- The River Wye is a 215km long (134 miles) river, starting at its source in the Plynlion Hills in central Wales, flowing south-eastwards and joining the Severn Estuary at Chepstow.
- It forms much of the England-Wales border and flows through/past towns/villages including Rhayader, Builth Wells, Hay-on-Wye, Hereford and Tintern.
- Its length makes it the 5th longest river in the UK. Some of its tributaries are the Lugg, Monnow, Tarennig and Bidno.
- It is renowned for being an ideal place for salmon, however this is not always the case. The salmon travel 6000 miles from the Atlantic Ocean to reach the Wye.
- The river is generally very unpolluted, which meant that it used to be one of the best places for salmon fishing in the UK.
- The lower Wye has even been a designated salmon fishery.
- In 2002, however, there was a massive low, at just a 357 catch. Work has been put in the increase it again, so by 2015, there was a 5-year average of a catch of 1000.
- The Wye has been classed as a Site of Special Scientific Interest, as well as a Special Area of Conservation, due to it being a vital migration route for lots of wildlife.
- In addition, much of the lower valley is classed as an Area of Outstanding Natural Beauty and was designated as this in 1971.
- In the upper valleys, there is steep relief and acidic soils. The rocks are impermeable mudstones, shales and grits.
- A key aspect is that deforestation has taken place to make room for pasture and sheep farming.
- This has meant that interception is reduced so soils become saturated more quickly and, especially with impermeable rocks, there is more chance of overland flow.
- They have implicated ditches in an attempt to drain the land, making it more productive, but it has had adverse effects, increasing the speed of water transfer so the river is more prone to flooding.
- In the lower valley, in the South, it starts off as sandstones, but then cuts through a limestone gorge between Symonds Yat and Chepstow.
- The underlying impermeable rocks, particularly in the upper valley, limit the groundwater flow through the basin, so soils quickly become saturated.
- This encourages overland flow so there is an increased risk of flooding downstream, for example, in Hereford, they have experienced flooding on many occasions.
- The highest amount of rainfall comes in the Western upland parts of the basin. In the East, there are higher temperatures, and therefore higher evapotranspiration rates.
- The highest runoff comes during the winter, as there is lots of rainfall, combined with reduced temperatures. This means low plant growth and less evapotranspiration, so more water in and on the ground to run to the rivers, increasing the runoff.