This exercise how to practice CROPWAT for irrigation scheduling

1. Exercise CROP WAT ON IRRIGATION WATER
REQUIREMENT AND SCHEDULING AT BELES
SUGAR DEVELOPMENT PROJECT
Arba Minch University
Institute of Technology
School of Graduate Studies
Department of Water Resources and Irrigation Engineering
BY Hunda Tolina
September, 2019

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Table of Contents
LISTS OF FIGURES AND EQUATIONS..................................................................................... 2
1. INTRODUCTION ...................................................................................................................... 3
2. DESCRIPTIONOFTHE STUDYAREA .................................................................................... 5
2.1 Location ................................................................................................................................ 5
2.2 Climate.................................................................................................................................. 6
2.3 Command Area ..................................................................................................................... 7
2.4 Diversion Head Works and Irrigation System...................................................................... 7
2.5 The Command Soil ............................................................................................................... 8
2.6 Methods................................................................................................................................. 8
3. RESULTS AND DISCUSSION ............................................................................................... 10
3.1. Secondary data used........................................................................................................... 10
3.2. Irrigation Schedule............................................................................................................. 10
3.2.1. Depth of irrigation application.................................................................................... 10
3.3 Procedure of CROWAT...................................................................................................... 12
4. CONCLUSIONS AND RECOMMENDATION ..................................................................... 19
LISTS OF TABLES
Table 1: Tana abeles metrological data........................................................................................... 6
Table 2: rainfall data ....................................................................................................................... 7
Table 3: Slope classes of the irrigation command area................................................................... 7
Table 4: Beles Soil Area Coverage................................................................................................. 8
Table 5: Description of sugarcane (KC) ....................................................................................... 10
Table 6: Net and gross depth of application ................................................................................. 11
LISTS OF FIGURES AND EQUATIONS
Figure 1: ETo of sugarcane at Beles...................................................................................................12
Figure 2: Graph representation of ETO ..............................................................................................13
Figure 3: Effective Rainfall of pawi station ........................................................................................13
Figure 4: description of sugarcane coefficient .....................................................................................14
Figure 5: soil moisture content and available water content of Beles ....................................................14
Figure 6: CWR representation ...........................................................................................................16
Figure 7: Graphical representation of irrigation required......................................................................16
Figure 8: irrigation scheduling...........................................................................................................18
Figure 9: Graph Representation of irrigation scheduling......................................................................18
ETc = Kc * ETo (Equation 1) ..............................................................................................................9
Dn = TAW * ρ * Dr (Equation 2)........................................................................................................9
I = Dn/Etc (Equation 3).....................................................................................................................9

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1. INTRODUCTION
Improved water management through precise crop water requirement determination is needed to improve
the efficiency of water use in agricultural production. As a result, appropriate irrigation scheduling which
can lead to water saving, improvements in the yield and income can be designed (Mengistu et al., 2009).
Good irrigation water management increase yields, improve crop quality, conserve water, save energy,
decrease fertilizer requirements, and reduce non‐point source pollution. To reach these goals, it is
necessary to schedule irrigation accordingly, in other words, to decide which fields to irrigate, when and
how much. Effectively irrigating a specific crop in a specific soil requires the development of a good
irrigation schedule. An effective irrigation schedule helps to maximize profit while minimizing water and
energy use (Robert et al., 1996).
About 85 % of the people of the country are engaged in agriculture. And the country is gifted with
sufficient water and land resources, having 12 river basins that can potentially be used for irrigation.
Considering the whole scenario of need and status of agricultural development in the country, the Federal
Democratic Republic of Ethiopia has given one of the highest priorities to Agriculture. However the
activity still depends on rain –fed; rainfall distribution is seasonal and variable and suffers from the most
unstable rainfall regime. As a result the increase in crop production does not match with the population
growth of the country (Hailegebriel.S, 2007).
Therefore, the best alternatives to consider for reliable and sustainable food security
development, poverty alleviation as well as to increase crop yield per hectare, expanding
irrigation development on various scales, through constructing dams, river diversion, spate
irrigation and other water harvesting structures are very important. The development of irrigation
and improved agricultural water management has many potential benefits to reduce vulnerability
and improve productivity (Seleshi, 2010). Specifically, primary rationales for developing the
irrigation sector in Ethiopia include:
■ Increased productivity of land and labor, which is especially pertinent given future constraints
from population growth
■ Reduced reliance on rainfall, thereby mitigating vulnerability to variability in rainfall
■ Reduced degradation of natural resources
■ Increased exports
■ Increased job opportunities, and promotion of a dynamic economy with rural entrepreneurship.

