Some aspects of the form & origin of hillslopes in western New Territories, Hong Kong
An appraisal of research on hillslopes suggests that a morpholo-
gical approach is conductive to the explanation of spatial variations in
slope form and the making of inferences on slope development.
A systems approach is adopted in the study of hillslope forms in
four selected drainage basins in the western part of the New Territories,
Hong Kong. Map data and other relevant background information have been
used to justify the feasibility of the project design. A modified tape-
and-abney method has been employed to measure 100 hillslope profiles
selected at random in three of the four drainage basins. Specific
techniques have been developed to identify and describe quantitatively the slope units of the measured profiles.
Attempts at classification of the profiles reveal a dominance of
convex-straight-concave slope series in the sample basins and the
existence of a relationship between profile groupings and specific slope
units in a slope-angle mean-variance scatter. Analysis of variations in
decli vi ties downslope and across slope units suggests that significant
differences exist both at a within-basin and a within-profile level. An
examination of the collected data supports the contention that 'characteristic slope angles' at 380, 33? 260, and 210 occur in the selected
basins. A morphological model has been erected to represent tpe slope
uni ts in these basins. Incl uded in the model are an upper straight
slope unit, an upper convex slope unit, an upper rock face unit, a midstraight slope unit, a lower concave slope unit, a lower convex slope
unit, and a basal rock face unit.
The pattern of spatial variations in slope declivity has been explained at three different levels of aggregation. Basin orientation and structure are s1gni?cant factors at an inter-basin level; lithology, relief, and channel charac teristic s at a 'tn thin-basin level,; and vegetation cover at a within-profile level. In addition, differences in the amount of explained variation between basins are considerable. Under condi tions of dynamic equilibri urn, mean valleyside slope angle is well adjusted to other variables of the landsurface set but a lack of adjustment occurs when the system is dominated by disequilibrium forms.
Slope development is studied within both 'partial cyclic' and 'graded' time spans. In partial cyclic time, a decline in slope angle
is accorrpanied by an increase in the importance of the upper convex slope expressed as a percentage of the total slope distance. Slope retreat occurs locally where rapid down cutting as a result of ,tructural control is eminent. A model of slope development based on the input-output budget of the t colluvial sub-system' at slope-foot locations is tested against the collected data. The notion of 'threshold slope angles' in slope development in graded time is found to be applicable and the model is thus partially substantiated.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:slopes physical geography geology china hong kong new territories
Date of Publication:01/01/1972