December 14, 2011

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Analysis of your system: what could you do…

ICID/History

Water Resources / Civil Engineering and Geosciences

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Pampa de Chaparrí, Peru

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Pampa de Chaparrí, Peru

• Arid Peruvian north coast

• Pre-Colombian civilizations

• Sicán, Chimú and Inca

• Between 900 AD and 1532 AD

• Abandoned in the 16th century

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Irrigated areas

• Three areas irrigated from Río Chancay

• One area from Río La Leche

• Río Chancay diverts to Río La Leche

• Chaparrí derived about 1/3 of the discharge

RiverCanal

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Discharges of Río Chancay

0

500

1000

1500

2000

2500

3000

3500

1914

/15

1916

/17

1918

/19

1920

/21

1922

/23

1924

/25

1926

/27

1928

/29

1930

/31

1932

/33

1934

/35

1936

/37

1938

/39

1940

/41

1942

/43

1944

/45

1946

/47

1948

/49

1950

/51

1952

/53

1954

/55

1956

/57

1958

/59

Year

mil

lio

n m

3

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Irrigation: when did it go wrong?

• Lower discharges

• Start of higher discharges too late

• But also

• End of higher discharges too early (in graph)

Rio Chancay in year with shortage(low flow from May)

0.00

20.00

40.00

60.00

80.00

100.00

120.00

8 9 10 11 12 1 2 3 4 5 6 7

Month

Q (

m3/

s)

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Irrigation: how often did it go wrong?

Water shortages:

• 70% cultivated: • 6 out of 45 years (less

severe)

• 80% cultivated: • 8 out of 45 years (1 to 3

months)

• 100% cultivated:

• 11 out of 45 years (severe)

70% cultivation

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

1914

/1519

16/17

1918

/1919

20/21

1922

/2319

24/25

1926

/2719

28/29

1930

/3119

32/33

1934

/3519

36/37

1938

/3919

40/41

1942

/4319

44/45

1946

/4719

48/49

1950

/5119

52/53

1954

/5519

56/57

1958

/59

Season

Riv

er w

ater

use

d (f

ract

ion)

May June July

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What about the canal system?(Hayashida 2006)

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Simplified to this:http://delftsoftware.wldelft.nl/index.php?option=com_content&task=view&id=110

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Three scenarios

Racarumi I Racarumi Ia Racarumi Ib Racarumi Ic

Racaru

mi

IIa Racaru

mi

IIb Racaru

mi

IIc

Inflow

Racarumi I Racarumi Ia Racarumi Ib Racarumi Ic

Racaru

mi IIa

Racaru

mi IIb

Racaru

mi IIc

Inflow

Racarumi I Racarumi Ia Racarumi Ib Racarumi Ic

Racaru

mi IIa

Racaru

mi IIb

Racaru

mi IIc

Inflow

A - Reference:- Inflow gradual- Inflow variable

B - Main system:- Both inflows

weir

C - Proportional:- Both inflows

weirs

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Reference layout and fluctuations

0

2

4

6

8

10

12

14

0 24 48 72

Hours

Dis

char

ge

(m3/

s)

RI RIIa RIIc

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Fluctuations with weirs

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

0 24 48 72

Hours

Rel

ativ

e d

isch

arg

e

RIIa prop RIIa main RIIc prop RIIc main

Low discharge, but highly variable

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Fit with reality?

A 900 hectares area in the upstream area shows a highly regular canal system.

In the middle area canals and fields are more variable in shape, although still fairly regular.

The area downstream appears as a patchwork of varied plots and canals.

(Hayashida 2006)

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Renault et al

FAO - MASSCOTE

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Procedure to describe and analyse

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18

19

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Bring back to this for the modeling

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The SOBEK scheme

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Detail in the schematization

Gate 1

Gate 2

Gate 3

Off-take

Emergency spill

Incoming canal

Ongoing canal

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Step 1 for your own design

Try to bring your system back to something similar to the image to the right: select the main features of your system, take a representative stretch/part

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Step 2 Develop a model in Sobek.

Please note that all values to be put in Sobek need to be known beforehand.

See the hints and tips on Blackboard.

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Step 3Run the scenario of a ‘typical day’ in the system.

Does the system function as planned on such a ‘typical day’?

Try to predict how your system would respond to several “what happens if…” scenarios.

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Improving and testing your system

• 1) Technicalities

• Can all the fields/tertiary units be irrigated?

• Is there a canal?

• Is the energy head available sufficient?

• Can all the fields/tertiary units be drained?

• Are the calculations applicable and correct?

• …

• 2) Functionality of the system

• Is it clear how the system has to function?

• Are the solutions selected suitable for the functions to be realized?

• How does a ‘typical day’ in the system look like?

• Does the system function on such a ‘typical day’?

• …

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What happens if?• 3) What happens if…• All or some tertiary units do not irrigate?• All or some tertiary units want to irrigate at the same time?• Other crops are grown?• Structures are damaged or reset?• The maximum rainfall event and no irrigation coincide?• There is no rainfall?• …• 4) Emergency scenarios: how vulnerable is the system?• Upstream users decide to take all the water?• Farmers outside the area want to irrigate?• A very dry year: minimum flows in the river are just half of mean

minimum flow?• …

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Storage in the system??

• Could increase operational flexibility

• Could decrease dependence on the canal system

• On what level?• Within the farm?

• Within tertiary unit?

• Within the secondary unit?

• In reservoirs?

• Or in canals?

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Boils down to hydraulic design of the (main) system

• Hydraulic flexibility• How does the system behave and respond?

• Operational flexibility• How easy is it to change operation and flows?

• Reaction time of the system• How quickly does the system transport the flows according to

the new setting?

• Unsteady flow conditions may govern your system!!!!

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For now: let’s move to room 1.97

• Do the Sobek tutorial, if you have not done already

• Check the two example Sobek schemes on Blackboard

• Play with them, change them, understand them

• I have an example scheme available for you to build into Sobek

• Goal: learn Sobek en learn what information your own design should contain in order to model it properly