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Tana Beles Sugar development project is one of the new developing sugar projects in the
country which expected to covers about 75,000 ha. Currently the total area covered by
sugarcane has reached 13000ha and the land development is ongoing. The irrigation
method in the project area is currently sprinkler irrigation
The Federal Democratic Republic of Ethiopia has launched sugar development program to
undertake new and Expansion projects across the country with a clear objective of boosting sugar
production to satisfy the domestic sugar demand as well as for any possible export.
Accordingly TanaBeles Integrated Sugar Development Project is the one among the new sugar
development projects. According to the government plan, the development of massive irrigation
projects for sugar production in different parts of the country is involved. One of these very
important schemes is TanaBeles Irrigation Project which includes Upper Beles and Ayma
Irrigation sites. The major crop to be cultivated is Sugar cane which is estimated to be around
75,000 ha of land and this is to be utilized as raw material for the sugar factory to be established
around the area (UBGSDR,2011).
The project has started seed and commercial cane plantation activities in 2012 using irrigation
water from Beles River with the aid of Diversion Weir using both surface and pressurized
irrigation methods.Currently the project has covered a total of around 12,000 hectare of cane
plantation area. The sprinkler irrigation system is a gravity hose move sprinkler irrigation
system. The whole sprinkler irrigation system supplied water from the main canal with the aid of
gravity off take pipe and deliver water to the fields through a network of supply mains, Branch
mains, Sub Mains, Mani Folds, Laterals, Drag Hoses and Sprinklers. The project after the start of
cane plantation activity, it faces poor filed irrigation water management,such as inappropriate
filed water application that means uniform application of water with irrespective of soil, stage of
growth and growing month, and poor service and maintenance. Due to this,under watering in
most fields, over watering in some fields, non-uniformity of water application, (pipe, nozzle
breakage and leakage) are observed. As a result, the canegrowth is not uniform, showing yellow
color and wilt. Finally this causes mortality, and reduction of expected can yield per hectare.
Therefore, this study is important to evaluate appropriate irrigation scheduling and uniformity of
the existing sprinkler water application of TBISDP.

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2. DESCRIPTIONOFTHE STUDYAREA
2.1 Location
TanaBeles Integrated Sugar Development Project is located near Fandica Town, capital of
JawiWoreda, which is foundin the western periphery of Amhara National Regional State, 149
and 70 km from Bahir Dar and Dangela towns, respectively, and BenishangulGumuz National
Regional State. The project area covers about 57,164ha of land situated at Upper Ayma and
feasibility updating study of Upper Beles of about 38,334ha of land placed at Right Side of
BelesRiver. Overall the study included a total area of about 95,948ha of land in JawiWoreda of
Amhara, and Dangur and PawiWoreda of Benishangul National Regional States.
A totally of 72,944ha of land were demarcated for TanaBeles Integrated Sugar Development
Project, among this 37,207ha and 35,737ha were located at Upper Beles and Aymarespectively.
The project activity started on the south from the weir site after 11.9km following the main canal
for Upper Beles and south eastern tip of Upper Ayma. The total proposed irrigated area of about
50,000ha (Gross) for two sugar estates in Upper Beles and Upper Ayma, has to be supplied water
by the main canal running along higher ground along the northwest side of the project area.The
project has been supplied water diverted from the Beles River by a diversion head works
comprising of a diversion weir, under sluices and a head regulator at the right bank of the river.
The head works is located at about 28km from Fendika town. The Beles River is supplied by
natural runoff from the upstream catchment and more recently by the TanaBeles
hydropowerscheme which uses water from Lake Tana and discharges into the Beles River
upstream of the diversion works.
The study area has low to medium relief differences with an altitude range of 806 to 1242 meters
above sea level. The Upper Beles (Right side) irrigation command area has an altitude ranged
from 962 to 1,242 m.a.s.l, which is characterized by flat topography (plain land), whereas the
Upper Aymairrigation command area is between 806 to 1154 m.a.s.l, mainly characterized by
undulating topography. The Upper Ayma irrigation command area is situated on the right and
left banks of Ayma River Gorge, originated from the head of Fendica Town. The area is
geographically located between 0198473m to 0225347m East and 1277734m to 1308983m
North UTM stretch from Jawi capital town Fendika to Quarit village. The proposed suitable land
for irrigated and mechanized sugarcane production is found at lower elevation of the surrounding
ridges defined by natural boundaries, being bounded to the south by the slopes of Belaya

