THE YAN YEAN RESERVOIR, VICTORIA. 3 
about 8 miles in length, partly natural and partly paved, which comes from 
the Wallaby Creek Weir, a dam at almost a thousand feet greater altitude. 
The water of the Wallaby Creek Weir is in a like manner partly brought 
along an open paved channel from a still higher dam, the Silver Creek Weir, 
distant about 5 miles. 
À constant supply of water along the aqueduct to the Yan Yean Reservoir 
is assured by the dams at Toorourong, Wallaby Creek, and Silver Creek. 
The catchment area for the two upper dams is 11,500 acres, and the outflow 
streams find their way into King Parrot Creek. The catchment area of the 
Toorourong Reservoir 1s 10,500 acres, the water-supply from which is addi- 
tional to that along the open channel from the upper dams, and the outflow 
of the reservoir is the east branch of the Plenty River. 
The following records of the rainfall, although incomplete, indicate a great 
increase in the amount registered corresponding to a relatively small increase 
in altitude :— 
| 
Yan Yean. | — Toorourong. Wallaby Creek. Silver Creek. 
Altit. 400 ft. | А. 736 ft. Altit. 1717 ft. Altit. 1740 ft. 
| | 
| 
Catchment area | Catchment area | Catehment area 11.500 acres 
4500 acres. | 10,500 acres. 
( 1903. 29°03 ins, 36:85 ins. | 51:7 ins. 
Registered 
1904. 26:67 ,, 3375 ,, | 5639 ,, No records. 
rainfall 
1905. 2963 „ = — | — | 
| | | | 
As the chief part of the water-supply of the Yan Yean Reservoir (some 
six-sevenths of the total volume) comes along the aqueduct from the 
Toorourong Reservoir, which is in turn largely supplied from the Wallaby 
Creek dam, it is therefore derived from a large area in which the rainfall 
is considerably greater than that which actually obtains in the Yan Yean 
catchment basin itself. 
The full capacity of the reservoir is 6,400,000,000 gallons, and its average 
depth is a little over 24 feet. 
The geological formations of the entire drainage area are Silurian and 
Granitie. 'lhe more distant supplies come from the granite of Mt. Disap- 
pointment (2630 feet), about 8 miles to the north, and the rest of the 
drainage is on outcrops of Silurian. 
Some of the banks of the Yan Yean Reservoir are natural, others are 
stone-faced from below the low-level to above the high-water mark, and an 
embankment forms an artificial boundary at the south-west corner. The 
shores when gently sloping are weedy, but away from the margin the lake is 
fairly free from evident vegetation. 
B 2 
