In focus; River restoration ground investigations
In focus; River restoration ground investigations
Why ground investigations are fundamental to new developments close to our watercourses
By Iain Cairns (Principal Geoenvironmental Engineer) and Lucy Chapman (Senior Engineer)
Over many years the meandering natural surface watercourses which run through our towns and cities have changed. Canalisation or channelisation of natural river channels involves artificial modification of a river’s course for purposes such as improving navigability, controlling flooding, providing drainage and supplying the ever-increasing demand for development land. Straightening channels and lining channels with hard engineered structures to achieve these aims has been commonplace, particularly in urban areas but also in many rural locations.
In some areas entire watercourses have been realigned, dammed, embanked, diverted, culverted or forced to flow through concrete channels, effectively disconnecting rivers and streams from their floodplains. The results are typically the creation of constrained watercourses with poor ecological value, low aesthetic appearance, and overall have a negative visual and social effect on an area.
However, after much lobbying and political change, many river restoration schemes are underway to undo some of the problems.
River restoration focuses on improving the quality and function of river environments by removing structures and restoring a more natural channel form. This may include re-connecting the river with its floodplain in many cases. The creation or restoration of river corridors has many benefits including the creation of pleasant public open space, wildlife habitats and wildlife migration routes as well as improving water quality in many cases.
Geotechnics’ Involvement in River Restoration
Geotechnics has been playing its part in several such projects around the UK; working in conjunction with charitable trusts, river engineers and geomorphologists to provide valuable assessment work to assist designers of:
· Chalk Stream restoration (River Misbourne)
· Schemes to de-straighten river channels and reintroduce sinuosity (River Rom, Romford)
· De-culvertisation (day-lighting) an urban watercourse (Tang Hall Beck, City of York)
· Improving biodiversity with new wetland features to an existing floodplain (River Rom, Romford)
The Value and Purpose of Ground Investigation in River Restoration
Ground investigation is an integral design input to river restoration schemes, to enable designers to understand the interactions between the soil, rock, groundwater and surface water. It is necessary to:
· Identify potential project design constraints and opportunities at a desk-based level by in-depth review and analysis of available geological and environmental data
· Locate suitable areas into which a channel could be realigned – soil or rock conditions can govern this, and there is a need to delineate areas to be avoided (such as landfill materials, ground obstructions or abstraction boreholes)
· Provide information on the permeability of the ground (for swales, wetlands or pond areas)
· Provide geochemical test data (soil, surface water and groundwater chemistry) to establish baseline conditions to enable improvements in water quality over time. Where rivers are to be de-culverted (daylighted), then consideration of the interaction between surface water and surrounding soil chemistry or perched groundwater is imperative.
· Provide hydrometric information (such as groundwater levels, using dip meters or in-hole pressure transducers to take groundwater level measurements automatically)
When a suitably detailed set of data has been obtained and a thorough ground model produced, designers can proceed with their schemes with confidence that the uncertainty associated with the ground has been significantly reduced.
In summary, it is clear that successful reversal or reduction of the impacts of river canalisation or channelization can be achieved, as illustrated by the wide number of schemes completed to date across towns, villages and cities across the UK. The appetite for river restoration is continuing to grow, often hand in hand with the demand for ‘soft’ flood protection and Government environmental targets. It is clear that such schemes achieving success will continue to require the input of specialist skills from designers, environmentalists and specialist engineers, with all solutions tailor-made to the individual catchment or watercourse.
Get in touch with Iain Cairns to discuss how Geotechnics can assist on your next River Restoration or Contaminated Land project. You can email him at firstname.lastname@example.org or call him on 01977 525037
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