Muddy secrets of the Humber

The river's estuary, a vital drain for a third of England, faces serious environmental pressure. Simon Hadlington reports on an ambitious project to monitor its well-being

As the ferry Norsea daily plies its way between Hull and Rotterdam, it is doing more than transporting passengers and vehicles. Deep inside the ship's body an array of scientific instruments has been plumbed into one of the pipes that sucks in seawater to cool the engines.

On the roof of the ferry sits a receiver that is in contact with a satellite. Whenever the satellite tells the receiver that the ferry has moved forward 100 metres, a signal is sent via a computer to the instruments in the engine room, instructing them to measure the temperature, pH and oxygen content of the seawater, and how much sediment it contains.

The results are recorded on the computer, and once a fortnight a researcher boards the ferry to download the information and take it away for analysis.

North Sea Ferries' Norsea is the latest recruit to an ambitious project devised by Professor Jack Hardisty, dean of the School of Geography and Earth Sciences at the University of Hull. The Humber Observatory project aims to measure key environmental factors relating to the Humber estuary and its surroundings.

A few stark figures make it clear how important the Humber estuary is and underline how surprising it is that no serious long-term effort has been made until now to try to understand how it works. The estuary drains nearly 30 per cent of the land area of England. Its catchment area, in which around 11 million people live, includes some of the biggest industrial towns and cities in the country, including Leeds and Birmingham.

Every six hours the tide brings in 1.6 cubic kilometres of water, laden with 100,000 tonnes of sediment. This is removed on its outward journey, together with whatever has entered from the catchment area. Or at least that is the assumption; no one knows precisely.

According to Professor Hardisty, we need to know what happens because, environmentally, the scene is changing rapidly. "The demand that industry and society is making on this environmental resource is rising extremely rapidly. There's a huge increase in the environmental stress to which it is being subjected," he says.

The Humber Observatory project was officially launched in March 1994, with funding from the Natural Environment Research Council, under its Lois (Land-Ocean Interaction Study) programme, and the National Rivers Authority.

The observatory mainly comprises a number of remote outstations in the estuary linked by radio to a central control room in the university. In collaboration with Associated British Ports, the agency that administers shipping within the estuary, Professor Hardisty's team has attached instruments to five unmanned navigational lightships, which are moored across the mouth of the Humber. These form what is termed a "flux curtain", analysing the water as it ebbs and flows. Eventually there are to be four more outstations running longitudinally up the estuary.

As on the Norsea, the instruments measure pH, oxygen content, sediment content and temperature of the water, as well as how fast it is flowing. Wind generators on board the ships charge batteries that power the instruments. Every hour a radio signal is sent from the control centre in the university, instructing the instruments to take their measurements and relay the results to base.

The information about the sediment is particularly significant, because it is the sediment that contains most of the important chemistry of the estuary. The "flux" of the sediment is especially important. This is a measure of how much sediment is moving and at what rate.

One big problem the project faces is the sheer hostility of the environment. Corrosion is a headache, as is the incessant buffeting the instruments receive both from nature and man: one lot of instrumentation was ruined when a passing freighter collided with one of the lightships.

Such difficulties are not unknown to Professor Hardisty. Some years ago a buoy containing instruments disappeared, having become detached from its mooring. It was later reported washed up in Denmark.

Already a discovery of potentially great importance has been made. Professor Hardisty explains: "It has always been assumed that the suspended sediment in the estuary is well mixed and fairly uniformly distributed in the water. However, satellite images of the estuary showed a distinct banding - a bit like streaky bacon. The streaks appeared to be concentrations of sediment. So we took readings across the estuary. These confirmed what the satellite pictures seemed to show, that the suspended sediment that moves in and out of the estuary does so in narrow jets, about 100 metres wide, of highly concentrated silt. Back-of-the-envelope calculations suggest that perhaps 50 per cent of the suspended sediment is in these relatively tiny jets.

"We don't yet understand how they work or why they are generated. But they appear to be a novel environmental phenomenon." The team has named these mysterious streams Snarks, after Lewis Carroll's equally enigmatic creation.

In addition to the estuary work, the observatory is collaborating with Hull City Council in monitoring air quality around the city. As with the estuary studies, the aim is to feed data into computer models so accurate predictions can be made about the consequences of future activities. "It may be that city planners will need to know what effect a new industrial estate would have on a residential suburb across the city. That's the sort of question we would hope to answer," says Professor Hardisty.