DEVELOPMENTOF IRRIGATION WATER DISTRIBUTION DECISION

SUPPORT TOOL FOR MWEA IRRIGATION SCHEME

Mohammed Abdullahi (PhD)-Technical University of Kenya

Benedict P.O Owilla-MIAD Dennis Okinyi -MIAD

Content

• Background• Objectives• Research Methodology• Reconnaissance Survey Results• Irrigated Area Mapping Using LANDSAT• Water Demand Calculation Module• Remaining work

Background

• In an effort to increase food production and create employment, the government has embarked on a programme to – develop new irrigation scheme,– expand and/or rehabilitate the old ones.

Scarcity of Water Resources

• There is increasing competition for the scarce water resources by various sectors in the country notably between agriculture, industrial and municipal.

• With the expansion of irrigation schemes competition within the agriculture sector has intensified hence the need to improve water productivity

• Large scale irrigation schemes typically suffer from unequal distribution of irrigation water

– unreliable deliveries of water due to either lack of a distribution plan or

– difficulties in implementing one where available.

• In 2007, the Water Resources Management Authority introduced charges for water use in the agricultural sector,

• this meant that each scheme will pay for the amount abstracted/pumped irrespective of the irrigation efficiencies. – Thus there is great incentive to improve the water

use efficiencies since this will translate to lower charges and hence savings for the farmers.

• Irrigation infrastructure in Mwea Irrigation Scheme has been rehabilitated by the National Irrigation Board in the last few years– improved conveyance efficiencies

• the next critical step in improving the overall scheme efficiency is to improve the decision making process in water distribution management – this tool goes a long in aiding the achievement of this

goal

• The Irrigation Water Distribution Support tool will enable staff and farmers to understand– the scheme water requirement at various stages in

the growing season,– the available water resources – and the best way to distribute it.

OBJECTIVES • Determine the irrigated area for the Mwea Irrigation Scheme

using Remote Sensing • Determine the seasonal irrigation water requirement for the

Mwea Scheme

• Develop a simple yet versatile irrigation water distribution support tool for each scheme that links demand to supply

• Select and calibrate water measurement facilities to be used together with the tool developed above.

MethodologyData Collection and reconnaissance survey

Remote Sensing data analysis (Irrigated area)

Irrigation Typology Module

Water Demand Calculation Module

Water Resources Assessment Module

Irrigation Water Distribution Module

Reporting Module

Flowchart of Development of Irrigation Water Distribution Support Tool

Legend

Main Module

Progress so far

Scheme Reconnaissance Survey

• Meteorological and River Discharge Data collected

• Scheme Main, Branch canals, intake points mapped

• Lined and unlined canal distance quantified• Number and condition of water measuring

facilities assessed

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TBC2

TBC3

T8T7

T5

H2

H6

w4

W7W7

T25

T23T22

T11T19

T18T16

T20

CP4

H20

M17

M11

TBC1

TBC4

TBC2

W6-W5

M12 B

M12 C

TBC1A

T2- T3

Ndekia

w7-K10

M9-M10

TBC1AB

Kianugu

T20-Dam

T9-Keriko

T16 LowerT17 lower

TBC4-TBD1

Marura A

Ndekia TwoNdekia Two

K4 OfftakeK5 Offtake

K6 Offtake

KI Offtake

H5-Gitumbi

End of LC1Head Works

K9-K6-K7-K8

M14-M15-M16

K2,K3Offtake

TBC3-TBC4-H2

H18-Ciumbiri

Women Project

T4 offtke 1

Kandongu/Ngothi

MIAD-Pilot farm

T16 Lower part

T13 offtake # 1

T23-T25 Extension

Possible Rec Weir

T12-Kari-Jua Kali

Nyamindi headwork

Rubble weir intake

Ndekia One-Offtake 2Ndekia One-Offtake 1

H4-Gitumbi Extension

M9-M10 suppl offtake

Ndekia four-Offtake 1

T16, T14 Jua Kali ext

Ndekia four-offtake -3

Ndekia Three-Offtake 2

H3-Mbui Njeru jua kali

M13/M12A/Muga Kandongu

H19-Ciumbiri 2-Kiandegwa

T16, T13 offtake Junction

T4 Offtake 2 (+ Kari Pipe)

Ndekia four-Offtake with spring

T5

T22T20

CP5

CP6

CP4

H6-8

Marura A

4DA10 G.P

CP 1 & CP 2

K2,K3Offtake

W6-W5 Cippoleti

Possible Rec Weir

H20-Parshall Flume

Ndekia One-Offtake 1

NBC2 Rectangular Weir

MIS Canal and Offtake Network Map

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LegendX Off_takes_Locations_MIS

Canal_Network<all other values>

IdLined Headrace

Lined Link Canal

Unlined Main canal

Lined Main Canal

Lined Brach Canal

Unlined Branch canal

River

<all other values>

Measuring StructureExisting

Potential Site

0 0.8 1.6 2.4 3.20.4Kilometers

Note: This map is based on Field Survey done on Nov. 18-22, 2013 by Mohammed Abdullahi

