ct4410: requirement and delivery

1

Irrigation: crops and water delivery

Irrigation and Drainage CT4410

Maurits Ertsen

Water Resources Management

December 14, 2011 2

Nevada Irrigation District

December 14, 2011 3

Nevada Irrigation District

December 14, 2011 4

A little history of NID

December 14, 2011 5

Transforming a ditch for mines to a ditch for irrigation

• High canals

• Continuous flow

• Reservoirs

• Water measurement in NID

December 14, 2011 6

The system

December 14, 2011 7

Water measurement• The miners inch

• Amount of water flowing through a surface of one square inch with a head of six inches.

• How many liters per second??

December 14, 2011 8

Controlling the canal

• What if a farmer does not needs his water?

• How to keep the constant head?

December 14, 2011 9

December 14, 2011 10


Water requirements

• How to determine water requirements?

• How to predict water demand?


Design problem

What cropping pattern do you take?

How correct is the ET calculation?

How correct is the ET and rainfall for the entire area?

How would you take into account “real” soil processes?

In other words: how to take into account heterogeneity?

Lankford (2004) discusses this.

How to use remotely sensed ET in DESIGN ??


How to irrigate crops?

• Pressurized system


Crop water requirement calculation: example

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 50 100 150 200 250 300 350 400

Days

Cro

p c

oef

fici

ent

Blue beans Start 1/1

Growth stage LengthCrop

coefficient Root depth

Days Meter

Initial 90 0.5 2

Development 90 >>

Mid 90 1.2 2

Late 95 0.8 2

365


ClimateRain ETo

mm/stage mm/day

Initial 90 5

Development 65 6

Mid 40 7

Late 80 5

CRW mm/day

Rain Eto kc Etg Etn

Initial 1.00 5 0.5 2.5 1.50

Development 0.72 6 0.85 5.1 4.38

Mid 0.44 7 1.2 8.4 7.96

Late 0.84 5 0.8 4 3.16

Remarks:

Assuming all rain is effective

Simplifying development stage

Significant numbers??


How to distribute that?

Flow for a farm of one hectare

mm/day m3/s l/s

Continuous 8 0.0009259 1

Continuous during day 8 0.0018519 2

Every week for 10 hours 8 0.0155556 16

Every week for 1 hour 8 0.1555556 156

Every month for 1 hour 8 0.6666667 667

1. Suppose I have 10 farms, how much should my canal carry?

2. Suppose I have 1200 l/s, how many farms can irrigate at the same time?

3. In case 2, how large would my surface area per canal become?


Your assignment

1. Calculate total water demand for a 1000 hectare area in the NID over a year.

2. Describe how this water would be supplied within the NID water delivery philosophy.

3. Calculate required canal flows at the intake for this 1000 hectare area.

4. Design the canal and outlets for this area, assuming that 20 farmers with each 50 hectares take water. Assume the canal being 10 kilometers long, with farm intakes evenly spread on one side.


Example information Trees 35% of total area Start 1/4

Growth stage Length Crop coefficient Root depth

Days Meter

Initial 140 0.9 2

Development 30 >>

Mid 150 0.95 2

Late 45 0.9 2

365

C r op c oe f f i c i e nt Tr e e s

0.000.200.400.600.801.001.20

0 50 100 150 200 250 300 350

Days

Kc


First, a little warning: physical reality needed


What did I do? Water requirements

-8

-6

-4

-2

0

2

4

6

8

10

1 31 61 91 121 151 181 211 241 271 301 331 361

days

mm

/day

ET crops Rain ET net


Water need in l/s and miners inches/farm

-100

-80

-60

-40

-20

0

20

40

60

80

1 31 61 91 121 151 181 211 241 271 301 331 361

Flow in l/s/10 Miners inch per farm


So why start per April 1??

• What if a farmer is an early vegetable grower?

• What if it does not rain in April?

• What if … ?

And the canal?

I know I will have fluctuating flows and that there is a need to maintain the same water level. So, one uniform flow calculation will not suffice. And I probably need some kind of water level control, and perhaps some spills.


Canal calculation

Not that straightforward designing a fitting canal and structures

canal AB

L 10000

H control 0.64

y 0.64

A 2.97

Q 0.66

m 1

v 0.22

R 0.51

s 0.0001

k 35

b 4

n 6.3

canal AB

L 10000

H control 0.71

y 0.71

A 3.34

Q 0.8

m 1

v 0.24

R 0.56

s 0.0001

k 35

b 4

n 5.6

Q increases:

canal AB

L 10000

H control 0.47

y 0.47

A 2.10

Q 0.4

m 1

v 0.19

R 0.39

s 0.0001

k 35

b 4

n 8.5

Q decreases:


Canal calculation

So probably we need water level controls somewhere.

Weirs?

Spills?

How many?

Dimensions?


And what if I have farmers with only fuit and vegetables????

0

1

2

3

4

5

6

7

8

1 31 61 91 121 151 181 211 241 271 301 331 361

Days

mm

/day

ET average ET fr and veg


What did I do?

Design discharge of 1 m3/s

Water depth of 1 meter, bed width of 2 meters

Slope of 1 in 10000

Side slope of 1

Roughness of about 45 (Strickler)


Result with inflow and all outlets are open.

NO LEVEL CONTROL


LEVEL CONTROL WITH WEIR

But as discharges downstream are very low and as there is no flow over the weir, no real improvement.


LEVEL CONTROL WITH WEIR

With extra discharge, there is flow over the weir.