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Mountain and to the west by the rising land of the Bakussa Escarpment; to the north and east by
confined ridges and uplands associated with AboyGara Mountain and Fendica Ridges,
respectively. Ayma River flows through the heart of the study area towards at northwest to
QuaraWoreda. The actual surveyed area covers some area of about 57,614 ha in the left and right
sides of Ayma River, with a maximum width of 16 km, east to west and length of 34 km south to
north. It lay between an altitude of about 806 m.a.s.l at the outlet of Ayma River and 1154
m.a.s.l at the southern tip of the study area and lower point of Fendica Ridge. Ayma area is
located at a distance of 5km from Upper Belesboundary in the northwest direction.
2.2 Climate
The project area is located close to Pawe station, can be characterized as warm humid climate
with mean annual humidity reaching to 92 % and the maximum temperature fluctuating between
37.40C in April and 19.560C.
Over all, the project area is considered to be humid with relative humidity ranging between 51
and 92%. The actual sunshine hour also varies between 7 and 10 hours per day during most of
the year except the rainy seasons of July- September where this decreases to less than 7 hours a
day. Particularly, the decrease reaches to less than 5 hours a day during July and August.
Year(2016) Tmin Tmax hum wind sun
Jan 14.15 32.52 52 1.27 7.24
Feb 14.56 33.66 51 1.75 7.41
Mar 17.41 37.40 56 1.70 8.50
Apr 18.22 36.55 62 1.74 7.20
May 17.39 32.57 81 2.97 0.00
Jun 16.34 29.85 92 1.59 0.00
Jul 16.09 26.93 85 1.36 0.00
Aug 15.91 27.28 85 1.45 0.00
Sep 11.25 19.56 59 1.31 4.80
Oct 15.87 29.58 83 1.14 6.29
Nov 12.79 32.03 77 0.85 8.87
Dec 8.92 22.70 56 0.85 6.43
Table 1: Tana abelesmetrological data
The mean annual rainfall around the irrigation scheme is represented byPawi station ;

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year/month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2016 0.00 0.00 0.00 0.00 81.90 208.80 398.50 326.90 145.10 133.34 0.00 0.00
Table 2: rainfall data
2.3 CommandArea
The command area is bounded by the main canal to the north- west. The alignment of the canal
is defined by the need to be able to command the right bank and Upper Ayma irrigation area.
The main canal therefore follows the high ground all the way around the command area and
defines the project area except where the main canal goes south of Fendika which means a very
small part of the project area is to the north of this canal. Slope is most important site
characteristics as it influences the suitability to irrigation and methods of irrigation and type and
kinds of farm operations and machineries. In this regard, the majority of the irrigation command
area is flat and gently sloping, still other slope classes also constitute limited proportions.
NO Slope class Area (ha) Cover (%)
1 Flat (0-2%) 36250 37.78
2 Gently sloping (2-5%) 42559 44.36
3 Undulating to sloping (5-8%) 12494 13.02
4 Rolling (8-12%) 3158 3.29
5 Rolling to hilly (12-16%) 925 0.96
6 Hilly (> 16%) 561 0.59
Table 3: Slope classes of the irrigation command area.
Source: Feasibility and Design Study of TBISDP (2013)
2.4 DiversionHeadWorks and IrrigationSystem
The diversion work for TanaBeles Integrated sugar Development Project is located at Beles
River at about 28km from Jawi / Fendika. Geographically the weir is located at 247847.76m
Easting and 1289961.39m Northing.Main Canal is approximately 30 km and ends near Jawi
Town from where Trunk mains for Sprinkler Irrigation for Phase I & Phase II of Upper Beles
and Upper Ayma left side command areas, take off.The main canal is lined, with concrete bed

