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

1. Problems and issues encountered on river restoration projects – a consultants view Sally German, Senior Fluvial Geomorphologist, Arup

2. 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

3. 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

4. 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)

5. Acceptance of natural processes occurring • Sediment accumulation and erosion – acceptance (by client) that these processes may occur

6. 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

7. 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

8. Tregaron - before

9. Tregaron - during

10. Tregaron - after

11. Beam Parklands - before

12. Beam Parkland - during

13. Beam Parkland - after