Abstract The Rarh plain in the Lower Ganga Basin in India, best known for its lateritic landscape and gullied tracts, faces grave problems brought about by all types of soil erosion, of which gully erosion is the most conspicuous. The present study uses data collected through field measurements at 110 gully heads in ten sites of the Rarh plain, to first assess the applicability of various methods used to construct critical topographic threshold lines, and secondly, to characterise topographic threshold conditions of the permanent gullies in the Rarh plain as well as to identify main factors that promoted gully initiation in this region. It is concluded that thresholds defined though orthogonal regression are more apposite than manual fitting of threshold line or employing quantile or nonlinear regression techniques for the same. The critical topographic threshold conditions of gullying in the Rarh plain, expressed by the relationship S=0.118A-0.111 between the gully head slope gradient (S) and upslope catchment area (A) can be used to map areas under risk of gully head development in the lateritic terrain, mainly in the deforestation fronts. The value of the exponent (0.111) suggests that subsurface processes and mass failures are the main processes of gully growth at present, and it is suspected that gully erosion in this region is not a recent phenomenon, judging by rather small gully head catchment areas as well as the low AS2 range of 2–170 m2. Although statistical evidence in favour of distinct site-specific thresholds is not found, results of this study indicate that gullies under eucalyptus stands have a significantly lower threshold than those in other land cover types. Gully erosion in this region was most likely triggered by massive changes in land cover and land use that commenced from the middle of 20th century and continued into the first few decades of 21st century. However, gullies observed under eucalyptus stands are much younger, judging by their larger upslope catchment areas compared to gullies found in other land covers. Albeit it is observed that the lateritic terrain of Rarh plain offers more resistance to gully incision than croplands or Mediterranean badlands, the threshold of gully head development is much lower than that of the primary laterites of the adjacent Chhotanagpur plateau fringe as well as other comparable soil types from around the world.

中文翻译：

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估计沟壑侵蚀的地形阈值的最佳技术是什么？印度拉尔平原永久沟渠案例研究的见解

摘要 印度下恒河盆地的拉尔平原以红土地貌和沟壑地貌着称，面临着各种类型的水土流失带来的严重问题，其中沟壑侵蚀最为突出。本研究使用在拉尔平原 10 个地点的 110 个沟头进行实地测量收集的数据，首先评估用于构建关键地形阈值线的各种方法的适用性，其次，表征永久沟渠的地形阈值条件。 Rarh 平原，并确定促进该地区沟壑萌生的主要因素。结论是，通过正交回归定义的阈值比手动拟合阈值线或采用分位数或非线性回归技术更合适。Rarh平原冲沟的临界地形阈值条件，用冲沟头坡度（S）和上坡汇水区（A）之间的关系S=0.118A-0.111表示，可用于绘制沟头发育风险区域在红土地带，主要是在森林砍伐前沿。指数值（0.111）表明地下过程和质量破坏是目前沟壑生长的主要过程，从相当小的沟头汇水面积来看，怀疑该地区的沟壑侵蚀不是最近出现的现象。以及 2–170 平方米的低 AS2 范围。虽然没有找到支持不同站点特定阈值的统计证据，这项研究的结果表明，桉树林下的沟渠的阈值明显低于其他土地覆盖类型的沟渠。该地区的沟壑侵蚀很可能是由从 20 世纪中叶开始并持续到 21 世纪头几十年的土地覆盖和土地利用的巨大变化引发的。然而，与在其他土地覆盖物中发现的沟渠相比，桉树林下观察到的沟渠要年轻得多，从它们更大的上坡集水区来看。尽管观察到 Rarh 平原的红土地形比农田或地中海荒地更能抵抗沟渠切割，但沟头发育的门槛远低于相邻 Chhotanagpur 高原边缘的原生红土以及其他可比土壤来自世界各地的类型。该地区的沟壑侵蚀很可能是由从 20 世纪中叶开始并持续到 21 世纪头几十年的土地覆盖和土地利用的巨大变化引发的。然而，与在其他土地覆盖物中发现的沟渠相比，桉树林下观察到的沟渠要年轻得多，从它们更大的上坡集水区来看。尽管观察到 Rarh 平原的红土地形比农田或地中海荒地更能抵抗沟渠切割，但沟头发育的门槛远低于相邻 Chhotanagpur 高原边缘的原生红土以及其他可比土壤来自世界各地的类型。该地区的沟壑侵蚀很可能是由从 20 世纪中叶开始并持续到 21 世纪头几十年的土地覆盖和土地利用的巨大变化引发的。然而，与在其他土地覆盖物中发现的沟渠相比，桉树林下观察到的沟渠要年轻得多，从它们更大的上坡集水区来看。尽管观察到 Rarh 平原的红土地形比农田或地中海荒地更能抵抗沟渠切割，但沟头发育的门槛远低于相邻的 Chhotanagpur 高原边缘的原生红土以及其他可比土壤来自世界各地的类型。