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Eccup is an impounding reservoir north of Leeds, constructed in 1840 and enlarged from 1885-1897 with a 225m long earth (clay core) dam. It retains 6.4 million cubic metres of water at a depth of up to 19 metres. Top water level (TWL) is 114.68m AOD. The surface area of 77 hectares makes it the largest reservoir by area in West Yorkshire although Scammonden, being deeper, has a greater capacity.

Although it is fed directly by a few small streams, most of the water comes down from the Washburn Valley, supplemented by water pumped from the River Ouse. It is therefore classed as an “en-route” storage reservoir (ESR) by Yorkshire Water, similarly to Ardsley Reservoir (q.v.).

Abstraction to supply (to the Headingley water treatment works in North Leeds) is by pumps taking water from the south bank of the reservoir rather than by gravity from the dam end. This means the pipework arrangement is somewhat complicated, as these photos show.

The complexity was increased by the 2014/15 construction project that replaced the original bottom outlet through the dam with a syphon arrangement that takes water up and over the clay core to avoid having to penetrate the core itself. This was to meet a legal requirement to be able to draw down the water level at a rate of no less than 1m per day. Source: Link

The reservoir and the surrounding woodlands are a Site of Special Scientific Interest. The SSSI is designated for its importance to wildfowl in particular for its over wintering birds including goosanders.