Good rains elude dam catchment areas
Rainfall closer to the coast is higher than inland
WHILE the perception exists that the soaking rains are helping relieve the serious drought conditions affecting eShowe and Melmoth in particular, very little of the welcome rain is falling in the catchment of the Goedertrouw Dam.
The Mhlathuze catchment area consists of nine quaternary catchments, of which only two contribute to the inflow of the Goedertrouw Dam – W12A and W12B.
Quaternary catchment W12A, which rises south of Babanango, has a total area of 623 square kilometres, an average annual rainfall of 876mm and average evaporation rate of 1 450mm per annum.
The second quaternary catchment has an area of 656 square kilometres, an average annual rainfall of 932mm and annual evaporation of 1 400mm.
The mean catchment run-off in million cubic metres for quaternary catchment W12A is 69 (12.6%) and for W12B it is 94 (16.2%).
Rainfall closer to the coast is higher than inland.
Rainfall figures for quaternary catchments W12E (1 350mm), W12F (1 285mm), W12H (1 039mm) and W12J (1 280mm) show that they receive the highest average rainfall.
Evaporation varies from 1 450mm in the west to as low as 1 300mm in the east, but is relatively low compared to the rest of South Africa.
This is, however, still higher than the average rainfall, meaning that there will always be a net loss from water surfaces in the Mhlathuze catchment.
Coastal rains
With the above in mind, it is easier to understand why rain in the towns of eShowe and Melmoth have little affect on the levels of the Goedertrouw Dam, even in good rainfall seasons.
Added to this is the fact that many more users have been added to the pipelines from the Goedertrouw Dam.
Besides eShowe and Melmoth extracting directly out of the dam, large rural communities have also been added with little provision for extra intakes.
Even if the area was not experiencing a drought it is doubtful that the Goedertrouw Dam would have kept pace with the demand.
The Goedertrouw supply is supplemented by the pipeline from the Tugela River and plans are being put in place to double the volume of water being harvested from the Tugela with the laying of a second pipeline.
Richards Bay supply
Mhlathuze Water abstracts water at the Mhlathuze Weir, 35km downstream of the Goedertrouw Dam to supply urban and industrial users in Richards Bay.
This is supplemented with water from Lake Msingazi (Richards Bay), Lake Cubhu (eSikhaleni), Lake Mangeza (Vulindlela) and Lake Nsezi (Empangeni and Ngwelezana).
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