S. BHALAI – Landslide susceptibility of Portland, Jamaica
Figure 1. Rainfall-induced landslide (November 2005) at London along the Seamans Valley to Moore Town Road, Rio Grande Valley, in weathered volcanic rock and shale. Classified as a rock slump–debris/earth flow. Damage included blocked road, four houses obliterated along with personal effects of occupants, light pole toppled and water main severed. (A) View up-slope of landslide (left-hand side facing the landslide). The scarp is the source area for the material. Perched groundwater emerging from the landslide body results in the spring. (B) View along road looking towards Moore Town (right-hand side facing the landslide). The spring in (A) has eroded a channel in the road. Unstable debris continued blocking the road as the material settled. The partly stable boulder in the foreground threatened road users. The inset shows the size of the boulder compared to the size of a man. (C) Remains of houses destroyed by the landslide (toe-area of landslide). Three of the obliterated houses were at this location; only two are visible. Note the toppled electrical pole. [S. Bhalai, Dec. 2005 and R. Green, Nov. 30, 2006].
Figure 2. Rainfall-induced landslide at 4 Red Hassle Road between Port Antonio and Breastworks. Rainfall period Nov. 19 – 25, 2006. A: View from main road at base of landslide; note that the house has been mangled with the landslide debris. B: Side view of destroyed house. The body of a woman that died was dug from the doorway of this partially intact bedroom (marked by arrow). [R. Green, Nov. 30, 2006].
Eastern Jamaica receives on average 500 cm of rainfall annually with Portland receiving more rainfall than any other parish. During the period of rainfall from January 3 to 4, 1998, Portland received between 200 mm and 300 mm of rainfall. Many landslides were triggered causing severe damage and destruction to agriculture, buildings, roads and infrastructure. Thirty-five houses were damaged and 25 were destroyed. Damaged roadways total 1.27 km and 0.8 km was destroyed. Of the total damage estimate of JA$384.2 million (1998 dollars), 60% or JA$231.1 million was accountable to landslide events (Harris, 2002). Landslides continue to cause large economic losses through damage of property and infrastructure; unfortunately sometimes lives are lost (Figures 1-5).
Figure 3. Composite showing break-away at Section, Newcastle to Buff Bay main road. The source area of the landslide is continually retreating, constantly destroying the footpath cut on the left. At the extreme bottom-right-hand corner of the plate is the remediation gabion works under construction (thick arrow). Informal communication with resident in 2006 revealed that this installation will cost $3 million. [S Bhalai, Aug. 2006]