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The theoretical behaviour or the limitations to the interactions between river flow and the seepage flow is not so clear up to date, though there are several publications about these interactions in the environmental and biological point of view. The stability of these flow interactions (also known as hyporheic interactions) is analyzed using the linear stability analysis technique. Stability diagrams are discussed with several slopes of the layers against the dimensionless particle diameter and wave number. It has been understood that the range for the occurrence of instability region increases with the slope of the combined river and seepage layers. This means that the occurrence of interactions is increased with the longitudinal slope. Later, some experiments are carried out, in order to understand the hyporheic interactions using a Hele- Shaw which is a longitudinal parallel plate model. It is found that the dimensionless dominant wave numbers have an effect on the combined channel slope as it is obtained from the theoretical analysis, and the Froude number of the river flow.

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Upaka Sanjeewa Rathnayake graduated in Civil Engineering from the University of Peradeniya, Sri Lanka as the best student in Engineering for 2006 followed by a Master in Engineering from Hokkaido University, Japan in 2009. His main research interests are in hydrology and hydraulics, water resource developments and sustainable development.

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