The River Thames is 215 miles long with a tidal extent of approximately 95 miles. This makes it a valuable system for those people using it as a means of transport and trade, but it’s also an important habitat for the wildlife. So what is it that makes the Thames such a productive system? To find out, we need to delve into the physical properties that govern it.
The Thames Estuary is generally a well-mixed estuary, meaning that river flow is small compared with the volume of the tide. The whole water mass migrates up and down the estuary with the flood (incoming) and ebb (outgoing) tides.
These tides happen because of the gravitational pull exerted on the water by the sun and moon. This pull causes a giant ‘wave’ that propagates around the oceans and coastal seas and into estuaries. In the case of the Thames, there are two interacting waves travelling toward it, one from the English Channel and the other from the North Sea. These waves (tide) enter the estuary into a converging area and form just like waves on a beach, with the amplitude of the wave increasing as it travels upstream, with its highest point reached at London Bridge (7 metres).
It’s a common misconception that because the Thames is brown and murky, it must be dirty and polluted. But this isn’t the case! All estuaries are hugely important for sediment transportation, so the reason the Thames is brown is because of the huge amounts of sediment and mud naturally transported with the daily tides. In fact, over the last 50 years, thanks to the enormous clean-up efforts made by both government and NGO’s, the Thames is now one of the cleanest rivers in the world flowing through a major city. A big victory for both Londoners and local wildlife!
So it’s these physical and geographical properties that help make the Thames so productive and therefore valuable for wildlife. Estuaries are extremely rich habitats supplying a large number of species with a safe haven to feed and raise their young. This is because they’re nutrient-rich and sheltered, making them perfect nursery grounds for species such as fish and birds. The mud flats that accumulate throughout the estuary, and in particular towards the outer estuary, make great habitats for mud-dwelling invertebrates such as worms, beetles and larvae. This in turn makes them excellent feeding grounds for many wading and migratory bird species.
Climate change means that the water levels and temperatures of the Thames will rise, along with potentially more dramatic surge events. This will increase pressure on the current flood defences in the Thames. There are many organisations ensuring communities, businesses and wildlife in London are protected from flooding. TE2100, the Environment Agency department managing tidal flood risk in the Thames until the year 2100, is working hard to review the current barriers.
You can listen to our previous podcast episode discussing London's flood defences with TE2100 below.