The effects of sediment transport on contaminant dispersal: An example from Milford Haven

Milford Haven is an estuary that has been subjected to industrial pollution from tanker operations and refinery and power station effluents since about 1962. Consequently build-up of various anthropogenic heavy metals and hydrocarbons has been observed in the bottom sediments. This paper describes 1. a new technique whereby the patterns of net sediment transport are determined from the relative changes of grain-size distributions in 125 grab samples, and 2. how net sediment transport correlates with the quantity of contaminants contained in the bottom sediments.The analysis demonstrates that sediment movement in the flood direction dominates the central channel and the northern half of the estuary. Transport in the ebb direction is confined to the southern coastal zone. A comparison of the transport paths with contaminant concentrations shows clearly that the flood-dominant movement leads to concentration of heavy metals and hydrocarbons. As a result, an area of fine-grained deposition near the head of the estuary receives exceptionally high concentrations of contaminants. The ebbdominant transport, on the other hand, causes dilution in the amount of pollutants contained in the sediments.The derived transport paths agree well with known current patterns, and this technique is shown to be a rapid and inexpensive method for 1. environmental impact assessment, 2. establishing effective monitoring programmes, 3. predicting areas vulnerable to contamination, and 4. rational contingency planning.