder 1997;McJannet et al 2017). Field studies are underway to develop improved estimates for evaporation in pit lakes.…”

Section: Pan Factor Sensitivity Analysis Methodologymentioning

confidence: 99%

Simplified method to predict final void water levels

Morgan¹,

Hocking²,

Henderson³

2019

Proceedings of the International Conference on Mine Closure

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“…Solar radiation input is a key driver of evaporation from lakes, but in a pit lake environment the steep walls can cause shading of the water surface (McJannet et al 2017). The height of the pit walls and the dimensions and orientation of the pit will dictate how much solar radiation the lake receives; as such, shading is an important consideration in any estimates of pit lake evaporation.…”

Section: The Unique Evaporation Environment Of a Mine Voidmentioning

confidence: 99%

“…The immersed pan evaporation ( pan ) was calculated for each 24-hour period by subtracting water depth at the end of the measurement period from depth recorded at the start of the measurement period. Immersed pan evaporation was converted to pit lake evaporation ( ) using a correction factor that adjusts for any differences in temperature of water in the pan relative to the surrounding lake (McJannet et al 2017). This approach relies on the fact that the meteorological conditions (i.e.…”

Section: Floating Evaporation Panmentioning

confidence: 99%

Evaporation from coal mine pit lakes: measurements and modelling

McJannet¹,

Hawdon²,

Baker³

et al. 2019

Proceedings of the International Conference on Mine Closure

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Open cut coal mines can have large surface water catchments and often extend to depths below the natural water table level with constant dewatering required to maintain coal extraction. When mining ceases, surface water runoff and groundwater start to fill the void, and pit lakes form. Understanding the hydrological and chemical evolution of these lakes is important for appropriate closure planning. One of the key processes controlling pit lake evolution is evaporation loss, and current estimates of this process are highly uncertain. Recognising the importance of evaporation and the uncertainty in current estimation methods, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) has been working in conjunction with BHP to measure and model evaporation from pit lake environments at Norwich Park Mine, a large open cut coal mine in Central Queensland. Compared with typical lakes and reservoirs, pit lakes are a unique environment because of the depth to the water surface below the original land surface. The water surface in a pit is likely to be sheltered from winds experienced at the land surface, and the steep pit walls can shade the water body within. Based on a number of evaporation studies in pit lake environments, CSIRO has developed a pit lake evaporation model that can be run using readily available data sources, but this model is yet to be tested in a coal mine environment. Open cut coal mines in Central Queensland are typically strip mined, resulting in long, rectangular, box-shaped voids. The aim of this study was to measure evaporation in a pit lake at Norwich Park Mine and to use the results to test the performance of the pit lake evaporation model. In addition, the measurement dataset was used to test the performance of the pan coefficient evaporation-modelling approach, which is commonly used in the mining industry for specifying evaporation from pit lakes. Successful measurements were collected over a six-month period using a custom-built floating evaporation monitoring system, and this data was used as the baseline dataset against which to test the performance of two evaporation-modelling approaches. Despite its widespread use, the pan coefficient model was shown to be a very poor predictor of daily evaporation. The CSIRO pit lake evaporation model showed the same trends as daily evaporation measurements, but the model consistently tended to underestimate evaporation totals. Further investigations showed that the wind speed scaling procedure utilised in the model for reducing wind speed at land surface level to that at water level was not suitable for coal mine pits. Observations showed that wind speeds at pit level at the study location were actually greater than those at land level. It is suspected that the long, narrow shape of the coal pits acts to funnel wind flow into the pit, thereby, resulting in an acceleration of airflow. When appropriate wind speed scaling was applied, the CSIRO pit lake model performance was excellent. Total predicted evaporation was within 5% of that me...

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“…Additionally, quantifying the changes in lake area is necessary to determine the water volume consumed by lakes. For the water-limited areas, evaporation is the predominant component of active water consumption and represents the largest component of the water balance of a lake [12,13]. Knowledge of the temporal variability in lake evaporation could facilitate the quantification of the water consumption and water demands and, thus, improve the allocation of water resources in these regions [2].…”

Section: Introductionmentioning

confidence: 99%

Estimating Dynamics of Terminal Lakes in the Second Largest Endorheic River Basin of Northwestern China from 2000 to 2017 with Landsat Imagery

Zhang

Wang

et al. 2019

Remote Sensing

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Quantifying terminal-lake dynamics is crucial for understanding water-ecosystem-economy relationship across endorheic river basins in arid environments. In this study, the spatio-temporal variations in terminal lakes of the lower Heihe River Basin were investigated for the first time since the Ecological Water Diversion Project commenced in 2000. The lake area and corresponding water consumption were determined with 248 Landsat images. Vital recovery of lakes occurred two years after the implementation of the project, and the total lake area increased by 382.6%, from 30.7 to 148.2 km2, during 2002–2017. East Juyan Lake (EJL) was first restored as a project target and subsequently reached a maximum area of 70.1 km2. Water dispersion was initiated in 2003, with the East river prioritized for restoration. Swan Lake in the East river enlarged to 67.7 km2 by 2017, while the other four lakes temporarily existed or maintained an area < 7 km2, such as West Juyan Lake. Water consumed by lakes increased synchronously with lake area. The average water consumption of the six lakes was 1.03 × 108 m3/year, with 63% from EJL. The increasing terminal lakes; however, highlight the seasonal competition for water use between riparian vegetation and lake ecosystems in water-limited areas.

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Measurements of evaporation from a mine void lake and testing of modelling approaches

Cited by 31 publications

References 40 publications

Simplified method to predict final void water levels

Simplified method to predict final void water levels

Evaporation from coal mine pit lakes: measurements and modelling

Estimating Dynamics of Terminal Lakes in the Second Largest Endorheic River Basin of Northwestern China from 2000 to 2017 with Landsat Imagery

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