Transcript
December 14, 2011
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Farmers and irrigation
Irrigation and Drainage CT4410
Maurits Ertsen
Water Resources Management
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What does the figure show?
An intake / outlet is not just a technical ‘thing’.
It is also a social ‘thing’: it creates social action.
And it is the result of social action.
Outlet structures in India (Mollinga and Bolding)
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Groundwater use in Pakistan
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Campo de Cartagena
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Original design
Pressurized system
Constant flow
Time measurement
Prepared for sprinkler, suitable for surface irrigation
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But, what happened?
Constant flow appeared to be less constant…
Two responses from farmers:
Water meters: from time to flow On-farm storage
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Proyecto Rio Dulce
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Tertiary unit CT3CT3
C2
C9C3 C5 C7
C4
C1
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The average farmer in CT3 irrigated about 7 hectares,
using a flow of 200 l/s for three hours,
thus putting on a hectare about 2.200 m3 (220 mm).
This same average farmer irrigated 2 times in the season.
Canal Mean Maximum Minimum
C2 1.2 2 1
C4 1.7 3 1
C5 1.9 3 1
C3 2 3 1
CT3 (Tertiairy canal) 2.1 6 1
C7 2.3 4 1
C9 3.3 6 1
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Comunero Flow max (l/s) Flow min (l/s) Min/max
C2 230 172 0.75
C3 235 198 0.84
C5 290 265 0.91
C9 238 122 0.51
C4 254 116 0.46
CT3 250 175 0.7
Responses:
Farmers irrigate longer or more often
Farmers decrease their irrigated area during the season
Farmers increase their irrigated area during the season
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Irrigation: water control
Irrigation and Drainage CT4410
Water Resources Management
December 14, 2011 2
What to do?
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Water control: Main issues
• Distribution: demand or supply
• Free demand or arranged demand
• Control: Upstream or downstream
• Type of (configurations of) structures to use
• Sensitivity and flexibility
Please note that water allocation
(and water rights) is a very important issue, but that we do
not discuss that now
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What is desirable on system level
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What can be selec-ted
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Proportional
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Proportional (splitted)
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What is this?
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Proportional, but arranged
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Variable (adjustable) flows: continuously
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Variable flow: intermittent
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Demand based, downstream control
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Which element supports downstream control and which element does not?
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Sensitivity
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Sensitivity
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Hydraulic flexibility
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Fluctuations in the system
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Examples
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Irrigation design
Irrigation and Drainage CT4410
Maurits Ertsen
Water Resources Management
December 14, 2011 2
Most of you worked a little mechanical on the irrigation needs. Looking at these from a slightly bigger distance shows that we have a cropping pattern that can be sustained on pre-sowing gifts and some additional irrigation later in the cropping cycle. Basically, in fall, things may become a little tricky. The rhythm of the cropping pattern suggests that you are dealing with an irrigation system that needs to give supplemental water, in addition to rainfall. The pre-sowing gift is likely to be one of the more important irrigation turns to consider.
Another issue is how to deal with water needs and water availability. Quite a few of you seem to confuse supply and demand management – which is a way to organize water allocation and distribution – with upstream of downstream control – which are hydraulic terms. I can have demand management with upstream control.
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Most of you show what the systems will look like. Not that many can clearly tell me what the system is supposed to do. I have not really seen any sensible arrangement of how water needs, water supply, canals and units are linked in terms of water quantities and timing of irrigation turns.
As your system needs to work in all kind of circumstances, you cannot base your design on a typical organizational model. Yet, you have to design a system with flows and controls, which is obviously somehow connected to an organizational model. A way to deal with this paradox is make it very clear what actions are needed in your system to ensure the functioning of the system. When should structures be opened or closed, that kind of issues. Who opens or closes them is almost irrelevant.
I have seen many different layouts, and with all of them I am not sure that you have the required head loss available to irrigate all fields. You need to check much more carefully whether the available energy levels and gradients allow the designs you want.
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Delivering water in a gravity system is a combination ofMatching needs with availabilityThinking of a smart irrigation rhythmThink of control actions and structures Fit the infrastructure in the topography
Linking water needs and water availability typically could be arranged with two strategies. Either one aims to ensure that the correct flow is on the correct place at the correct time – this requires pretty precise water control – or one ensures that the correct amount can be drawn on (almost) any place at the time needed, which decouples main system supply and water use. Obviously, storage will be needed between main system and water use.
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22 m
19 m
17 m
15 m
12 m
10 m in about 8 km
Gradient = 10/8000 = 0.00125
If I could use a canal gradient of 0.0001 for some 4 km, I need about 4000*0.0001 = 0.4 m of head
That leaves plenty of meters for storage upstream
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