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8. Assessment of rip lines using CAESAR‐Lisflood on a trial landform at the Ranger Uranium Mine.

Author

Saynor, Mike J., Lowry, John B.C., and Boyden, James M.

Subjects
LANDFORMS, URANIUM mining, SOIL erosion, SEDIMENT transport, SOIL conservation
Abstract

The Ranger Mine in the Northern Territory of Australia is to be rehabilitated by 2026. The rehabilitated landform will require some form of erosion control, or surface amelioration to reduce water and sediment leaving the landform. One method of surface amelioration is the construction of rip lines. Rip lines have been used in both mining and agricultural environments to reduce surface water velocity, trap fine sediment and nutrients, and reduce erosion from the landform. However, there is little quantitative information on the extent to which rip lines influence erosion. In a desktop study using the CAESAR‐Lisflood landform evolution model, we assessed the effectiveness of rip lines by simulating the evolution of both ripped and nonripped surfaces on a range of slopes from 2% to 12% for simulated periods of up to 50 years. We found that rip lines are most effective at controlling erosion on slopes of up to 4%. However, this study also demonstrated that as slope increases, rip lines become less effective over time. These results, in the context of the proposed rehabilitated landform for Ranger Mine, on which the majority of slopes will be between 2% and 4%, indicate that rip lines would be an effective way of mitigating soil loss and sediment transport. Furthermore, model simulations of ripped surfaces show that the structure of the rip lines break down over time, with the rip line depressions infilling and the peaks being eroded, lowered, or reduced in height. This finding is important because it demonstrates that rip lines will not exist in perpetuity in the landscape and long‐term erosion control plans cannot be based on their existence. [ABSTRACT FROM AUTHOR]

Published
2019
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9. Bedload yields for sand-bed streams in the Ngarradj Creek catchment, Northern Territory, Australia

Author

Erskine, Wayne D., Saynor, Mike J., Erskine, Wayne D., and Saynor, Mike J.

Abstract

Bedload yields were calculated by 39 methods at the East Tributary gauge, nine methods at Upper Swift Creek gauge and 11 methods at Swift Creek gauge in the Ngarradj Creek catchment in northern Australia. These methods involved combining various significant bedload rating curves determined for a measured bedload data set for a 4-year period with either the hourly or daily hydrographs or flow duration curves for the same period, 1 September 1998 to 31 August 2002. Bedload ratings were both statistically significant (ρ ≤ 0.05) and explained at least 60% of the variance in bedload flux. Bias corrections were used with all methods based on log10-transformed ratings. Estimated mean annual bedload yields varied by three orders of magnitude at the East Tributary gauge and by two orders of magnitude at Upper Swift Creek and Swift Creek gauges. Hourly discharges usually produced higher estimated yields than daily discharges. The bedload rating-flow duration curve technique overestimates yields and bias correction methods always produce even higher yields. Ratings using both immersed bedload weight and adjusted immersed bedload weight always under-predicted yields because they contain an implicit threshold of motion condition that is at least four times greater than that predicted by Bagnold's threshold equation. Such a result questions the applicability of Bagnold's threshold equation to the Ngarradj Creek catchment. The best estimates of mean annual bedload yield at East Tributary, Upper Swift Creek and Swift Creek gauges are 600 ± 170 (SE), 1065 ± 150 and 1795 ± 270 t/year, respectively.

Published
2015

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