Lee Catchment Flood Risk Assessment and Management Study

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Computer modelling

One of the key phases of the Lee CFRAMS is the computer modelling of the rivers and harbour in the catchment. Due to the differing nature of the water bodies, the river network and Cork Harbour are being modelled separately using different types of software. Further details of the modelling of Cork Harbour and the main rivers in the catchment can be found below.

Computer flow modelling of Cork Harbour

The computer modelling of Cork Harbour has been carried out by our project partners MarCon Computations International Ltd., using a two dimensional (2D) hydraulic computer model of Cork Harbour (the map below shows the extent of the Cork Harbour computer model). The water levels calculated by the computer model are being used to produce flood extent maps around the harbour for storm events of various magnitudes.

Harbour Model Map
Loaded on: 21/09/07 - Size: 300kb


The 2D computer model of the harbour was developed using bathymetric survey data. The bathymetric surveys were carried out by boats using special measuring devices to provide detailed information on the depth and shape of the sea bed in the harbour.

The model encompasses the estuarine and marine system from the lower exits of the River Lee southwards to the open sea, covering an area of approximately 354 kilometers squared. Fresh water inflows to the harbour include the River Lee, the Glashaboy River, the Owennacurra River and the Owenboy River.

In order to estimate storm water levels in Cork Harbour a detailed analysis of surge, tide and meteorological data has been carried out. Surge is caused by low pressure weather systems and wind which causes the water level to rise higher than the normal sea level. Surge data at the entrance to Cork Harbour has been obtained from the PRISM (Predictive Irish Sea Model) surge modelling project of the Celtic and Irish Seas which has been undertaken by the Marine Modelling Centre at NUI Galway. A number of tide gauges around Cork Harbour and the Celtic Sea have provided historical records on tide levels. These have been analysed to determine maximum tide levels over the last 50 years.

The effect of wind on water levels has also be assessed using data provided by Met Éireann. The analysis also considers the joint probability of occurrence of surges, high tide conditions and river flows and the impact of climate change on future sea levels.

Computer flow modelling of rivers

Approximately 250km of river channel in the Lee catchment is represented using computer models. The models are being constructed from over 1800 cross-sections of the river channels and structures obtained during the channel and structure cross sectional survey. The channel cross sections have been combined with LiDAR survey data of the floodplains to form integrated channel - floodplain cross sections.

The hydraulic modelling of the rivers involves using ISIS 1 dimensional (1D) and 2 dimensional (2D) flow computer models to solve advanced mathematical equations to estimate water levels along the river channels and floodplains for storm events of various magnitudes. Data for these storm events was developed as part of the hydrological asssessment.

Eight separate hydraulic models of the rivers in the catchment are being constructed (see the map below). 2D modelling is being used in complex urban areas, such as Cork City, which would be difficult to represent in a 1D manner. The results from the computer modelling are being used in the flood mapping process.

River Model Map
Loaded on: 30/05/07 - Size: 643kb

In order to ensure the computer models are working correctly, they are calibrated against historic flood events. Information collected about these flood events, including descriptions of the flooding together with recorded rainfall, river flows and tidal data has been used to reproduce the flooding in the hydraulic computer models. The impact of climate and land use changes on river flows has also been assessed.

Photos

Cork Harbour at Fota island

Cork Harbour from Cobh

Sluice gate on canal at Ballincollig

River Curragheen

River Owenacurra at Midleton

Key Activities

The key activities to the project are

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Final edition of Lee CFRAMS newsletter (more)

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Non-Technical Summary for SEA Environmental Report published(more)

Consultation on the draft Flood Risk Management Plan (more)

Consultation on Lee Predictive Floodmaps (more)