Historical water management in the river basin of the Baaksche Beek and the adaptations to the water system as a result of change in land use

In the 19th and the first part of the 20th century large parts of the sandy area of The Netherlands were transformed from heath and woodland into agricultural areas. These areas were made suitable for agricultural use by significantly adapting the existing water systems (improving existing brooks, digging new watercourses, etc.). Adaptations will once again be needed, as climate change will increase both precipitation and the peak flow flood waves in the Dutch large rivers. New, pre-emptive adaptations of the current waters system are needed to maintain good agricultural and living conditions, and to prevent catastrophes. Study of the reaction of the water system as a result of previous adaptations is directly relevant to current planning, since such study should reveal the likely long-term outcomes of future adaptations necessitated by climate change. To select an area for this study, preliminary information was gathered about hydrological properties and hydrological data, such as surface water levels and discharges in various parts of the country; data sources included historical maps, reports on hydrological measurements and historical descriptions. From these data, a drainage basin in the relatively high and sandy part of The Netherlands-the Baaksche Beek basin in the eastern part of The Netherlands-was selected. The period chosen for investigation was 1850-2000. In 1850 the basin was in a fairly natural state, with large areas of woods and moorland. Sufficient data were available in the following period till 2000. It was found that great changes took place in the water system following reclamation. Before reclamation, the water management used the capacity of the river basin to store great amounts of water temporarily in local depressions and along the river basin, reducing peak flows in the river. Since reclamation of the heath and woodland, many of these natural depressions in the landscape have been connected with a water course, decreasing their ability to store water. This reduced the basin's ability to act as a hydrological sponge by storing flood water temporarily on the soil surface in depressions and releasing it slowly later on. Thus, while in the past, smaller water courses inundated the adjacent areas annually, such inundations are very rare nowadays, occurring about once every 100 years. Instead, peak flow flood waves on the river have increased. Recovering the hydrological sponge property can be used as a strategy against increased peak flow flood waves brought by climate change. Thus a partial convalescence of the historical situation, restoring the hydrological sponge function, would aid in counteracting the negative effects of climate change on the water system. However some adaptations, like flattening of the soil surface, are irreversible and so additional means to reach the same end need to be considered. These could include re-meandering and re-dimensioning rivers, which would also increase the possibility to store water in or along a river, or removing watercourses to increase the possibility to store water in the soil and on the soil surface. (C) 2008 Elsevier Ltd. All rights reserved.