Agricultural terraces are common in mountain regions. They are built to provide a larger surface area for cultivation on hillslopes and to aid farming production in the long term. This paper reviews the hydrological and geomorphological behaviour of constructing, working on and abandoning farming terraces based on recent scientific papers (1982–2014). Terraces increase infiltration and reduce runoff. In Mediterranean areas, the runoff coefficient on abandoned terraces is between 20% and 40%, depending on the percentage of plant cover or the amount of grazing. On cultivated terraces in warm, humid climates, the coefficients are lower (10%–25%). The internal and external sections of terraces have hydrological differences. Soil saturation is reached faster in the inner parts of terraces with shallower soil, causing a rapid hydrological response (saturation runoff); high infiltration rates in external sections can generate subsurface runoff. Furthermore, a reduction in hydrological connectivity, which affects the contributing areas and peak flows, is to be expected in terraced catchments. Collapsed stone walls, small mass movements, sheet wash erosion, piping, rills, gullies and debris flows are all found in terraced landscapes. The erosion of abandoned terraces is directly related to the amount of plant cover, soil characteristics, environmental conditions and the abandonment age. On this type of terrace, the rates of erosion due to overland flow are less than 3 t ha − 1  yr − 1 . The rate increases if the terrace is affected by mass movements, pipes or gullies (more than 100 t ha − 1  yr − 1 ). On cultivated terraces, erosion rates less than 1 t ha − 1  yr − 1 have been recorded for rice crops, and erosion rates greater than 80 t ha − 1  yr − 1 have been recorded for cassava or terraces with bare soil. The scientific literature notes that the soil loss from cultivated slopes is greater if conservation measures, such as terraces, are not included. However, this general result may vary significantly due to factors related to the geo-environmental characteristics of the region and, in particular, the management and use of the terraced slopes.

http://digital.csic.es/bitstream/10261/113273/1/restringido.pdf

Effects of farming terraces on hydrological and geomorphological processes. A review

/pdf/global-synthesis-of-the-classifications-distributions-53jeafut9m.pdf

Global synthesis of the classifications, distributions, benefits and issues of terracing

Properties, best management practices and conservation of terraced soils in Southern Europe (from Mediterranean areas to the Alps): A review

http://digital.csic.es/bitstream/10261/202494/1/Hydro-geomorphological%20consequences%20of%20the%20abandonment%20of%20agricultural%20terraces%20in%20the%20Mediterranean%20region.pdf

Hydro-geomorphological consequences of the abandonment of agricultural terraces in the Mediterranean region: Key controlling factors and landscape stability patterns

Persistent Scatterers Interferometry (PSI) techniques are widely employed in geosciences to detect and monitor landslides with high accuracy over large areas, but they also suffer from physical and technological constraints that restrict their field of application. These limitations prevent us from collecting information from several critical areas within the investigated region. In this paper, we present a novel approach that exploits the results of PSI analysis for the implementation of a statistical model for landslide susceptibility. The attempt is to identify active mass movements by means of PSI and to avoid, as input data, time-/cost-consuming and seldom updated landslide inventories. The study has been performed along the northwestern coast of Malta (central Mediterranean Sea), where the peculiar geological and geomorphological settings favor the occurrence of a series of extensive slow-moving landslides. Most of these consist in rock spreads, evolving into block slides, with large limestone blocks characterized by scarce vegetation and proper inclination, which represent suitable natural radar reflectors for applying PSI. Based on geomorphometric analyses and geomorphological investigations, a series of landslide predisposing factors were selected and a susceptibility map created. The result was validated by means of cross-validation technique, field surveys and global navigation satellite system in situ monitoring activities. The final outcome shows a good reliability and could represent an adequate response to the increasing demand for effective and low-cost tools for landslide susceptibility assessment.

/pdf/landslide-susceptibility-modeling-assisted-by-persistent-16li8c3auj.pdf

Landslide susceptibility modeling assisted by Persistent Scatterers Interferometry (PSI): an example from the northwestern coast of Malta

CYFFKA B. & BOCK M., Degradation of Field Terraces in the Maltese Islands Reasons, Processes, and Effects. (IT ISSN 0391-9838, 2008). There are several reasons for severe land and terrace degradation in the Maltese Islands. The main reason is the land abandonment which took place from the 1960s. Cultivated fields have constant protection against soil erosion by the crops and the farmer’s care for both the field itself and the field terraces, as well as the rubble walls which are part of the cultural heritage in the Maltese Islands. Once a rubble wall is broken down, intensive soil erosion starts because then the tracks for the erosion processes are predetermined. Usually the natural vegetation is able to reclaim abandoned land in a short period, but the dry, hot, and windy climate in the Maltese Islands creates unfavourable conditions. (*) University of Eichstaett-Ingolstadt, Ostenstrasse 18 D-85072 Eichstaett, Germany. (**) Scilands GmBH Scientific Landscapes, Goetheallee 11 D-37073 Goettingen, Germany. Meanwhile it is proven that global climate change is producing heavier rainfall than in previous decades. Starting in autumn every year rainstorms occur and cover the mainly unprotected land with flash floods. With the help of old aerial photographs (1957) and high resolution satellite images (Ikonos, 2004) the percentage of abandoned land in the Gnejna Valley in Malta was determined. A Digital Elevation Model gave, via relief analysis, the possibility to assess the possible erosion tracks on an island which has no perennial streams. Field research gave major insight to the composition of the vegetation cover on the abandoned field terraces and other parts of the valley. The results are a forerunner to a solution to the problem in the entire Maltese Islands as well as, probably, other Mediterranean Islands with a dry climate.

Michael Bock

Papers

Degradation of Field Terraces in the Maltese Islands – Reasons, Processes, and Effects

Remediation of the Danube floodplain between Neuburg and Ingolstadt (Bavaria, Germany) : GIS supported modelling of ecological flooding