Influence of DEM resolution on modelling hydrological connectivity in a complex agricultural catchment with woody crops

Abstract

Digital elevation model (DEM) resolution influences hydrological simulation. However, its influence when modelling hydrological connectivity (HC) in woody crops remains to be seen. We assessed surface topography, microtopography and HC in an agricultural sub‐catchment (27.4 ha) using six photogrammetry‐derived DEMs with 0.03, 0.05, 0.1, 0.2, 0.5 and 1 m cell sizes. Land uses included vineyards, olive groves, cereal fields, and forestry patches. We ran an updated version of Borselli's HC index (IC) using the D‐Infinity approach. We assessed HC in woody crops at high spatial resolution for the first time. After analysing the differences in the contributing area, the flow width, the soil roughness, the convergence index and the IC (normalised and non‐normalised) at different scales (hillslope, land uses and compartments, ephemeral gullies, depositional areas and the sub‐catchment outlet) and accounting for the field vertical components, we propose an optimum DEM resolution (0.2 m) to improve modelling of structural HC in woody crops. The modelled hydrological features at this threshold resolution matched well with the geomorphic features associated with the short‐ and medium‐term patterns of soil redistribution. Higher DEM resolutions, especially at 0.03 and 0.05 m, introduced bias in the input data and the IC computations. Finally, we observed good agreement between the outputs at the lowest resolution, 1 × 1 m, and the long‐term soil redistribution patterns (functional connectivity). Copyright © 2017 John Wiley & Sons, Ltd.

Soil and Water Conservation in Rainfed Vineyards with Common Sainfoin and Spontaneous Vegetation under Different Ground Conditions

“…Various ephemeral gullies affect the soils in VY1, VY3 and VY4, two cereal fields and the olive orchard in "Los Oncenos" sub-catchment [46]. Sediment delivery processes are intense, bringing the formation of four depositional areas (alluvial fans) at the foot of the vineyards VY1 and VY4 (1480 m 2 ), one cereal field and of the commercial olive grove (Figure 1b …”

“…The contributing areas (CAs) of the ST2 and ST3 were 3286 and 6214 m 2 , with a mean slope gradient of 17.0% and 9.2%, respectively (Figure 1c,d) ( Table 2) (more details about the overland flow patterns in [46]). Concerning the vegetation cover, the soil surface of the CA of the ST2 had less vegetation with an average percentage of bare soil of 18.4%, whereas the CA of the ST3 only had 10.6% of the soil surface without vegetation (Figure 2c,d).…”

“…Significant changes in the surface cover were observed over the twelve months of the year due to the phenology of the grapevines, the cover crop, the spontaneous vegetation and the tillage practices (e.g., grape harvest and mowing pass) (Figure 3). In a recent study, López-Vicente and Álvarez [46] calculated several topographic parameters in "Los Oncenos" sub-catchment (Table 2). Soil roughness and flow and sediment connectivity (water-mediated transfer of soil and sediments within a hydrological unit) were higher in CA-ST2 than in CA-ST3, indicating active processes of sediment delivery.…”

“…Moreover, CA-ST2 was closer to a concave topography, whereas CA-ST3 indicated a general convex surface. All the topographic information used in this study was derived from a digital elevation model (DEM) at 0.2 m of cell size [46]. …”

“…Smets et al [56] also found considerable differences between the runoff and sediment yields during laboratory experiments with simulated rainfall (60 min) on a silt loam cultivated topsoil. Although CAs were calculated using an accurate DEM at a 0.2-m cell size, the topographic thresholds that delineate the divides are elevated between 1.8 and 12.4 cm, and the estimated CAs depend on the spatial resolution of the DEM (see details about fractal geometry in López-Vicente and Álvarez [46]). Thus, we did not calculate the specific values of runoff (L m −2 TIS −1 ) and sediment (g m −2 TIS −1 ) yields because the actual CAs of each ST may vary during the low, medium, high and very high rainfall erosivity events that generate different runoff depths.…”