General informations
Description
Storing water in soil decreases the negative impacts of droughts. Several grey measures are available, and include measures based on the use of technology in agriculture, e.g. no-tillage, or cropping systems implemented to reduce water runoff. Runoff, depending on soil characteristics, can be delayed by tillage methods combined with plants having a high root density and lush surface cover. Conservation tillage, including both no-tillage and minimum tillage, is the practice of limiting or eliminating tillage practices (ploughing in particular), leaving some of the previous season's crop residues on the soil surface. It reduces evaporation from the soil surface, preserving soil organic matter in the upper soil layers and, consequently, increasing water retention capacity of the soil. Terracing and contour ploughing terrace is another method of soil conservation to slow or prevent the rapid surface runoff. Contour ploughing is the farming practice of ploughing across a slope following its contours, which have the effect of slowing water run-off during rainstorms so that the soil is not washed away and allows the water to percolate into the soil. The rows made by the plough run perpendicular rather than parallel to slopes, generally resulting in furrows that curve around the land. Efficient use of irrigation systems also helps to store the water.Moreover, at wider landscape level, increasing the water retention capability in rural areas can either aim to increase the natural water retention capacity of an entire landscape, or to increase the water storage capacity with man-made structures. Winter water storage reservoirs, for example, reduce abstraction during the summer, increase flood storage capacity, and benefit wildlife. The water retention capacity of an agricultural landscape can be improved by:<ul><li>checking and rebuilding old drainage systems;</li><li>establishing a variable water flow regime;</li><li>rehabilitating and reconstructing/adapting morphological structures in rivers;</li><li>adopting ad hoc crop rotations and association and agricultural practices (tillage systems, soil cover management, ec.);</li><li>setting up of flood control reservoirs, which are both very different varieties of water impoundments, typically with large capacity and designed to only take up water levels that have been reached.</li></ul>Water storage on farmland is defined as the storage of excess water, either in the soil under low groundwater conditions, in open water-like ditches, water courses, lakes and ponds or on the soil surface, assuming the soil and open water offer insufficient storage capacity.Much literature on this topic is about specific cases and is addressing planning and policies (Brandenburg, Saxony, Green blue services in the Netherlands, South East England Regional Assembly). There is a small number of publications on experiences and on effectiveness and risks of water retention in rural areas in general. Krysanova et.al. (2008; see link at the Websites section) analyse six river basins in an attempt to draw generic lessons. Water retention in rural areas is part of the analysis Specific attention is paid to water storage reservoirs for flood control on agricultural lands and off-stream polders or flood retardation ponds. The importance of this type of measures is recognized in all basins (Amudarya, Elbe, Guadiana, Orange, Rhine, Tisza) although the implementation differs between the river basins. In the Rhine and Elbe basins, these measures are part of a flood management strategy which gives first priority to retention measures, second priority to storage and last priority to discharge. This strategy aims at slowing down extreme runoff to mitigate high river discharges, while at the same time safeguarding water for times of scarcity.