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