124 J0URN.1L OF THE DEPARTMENT OF AGRICULTURE. AuG., 1922. 



is being rapidly eroded, (a) by surface erosion by wind, (h) by suiface 

 erosion by water, and (c) by donga or sloot formation. The surface 

 erosion is the most dangerous, insidiously eating away the soil of the 

 Union, which is a definitely limited and irreplaceable quantity. This 

 being so we are morally and economically bound to conserve it. 

 Erosion by slooting is always evident, while surface erosion frequently 

 takes place without being easily noticed, but by removing great 

 layers of the country's most valuable soil and plant food, it is causing 

 enormous loss. The wind is similar in its action, removing first the 

 rich surface soil which has taken centuries to form. Sometimes it 

 bodily removes ploughed fields, but the greatest damage is caused by 

 the strong dust-bearing winds that sweep the country. AVhile water 

 carries the eroded material direct to the sea, the wind may carry it in 

 all directions, yet its ultimate destination is in the direction of the 

 prevailing wind of the dry season. 



In addition to surface erosion, and greatly assisted by it, pro- 

 ceeds the slooting of the country, that is, the cutting up of the veld 

 by runlets and gulleys, which eventually form the deep water courses 

 known as sloots or dongas, and which remove both soil and water. 

 The gradual deepening of these sloots increases the gradient of the 

 surface water on its banks, and innumerable branch sloots eat their 

 way back from the banks, and in this manner all the surface soil is 

 eventually removed in the vicinity of sloots, and the resultant 

 bareness produces an increased run-off. The latter running into the 

 sloots aids in the undercutting of their banks, increasing the size and 

 multiplying the number of the sloots. Thus the damage is accumula- 

 tive, and so it proceeds each year. 



Water which should have soaked into the ground to feed plants 

 and replenish the underground supply, is carried to the sea, and in 

 eroded areas, badly slooted, the level of the water table is continually 

 receding, constituting an economic loss, as the sinking of the water 

 table connotes greater labour in making available underground sup- 

 plies. The ever-increasing sloots with their accelerating ruu-ofi, 

 result in river floods, which may be exnected to increase in severity 

 with the years, but decrease in time of Bow, wbile periods of no flow 

 will naturally become proportionately longer. 



In this way irrigation enterprise, on which the country so greatly 

 depends, is hampered, frequently being made uneconomic owing to 

 tlie costly protective and other works needed to cope with high and 

 low floods, and as a consequence increasing the cost of producing food- 

 stuffs in this country. The remedial measure recommended is to 

 build reservoirs for the purpose of regulating the flow, but the silt 

 brought down reduces the useful life of the reservoir, and adds to 

 the cost of the scheme. There are parts where the silt carried down 

 by rivers is useful, but this is not always the case, as in some 

 instances the very fine silt chokes or suffocates plant growth, so that 

 its presence in water renders it unfit for irrigation, while in many 

 other cases coarse material brought down kills off all vegetation. 

 But the greater portion of the silt finds its way, unused, to the sea. 



The erosive power of water is enormously increased by concen- 

 tration and increased ^-elocity which are brought about by such factors 

 as climate, temperature, humidity of the air, the annual rainfall and 

 its intensity, composition of the soil, its situation, prevailing winds, 



