On rough agricultural soils, initiation of overland flow is primarily related to the gradual filling of small depressions. As the volume of water ponding in local depressions increases, the connectivity of those depressions increases, and that connectivity permits flow across the field boundaries. Previous studies have aimed at predicting overland flow connectivity by means of depression storage, but this is exceedingly difficult to quantify during an irrigation or rainfall event. There has been little work linking overland flow connectivity through variables that are more readily-measured than depression storage, such as the proportion of the soil surface covered in water (A_SW).

We propose using A_SW as a proxy for hydrological connectivity, which can be measured using proximal remote sensing. A series of overland flow experiments were conducted in two contrasting plots of ~1.5 m². Outlet discharge and changes in soil surface covered in water were continuously recorded during the experiments. The experiments demonstrated that the rougher soil surface experienced a delayed initiation of overland flow. The results also showed overland flow initiation was characterised by a distinct connectivity threshold and showed a clear response of overland flow to A_SW. We further investigated the hydrological connectivity in twenty-one additional agricultural soils with contrasting micro-topographic conditions. Our results suggest that a predictor based on A_SW has substantial potential to predict initiation of overland flow. The prediction is sufficiently early that it could be used in modern variable-rate irrigation systems, in combination with a sensor to measure A_SW in real time, to prevent substantial flow from fields during irrigation.

在粗糙的农业土壤上，陆上径流的产生主要与小洼地的逐渐填充有关。随着局部洼地中积水量的增加，这些洼地的连通性增加，并且该连通性允许流过田间边界。先前的研究旨在通过洼地存储来预测陆上水流的连通性，但这在灌溉或降雨事件中很难量化。几乎没有什么工作可以通过比洼地存储更容易测量的变量将陆上水流的连通性联系起来，例如，被水覆盖的土壤表层的比例（A _SW）。

我们建议使用甲_SW作为水文连接的代理，其可以使用近端遥感来测定。在〜1.5 m ^2的两个对比图中进行了一系列陆上水流实验。在实验过程中，连续记录出水口的排水情况和被水覆盖的土壤表面的变化。实验表明，较粗糙的土壤表面经历了陆流的延迟启动。结果还表明，陆上流动的启动具有明显的连通性阈值，并表现出陆上流动对A _SW的清晰反应。我们进一步研究了微地形条件相反的另外21种农业土壤中的水文连通性。我们的结果表明，基于A _SW的预测器具有很大的潜力来预测陆上水流的启动。该预测还为时过早，可以与传感器实时测量A _SW一起用于现代可变速率灌溉系统中，以防止灌溉过程中田间有大量水流。