-7-
12
34. The catchwaters would, in the absence of other arrange-
ments, intercept water which now supplies rice fields, and in
estimating the amount of water which can be obtained after their
construction, it has been deemed advisable to assume that the
catchwaters will only divert into the reservoir the runoff of
the monsoon period.
Rainfall.
35. A gauge has been established on the catchment area at
level 190 but only the readings for the year 1939 are available,
and it has therefore been necessary to estimate the average rain-
fall from the gauge at the Royal Observatory, and from the readings
of the gauges which have been placed on the Shing Mun Catchment
area.
36. There is a distinct relationship between altitude and
average rainfall, which is brought out by the following Table
showing the average annual rainfall for the years 1927-1939
inclusive.
Gauge.
Altitude.
Average Rainfall
(1927-1939)
No. 2 Shing Kun
1100
98.4 ins.
No. 1
Do.
1050
90.0
No. 3
Do.
675
85.1
Royal Observatory
103
80.2
37.
Taking into consideration the average altitude of the
Tai Lam Chung catchment area and the relationship between the
average rainfall for the years 1927-1939 and the long term average
as ascertained at the Royal Observatory, we have arrived at
figure of 87 inches for the probable annual average rainfall.
Relationship between Rainfall and Runoff.
38.
The gaugings which were made of the flow of the Tai
Lam Chung Råver extended over so short a period that no reliable