Солтүстік-Батыс Англиядағы Дуглас өзені

River in north west England

The River Douglas, also known as the River Asland or Astland, flows through parts of Lancashire and Greater Manchester in North West England. It is a tributary of the River Ribble and has several tributaries, the major ones being the River Tawd and the River Yarrow. In 1720 an act of Parliament was passed allowing Thomas Steers and William Squire to make the Douglas navigable to small ships between Wigan and its mouth. Amid financial irregularities, the Douglas Navigation was not completed until 1742, and by 1783, it had been superseded by the Leeds and Liverpool Canal. It reverted to being a river, although the remains of several locks can still be seen between Parbold and Gathurst. The Rufford Branch of the canal joins the river at Tarleton. The river rises on Winter Hill on the West Pennine Moors, and flows for 35 mile (56 km) through several towns and onto the Ribble estuary past Tarleton, the last 10 mile (16 km) or so being tidal. In 1892 the Douglas was diverted in Wigan to allow the construction of Wigan Central railway station.

The Douglas is derived from the Brittonic elements dūβ , meaning "black", and *glẹ:ss, "stream, rivulet, watercourse" (Welsh du glais). The Douglas descends rapidly, dropping below the 430 feet (131 m) contour before it empties into the Lower Rivington Reservoir, just to the north of Horwich. Below the dam, flow in the river is maintained by compensation water released from the reservoir, and marks the county boundary between Greater Manchester and Lancashire. The river is crossed by the M61 motorway near Rivington services, and then turns to the north west to reach the southern edge of Adlington. As it weaves its way in a generally south westerly direction, it is crossed by the Leeds and Liverpool Canal, Next, it by passes Worthington Lakes, three reservoirs built in the 1860s to provide drinking water for Wigan, and now managed as a country park by United Utilities. The river ceases to form the county boundary just before the lakes, and re emerges from a tunnel below the reservoir dam, passing to the east of Standish. It continues southwards to Wigan, where it passes through a long culvert under the railway near Wigan North Western station, is crossed again by the Leeds and Liverpool Canal, and heads north west, closely paralleled by the canal. The river drops below the 33 feet (10 m) contour at Parbold, and continues across open countryside where it is joined by the River Tawd, flowing north from Skelmersdale, becoming tidal before it reaches the village of Rufford. White Bridge at Rufford is a grade II listed structure with three spans, constructed of squared sandstone. It carries the B5246 Station Road over the river, and dates from the time of the construction of the Douglas Navigation, between 1720 and 1742. Below the bridge, the channel is rather straighter. After its junction with the canal at Tarleton Lock, the final 4 mile (6 km) of the river to its junction with the River Ribble, here also known as the River Asland, is used by boat traffic transferring from the Leeds and Liverpool Canal to the Lancaster Canal since the opening of the Ribble Link in 2002.

The reservoirs of the Rivington Chain capture and store run off from Winter Hill and Rivington Moor, much of which is used to provide a public water supply to areas of Lancashire and Greater Manchester. However, as a result of the original statutes that allowed them to be built, the water company is required to maintain some flow in the river below the reservoirs, and this compensation flow provides a fairly steady baseline flow in the river throughout the year. It is only normally exceeded if the reservoirs become full. On the upper reaches of the Douglas, the river bed is relatively steep, and consequently the river level can change quickly as a result of rainfall. As the river progresses to the west, the gradient lessens, and level changes occur more slowly. There are two locations on the river where water is abstracted to maintain levels in the Leeds and Liverpool Canal. On many sections of the river, flows are augmented by the discharge from sewage treatment works. Major treatment works are located at Horwich on the upper river, at Wigan Wastewater Treatment works in Lathom on the lower section, and at Skelmersdale on the River Tawd. Upgrades to the Wigan and Skelmersdale Treatment Works have been carried out, to improve the quality of the final effluent before discharge into the river system, while in Wigan, the sewage system has been improved, to reduce the amount of raw sewage discharged into the river by combined sewer overflows. In Standish, the pumping station at Chorley Road has been upgraded to reduce its impact on the river, while in Horwich, there was an ongoing scheme in 2014 in which volunteers walked the river to identify pollution points, which were then followed up by officers from the Environment Agency. Run off of nutrients and other pollutants from agricultural land has also been addressed through the Catchment Sensitive Farming project, run jointly by Natural England, the Environment Agency and the Department for Environment, Food and Rural Affairs. Another joint initiative between the Environment Agency and the Royal Society for the Protection of Birds has seen sea defences improved and of saltmarsh created as part of the Hesketh Outmarsh Coastal Realignment project.

The Environment Agency measure the water quality of the river systems in England. Each is given an overall ecological status, which may be one of five levels: high, good, moderate, poor and bad. There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of invertebrates, angiosperms and fish, and chemical status, which compares the concentrations of various chemicals against known safe concentrations. Chemical status is rated good or fail. The water quality of the River Douglas system was as follows in 2016. The section marked Ribble covers the tidal River Ribble and the lower 4 mile (6 km) of tidal River Douglas. Reasons for the quality being less than good include sewage discharge for most of the river, together with physical modification of the channel and poor nutrient management of agricultural land on the lower sections. Section Ecological Status Chemical Status Overall Status Length Catchment Channel 8.8 mile (14 km) 17.78 square miles (46 km2) heavily modified 5.9 mile (9 km) 3.64 square miles (9 km2) heavily modified 5.8 mile (9 km) 6.65 square miles (17 km2) heavily modified 15.3 mile (25 km) 28.85 square miles (75 km2) heavily modified heavily modified