"The total mean annual runoff is approximately 2400 million cubic metres per year." (www.csir.co.za/rhp/state_of_rivers/state_of_crocsabieolif_01/olif_eco.htm)

The mean annual rainfall falls in the range 500 mm in the Lowveld region, reaching 1000 mm in the mountains and reducing to 700 mm in the South in the Mpumalanga Highveld region of the water management area. The potential evaporation is well in excess of the rainfall.

The water availability in this sub-area is impacted on by coal mining. The mining process impacts on the natural hydrological system by disturbing the integrity of the overlying rock and soil strata resulting in increased infiltration and recharge of the groundwater system. This “additional” water, although of poor quality, represents extra water which can be utilised in the sub-area. The quantity of the “additional” water needs to be determined. The water volumes stored in the mine workings can also be utilised as dams during drought periods to augment the yield of the system.