Flooded fields along Hobøl River (Dominika Krzeminska)
Flood prone areas are located close to watercourses (up to 22m from the watercourse) and are flooded regularly - at least once every ten years. If the area is considered as “flood prone” area must be assessed locally and approved at municipality or county level. Areas prone to erosion are the areas in the erosion class 2 (if there is a gully erosion), 3 and 4 (based on the erosion risk map; kilden.nibio.no).
Purpose/Aim: The main purpose of establishing grass cover (or at least maintaining stubble over winter) in the areas prone to erosion and flooding is to reduce soil erosion and nutrient losses. Grass cover protects the surface from detachment of particles and erosion processes. Grass covered areas enhance infiltration and provide good conditions for the uptake and storage of water during temporary floods. As such, the measure offers the potential for temporary flood storage, increased water retention in the landscape and runoff attenuation.
Perennial grass cover in the areas prone to flooding also protects water quality by enhanced sedimentation of suspended materials and increased adsorption of material to vegetation and soil surface.
Maintaining grass or stubble in areas prone to flooding and erosion is a subject for subsidies within Regional Environmental Programme RMP. The purpose of subsidies for is to reduced flood erosion. It includes both reducing soil erosion and preventing loss of nutrients.
Establishment/maintenance: vegetated zones or permanent meadows should be established and maintained within agricultural flood prone areas. As a minimum these areas should be left in stubble through the winter. These areas should not be fertilized, and grass should be harvested to reduce nutrient leakage to the watercourse. Where farmers persist in growing cereals in these areas they should at least leave the flood prone areas unploughed and covered in stubble over winter.
Benefit/Impact: The effect of (any) vegetation zones depends on several factors such as the flow properties and the characteristics of the vegetative surface. Studies of Norwegian conditions indicate that the most relevant factor for function of the vegetation zone is the character of the vegetation (height, robustness, and density), rather than the type of vegetation (Blankenberg & Hougsrud 2010). As the efficiency of vegetation is composed of a variety of factors, the implementation of the measures is to a large degree site specific (Kværnø & Stolte 2012). There is insufficient documentation on how the level of erosion is affected by floods. In Norway, there are no direct figures for the efficiency of grass cover on the areas prone to flooding.
Recent trends in climatic changes are expected to result in increase in extreme meteorological events and related natural hazards. The area along the streams and rivers are among the landscape elements, which first will notice the impact of climate change in the form of floods and consequent erosion. Therefore, measures dedicated to these areas might become more and more important.
Natural / human environment: The information about Technology is based on the investigations and/or reports from the Vansjø-Hobøl catchment. For the purpose of OPTAIN project (https://www.optain.eu/), the technology is further presented in the natural and human environment context of the Kråkstad River catchment - a Norwegian Case Study catchment within OPTAIN project.
The Kråkstad River is mainly situated in Ski municipality in South-Eastern parts of Norway. The river catchment is a western tributary of the Vansjø-Hobøl watercourse, also known as the Morsa watercourse. The Kråkstad River catchment area is c.a 51 km², 43% of which is agricultural land, where mostly cereals are produced on heavy clays soils. The main environmental challenge in the area is water quality (incl. high phosphorus pollution) and soil erosion (incl. riverbank erosion and quick-clay landslides).The Morsa watercourse is a drinking water resource and there are specific environmental regulations for land management followed by subsidies through the Regional Environmental Programme (RMP). Management of areas prone to flooding are part of these regulations.
Location: The Vansjø-Hobøl catchment, Viken county, Norway
No. of Technology sites analysed: 2-10 sites
Spread of the Technology: applied at specific points/ concentrated on a small area
In a permanently protected area?: Nee
Date of implementation: 10-50 years ago
Type of introduction
Crop production will be reduced if there is permanent grass cover. However, with frequent flooding events the area is not 100% productive anyway.
depending on subsidies or whether the grass are being harvested or not
The costs of establishment and management of grass cover on the areas prone to flooding are not deviating for costs connected to regular crop land management
In the areas with permanent grass cover
Minimum that is expected, not measures/monitored yet.
Minimum that is expected, not measures/monitored yet.
