NOTKS ON ll!ia(;.VTU»N IN" C.Vl'E ("OLUXV, 



81 



sea.suii, wliieh would generally I»e between Ma,y ami August, when 

 the seed should be sown. Some of the rivers of the colony, notablv 

 the Zak River in the north-west, almost invariably come down some- 

 time durini;' the period named, and large quantities of wheat are 

 grown. One gt)()d wetting before the seed is sown will usually jjro- 

 duce a crop, though if a second wetting can be obtained during the 

 period of growth it will be beneficial. 



In conjunction with this method of flood irrigation is practised 

 the constructitm of zaai dams (i.e. sowing dams). These are low earth 

 dams from 1 to 3 ft. or so high, thrown up to hold the flood-water on 

 the land after it has been spilled o\er from the river as alread}' de- 

 scribed. Such /aai dams may enclose areas up to 100 acres or more 

 according to the slope of the land, and will be so built as to prevent 

 the water spilled by the river in flood from draining back to it as the 

 flood falls. Sketch plan, fig. 2, shows an arrangement of a series ot 

 zaai dams alonj^ a river bank. 



''!'}'^^i'/c^y^^ 



^s\^ 



;A<^,/,.'i;,;.^/i,\\^>^,.. '■'■ 



Fig. 2. 



A is the temporary weir across the river channel which tui-ns the 

 flood-water out. B, C, D are zaai dams. These may be flooded by 

 passing the water down from one to another by means of temporary 

 gaps in the dams, or they may be fed by a furrow cut along either the 

 river bank or on the foot of the kopjes which bound the valley as 

 shown in dotted lines on the sketch, or the dams may be so built that 

 the flood-water is thrown over against the foot of the kopjes and flows 

 between them and the ends of the dams remote from the river, and so 

 fills each dam in turn. The last method would generally be effective 

 where the i-round fell away from the river banks as illustrated in 



In these dams the water is held on the ground as long as is con- 

 sidered necessary in order to soak it thoroughly, or if the water comes 

 x-ather early in the season it is held until sowing time approaches. The 

 water is then allowed to drain away, and the area which was submerged 

 fe sown with wheat. The cost of such flood irrigation is extremely 

 small, even with the /aai dams included. 



