River Winster and Meathop Drain flood risk

Transcription

1 Managing legacy infrastructure into the future: River Winster and Meathop Drain flood risk Alan Forster, Principal Coastal Specialist, AECOM Daniel Glasson, Associate, AECOM

2 Study area

3 Study area 3

4 Study area: Kent estuary 4

5 Study area: River Winster catchment 5

6 Study area: River Winster under railway embankment 6

7 Study area: upstream of gates 7

8 Study area: training walls 8

9 Issues and objectives Issues Public s perception of increased flood risk in recent years Gates stuck either open or closed River Winster not draining quickly enough Poor drainage of the Meathop Drain into the River Winster Changing land use and ownership Geomorphology of the estuary Low number of assets at risk of flooding Objective To develop a better understanding of the flood mechanisms within the River Winster and Meathop Drain catchment to provide Network Rail with the necessary information to develop a strategy for the management and maintenance of their assets within the catchment 9

10 Investigations included Desk study Background Information Environmental Constraints Stakeholder Engagement Review of coastal processes Estuary geomorphology Normal and extreme water levels Condition assessment Tidal Gates Track Geometry 10 Catchment analysis Topographic Assessment Peak Fluvial Flows Hydrometric analysis River Gauging Review Rainfall Analysis Hydraulic modelling Existing Situation Rainfall Only Fluvial (No tidal inputs) Existing with no d/s restriction Gate Operation/Failure Pumping

11 Observed water levels

12 Observed water levels: downstream channel 12

13 Observed water levels: downstream channel 13

14 Observed water levels: downstream channel 14

15 Tidal gates condition

16 Tidal gates condition Failed Gate Failed Arnside gate Failed Hinge Mechanism History of Intermittent Operation Condition Survey (July 2016) Found Gates Operational Fair Condition Gate Failure (October 2016) Arnside Gate Failure Restricted Operation of Grange Gate Gate replacement Arnside gate has now been replaced with a more responsive flap gate Grange Gate replacement is in asset management plan 16

17 Hydraulic modelling

18 Hydraulic model: downstream channel Build up of material restricting flow in the channel 18

19 Animation of flooding Existing situation Downstream restriction removed 19

20 Comparison with existing situation 20 Presentation Title

21 Conclusion

22 Conclusion Tidal Gates o Generally working as intended- with routine maintenance being undertaken o Improved with new lighter gate o Other gate to be replaced in line with asset management plan Downstream water levels remain elevated due to the sand banks Worst case is that the gates will be blocked by further sand movement o Channel clearance considered o Unlikely to provide a permanent solution Observed water levels o Measured data proved to be important for the project and future management o Continue to monitor as much as possible Review pumping strategy / volumes for the golf course 22

23 Wider considerations Victorian engineers o Considered flow through the embankment but not the dynamic sands of the estuary Victorian developer o Built a structure that has stood the test of time but was allowed to manage costs by selling the reclaimed land behind the embankment. Network Rail (and predecessors) o Managed the infrastructure and maintained the structures in working order and continues to do so. Are we sowing any seeds of legacy problems for the future with our new developments? o Engineering design has improved (consideration of environment, climate change etc) o Could partnership funding or private development be storing up problems for the future in the same way? 23

24 Thank you

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