The study of ground-water levels and infiltration of rainwater in the steep natural slopes of Hong Kong

by Koo, Yuk-chan

(Uncorrected OCR) Abstract of thesis entitled 'THE STUDY OF GROUND-

WATER LEVELS AND INFILTRATION OF RAIWNATER IN THE STEEP NATURAL SLOPES OF HONG KONG I

submitted by Roo Yuk Chan , B.Sc.(En~.). H.K.U.

f.or the degree of Master of Philosophy

at the University of Hong Kong in July, 1978.

ABSTRACT

In Hong Kong, after the 1912 disastrous slope failures in which 185 slips oooured after three daYs of heavy rainfall,

variations in ground-water levels in some seleoted areas in the steep natural slopes have been monit,red, and on same of these slopes the water levels show a strong and rapid response to

rainfall.

In this research, field measurements of ground-water

levels, taken at a number of sites in the steep natural slopes of

Hong Kong during the period 1915 to 1977, have been analysed and correlated with daily rainfall reoords. The examination and

interpretation of the response in ground-water level reoords reveal

that as the down-slope. distanoe from the area oovered only with

natural vegetation increases, the peak response in the rise of

ground-water levels is of smaller magnitude and ocours at longer

elapses of time after rainfall. Henoe, variations in ground~water

levels in proteoted areas, after heavy rainfall, are due to the development of rainwater mounds in areas subjeoted to infiltration

of rainwater directly from rainfall or looal ooncentration of run-

off, and the subsequent down-slope movement of suoh rainwater mounds

beneath the protected areas.

A Hele-Shaw Model, consisting of two olosely-spaced

paralled plates through which a visoous fluid flows, is used to

demonstrate the unoonfined, unsteady down-slope movement of a fluid

mound on an inclined bed at slope angles of the order of 30 degrees.

1?? .. "???. -.??

o

~

I

From scaled model tests, the influence of a steeply dipping

impermeable bed on the response is briefly as follows.

For equal inclined distances measured down-slope from the souroe,

as the slope angle inoreases :

(1) The maximum rise in magn1 tude of the phreatio surfaoe

increases,

(2) The elapse in time before the maximUm rise of the

phreatio surfaoe deoreases.