Cowes Outer Harbour Project

Bill Cooper and Gordon Osborn

19 May 2016

1

Solent and Cowes tidal regime

Cowes water level

Solent tidal flows

2

Solent and Cowes tidal regime

Cowes water level

Solent tidal flows

3

Cowes tidal regime

Harbour area tidal flow

Cowes water level

4

Cowes tidal regime

Harbour area tidal flow

Flow offshore of breakwater

5

Harbour flow - post breakwater

HW-1

At HW-1:! Cross harbour flow

deflected and increased! Reduced cross harbour

flow in the lee of the breakwater

! Increased flow north and south along west Cowes

! Slight increase in flow rotation

Changes at other states of the tide more subtle

Improved wave protection

6

Differences in predicted flows

HW-1

! Offshore flow increase! Cross harbour flow

increase! West Cowes flow slightly

increased! West entrance flow

reversal earlier! Majority of tide correctly

predicted

7

Advantages offered by new model

! Bathymetry update! Coastal developments! Different periods in time! Improvements in

modelling technology, including flexible mesh structure

8

Confidence of new modelling

! Hydrodynamic and Sediment transport models judged “fit for purpose” by HRW.

! Calibration proves good reproduction of measured tidal flows.

! Confidence in absolute levels of sedimentation, is not possible.

! Confidence in the model is high, particularly in predicting the relativeeffects of the development.

9

Tidal Differences – Conclusions

Review has included:! Investigation of observed data; and! Testing of suggested causes including;

! Bathymetry changes! Location of observed data! Design and geographical extent of the old

model

Conclusions;! Lunar nodal cycle and resulting tidal phase

changes! Discrepancy in the originally observed data

10

Harbour sedimentation

! Complex flow patterns and processes make sedimentation more difficult to predict than tidal flows

! Dynamic equilibrium of sediment exchange within the estuary and Solent

! Man made interventions disturb this equilibrium

! Dredging results in a natural increase in sedimentation rates

! Providing sheltered waters results in a natural increase in sedimentation rates

! Majority of sediment comes from Solent but there are other sources

! Storms and rainfall influence sedimentation rates

11

Harbour sedimentation

! Variation in sediment rates over time! Observations show an increasing trend,

and higher since 2013! Model simulation does not include

! Vessel movements! Moored vessels! Marina structures

12

Sedimentation - post breakwater

! Little change to the total harbour sedimentation! General trend:

! Some reductions in sedimentation in West Cowes! Some increase in sedimentation in East Cowes

Net change in sedimentation due to the breakwater

Breakwater – No Breakwater

13

Consented scheme tidal differences

Breakwater only

Full Scheme

Influence of the dredging and Shrapeextension at HW-1:! Cross harbour flow

! Slight increase; and! Deflected further north

! Flow rotation offset to the left

Changes at other states of the tide:! Some changes near to Victoria Marina! More subtle changes elsewhere

14

Consented scheme sediment differences

! Some increase to the total harbour sedimentation! Sedimentation in the dredged area of the new marina! General pattern of sedimentation in West Cowes similar to

the existing breakwater condition

Breakwater – No BreakwaterBreakwater – No Breakwater Full Scheme – No Breakwater

15

Optimised scheme tidal differences

Breakwater only

Comparing flow with breakwater only configuration, at HW-1:! Cross harbour flow

! Similar flow speeds, but some reductions in main channel south

! Slight deflection further north to give a wider spread of flow

! Some reduction in flow rotation

Changes at other states of the tide:! Some changes near to Victoria Marina! More subtle changes elsewhereAmended

Scheme

16

Optimised scheme sediment differences

! Some increase to the total harbour sedimentation! Sedimentation in the additional dredged areas! General pattern of sedimentation in West Cowes similar to

the Consented Scheme condition

Full Scheme – No Breakwater Optimised Scheme – No Breakwater

Thank you for your attention

Note

ABPmer Page 1 of 1

Ref: R/4238

Subject: Cowes Outer Breakwater – Public Consultation Meeting These slides have been prepared to inform the public meeting held on the 19 May 2016. The information provided should not be used or quoted out of context and may be subject to change at a later date. Please refer to the full published reports for more details of the modelling services undertaken as part of the Outer Harbour Project. Prepared by G. Osborn 19 May 2016