98
B
mm
0 < 1400
8
1400·1600
1600·1800
1800·2000
2000·2200
2200·2400
•
~ 2400
Fig. 6. Mean annual evaporation over South Africa (adapted from Department of Water Affairs, 1986).
600
500
400 .. _ .. _._._ ..... - ......... - ........ - -... - - •.. - .. - ............ ---.--..•
E
E
' - '
...J 300
~ z
~
200
100
o a
10
20
30
WEEK
40
50
1221 YEAR81 82
~ YEAR8283
WJ YEAR8384
o YEAR8485
o YEAR8586
gx:j YEAR8687
II!i!i!l!! YEAR8788
II!I!i!iI YEAR8889
~ YEAR8990
~ YEAR9091
Fig. 7. Cumulative rainfall at Bloemfontein over ten seasons from 1981 to 1991.
Inundation versus rainfall in Rain s Vlei pans
Plotted against volume per rainfall episode, a curvilinear relationship resulted (Fig. 9). Below 20 mm of rain
no inundation resulted because the water was soaked
up by the dry earth and no surface flow was possible. Above about 80 mm of rain the pan was full and
it overflowed resulting in the flattening of the graph,
so inundation always lasted less than 20 days because
B
mm
0 < 1400
8
1400·1600
1600·1800
1800·2000
2000·2200
2200·2400
•
~ 2400
Fig. 6. Mean annual evaporation over South Africa (adapted from Department of Water Affairs, 1986).
600
500
400 .. _ .. _._._ ..... - ......... - ........ - -... - - •.. - .. - ............ ---.--..•
E
E
' - '
...J 300
~ z
~
200
100
o a
10
20
30
WEEK
40
50
1221 YEAR81 82
~ YEAR8283
WJ YEAR8384
o YEAR8485
o YEAR8586
gx:j YEAR8687
II!i!i!l!! YEAR8788
II!I!i!iI YEAR8889
~ YEAR8990
~ YEAR9091
Fig. 7. Cumulative rainfall at Bloemfontein over ten seasons from 1981 to 1991.
Inundation versus rainfall in Rain s Vlei pans
Plotted against volume per rainfall episode, a curvilinear relationship resulted (Fig. 9). Below 20 mm of rain
no inundation resulted because the water was soaked
up by the dry earth and no surface flow was possible. Above about 80 mm of rain the pan was full and
it overflowed resulting in the flattening of the graph,
so inundation always lasted less than 20 days because