Removing Instream Weirs; evaluating the Benefits and Pitfalls for a
Lowland Low E
Abstract
The removal of dams, weirs or barriers to river flow, is frequently a
contentious issue. This is because of the competing demands of flood
protection and the ecological, social, economic and cultural health of
the river. Many of the barriers are old or obsolete and there is an
international drive to create ‘free-flowing rivers’ with no or fewer
barriers, thereby increasing longitudinal connectivity. This has been
most noticeable in North America and continental Europe, and less
apparent in the UK. We explore the issues around weir removal with a
case study of a lowland southern English river, the River Rother, West
Sussex, in a predominantly agricultural catchment where weirs have been
constructed for a variety of purposes over the last ~1000
years. The river is dominated by inputs of sand-sized sediment with very
low organic matter content that is frequently stored upstream of
structures. The multiplicity of stakeholders and the strong interests of
the fishing and farming communities render decision-making about
structure removal or modification to improve fish passage difficult.
There is also the demand for potable water abstraction by the local
water company which would be affected by dam removal and the potential
release of the fine (mostly < 2mm dia.) sediments stored
immediately upstream of the weirs. This paper subsequently explores
selected issues around weir removal under the requirement of the
European Water Framework Directive to achieve Good Ecological Status and
explores guidance on best practice; including the decision which weirs
to remove and in which order.