ON THE DISSOLVED SOLIDS OF THE PONGOLO FLOOD PLAIN PANS

SUMMARY

The water retained in the Pongolo flood plain pans differs from that of the Pongolo River not only in having a higher TDS, but also in the composition of the solutes, which approximate to seawater in their equivalent ionic proportions at high concentrations. These solutes are shown to originate from very highly mineralised seepage water characteristic of soils overlying Cretaceous sediments of marine origin found elsewhere in South Africa. This feature of the soils of the flood plain precludes the use of irrigation seepage water to maintain the water levels in the pans, and stresses the need for the release of simulated floods from the Pongolo-poort Dam to flush the system if the present biological characteristics of the pans are to be maintained.