Sally German, Senior Fluvial Geomorphologist, Arup

Problems and issues encountered on river restoration projects – a consultants view

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Appreciation of the need for detailed information

The level of detailed information needed to develop a comprehensive design is often under estimated by the client – esp in the early stages of the project - therefore little budget to undertake geomorphological surveys/investigations to provide robust case for design parameters

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Translation of concept to construction drawing

Difficult to present complex and diverse features in a ‘proper’ engineering drawing (and contractors not experienced in undertaking this type of work) – often results in the need for a high level of specialised on-site supervision

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Engineering design issues

Disparities between designing features geomorphological vs engineering

Bed material – scour calcs to cope with 1in200yr flows vs ‘typical bed material’ or sediment size determined using sed transport rates

Bank slopes – natural slopes vs geotechnical stability Structures in the channel – appropriate size vs

engineering robustness (i.e. ability to withstand extreme conditions to ensure life of feature and reduce risk to flooding d/s if dislodged)

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Acceptance of natural processes occurring

Sediment accumulation and erosion – acceptance (by client) that these processes may occur

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Constraints on design

Issues relating to physical constraints – laterally due to development on the bank or the presence of a structure – design needed to manage this if risk considered high

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Contractors – in the ground

Getting contractors to be more ‘natural’ with excavations – i.e not getting everything flat/level

Getting contractors to understand the importance of relative levels of the long profile – not just the cross-section – are v important – hard bed needs to be right

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Tregaron - before

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Tregaron - during

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Tregaron - after

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Beam Parklands - before

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Beam Parkland - during

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Beam Parkland - after