Land use change and gully formation over the last 200 years in a hilly catchment

Gully erosion can be widely observed on cultivated hillslopes in Hungary. Loose sediments covering two thirds of the total area of the country are prone to gully erosion. A detailed study of gully formation was carried out in the Rakaca catchment (58 km(2)), northeastern Hungary. The objectives include (1) a detailed survey of the present gullies, (2) an explanation of differences in gully distribution within the catchment, (3) clarification of the role of influencing factors like slope gradient, vegetation cover and soil type and (4) a study of changes of gully distribution and development in time over the last 200 years based on the comparison of topographic maps. The present gully distribution was first surveyed by applying 1: 10 000 topographic maps and aerial photographs. The total length of the network is 70.9 km, i.e. 1.22 km/km(2). Distribution inhomogeneities within the catchment can well be explained by differences in slope gradient and vegetation cover. The rate of increase of the gully length per unit area (1 km(2)) calculated for different time periods shows the following trends: (1) until 1860, when more than 50% of the catchment was forested, it was 5 m year(-1) km(-2); (2) between 1860 and 1920, when forest area dropped to almost 25% and agricultural land use was extended to slopes steeper than 25%, it still remained at roughly 5 in year(-1) km(-2); (3) after 1920, with 24-25% forest cover and with the extension of farming activity to the steepest slopes, it reached 10 in year(-1) km(-2). It could be shown that gully erosion on cultivated slopes leads to the development of gully systems in 50-60 years even if slope gradient is below 12%. To prevent further development of gully systems, it is suggested that at least 30% of the area should be forested and slopes steeper than 17% should not be cultivated at all. (C) 2003 Elsevier Science B.V. All rights reserved.