Effect of dyke construction on water dynamics in the flooding savannahs of Venezuela

In the flooded savannahs water is the main factor determining the ecosystem and its change. During flooding, the level of water and the duration of flooding are highly dependent on the relative height position of the ecosystem unit. To understand the spatial processes in the ecosvstem one must know the water dynamics in the area. In order to quantify the water content during the year, a digital elevation model (DEM) is needed. Several areas in the Llanos de Orinoco have been dyked (modulos). A digital elevation model has been developed on a level of the dyked area of the modulo of Hato el Frio. Flooding has been studied at the regional level and a DEM has been developed for the modulo area. For the construction of the DEM various sources were explored for height information. Field measurements with GPS were necessary. After the high flooding period downstream of the dykes the area is totally dry. In the transition period between the dry and the wet season the distribution of water shows a clear influence of the dyke. In the natural situation the natural height differences create a complex system of sinks. The dyke construction has created a large artificial sink. Modulus form sinks by their banks preventing the outflow of the water. With the help of a DEM, inundation can be modelled with relatively little field research. Copyright (c) 2005 John Wiley & Sons, Ltd.