R. R. van der Ploeg

Elbe river flood peaks and postwar agricultural land use in East Germany

Collectivization of farmland since the 1950s has changed the agricultural land use in former East Germany. Single fields on the collective farms became increasingly large and were cultivated with increasingly heavy farm equipment. This led to large-scale physical degradation of arable soils, enhancing the formation of surface runoff in periods with prolonged and excessive precipitation. The extent to which this development may have affected the discharge behavior of the main East German river, the Elbe, has so far not been studied. We analyzed the flood peaks of the Elbe during the past century (1900–2000). The flood discharge behavior of the Elbe has apparently changed significantly since the 1950s. Although climate changes may be involved, we conclude that the Elbe flood peaks, recorded since 1950, are related to the changes in postwar agricultural land use in former East Germany. To restore the degraded farmland soils, a change in agricultural land use may be necessary.

Hooghoudt, Symen Barend

An outline of Hooghoudt’s early career is followed by a detailed discussion of his contributions to the improvement of methods for the physical characterization of soils, and to the development of the theory of drainage. The early motivation came from the need for a rational approach to drainage of the newly reclaimed soils of the IJsselmeer polders. Wide application in development of sport fields, parks, and airfields soon followed. Hooghoudt was also a pioneer of regional hydrological studies. In the 1950s, Dutch-born PhD students at Iowa State University and Cornell University effectively promoted Hooghoudt’s ideas, published originally mainly in Dutch.

Postwar Changes in Land Use in Former West Germany and the Increased Number of Inland Floods

In recent years, the number of inland floods in Germany has increased markedly. Developments along the River Rhine can be taken as an example. Recordings taken in Cologne since 1895, cited in [1] and [2], show that six of the 12 most extreme stages have occurred since 1983. A number of factors, such as climatic changes and hydraulically adverse development in the Rhine’s flood plain and catchment area, have been suggested as explanations for the increased number of extreme stages and floods in recent years. However, these factors alone cannot satisfactorily explain the change in the river discharge regime.

Potential theory for dual‐depth subsurface drainage of ponded land

Dual-depth subsurface drainage is considered to be more effective in removing excess water from soil than single-depth drainage, but this problem has not been analyzed in detail. Therefore, assuming that uniform, water-saturated soil covered by ponded water and overlying an impervious barrier is drained by equally spaced, alternating deep circular drain tubes, existing potential flow theory for a single-depth drainage system was extended. Sample calculations with the newly derived equations show that a dual-depth subsurface drainage system can be highly effective to remove excess water from soil. For example, a relative drain discharge of 160% is calculated when new drain tubes, added at the 0.60 m depth, are placed midway between the original drain tubes, which are 25 m apart and at the 1.20 m depth. In this calculation we have assumed that the impervious layer is at the 3.0 m depth, the radius of the tubes is 0.05 m, the soil hydraulic conductivity is 1 m/d, and the thickness of the ponded water is 0.0 m. For the same conditions, but with the additional tubes at the 1.20 m depth (same depth as original tubes), the relative drain discharge becomes nearly 200%, and with the additional tubes at the 2.40 depth (1.20 m below original tubes) it is more than 250%. When the impervious layer is at a greater depth and when the original drain spacing is more than 25.0 m, the relative drain discharge becomes even larger. The effectiveness of the dual-depth tube system becomes particularly large, if the second tube system is placed below the level of the first one.

Developments in Agriculture and the Loss of Natural Stormwater Runoff Control in Central Europe

In the past decade, Germany has been struck by a number of extreme river floods, e.g. of the Rhine in 1993 and 1995, the Oder River in 1997, and the Danube River in 1999. The question as to why the frequency of such events may have increased has been posed repeatedly. The answers that have been given to this question include natural climatic and hydrological fluctuations, climate change, and improper management of waterways and floodplains (see e.g. Immendorf [1]; Marsalek [2]). However, it has also been suggested that changes in land use, accompanied by a partial or total sealing of the land surface, might be responsible for increased surface runoff and peak river discharge. Sieker [3, 4], for example, has pointed at the rapidly increasing urban area in Germany and the high degree of surface sealing in urban areas. He has triggered new developments in urban stormwater control that help to reduce urban peak discharge and flash floods.