CUT-SLOPE INSTABILITY AND ASSOCIATED SUB-WATERSHED DEVELOPMENT CARENAGE/CHAGUARAMAS, TRINIDAD
STANLEY RICH WHARTON
Ministry of Energy, Port of Spain,
Trinidad and Tobago.
Evaluation of cut-slope instability involves a multi-disciplinary approach that includes an analysis of the geomorphology
of an area. At mountain fronts in the Carenage/Chaguaramas area, the topographic expression is controlled by rock
structure which defines small catchment areas or sub-watersheds. The expansion of residential areas within these
sub-watersheds, and other human activities, severely impinge on the balance of nature and contribute to cut-slope
instability.
Three sub-watersheds along the Western Main Road, in the Carenage/Chaguaramas area slope Sub-Watershed Model based
on the morphology of forked topographic ridges was identified and used in the project design. The model was used
to predict the specific locations of debris and rockslides, and to evaluate the characteristics of these slope
failures which represent a hazard to road communication.
The approach to the study was divided into four phases: Sub-Watershed Analysis, Morphometric Analysis, Stereographic
Analysis, and Photo-Interpretation of spatial and temporal Sub-Watershed Development.
The data included: the area and orientation of the catchment, slope analysis, and the evaluation of the relative
thicknesses of zones within the weathering profile; failed slope dimensions, height, angle, orientation and volume
of each failure; structural orientations of discontinuities and kinematic analysis; and aerial photo-interpretation
of hillslope development within sub-watersheds over a 32 year period.
It was found that slope failure activity was associated with:
1. the specific locations within sub-water sheds; debris slides occurred at the base of the catchment area, slopes
and rock slides at the base of the divide slopes;
2. the size of sub-watersheds; the largest sub-watershed wsi experienced the highest number of slope failures;
3. deeper weathering zones within the catchment area than the divide areas: debris slides occurred in residual
soils within the catchment and rock slides in weathered rock on the divide slopes; debris slides were involved
with large volumes of material
4. preferred foliation, joint and slope orientations: mean slope N67 W41oS and mean foliation N79E 4105; joint
orientations showed a bimodal distribution trending generally SW and NE.
5. irresponsible deforestation of areas within the watersheds for cultivation purposes, along with the development
of the upper sub-watershed divide and catchment areas for housing and road construction.
The identification of a hillslope Sub- Water-Model was useful for the evaluation of factors that contribute to
slope failure. The method used in the pilot study provides an approach for landslide hazard prediction, prevention
and planning within sub-watershed areas in the hilly Northern Range.
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