Channel change and vegetation diversity on a low-angle alluvial fan, River Feshie, Scotland

Abstract

1. The River Feshie, a wandering gravel-bed river, has a prominent alluvial fan at its confluence with the River Spey forming a site of high conservation importance. The River Feshie is the best example of a relatively natural highly active gravel-bed river in the UK and the fan also contains one of the few remnants of Scotland's original floodplain forest cover. 2. Channel switching and changes in gravel-bar morphology are a characteristic feature of this river. In recent years the river occupied a central position within the alluvial fan, until a major shift in the position of the channel to the southern sector of the fan occurred in 1990. However, riparian owners restored the flow to the original channel. In 1996, following this study, the channel again shifted course. This time no restoration of flow to the original course of the channel occurred and the river now follows a more northerly course. The old course is thus currently devoid of flow and pioneer species are starting to colonize the gravels. 3. The natural vegetation on the alluvial fan and islands along the River Spey are a mosaic of grassland, partially vegetated gravel bars and woodland, the mosaic reflecting both channel and fan morphology and dynamics. Highest species diversity was on the riverine islands, followed by the woodland and grassland respectively. In total 129 plant species were recorded and identified within the area. 4. In recent years there have been proposals to alter the location of the River Feshie and confine it to a more stable channel. In association with these channel works, dredging of the River Spey at the Feshie confluence would also be undertaken. These proposals prompted the research presented within this paper, and the results illustrate that the implementation of river training would lead to a loss of the site's unique character and vegetation diversity. Copyright © 2000 John Wiley & Sons, Ltd.