But the great reservoir known as Lake Vyrnwy, which supplies Liverpool with water, is equal in size to Bala; and the chain of four artificial lakes constructed by the Birmingham corporation in the valleys of the Elan and Claerwen covers a large area in west Radnorshire.
There are several lakes: that of Bala being the largest, except the old lake of Vyrnwy, reconstituted artificially to store the rainfall for the water-supply of Liverpool, 68 m.
The Vyrnwy is tributary to the Severn; but north of it the streams gather into the Dee, and flow eventually northward.
In the construction of the Vyrnwy masonry dam Portland cement concrete was used in the joints.
Silurian formation, used' in the case of the Vyrnwy dam, had an ultimate crushing strength of from 700 to 1000 tons per sq.
Such stones may be of any size subject to each of them covering only a small proportion of the width of the structure (in the Vyrnwy dam they reached 8 or 10 tons each), and the spaces between them, where large enough, must be similarly built in with smaller, but always the largest possible, stones; spaces too small for this treatment must be filled and rammed with concrete.
The first masonry dam of importance constructed in Great Britain was that upon the river Vyrnwy, a tributary of the Severn, in connexion with the Liverpool water-supply (Plate I.).
The Bear Valley dam, California, is the most THE Vyrnwy Valley, Montgomeryshire, June 1888.
Lake Vyrnwy, December 1889.
From Thirlmere in Cumberland, in the case of Manchester; from the river Vyrnwy, Montgomeryshire, a tributary of the Severn, in the case of Liverpool; and from the rivers Elan and Claerwen in Radnorshire, tributaries of the Wye, in the case of Birmingham.
Lake Vyrnwy, completed in 1889, includes a reservoir which is still by far the largest in Europe.