RESTORATION DESIGN FOR REROUTED WATERCOURSES

Transcription

1 With thanks to: Thames Water Utilities Limited RESTORATION DESIGN FOR REROUTED WATERCOURSES

2 Project Design Team Colin Thorne, Nick Clifford Gary Priestnall Philip Soar Kieran Conlan, Steve Dangerfield Tom Coulthard Steve Dunthorne Jenny Mant Nick Reynard Geomorphology GIS and Mapping Channel Design Project Management Sediment Modelling Hydraulics River Restoration Climate Change

3 1. Project Context Overview 2. Need to Reroute Watercourses 3. Watercourse Design Objectives 4. Design Elements and Tools 5. Design Outcome 6. Conclusions

4 Significant difficulties prediucted in supplying sufficient water in the Southeast over the next 25 years. A preferred solution is a an embanked reservoir. But, there are objectors who will challenge ever aspect during Planning Enquiries. 1. Project Context

5 2. Need to Reroute Watercourses

6 3. Watercourse Design Objectives Core design criteria: Flood storage compensation Surface water drainage and conveyance Maintain sediment regime Biodiversity gains Key assessment criteria: Local community acceptability Minimise future maintenance

7 Land Drainage & Flood Storage Design Objectives Constraints e.g. gradients & topography Existing hydrology Climate change Initial with-reservoir flood modelling Watercourse routes, connections & flood compensation Initial design Regime & hydraulic geometry analyses Initial watercourse & floodplain cross-sections, planform & slope Constraints e.g. land use & services Amend design Field sediment monitoring CBS & FA Sediment balancing (Copeland) Reference reaches In-channel & riparian habitats & features (VISION) RRC channel design guidance River Ock ecological baseline information Review with-reservoir flood modelling outputs Climate change Post-EIA Post-project appraisal and adaptive management Detailed design of channel & floodplain form and habitats/features Long term sediment modelling (CAESAR) Establish auditable, sitespecific geomorphological success criteria Detailed design of channel crossings & stabilisation structures Input to final design (Inter-active CD-ROM)

8 Catchment Baseline Survey

9 Underlying Geology

10 Geomorphic Susceptibility

11 Fluvial Audit

12 Wood jams and complex flows Riparian corridor to trap and store silt Reference Reaches Meandering planform with cut banks Complex cross-sections and margins

13 Regime & Hydraulic Geometry Analysis

14 River Wandle 8 years on (2006) RRC experience with clay streams Above all, remember that whatever bank profile you dig will be there for a long time and that re-adjustment can be a very slow process River Wandle as built (1998) What you build is what you get!

15 Hydraulic Modelling & Flood Compensation

16 Sediment Monitoring

17 Sediment Monitoring Results Turbidity not simply related to suspended sediment concentration No significant relationship between suspended load and flow intensity Channels prone to siltation Gravel/sand bed smothered by layer of silt-clay 0.1 to 0.8 m thick

18 Copeland Method - Design Curves Depth Top width Bed width

19 Climate Change Predictions Rainfall Average Discharges Evapotranspiration Flow Duration

20 Longterm Sediment Modelling with project 2050 without project with project and climate change

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22 5. Design Outcome

23 Watercourse Diversion Design Template

24 6. Conclusions Provided a practical demonstration of the value of using of multiple design tools and team work. Highlighted the challenges of river restoration design with tight budgets and time constraints. Produced a design template that meets the needs of the client AND is acceptable to regulators. Demonstrates the value of interdisciplinary collaboration. Design matches form to function, providing a sustainable basis for optimisation of biodiversity.