122 The N.Z. Journal of Science and Technology. [Mar. 
same problems apply to other works now under consideration. At the 
present time (October, 1918) the inflow is sufficient on an average to 
maintain an output of energy from the power-house of some 27,000,000 
units per annum with a variation in lake-level of some 2-| ft.; but in 
order to provide for extensions of the power plant up to the limit of the 
present head works the present inflow must be augmented, and the 
readiest means of doing so is to divert a portion of the Harper River. 
This presents no difficulty, but when the capacity of the power plant is 
still further increased provision must be made for diverting the whole of 
the Harper River into the lake, and of utilizing and otherwise dealing 
with the flood-waters so as to keep the rise of level within limits imposed 
by the necessities of the case. 
D 66 shows in plan a configuration of the lake, the position of the 
various rivers which are or can be made tributary to it, the position of 
the present head works at A, and the effluent from the lake at D, where 
there is a weir provided with a gauge for measuring the overflow. The 
area of the lake is 14-J- square miles, or 400 x 10 r> square feet; the banks 
are steep, and the area is not much altered by a change in level. The 
method of developing the power is by means of a tunnel 20 ft. below 