Now it would be a matter of optimization…

14-12-2011

Challenge the future

DelftUniversity ofTechnology

Structures as the key of a system. Example Elche, Spain

Maurits Willem Ertsen

Delft University of Technology

Third largest city of the Autonomous Community of Valencia, Spain

Some 200,000 inhabitants

Irrigated agriculture

Huertas

Elche Palmeral: a little over 500 hectares (about 5,000,000 m2)

Landscape

Water

sources

Canal system

Canals

Walking along

the water

Walking further along

the water

Canals

What is

irrigation

about?

A structure as expression of water rights.

Remember?

1

Irrigation: main system layout

Water Resources Management

December 14, 2011 2

Ordering the disorder?

• You know water demand and water availability

• Therefore you know the potential area

• You know the smallest unit you have to deliver water to

• You know how you want to deliver water

• You have ideas about structures to be applied

• It’s time for the canals!

Goal: smallest unit

Source: river Goal: smallest unit

Goal: smallest unit

Goal: smallest unit

???

December 14, 2011 3

Main issues

• Layout of the main system• Every canal above tertiary units

• Determined by natural terrain and units

• Capacities of main system• Losses

• Rotation

• Statistics

• Behavior of the main system• Hydraulic flexibility

• Operational flexibility

• Reaction times

December 14, 2011 4

Layout

1 2 3 4 5 6 7 8 9 10 km

(contour lines in meters)

December 14, 2011 5

Layout

1 2 3 4 5 6 7 8 9 10 km

(contour lines in meters)

December 14, 2011 6

Capacities Q is known

Is total Q known???

Results in a Q here

But here????

Q at a certain level is not necessarily the

sum of all Q’s at lower levels.

December 14, 2011 7

Capacities: example 1

0

0,2

0,4

0,6

0,8

1

1,2

1 10 25 50 150 500 1000 1500 5000

Hectares

l/s/

ha

Proportional

December 14, 2011 8


0

0,5

1

1,5

2

2,5

1 10 25 50 150 500 1000 1500 5000

Hectares

l/s/

ha

Proportional, taking into account losses

December 14, 2011 9


0

0,5

1

1,5

2

2,5

3

3,5

1 367 732 1097 1462 1828 2193 2558 2923 3289 3654 4019 4384 4750

Hectares

l/s/

ha

Higher potential demands on lower levels


Capacities of the drainage system

Loads on the system: rainfall of 100 mm in 2 hours

• Assuming an irrigated area of 5000 hectares, this would give a volume of

5,000,000 m3

But: how to discharge this volume?

• In 2 hours: 694 m3/s

• In 5 days: about 6 m3/s

• Water will be stored in the system: on the fields, in the canals, in the soil (?)


In short: enough to decide.

Again……

• The load: how often does it occur? Probability?

• Design a drainage canal for a certain maximum Q with freeboard, and allow a higher Q at times (without freeboard)?

• Need to drain the irrigation supply? For example when nobody wants to irrigate?

• Furthermore: like with supply canals, the sum of all individual canals does not have to be the same as the maximum drainage discharge capacity.

Drainage capacities: decision time

Like with the peak demand for soil preparation!


Three rainfall scenarios

• Rainfall is showers (about every 10 to 15 days)

• Rainfall averaged over all the days

• Rainfall in showers with maximum shower at 100 mm/day

• All other parameters equal

• Irrigation at 100 mm per 10 days

• Silty loam

• Initial groundwater at 3 meter below surface


Rain in showers

0

20

40

60

80

100

120

1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361

Days

mm

0

0.5

1

1.5

2

2.5

3

3.5

m

Rain Irrigation Groundwater


Showers plus maximum

0

20

40

60

80

100

120

1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361

days

mm

0

0.5

1

1.5

2

2.5

3

3.5

Rainfall Irrigation Groundwater


Average

0

20

40

60

80

100

120

1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361

days

mm

0

0.5

1

1.5

2

2.5

3

3.5

m

Rain Irrigation Groundwater


And the runoff??

0

10

20

30

40

50

60

70

1 20 39 58 77 96 115 134 153 172 191 210 229 248 267 286 305 324 343 362

days

mm

Average Showers Showers maximum


Layout

Unit 1a

Unit 1b

Unit 2a

Unit 2b


Water levels in the system??

+ 13 m

+ 12 m

+ 10.4 m

+ 15 m

+ 10.4 + 0.20 + 0.20 + 0.20 = 11 m

+ 12 + 0.20 + 0.15 + 0.20 = 12.55 m

+ 13 + 0.20 + 0.20 + 0.20 = 13.6 m

+ 9.5 m


Thus required water levels are:

8

9

10

11

12

13

14

15

16

0 1000 2000 3000 4000 5000 6000


Design a canal (calculate) and determine control structures for offtakes/canal. Each offtake requires 1 m3/s in the peak season and may

need less or nothing during the remaining months.

Remember your NID task????


Your own designIssue 1: Water demand versus water availability

• Timing of the demand

• Timing of availability

• Amount of hectares to be irrigated

• Associated risk in balancing demand and availability

• Issue 2: Bringing water to the field(s)

• Continuously, rotation, fixed turns, days, hours, what flow is available for farmers?

• Issue 3: Grouping farmers or not - units

• Issue 4: Who decides?

• Water delivery

• Demand-based, request-based, supply-based?

• Upstream or downstream control?

• Issue 5: Water control structures

• Discharge control, measurement, fixed or adjustable, sensitivity?


Dimensioning your irrigation system

• Take a typical stretch of your system

• Determine required water levels along this stretch, taking into account requirements from smaller canals, structures etcetera

• Determine available energy gradient per section

• Design canals and structures (steady flow)

• Check, check and check! What happens when Q is lower, or higher, or whatever (steady flow).

ct4410: requirement and delivery

Education

crop water

water requirements10

water level controls

total water demand

kind of water level

canal ab canal ab y

fitting canal

canal calculationnot