The need for river bank protection in an ecologically appropriate manner has led to the investigation of shallow groynes as a nature-oriented countermeasure against bank erosion. Shallow groynes are in-stream structures which have a horizontal crest and are submerged even during low flow conditions in order to minimize the effect on the flood level. Rather than enhancing the resisting forces like traditional bank protection measures, e.g. riprap, shallow groynes are used to redirect the attacking flow away from the river bank. In this way, the bank itself becomes available as habitat and the water-land interface is rehabilitated or preserved. Moreover, the shallow groynes increase the heterogeneity of the flow field, bed topography, and bed material, which is one of the key elements requested by the EU Water Framework Directive to improve the ecological condition of rivers. However, guidelines are necessary for a successful and sustainable design of shallow groynes. The objective of the study was to develop design guidelines for shallow groynes in river bends by experimentally investigating the design parameters, namely groyne inclination, length, width, location and spacing in a river bend. The experiments were carried out in a curved flume in the laboratory of Leichtweiß-Institut für Wasserbau (LWI). The three-dimensional flow field was measured with an Acoustic Doppler Velocimeter. The hydraulic boundary conditions were kept constant throughout the experiments. A reference run was carried out without a groyne providing the basis for quantification of the hydraulic effects due to the shallow groynes. The optimum groyne parameters were defined based on the highest reduction of stream-wise velocity close to the outer bank. The manipulation of the flow field throughout the bend was investigated with a single groyne as well as with a group of groynes varying the number of groynes as well as the spacing. Further experiments with a fixed bed and a mobile outer bank confirmed the effectiveness of shallow groynes for bank protection. The results of the different sets of experiments were combined to develop a design method for bank protection with shallow groynes throughout a river bend. The method incorporates geometric parameters of the bend as well as the hydraulic boundary conditions.


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    Title :

    Development of Design Guidelines for Shallow Groynes


    Additional title:

    Entwicklung von Designrichtlinien für Lenkbuhnen


    Contributors:

    Publication date :

    2018



    Type of media :

    Miscellaneous


    Type of material :

    Electronic Resource


    Language :

    English


    Classification :

    DDC:    627





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