Whitehaven Harbour Water Quality Case Study
Project: Assessing the impact of dock gates on water quality, Whitehaven Harbour.
Client: Lancaster University MSc Project
The Challenge
In a bid to protect Whitehaven town from tidal flooding, a sealock was installed in the harbour during 1998 at a cost of £6.7 million. Although the impoundment of the harbour and the resultant provision of a permanently wet inner harbour resulted in a significant increase in the number of fishing and leisure craft (>200) berthed in the marina, the impact of the sealock on the hydrodynamics and flushing characteristics of the harbour was unknown. This study focused on determining lock gate impact on effluent flushing times.
Current Flow and Direction
Effluent Concentration Mapping
The Solution
- MIKE21 was used to develop a numerical model of Whitehaven harbour in order to determine the effect of impounding the inner harbour on flushing characteristics.
A grid interval of 2 m was used to get a sufficient resolution. - Validation of the harbour model using tidal gauge data obtained from Workington harbour, 11 km due north of Whitehaven, revealed that MIKE 21 was able to produce a realistic model of the hydrodynamics of Whitehaven harbour.
- Four scenarios of opening period for the sealock were used in order to determine the flushing time.
The impact of the sealock on the flushing time was determined by simulating the dispersion of an initial concentration of a dissolved substance in each dock and calculating the concentration left after a period of two days. The assessment was repeated for spring and neap periods, three different point sources, and various opening periods of the sealock. - The flushing time was calculated to range from 2 to 12 days after impoundment of the harbour depending on the different scenarios
Results
Simulated studies on the dispersion of a conservative pollutant such as diesel from a point source, revealed that impounding the harbour significantly increased flushing time of the inner harbour. Prior to impoundment, theoretical flushing times, required to reduce an initial diesel concentration by 95% were calculated to be between 24 and 52 hours depending on location of the point source and tidal cycle (spring or neap). After impoundment, theoretical flushing times ranged between 38 and 285 hours depending on location of the point source and how long the sealock remained open during high water.