Protecting headwater streams is essential to minimise downstream sediment loads to rivers, estuaries, and oceans. This study analyses the gully and sheet erosion risk from a 33,000 ha agricultural development proposal in the Normanby catchment draining to the Great Barrier Reef (GBR) Lagoon, Australia. The slope‐area threshold for channel initiation was assessed for existing gully channel head locations using satellite images and a hydrologically enforced digital elevation model (SRTM). Thresholds were used to predict whether other stream lines (1:25k scale) were prone to gully incision under development. Results indicated that 430 km out of 1,200 km of streams were at risk of gullying, which could increase erosion by 2‐times, delivering 7,500 t yr⁻¹ locally and 1,700 t yr⁻¹ (worth A$1.8 million) to the GBR. Sheet erosion under agriculture is estimated (RUSLE) to increase by 13‐times from 0.12 to 1.5 t ha⁻¹ yr⁻¹, with 2,200 t yr⁻¹ to streams and 900 t yr⁻¹ (worth A$1 million) to the GBR. Buffering (±50 m) 560 km of headwater streams would cover 5,600 ha or 17% of the area. Precision agriculture using higher resolution topographic data (LiDAR) and improved slope‐area thresholds for gully erosion should be a minimum prerequisite for development, which would reduce but not eliminate increased sediment loads to the GBR. Forest clearance for agriculture is ongoing in Australia, but this first‐world country does not have effective policies or regulations to protect headwater streams or cumulative impacts to the World Heritage Great Barrier Reef, despite millions of dollars spent annually to reduce past land degradation.

中文翻译：

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农业发展有可能增加大堡礁流域的源头水流的沟壑侵蚀和累积沉积物产量的风险

保护上游水源对于最大限度地减少下游向河流，河口和海洋的沉积物负荷至关重要。这项研究分析了诺曼比流域排水至澳大利亚大堡礁（GBR）泻湖的33,000公顷农业发展提案中的沟壑和表层侵蚀风险。使用卫星图像和水文强制数字高程模型（SRTM）对现有沟壑通道头部位置评估了通道启动的斜坡区域阈值。使用阈值来预测是否其他流线（比例为1：25k）在开发中容易发生沟壑切口。结果表明，在1,200 km的溪流中有430 km存在流淌的风险，这可能使侵蚀增加2倍，局部输送7,500 t yr ^-1和1,700 t yr ^-1（价值180万澳元）。估计农业下的表层侵蚀（RUSLE）从0.12到1.5 t ha ^-1  yr ^-1增加13倍，其中流向2,200 t yr ^-1和900 t yr ^-1（价值100万澳元）。缓冲（±50 m）560公里的源头水流将覆盖5,600公顷或该地区的17％。使用高分辨率地形数据（LiDAR）和改善坡地侵蚀阈值的精细农业应该是发展的最低先决条件，这将减少但不能消除GBR的增加的泥沙负荷。澳大利亚一直在进行农业森林砍伐，但这个第一世界国家没有有效的政策或法规来保护源头水流或对世界遗产大堡礁的累积影响，尽管每年花费数百万美元来减少过去的土地退化。