rivers and the cutting of canals (known as Slots). This causes some of the greatest damage that the oil industry inflicts to the Fresh and Brackish water ecozones, and especially to the dynamic and spatially extensive ecotone where the two ecozones meet. The World Bank, in its 1995 report, identifies nine specific problems associated with canalisation. These are:
- destruction of fishing grounds;
- changes in soil salinity with negative effects on forest vegetation;
- changes in water flow patterns, disturbing patterns of erosion and sediment deposition;
- dredging temporarily increases muddiness and reduces the water's oxygen content–this harms fish stocks;
- during the rainy season dredging spoils can erode, making water muddy and sometimes poisonous;
- a short-term increase in the biochemical oxygen demand because of dredging material and waste from houseboats;
- reduced farm yields because of toxic substances in the dredging spoil;
- reduced farm yields because of flooding; and
- destruction of mangrove and fresh water swamp forests.
A location and access channel will be dredged to the required depth. A bucket dredger will be used to remove the topsoil, in order to enable a dredging barge to move in. Main dredging is done using a suction dredger. The dredged material is put on land. Dredged spoils will be up to 2.5m high.
SPDC Environmental Fact Book, 1993.
Also, it should be remembered, regular dredging and deposition of dredging spoil, often onto farmland, is a necessary part of maintaining access.
To facilitate exploitation of the Okoroba oil field Shell has needed to dredge and straighten the river, and to construct a canal (known as a slot) beside Okoroba to provide access to a capped well head...the slot ...drained the fresh-water creek upon which the village depended, replacing it with a stagnant body of brackish water (for the slot is a sort of cul-de-sac) which is useless for drinking and dangerous for bathing. Also the spoil from the slot was dumped onto farmland blocking the natural surface drainage and causing flooding. One of many statements made at a meeting in Okoroba in November 1993 sums up the situation: "agriculture is the basis of our wealth. Before Shell, the river was not as wide as today and we caught a lot of fish. They came and surveyed the land and we did not know what was happening. ...They cleared the river and drilled a well destroying the fishponds, etc and trees. They made a lot of promises: the hospital and toilet houses were destroyed, as were the burying grounds. They pumped out water and destroyed the farmland..."
From an ERA report presented in August 1994
