1 200 000
1 000 000
800 000
R ² = 0.9799 600 000
400 000
200 000
0 50 % 55 % 60 % 65 % 70 % 75 % 80 % 85 % 90 % 95 % 100 %
SAPWAT |
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Figure 20 The SAPWAT4 table Kcb data curve , the observed data and the seventh repeat proposed Kcb growth curve based on observed data of lysimeter measured ETc data for peas planted on 27 June 2001 at Kenilworth near Bloemfontein
Figure 21 The SAPWAT4 table Kcb data curve , the observed data and the first repeat proposed Kcb growth curve based on observed data of lysimeter measured ETc data for maize planted on 17 December 2004 at Kenilworth near Bloemfontein
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Figure 22 The SAPWAT4 table Kcb data curve , the observed data and the fifth repeat proposed Kcb growth curve based on observed data of lysimeter measured ETc data for maize planted 17 on December 2004 at Kenilworth near Bloemfontein
Small irrigation dam water balances
Some users of SAPWAT3 , mainly from the Western Cape , have asked for the inclusion of an irrigation dam water balance module . Their problem stems mainly from the request that a farmer or group of farmers who use small irrigation dams to store runoff water during the rainy winter season for use during dry summer , need to do a good planning of water use in order to let the stored irrigation water last for the summer season , especially if the winter rainfall was lower than normal .
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YIELD Assurance |
Yield m ³ |
Pump |
50 % |
1 081 384 |
146 100 |
55 % |
1 054 606 |
139 769 |
60 % |
995 574 |
119 802 |
65 % |
939 763 |
103 731 |
70 % |
909 043 |
95 452 |
75 % |
876 884 |
85 225 |
80 % |
835 953 |
76 946 |
85 % |
801 508 |
70 615 |
90 % |
767 562 |
63 310 |
95 % |
664 332 |
42 369 |
98 % |
598 372 |
29 707 |
Dam water balances requires hydrological calculations outside the scope of SAPWAT4 . SAPWAT4 assumes a stable and ample water source as default , but does provide the user with the facility to plan for situations where the source does not supply enough .
Feelers were put out to consulting engineering firms explaining the need of a small irrigation dam water balance model and requesting information about such possible development . It transpired that the engineering consultancy Schoeman and Partners of Brits had developed an Irrigation Models suite in Excel [ 1 ] which includes a small dam water balance module .
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This author agreed to participate in the SAPWAT4 development . An export module for SAPWAT4 farm level irrigation requirement data that could be used as an import by the Dambalance module was designed , tested and found to be successful for the purpose . The resultant dam yield assurance is indicated in the accompanying figures .
m ³/ yr
Yield analysis
Assurance
y = b + c1x + c2x ² b = 1205074 c1 = 65004 c2 = -664157
During the discussions Hennie Schoeman [ 2 ] , the author , indicated that his Irrigation Models suite will be made available free of charge to SAPWAT4 users who require it , provided that they either do a short course on its use or that he is satisfied that they will be able to use it .
SAPWAT4 is freely available from the Water Research Commission at wrc . org . za , or contact the publications section at patrickk @ wrc . org . za
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[ 1 ]
Copyright of Microsoft Corporation [ 2 ] hennie @ landuse . co . za
38
Acknowledgement
--The Water Research Commission for funding .
--The use of experimental results and climate data from the Water Research Commission project reports ( WRC Report Nos . 1089 / 03 and 1359 / 07 ) and the cooperation of the authors ( Ehlers , L ., Bennie , A . T . P ., Du Preez , C . C ., Barnard , J . H ., Dikgwatlhe , S . B ., Van Rensburg , L . D . and Ceronio , G . M ) which was extensively used for the building of the crop coefficient verification module .
--To Hennie Schoeman of Schoeman and Partners for advice and assistance in the design and description of this SAPWAT4 module .
--To all SAPWAT3 users who have advised , recommended and commented on potential improvements .
SABI | FEBRUARY / MARCH 2017
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FAO ( 2002 ) Crops and Drops . Making the best use of water for agriculture . Available : http :// www . fao . org / docrep / 005 / y3918e / y3918e00 . htm [ 2 December 2013 ].
This article is available online . All Graphics ( Figures ) are full size .
http :// www . sabi . co . za /
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