Stream channel modification - ecological effects and economic feasibility of river restoration

Abstract

Whilst the flood related impact of channelization on the ecology of large order lowland rivers has been studied extensively, less data are available for channelized headwaters, yet most river restoration projects in UK target headwater sites. This study, compared effects of channelization and spate on benthic macroinvertebrates in a channelized and a non-channelized headwater reach in the Owenreagh catchment, Northern Ireland. Despite significant between-reach dissimilarity in hydromorphology, nMDS ordinations confirmed that differences in macroinvertebrate composition, due to channelization, were minimal and increased only slightly after floods. The small size of the observed differences is attributable to features of the channelized reach commonly associated with suitable habitat for lotic invertebrates, such as mature riparian vegetation, minimal bank erosion and a highly diverse substrate with a low fine sediment content.

In a review of 26 studies on channelization effects on stream biota, more than 76% reported a negative impact, almost 20% no adverse impact and approximately 4% found a positive impact. Stream fauna was correlated to current velocity (31%), habitat heterogeneity (21%), sedimentation (16%) and aquatic and riparian vegetation (10%). The review identified a research need to define the nature and scale of ecological impacts associated with individual channelization types.

By 2016, almost 60% of European rivers failed to meet WFD requirements. The hydromorphological restoration effort required was based on data for the River Blackwater in Co. Tyrone, Northern Ireland, as a case-study. Upon extrapolation to all 1308 currently non-compliant waterbodies within the British Isles, a conservative cost estimate for their hydromorphological restoration arrived at £22.9 billion and a timescale of 330 years, at the current level of effort.

These results confirm an urgent requirement to overhaul the WFD status goals and to extend phased deadlines, otherwise the directive risks becoming a relatively meaningless piece of legislation with unattainable targets.

Date of Award	Jan 2017
Original language	English
Sponsors	NI Department of Employment and Learning (DEL)
Supervisor	Joerg Arnscheidt (Supervisor) & Brian Rippey (Supervisor)