Have you ever wondered where the Ouse Washes got its name? The Ouse is the name of the river, which has already been discussed in the previous Blog “The Ouses of Britain”. This blog looks at the meaning of the word “Washes”.
Natural England describes a washland as ”an area of flood plain that is allowed to flood or is deliberately flooded for flood management”; this is indeed the main purpose of the Ouse Washes; to stop the fens from flooding.
The Ouse Washes has been classified as a floodplain which is different from a water meadow, but both have water flowing over them seasonally. The difference is that in the Ouse Washes the water can often be stagnant for a period of time while in a water meadow the water is always moving over the land and never becomes stagnant.
Water meadows are often found where there is a spring or a stream flowing over land at a slow rate and these areas are not meant to be flooded. The water flows through the grasses which grow in the water meadows thereby reducing the impact of frost on the plants during early spring so enabling the grass to grow (and thus harvested) several weeks earlier than usual. In the summer, during dry spells, the water flows through the roots meaning that the plants are watered and are also able to get nutrients and silt from the flowing water which has a positive result in reducing the risk of the level of nutrients in the water becoming too high which could cause eutrophication. This also means that plants on water meadows are fertilised so increasing the growth of the grass and plants and making more and more nutritious grass available for livestock to feed on through the summer.
Most floodplains exist naturally and are areas where water is stored when rivers burst their banks. However, the man-made Ouse Washes is purposely flooded thereby reducing the amount of water in the Great Ouse River in times of high rainfall upstream, stopping the flooding of surrounding farmland and settlements. It is usually only flooded during the winter and during the summer it is used as grazing land for livestock (although recent years have seen many unseasonal flooding events – see e.g. this previous post photo). The Ouse Washes is able to hold 900,000 cubic metres of floodwater from the River Great Ouse which would otherwise flood the fields of the Fens.
Other Washes in the UK
The Nene and Ouse Washes are the only two washland areas in East Anglia; both are located in the Fens and were built to control the flooding of the Fens.
The nearby Nene Washes are part of the River Nene which is the 10th longest river in the UK. The reason for the formation of the Nene Washes in the 18th century was to drain the Fens to allow the land to be suitable farming. The Nene Washes are used in the same way as the Ouse Washes, however it has a shorter length and only covers an area of 15 square kilometres, but it is still an important site for wildlife such as birds during the winter and summer and also prevents the Fens from flooding.
Shrinkage of the peat
The Land around the Nene and Ouse Washes has been sinking since the Fens were drained and the agricultural use of the resulting fields has caused a further decrease in the level of peat.
What are the main causes of the Fens subsiding? A relatively recent report provides several related reasons:
- Shrinkage has occurred in the Fens as the removal of the water from the peat has meant that there has been internal shrinkage at a rate of 1.8 cm/yr.
- Compression has happened after the removal of water, as the buoyancy effect has been reduced due to the removal of the water which held the weight up, so as the water was removed the peat shrank as the large weight was no longer partially suspended.
- Oxidation of the peat caused when the water was removed as before the drainage the water did not contain oxygen so there were aerobic conditions underneath the peat which slowed the decomposition. By removing the water the speed of the decomposition of material increased causing the land to sink.
Others lesser components of wastage of the peat include
- Wind erosion; loose surface soil due to strong winds
- Accidental burning of dry peat
The Fens will continue to sink as it is continuously farmed and drained. The best evidence for the peat shrinkage is shown by the Holme Post: it was drilled through the peat down into the clay in 1851 in order to monitor the peat loss. The post now rises 4m above the ground and provides an impressive record of the ground loss in the Holme Fens. This area of the Fens is the lowest point of all land in Britain as it is 2.75 metres below sea level.
In the summer the Ouse Washes and the Nene Washes are used for grazing animals which has meant that most of the land has not been ploughed for centuries, which has resulted in both Washes being at a much higher level than the surrounding Fenland. This is clearly shown in the below image which demonstrates that the washes have preserved more of their original peat layers than the surrounding arable farmland.