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News - 25/03/15

Tidal flows in Cowes Harbour

There was extensive tidal flow modelling prior to construction of the new detached Breakwater and whilst this modelling did predict certain changes to the tidal rates and directions within the harbour, some significant differences were noted between the modelling results and actual flows recorded after the construction of the gravel core in September 2014.

Cowes Local Notices advising mariners on the new tidal regime were issued in the late summer and early autumn of 2014, and updated in Local Notice to Mariners No 08 of 2015 which contains the most recent information on observed changes to the tidal system in the harbour at Mean High Water Springs. The Notice highlights the existence of a cross current of up to 1.5 knots that may be experienced south of the Cowes Breakwater between High Water -2.5hrs and High Water -1hr.

This cross current comes in from the east and travels across the main fairway in the vicinity of No. 4 fairway buoy and then splits, with one stream heading north towards the Island Sailing Club and the other stream heading south past Red Funnel’s Red Jet terminal. Discussions have taken place between CHC and Red Funnel and the situation is being managed. Meetings have also been held with representatives from CHC’s Advisory Committee, local yacht clubs and major event organisers.

Red Funnel vehicle ferry entering Cowes Harbour - No 4 buoy in the foreground
Cross current at No 4 buoy at HW-2hrs

CHC is currently working with the firm that undertook the tidal modelling of Cowes Harbour, ABPmer, and our project managers Atkins, in order to understand why the actual flows observed are not entirely as predicted and how to best mitigate the changes. The tides in the harbour are therefore under continuing detailed investigation and a new model has been commissioned. This new model will be used to carry out further modelling and design work on the design of the Shrape Breakwater extension, new Eastern Channel, and the proposed new marina in East Cowes with the aim of optimising the design and mitigating impacts on the final tidal flows within the harbour.

In the interim, CHC has already put in place a number of extra safety controls and will action further measures to assist harbour users, including:
– New signage will be installed in the harbour during the early part of the 2015 season.
– Extra harbour patrol boats will be on hand to advise mariners at times when the cross current may be significant, and will be available to escort car ferries when required.
– A local tidal atlas with diagrams for the various stages of the tidal cycle will be produced and promulgated.
– The CHC Advisory Committee has convened a working group to consider tidal impacts and recommend additional safety measures.

It is important that all harbour users should familiarise themselves with the tidal flow changes in Cowes Harbour; take these tide flows into account when navigating in the harbour and always navigate with particular caution in the vicinity of the harbour entrance and Inner Fairway.

Further information is contained in this year’s Cowes Port Handbook, and all safety controls will be kept under review as the season progresses with updates published in CHC’s monthly newsletters, in Cowes Local Notices to Mariners, and on the cowesharbourcommission.co.uk website.

Top photo: North flowing foreshore current at HW-2hrs