Scale effect on overland flow connectivity at the plot scale

Abstract

A major challenge in present-day hydrological sciences is to enhance the performance of existing distributed hydrological models through a better description of subgrid processes, in particular the subgrid connectivity of flow paths. The Relative Surface Connection (RSC) function was proposed by Antoine et al. (2009) as a functional indicator of runoff flow connectivity. For a given area, it expresses the percentage of the surface connected to the outflow boundary (<i>C</i>) as a function of the degree of filling of the depression storage. This function explicitly integrates the flow network at the soil surface and hence provides essential information regarding the flow paths' connectivity. It has been shown that this function could help improve the modeling of the hydrograph at the square meter scale, yet it is unknown how the scale affects the RSC function, and whether and how it can be extrapolated to other scales. The main objective of this research is to study the scale effect on overland flow connectivity (RSC function). For this purpose, digital elevation data of a real field (9 × 3 m) and three synthetic fields (6 × 6 m) with contrasting hydrological responses were used, and the RSC function was calculated at different scales by changing the length (<i>l</i>) or width (<i>w</i>) of the field. To different extents depending on the microtopography, border effects were observed for the smaller scales when decreasing <i>l</i> or <i>w</i>, which resulted in a strong decrease or increase of the maximum depression storage, respectively. There was no scale effect on the RSC function when changing <i>w</i>, but a remarkable scale effect was observed in the RSC function when changing <i>l</i>. In general, for a given degree of filling of the depression storage, <i>C</i> decreased as <i>l</i> increased, the change in <i>C</i> being inversely proportional to the change in <i>l</i>. However, this observation applied only up to approx. 50–70% (depending on the hydrological response of the field) of filling of depression storage, after which no correlation was found between <i>C</i> and <i>l</i>. The results of this study help identify the minimal scale to study overland flow connectivity. At scales larger than the minimal scale, the RSC function showed a great potential to be extrapolated to other scales

How do slope and surface roughness affect plot-scale overland flow connectivity?

“…When the excess cumulative rainfall volume exceeds a certain threshold value, a sharp increase in the generated overland flow is observed as a consequence of the rapid establishment of hydraulic connections between different parts of the system. This threshold phenomenon, which is consistent with percolation theory (Berkowitz and Ewing, 1998) and characteristic of random media (Berkowitz and Ewing, 1998), has been observed in overland flow at the plot scale (Darboux et al, 2002a;Frei et al, 2010;Peñuela et al, 2013;Yang and Chu, 2013). Around this threshold, the overland flow process evolves from a predominant filling process to a predominant spilling process.…”

“…First, the ratio of area connected to the outlet when DS is equal to 0. This is a border effect (Peñuela et al, 2013) that reflects the plot area already connected to the outlet before any water is added (Darboux et al, 2002a;Yang and Chu, 2013). Second, the connectivity threshold (CT) where the RSCf increases sharply for a small increase in depression storage (Peñuela et al, 2013).…”

“…The range of values of r and R were selected so as to reflect extreme but still realistic values observed in real fields (Table 1; Onstad, 1984;Zobeck and Onstad, 1987;Darboux et al, 2002a;Vidal Vázquez et al, 2005). The fields were 6 m  6 m size and the maximum R was 400 mm in order to minimize scale and boundary effects (Appels et al, 2011;Peñuela et al, 2013). R values lower than 50 mm were not considered in order to avoid large inaccuracies caused by the 10 mm/pixel horizontal spatial resolution of the digital elevation models (DEM).…”

“…However, some outflow may occur due to border effects. This initial and limited flow is generated from the depressions directly connected to the system's outlet and from nearby upstream depressions connected to these initially connected depressions (Peñuela et al, 2013). In a second stage, additional upstream micro-depressions get filled, and start to overflow and connect either to nearby depressions or to the outlet.…”

HASIL AIR HUTAN JATI PADA DUA SUB DAERAH ALIRAN SUNGAI DENGAN LUAS BERBEDA (Water yield of Teak Forest at two different catchment sizes)

“…Kedua penelitian tersebut terletak pada sub DAS yang mempunyai tipe batuan sedimen yang didominasi oleh batuan pasir (Sandstone). Pengaruh perbedaan mikro topografi yang lebih dominan terhadap limpasan pada areal yang kecil juga dikemukakan oleh (Peñuela, Javaux, & Bielders, 2013). Gambar (Figure) …”