Investigating Role of Vegetation in Protection of Houses During Floods

Flood flows have the potential to cause substantial damage to infrastructure, mankind, livestock and agricultural land which all stacks up to greatly affect the financial condition of the region. During 2010 Pakistan floods, more than two million houses were damaged partly or totally (Shah et al., 2013). To mitigate the extensive damage caused by floods, inland vegetation can act as a natural barrier to limit widespread inundation and dissipate the energy of flood. The study aims to minimize the destruction of houses by vegetation as a bio-shield to reduce the energy of floods flows.

Experimental study was conducted in a flume to figure out the role of vegetation in reduction of energy in flood flows in front of houses against different ‘vegetation densities’, ‘vegetation thickness’, ‘distance between vegetation and house’ and ‘flow conditions’. For a scale of 1/50, wooden cylinders having diameter of 10 mm were fixed in a staggered arrangement. Vegetation models were made against vegetation densities (G/d=1.09 and 2.25, G=spacing of each cylinder in cross-stream direction and d=diameter of cylinder), vegetation thickness (dn=1.8 and 3.8 No.cm, d=diameter of cylinder, n=number of cylinders in a stream-wise direction per unit of cross-stream width) and initial Froude number (Fr_o=0.85 and 0.92). In this phase of study, the house dimensions were kept constant, however the distance between vegetation and house (L_r) was varied to 3W, 4W and 5W, where W is the vegetation width.

On the upstream side of vegetation, the rise in backwater depth increased by increasing both vegetation density and thickness. Contrarily, on the downstream side of vegetation, an undular hydraulic jump was observed in between vegetation and a house. By increasing both the vegetation density and thickness, the energy loss increases. For constant vegetation conditions (G/d=1.09, dn=1.8, and Fr_o=0.92) and increase in house distance from 3W to 4W, the energy reduction increased from 2.5% to 8% which was further increased to 19% for another 1W increase in house distance. Thus, to minimize the structural damage, a structure must be located at a safe distance away from the vegetation where flow becomes sub-critical.

Keywords: Flood, Vegetation, Houses, Energy Dissipation.

Reference:

Shah, A., Khan H.M., Qazi, E.U., 2013. Damage assessment of flood affected mud houses in Pakistan. Journal of Himalayan Earth Sciences 46(1), 99-110.