Conceptualization of Water Flow Pathways in Agricultural Terraced Landscapes

Abstract

Agricultural terraces are often subject to degradation issues related to water movement. A better understanding of the main hydrological processes that govern surface and subsurface water flow pathways and that are responsible for terrace failure and dry-stone wall collapse is essential for appropriate water resource management and rural landscape maintenance in terraced areas. However, a clear conceptualization of different hydrological functioning related to wall instability issues is still missing. In this study, we monitored a terrace system in a hilly site of central Italy cultivated with vineyards. We adopted a multidisciplinary approach based on soil analysis, different geophysical techniques, hydrological monitoring, high-resolution grid terrain analysis and field experiments (infiltration and flooding tests) aiming to: (i) obtain new information of terrace soil and subsoil structure; (ii) test the hypothesis on wall instability based on the formation of preferential flow and water accumulation behind the wall; and (iii) develop a conceptual model of water circulation in agricultural terraces. Our results indicate that terrace soil was highly heterogeneous, including discontinuities and piping systems that facilitated a rapid infiltration and the development of fast subsurface flow. Groundwater rise did not occur, as observed in other terraced sites, but infiltrated water accumulated behind dry-stone walls, increasing pore water pressure and inducing wall bulging and instability. Our findings provided new field evidences of water circulation and led to the definition of a novel paradigm of hydrological functioning of farming terraced systems for addressing more efficient management and maintenance issues in these vulnerable landscapes. Copyright © 2017 John Wiley & Sons, Ltd

Spatial patterns of sediment connectivity in terraced lands: Anthropogenic controls of catchment sensitivity

“…Walls fail due to various processes that involve complex interactions of several factors such as land use, distance to valley bottom, time since ploughing, soil properties, and vegetation cover (Lesschen, Cammeraat, & Nieman, 2008). Agricultural terraces imply discontinuities in the soil hydraulic gradient along hillslopes, contributing to create preferential water pathways and the water accumulation near the walls, as has been documented by continuous monitoring of soil water distribution (Preti et al, 2017). These processes, involving saturation near the walls and pipe development, lead to progressive deformation of the walls previous to their downfall (Pallarès & Calvo-Cases, 1994).…”

Terraced Landscapes and Hydrogeological Risk. Effects of Land Abandonment in Cinque Terre (Italy) during Severe Rainfall Events

“…Recent publications discovered that the beneficial effects of terracing are more evident where the well-maintained surfaces are more extensive, and the farming system is more complex [12,13]. In fact, the main factor that triggers landslides seems to be the lack of runoff control which, even in terraced woodlands, is concentrated in areas where the saturation of surface soil layers leads to failure [11,40,41]. For such situations, the presence of abandoned and partially destroyed terraces under tree cover can constitute an aggravating factor of instability [42].…”

Catchment based hydrology under post farmland abandonment scenarios

“…The abandonment of agricultural terraces has been shown to enhance saturation of the inner parts of the terraces, increasing overland storm flow (Gallart et al, 1994). However, these findings may not be applicable to other terraced areas, as terraced areas have very complex hydrological behavior, characterized predominantly by saturation-excess runoff Nunes et al, 2016) or deep subsurface and pipe flow (Preti et al, 2017), depending on the properties of each site.…”