FLOODING OF PROPERTY BY RUNOFF FROM AGRICULTURAL LAND IN NORTHWESTERN EUROPE

In the last twenty years there has been an increase in the incidence of flooding of property by runoff from agricultural land in many areas of northwestern Europe. These events take the form of inundations by soil-laden water associated with erosion and the formation of ephemeral or talweg gullies developed in normally dry valley bottoms. Costs of such events may be considerable e.g. almost US$2M at Rottingdean, southern England, in 1987. These costs are largely borne by individual house occupants, insurance companies and local councils. The distribution of flooding is widespread but areas of high risk can be identified: the hilly area of central Belgium, parts of northern France, the South Downs in southern England and South-Limburg (the Netherlands). All these areas have silty, more or less loessial soils. Two types of flooding may be distinguished: winter flooding associated with wet soils and the cultivation of winter cereals, and summer flooding due to thunderstorm activity and runoff particularly from sugar beet, maize and potato crops. The distribution of these types of erosion varies in relation to the interaction between physical characteristics (soils and topography), climatic conditions and land use across the region. The reason for the recent increase in flooding events appears to be changes in land use, in the area of arable cropping, and the continued intensification of farming such as the use of chemical fertilizers, the decline in aggregate stability, the increase in the size of fields and compaction by farm vehicles. In some regions the risk of flooding has also increased because of expansion of urban areas in valley bottom locations. Communities have responded to the flooding hazard with emergency or protective measures usually involving engineered structures rather than land use change. The policy response to the increased risk of flooding has been very limited especially at the national and provincial level, the exception being plans developed with farming organisations in South-Limburg and the Pays de Caux. In southern England initiatives have been few and largely consist of protective measures undertaken by urban municipalities.