Flooding problems

The flood problem has been accentuated.

Let us review what has happened in the industrialised countries [Fig 9.10]. 9.10 In all the industrial countries, rivers have suffered from forest clearance in the uplands, farm drainage in the lowlands and water-proofing in urban areas. Forest clearance took place on the hills, in the valleys and on the plains. This accelerated water runoff. Ploughing and drainage took place in agricultural areas. This accelerated water runoff. River channels were deepened, widened, straightened and fixed. This accelerated water runoff. Large new urban areas were rendered partially impervious, with roofing and paving materials. This accelerated water runoff. The capacity of washlands and flood plains to accommodate peak volumes was diminished by building upon them. Accelerated water runoff raised flood peaks. It then became necessary to place urban rivers into underground culverts or concrete canals, or to supplement their capacity with 'flood relief channels'. The net effect of all the changes was a dramatic increase in peak storm discharge. Embankments had to be built to prevent overtopping by floodwater. When these works are viewed together it is clear that they do not constitute a good use of public or private expenditure.