Water, Sewage & Effluent May-June 2017 - Page 19

Structural damage to stormwater canal. and increases the flood levels as the river morphology changes,” he said. “Debris from the river banks and within the catchment makes the situation worse by blocking the watercourse at the crossings, restricting the flow, and resulting in further silt deposition.” He highlighted under-designed road crossings and formalised drainage structures as further aggravating factors, as these restrict water flow. “These structures may have been appropriately designed in the past, but the Water Sewage & Effluent May/June 2017 required for a development. As development shrinks the areas of permeable ground, more stormwater discharges into the river during rainstorms. This raises the levels of energy in the river — levels that exceed its natural capacity — causing erosion and instability of the banks, excessive loss of soil, and the deposition of this soil at man-made structures and bends in the river. “This results in siltation of the river bed, which decreases the flow capacity 17