Land occupation and flooding

Abstract

Each flood renews the polemic on establishing responsibilities. This paper aims to produce a bibliographic analysis of the relation between land occupation and flooding. It must first of all be remembered that flooding is caused by heavy rain and that, above a certain intensity, the effects of factors connected with the occupation of the area become secondary, if not negligible. This paper refers to certain fairly recent developments such as the increase of forests, the changes in population, the regression of agricultural land, the considerable reduction in the number of hedgerows, the recent slowing down in drainage and the increase of impermeable surfaces. Brittany is an example of how these developments vary in France. The bibliographic study emphasises the major role of the forests, notably pinewoods, on levelling out floods and increasing the volume of run-off water noted on cultivated land, especially during the winter. Amalgamating fields, in particular the work associated with this, can have a certain influence on the consequences of low to medium rainfall. Grubbing up hedges can increase the peak flow of small floods. Drainage can have contradictory effects, noticeably reducing the run-off water as well as increasing the volume of water evacuated. It is, however, difficult to determine its effect on the whole basin. More than land drainage, changes in the size of the open ditch network as well as downstream rivers has in general aggravated flooding. Town planning, with the increase in impermeable surfaces, shortens the response time. In conclusion, emphasis is placed on the need to continue studies and research and various subject for consideration are put forward.