CO129-588-16 Water Supply- report on the Tai Lam Chung Valley Scheme 3-1-1941 - 3-1-1941 — Page 12

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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