Number of Water Measuring Facilities

Type Number

1 Rectangular Weir/Cippoletti/Drop Structure

13

2 Parshal Flume 2

3 Broad Crested Weir 5

4 Canal locations with good gradient 4

Total 24

ConditionCondition Number

1 In working Condition 5

2 Requires gauge and calibration (head to discharge)

12

3 Require repair, gauge and calibration 7

Total 24

Main, Link and Branch Canals

CanalTotal

Length Lined Unlined

Name Abbreviation km km % km %Nyamindi Headrace NHR 0.85 0.85 100.00 0.00 0.00Link Canal 1 LC1 7.18Nyamindi Main Canal NMC 4.61 4.61 100.00 0.00 0.00Nyamindi Branch Canal 1 NBC1 7.40 5.11 69.05 2.29 30.95Nyamindi Branch Canal 2 NBC2 4.41 1.30 29.48 3.11 70.52Nyamindi Branch Canal 3 NBC3 3.40 0.00 0.00 3.40 100.00Thiba Main Canal TMC 11.41 8.21 71.95 3.20 28.05Thiba Branch Canal 1 A TBC1 A 2.08 Thiba Branch Canal 2 TBC2 7.24 0.00 0.00 7.24 100.00Thiba Branch Canal 3 TBC3 4.86 0.00 0.00 4.86 100.00Thiba Branch Canal 4 TBC4 12.91 2.40 18.59 10.51 81.41

Remote Sensing data analysis (Irrigated area)

The Irrigation command area is critical to calculating Scheme diversion requirement– The Mwea Irrigation Scheme has undergone

expansion since late 1990’s – Irrigated area keeps fluctuating seasonaly due to

availability of irrigation water among other factors

Determination of Irrigated Area

-The LANDSAT offers an inexpensive and relatively accurate method for determining the irrigated area.• It has a spatial resolution of 30m and

temporal resolution of about a month

– Visual analysis of LANDSAT scenes between 2000 and 2013 showed that 2013 had the biggest irrigated area.

METHODOLOGY•Two LANDSAT 8 Scenes for 2013 Short Rain Season were available just before the rainy season started, Late September and Late October. •Late October (30th October) was selected since

Most of the scheme were cropped and easily identifiable

•There are up to 11 bands in each scene, but of importance to this exercise is Band 4 (Red), and Band 5 (Near Infra red) .

•In order to bring out a good contrast in the vegetative index the division of band 5 over four is used(Konduris et al, 1998).

•Next since the Landsat scene is wide the area of interest (Mwea) and its environ is clipped

•Using an colour enhanced scene for October 30th, manual digitization of the irrigated units boundary was done since the automatic digitization didn’t produce clear boundaries.

•Manually produced units were named

•Area of each unit calculated using GIS software

CALCULATION OF IRRIGATED AREAS

Gross AreasUsing GIS software the areas the digitized polygons were calculated to give the gross areas (includes on farm infrastructure such as roads and canalsNet Irrigated areasThe roads & Canals were estimated at 6% as explained in the next slides. This was deducted from the gross areas to give net area

Calculation of Net Irrigated area

FIELD MEASUREMENTS

NB: 1. Length is an average of at least four measurements at different places. 2. Middle (bare section) of road, AV = 6.2 m

Unit Description Length (m)

M9 Entire road from drain to drain 9.73

M10 Entire road from drain to drain 9.7

M9 Feeder bunds 0.85

M10 Feeder bunds 1.1

M9 Drain bunds 0.83

M10 Drain bunds 0.72

Scheme Irrigated Area (2013 Short Rain Season)

Gross Area (ha) Net Area (ha) Net Area (acres)LANDSAT DELINEATED AREA

11,149.00 10,703.04 26,757.60 OFFICIAL DOCUMENTED AREA

_

7,673.20 19,183.00 DIFFERENCE _

3,029.84 7,574.60

Comparison of Irrigated Area (At Section Level)

Section (Check Point) Landsat Delineated Area (ha)

Official Area (ha) Difference (ha)

Tebere (CP.1) 1818.24 1316.4 501.84Kainugu (CP.1) 136.32 160 -23.68Ndekia (CP.2) 1296.96 434 862.96Mwea (CP 3, CP.4) 1534.08 1270.8 263.28Ciurukia, Kandongu (CP.3,CP4) 1101.12 858.8 242.32Thiba (CP. 3, CP. 4, CP.5) 1706.88 1315.4 391.48Wamumu (CP. 5, CP.6) 1230 1007 222.56Karaba (CP.7, CP. 8, CP.9) 1477.44 1118.4 359.04T20, Kiamanyeki (Rubble Weir) 387.84 367 20.64

This differences may be as a result of:-Wrong unit boundary,-Underestimation of official area: New

extensions not accounted for.To be confirmed during “ground truthing”

Causes of Area Differences

Water Demand Calculation Module

Data Needs for this Module

• Irrigated area under at each water measuring structure (Check points)

• Water requirement components Puddling/rotavation water requirement ET Field Losses Canal/Section losses

• Other parameters (no of tractors & rotavation rate…)

Irrigated area

• The water distribution calculation sheet picks up the irrigated area under each point from the cropping plan using lookup function =IF('Cropping Plan'!

$D$4<Water_Requirement_Check_Points!$A8, IF('CroppingPlan'!$F$4>Water_Requirement_Check_Points!$A8, 'Cropping Plan'!$C$4,0),0)

Water requirement components

• ET-Calculated using PENMAN Montheith and historical meteorology data

• Rotavation requirement 250mm (Mohammed & Tanaka 1995)

• Field Losses 2mm (Van Gessel 1980, Mohammed & Tanaka 1997)

• Section/canal losses 0.4mm (Mohammed & Tanaka 1995)

Remaining Work

• Ground truthing of Landsat irrigated area maps

• Development of Remaining modules and documentation

• Testing, Training and Deployment

Thank you