Prioritising restoration actions for river infrastructure at the catchment scale

 

River infrastructure is a major cause of habitat fragmentation in fluvial ecosystems, and can significantly impact populations of aquatic biota by impeding movement between habitats essential for feeding and reproduction. Effective river restoration requires mitigating the impacts barriers have on key ecological processes. It has been shown that the removal or mitigation (e.g. building fish passes) of barriers that block fish dispersal have led to some of the largest increases in fish production. Furthermore, the benefits of removing or mitigating the impact of barriers can be realised relatively quickly compared with other restoration methods. Catchment-scale mitigation activities, which reduce the environmental impacts of river infrastructure networks, are likely to provide the most effective and cost-efficient means by which to enhance fish populations and overall ecological status of fluvial systems.

ICER has reviewed current methodologies to assess the environmental impact of river infrastructure and how restoration efforts could be prioritised at a catchment scale. This project highlighted problems of bias towards specific structure types (e.g. culverts), adult life stages of upstream migrating economically significant fish, and criteria based on swimming capabilities, lacking consideration of behaviour. A need for standardised procedures to rapidly and cost-effectively survey large numbers of barriers over wide geographic areas was recognised. Further, simple cost-benefit analysis based on “scoring and ranking” systems to prioritise not only barrier repair and removal projects, but also the placement of river infrastructure, should be avoided. It is proposed that Optimisation Modelling offers a robust approach for efficiently prioritising decision-making in river restoration planning, allowing decision makers to take into account key uncertainties and effectively balance multiple, possibly competing, environmental and socioeconomic goals and constraints.

A case study example applied optimisation modelling at the catchment-scale. A complete inventory of river infrastructure in the River Wey catchment (South East England) was created by combining multiple existing Environment Agency databases into GIS maps to quantify the barrier network. A coarse resolution barrier passability score, for both upstream and downstream movement, based on fish swimming and leaping abilities, was included in the prioritisation process. During prioritisation, barrier passability, barrier density, impoundment effect, distance from the tidal limit, distance between barriers, habitat quality and socio-economic constraints were included in the optimisation model.

This work has been funded by the Scottish Environment Protection Agency and Environment Agency (England).

 

Media:

Conducting a SNIFFER assessment at a weir to assess passability for fish

 

Publications:

Kemp, P.S. & O’Hanley, J.R. (2010). Procedures for evaluating and prioritising the removal of fish passage barriers: a synthesis. Fisheries Management and Ecology 17: 297-322 (doi:10.1111/j.1365-2400.2010.00751.x).

 

People:

Dr Lynda Newbold

Prof. Paul Kemp

Dr Jesse O’Hanley

Dr. Kate Parks