The impact of tropical rainstorms on sediment and runoff generation from bare and grass‐covered surfaces: a plot study from Singapore

The characteristically short, intense rainstorms of Singapore occur throughout the year. The impact of such rainstorms on runoff and sediment generation from bare and grass‐covered slopes of urban Singapore is examined through observations made on an experimental plot for a representative sample of natural rainstorms. While the responses of the bare surfaces to the incoming rainfall are instantaneous and significant (runoff: up to 91 per cent of total rainfall), irrespective of the dimension of the rainfall, the grass‐covered slopes respond more slowly and gently (runoff: 4·8 per cent–17 per cent of the total rainfall). The sediment generating potential under the two types of landcover is closely linked to the short‐term intensities of the incoming rainfall, particularly on bare surfaces where high‐intensity rainstorms of less than 10 minute duration are capable of generating measurable sediment and runoff. The sediment discharge from the bare surfaces during the long construction period is not only controlled by the episodic heavy storms, but also to a considerable extent by the more frequent, low‐magnitude rainstorms, which contribute to a more sustained sediment movement. With a higher frequency of occurrence, such short‐duration, high‐intensity rainstorms have a significant impact on the sediment and runoff generation potential of the extensive bare surfaces at the construction sites in urban Singapore. © 1998 John Wiley & Sons, Ltd.