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Institut für Wasser- und Umweltsystemmodellierung - IWS

Abstract

 
   

"Guide for the river morphological restoration in Colombia: exemplary hydromorphological and habitat modeling"

The need of understanding the relationship between the physical habitat and ecology in the fluvial systems has become a major issue due to an increasing environmental conciousness but also because of the normativity which demand the achievement of the good status of the water bodies and its ecosystems. Exactly this requirement is prescribed by the European Water Framework Directive (WFD) which have included the hydromorphology as an important aspect of evaluation due to the influence that it has on the ecology of a river system. The hydromorphology gets relevance because it study the system as a whole, involving the interactions between ecology, hydrology and fluvial geomorphology.
As a response to the WFD each country has developed a method for guaranteeing the compliance of the normativity. Some of the best developed and documented are the Bund/Länderarbeitsgemeinschaft Wasser (LAWA) method from Germany and the River Habitat Survey (RHS) from England. Additionally two recent approaches, the Morphological Quality Index (MQI) developed and applied in Italy, and the Geomorphological Assessment Process (GAP) have been also taken into account. Besides, river classification approaches are described as an important aspect because they help to determine the behavior of the river, allow extrapolating geometric relationships for the similar channels and help to select the appropriate natural setting according to the channel type in case of a restoration. Mesohabitat approaches are also mentioned as one of the techniques developed for understanding in a fast, accurate and economic way the natural processes of the river in a scale between the macro and the micro scale. A ll the elements of the mentioned methods are collected for the development of a methodology that fulfill the gaps of the current Colombian water normativity and support the decision making in the environmental planning and impact assessment.
The proposed methodology is intended to be general and to take into account the information that can be available and possible to acquire in Colombia according to the context of the country. Summarizing the encountered problems and gaps in the Colombian water normativity, it is needed a methodology: that helps to achieve the good status and to maintain the minimum discharge; that can be used for the environmental restoration; that evaluates the hydromorphological conditions; that can be applied before and after the execution of a project in order to evaluate both conditions and assess the impact; that considers the preference of native species, and all the possible morphologies.
The proposed guide for the river morphological restoration in Colombia is a complete hydromorphological analysis of a selected river which main purpose is to make an approach to the general aspects of the river in the macro scale, followed by an assessment in the meso scale in which the river is segmented, classified and the hydromorphological conditions are scored; finally, a simulation is performed for a critical reach, called in this work the “bottle neck” reach. The simulation consists in a hydrodynamics model (or hydromorphodynamics model as optional), its results of depth, velocity and substrate in combination with the preferences of a fish indicator species, are computed in the software CASiMiR and give the habitat suitability in the study area for the simulated conditions.
The application of such methodology is applied in a mountainous river reach downstream the Punt da Gall dam in Switzerland for which the hydromorphological aspects in the macro and meso scale are assessed and in the micro scale the habitat distribution of fish indicator species are calculated.
The present work is an attempt to apply the habitat simulation as a tool for determining hydromorphological quality, for river restoration activities and for determining minimum habitat conditions when the discharge is regulated. Future investigations include the application in a Colombian river for which the collection of biological data still is a challenge.