Afon Clywedog
{{About|1=the river in Powys|2=other rivers of the same name|3=Clywedog (disambiguation){{!}}Clywedog}}
{{Use dmy dates|date=January 2018}}
{{Use British English|date=January 2018}}
{{Infobox river
| name = Afon Clywedog
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| image = Llyn Clywedog near Llanidloes.jpg
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| image_caption = Clywedog at the base of Clywedog reservoir
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| subdivision_type1 = Country
| subdivision_name1 = United Kingdom, Wales
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| subdivision_type3 = Region
| subdivision_name3 = Mid Wales
| subdivision_type4 = County
| subdivision_name4 = Powys
| subdivision_type5 = Settlement
| subdivision_name5 = Llanidloes, Staylittle
|length_km=29.0
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| discharge1_location= Llanidloes
| discharge1_min =
| discharge1_avg = {{convert|2.26|m3/s|cuft/s|abbr=on}}
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| source1 =
| source1_location = Plynlimon, Powys, Wales
| source1_coordinates= {{coord|52.5411|N|3.7168|W|display=inline}}
| source1_elevation =
| mouth =
| mouth_location = River Severn, Llanidloes
| mouth_coordinates = {{coord|52.4508|N|3.5406|W|display=inline,title}}
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The Afon Clywedog is an upland headwater tributary of the River Severn in Powys, Wales. It is approximately {{Convert|29|km|abbr=on}} long and has its source on the flanks of Plynlimon and has its confluence with the Severn in Llanidloes. The annual rainfall over the catchment is between {{Convert|1737|mm|abbr=on}} and {{Convert|1836|mm|abbr=on}}.{{cite web|url=http://nrfa.ceh.ac.uk/data/station/spatial/54013 |title=54013 - Clywedog at Cribynau Spatial data |work= National Rivers Flow Archive |publisher=Centre for Ecology & Hydrology|accessdate=25 April 2016}}
River regulation
A large part of the upper catchment of the river is inundated by the Clywedog reservoir which stores water from the catchment, especially during the winter months, and releases it during periods of low flow to support the flow in the Severn so that drinking water may be abstracted downstream.{{Cite web |url=http://www.stwater.co.uk/leisure-and-learning/reservoir-locations/llyn-clywedog/*/tab/about/ |title=Severn Trent Water - Llyn Clywedog |access-date=11 May 2014 |archive-url=https://web.archive.org/web/20140512214243/http://www.stwater.co.uk/leisure-and-learning/reservoir-locations/llyn-clywedog/*/tab/about/ |archive-date=12 May 2014 |url-status=dead }} The management rules also enable the reservoir to maintain the reservoir below maximum level during the winter so that there is capacity to absorb flood flows to reduce the impact of flooding further down the main river.[https://books.google.com/books?id=VXzG9oSFTlsC&dq=Clywedog+reservoir+flood+mitigation&pg=PA546 Hydrology in Practice. Shaw E] The Afon Clywedog thus has a highly regulated flow with relatively high flow in dry conditions and reduced flow in wetter weather.
See also
References
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