Lee Catchment Flood Risk Assessment and Management Study

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Computer model calibration

To ensure the the hydraulic computer models that are created as part of the hydraulic modelling process are representative of what is happening in both the rivers and Cork Harbour model calibration has been carried out.

River computer model calibration

The hydraulic computer models of the rivers operate by solving advanced mathematical equations, based on a variety of parameters, providing an estimate of water levels for a range of flood events. The calibration of the river computer models is based on a comparison of computed model results against observed data. This is then followed by an adjustment of the hydraulic computer model parameters until a level of acceptable agreement between the model results and observed data is reached. Some of the parameters used by the computer model to estimate water levels include:

The physical make up of the river affect the speed and depth of water in the river channel and floodplain and hence the extent over which the river may flood. This physical makeup is represented in the Computer model as roughness coefficients known as Manning's n values. These can vary significantly along a river reach and hence is usually the main parameter adjusted in a river model calibration.

Manning's n values for the hydraulic computer models were determined following examination of both site visit and aerial photos. The computer models were then run with observed flood event flows recorded on the river gauges in the catchment. The water levels predicted by the computer models were then compared to observed water levels for each flood event. The Manning's n values were adjusted until an acceptable agreement between the computer model results and the recorded flood level was reached.

Harbour computer model calibration

The Cork Harbour hydraulic model has been developed and calibrated by our project partners, Marcon Computations International Ltd. The harbour model is a 2D flow computer model. Calibration data sets used to calibrate the harbour model were water current velocities and directions, and water surface elevations. This data was gathered from gauges located in Cork Harbour. The technical parameters adjusted to calibrate the Harbour model were:

The computer model was calibrated by 'tuning' these parameters until good agreement with the calibration data sets was achieved.

The river and harbour models were also checked against historical flood extent data. The data is available in the form of photos, reports and newspaper articles on the OPW flood mapping website (www.floodmaps.ie).


Photos

Bridge at Carrigtohill

Bridge over the River Lee at Ballincollig

Cork Harbour from Cobh

Cork Harbour from Cobh

Sluice gate on canal at Ballincollig

River Lee

River Lee

Key Activities

The key activities to the project are

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