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Commencing from the structures at the head of the Tor-lonia tunnel, the black line , which forms the upper limit ofthe section coloured yéllow , represents the bottom of thelake , and the red line below the yellow the bottom of thecentral collector. This canal extends into the basin of the laketowards the East for a distance of 8 kilometres (4,96 miles)with a width of 15 metres (49.21 ft) at bottom, (see cross-section of canal, Plate V) and a slope of 0.000143 per metre. Ata distance of 8 kilometres from the weir dam at the head of theregulating basin, there is another dam with sluice gates or lock Kwhich forms the communication between the central collectorand the storage basin , into which the low r est part of the bedof the lake has been converted. We shall give further details ofthe storage basin in the description of Plates XVI and XVII.

Before reaching the lock K, at a distance of 3000 metres(3279 yds) from the regulating basin, the letter g marks thespot at which the secondary collectors issue into the principalone; it is here that the available waters of the basin are to beutilized as motive power with a fall of 5 metres (16.4 ft). Weshall speak of these also in the description of the above men-tioned Plates.

Beyond the lock K the central collector extends 4 kilo-metres (2.48 miles) further into the storage basin, being in all12kilom.long. Its bottom is in this part 2 m .05 (6 ft 8in) lower thanthe surface of the ground. In the last 4 kilometres of itscourse, the central canal gains in width what it loses in depth,in order to have always the same maximum delivery as thetunnel ; its slope is different from that of the first eight kilo-metres, being only 0 m .0001 per metre (1 in 10000).

Finally at a distance of 800 metres (874 yds) from the endof the central canal and continuing still to advance along theprolongation of its axis, the dike of the storage basin is again metwith. The height of this dike is calculated so as to enable thebasin to hold a depth of. 3 m ,60 (11.8 ft) of water, measuredover the greatest depression of its bottom, which is, as weknow, 14 m ,65 (48.064 ft) above datum. ;