Improved water retention in agricultural areas (2015)
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:
- checking and rebuilding old drainage systems;
- establishing a variable water flow regime;
- rehabilitating and reconstructing/adapting morphological structures in rivers;
- adopting ad hoc crop rotations and association and agricultural practices (tillage systems, soil cover management, ec.);
- 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.
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.
- Stakeholder participation
- Success and Limiting Factors
- Costs and Benefits
- Legal Aspects
- Implementation Time
- Life Time
Options involve long term time horizon from an individual's point of view and entail cooperation and trust among farmers and other stakeholders.
Success and Limiting Factors
In most cases, this type of measure is considered promising, although the characteristics of locations must be carefully considered before implementation, because these measures do not function everywhere. Adequate compensation of landowners is necessary and projects must not only address design and implementation, but also behavioural change of land users. Indeed this option requires change of traditional agricultural practices, and substantial investments. Lack of knowledge, training, e.g. on soil conservation practises, lack of environmental regulations and monitoring also pose a barrier. Management of water retention is needed as there are risks of failure with cascading effects on discharges. An issue in planning and implementation is the complexity of governance and coordination as usually private and several public parties are involved.
Costs and Benefits
This type of measure is potentially interesting because the design is often multi-functional and thus combines interests. Parallel to climate adaptation other users may benefit (nature/biodiversity development, recreation, tourism, landscape planning, green-blue services in agriculture) and as such this type of measure contributes to several EU policies (Natura 2000, second pillar of CAP).
Local area analysis of small scale retention measures on rural areas show potential effectiveness in coping with extreme runoff events and increasing water availability in dry periods. However, micro design of measures, which takes local conditions in consideration, is necessary, because the risk of adverse effects is existent. In addition, risks of damage to agricultural crops, due to higher groundwater tables must be considered. These results are based on cases in relatively flat regions. In hilly or mountainous regions, effectiveness is expected to be much lower or non-existent.
Conservation tillage and irrigation management are generally in accordance with nature protection principles. However, conservation tillage requires less labour, which can cause depopulation of rural area. Terracing reduces run-off and increases water infiltration, but there are problems also such as burial of original soils, changes in soil physical and biological properties, changes in the hydrological regime, and it has a significant visual impact in contrast with the surrounding natural vegetation and traditional plantations.
Even if options increases the availability of water for agriculture, improves soil qualities and can reduce soil erosion, under certain conditions they can increase salinity. Indeed most of human activities adversely affect the quality of freshwater resources. Options reduce agriculture production fluctuations, which brings more security for farmers and makes food production more reliable. Agricultural production can increase, often in peripheral regions. In practice, options are considered as effective but with high entrance costs. That is why enhancement from the public sector is usually crucial.
Option can be fostered by nature protection policies and the EU Common Agricultural Policy. Management tools must fit to the specific local context. Different land use management methods produce different results, depending upon the local context in which they are applied. Examples of policies are WFD, Flood Directive, Rural Development Regulation, Birds Directive, Habitat Directive, EU Biodiversity Action Plan, Solidarity Fund, Common Agricultural Policy, Council Regulation (EC) N° 1083/2006 lays down general provisions of the European Regional Development Fund, the European Social Fund and the Cohesion Fund. Funding is also provided under the Common Agricultural Policy. However the uptake of this measure is limited by conflicting land use interested trigged by the first pillar of CAP and renewable energy policies (bioenergy production).