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and masonry sides with vertical water face, where the rock is encountered and in the filled
reaches. Where the canal is in cutting in soils, trapezoidal sections with 1.2 mm thick HDPE film
as geo membrane have been adopted. The area for sprinkler irrigation is supplied by the trunk
main (TM) pipes tapped from the canal intakes at an elevation suitable to generate pressures
adequate for the functioning of sprinklers.
A gravity pipe off take (main pipe line connected to the main canal with concrete structure)
equipped with bar screens (trash rack) to prevent entry of debris, floating matter or some
livestock. These pipes then deliver water to the fields through a network of supply mains (SPM),
Branch mains (BM), Sub Mains (SBM), Mani Folds (MF), Laterals (L), Drag Hoses and
Sprinklers.
2.5 The CommandSoil
The type of soil in the command area of TanaBeles Integrated Sugar Development Project is
given in Table 4:
Type of soil Area coverage in percentage Area coverage in ha
Verti soils >50% >37000
Luvi soils 9% 6750
Nito soils 5% 3500
Cambi soils 5% 3500
Lepto sols 6% 4500
Table 4: Beles Soil Area Coverage
Source:Feasibility and Design Study of TBISDP (2013)
Verti sols:-cover more than 50% of the command area, heavy clay soil which is deep swell and
shrink. Luvisols: -covers 9% of the gross command area, which is deep reddish clay soils in
which silicate clay are transported form high nutrient content and good drainage. Nitosols:
covers 5% the gross command area, which is deep reddish clay soils more than 30% clay fertile
soil. Cambisols:-covers 5% the gross command area, which is a Brownish weakly developed soil
and it is unsuitable for sugar cane. Leptosols: - covers 6% the gross command area, Very shallow
and very stony soils (unsuitable for sugar cane production).
2.6 Methods
The reference evapotranspiration was calculated using the computer program called
CROPWAT which is developed by FAO. The program is based on Modified Penman-
Montieth method. For calculation of evapotranspiration a long year metrological data is

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needed but due to the absence of representative long year data, the two years data
generated from the newly established Kuraz metrological station in the project site was
used for estimation of reference evapotranspiration through the CROPWAT software.
The following meteorological factors were taken into consideration for calculation of
Reference Evapotranspiration by Modified Penman- Montieth Method: maximum and
minimum temperature, relative humidity, wind velocity and sunshine hours (Allen et al.,
1998). After the references evapotranspiration (ETo) was estimated, the crop water
requirement (ETc) was estimated using the equation. Then, the effective rainfall was
calculated using USDA method in CROPWAT software.
The soil classification and their properties generated by WWDSE (2011) were used.
Information for some Important crop characteristics (growth stages, crop coefficients and
factor of depletion) information were taken from literatures and other country`s
experience as they are not yet determined for local conditions; but cane rooting depth
survey result at Finchaa was used with some modification.
The relationship between Reference Evapotranspiration (ETo) and crop
evapotranspiration the crop water requirement is expressed though crop coefficient (Kc)
as:
ETc = Kc * ETo ...................................................(Equation1)
Depth of application was calculated using the following formula.
Dn = TAW * ρ * Dr .................................................(Equation2)
Where, TAW = total available water (mm/m),
ρ = allowable depletion (fraction),
Dr = effective root depth (m),
Dn = Net depth of application (mm),
The irrigation interval (I) in days was estimated using the following formula:
I = Dn/Etc ............................................................... (Equation3)

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3. RESULTS AND DISCUSSION
3.1. Secondary data used
The crop characteristics parameters important for the determination of irrigation schedule
are length of each growth phase, crop coefficient and rooting depth. However, none of
this information is identified for sugarcane in a well designed experiment in Ethiopia.
Thus, the respective values were adopted from other research in other countries.
Accordingly, by integrating information in FAO publications’ and experience gained
from Mauritius crop coefficient values in table 1 were used. However, the lengths of
growth periods were slightly modified to fit the conditions at the project area.
crop
Init.
Stage Dev. Stage
Mid
Stage
Late
Stage tatal(Days)
sugarcane
50 70 220 140 480
kc in kc mid kc end
0.2 1.2 0.7
Maximum Root
Depth(m)
Depletion Fraction2 (for ET= 5
mm/day)
1.2-2.0
0.65
Table 5: Description of sugarcane (KC)
3.2. IrrigationSchedule
Various methods and tools have been developed to determine when crops require water
and how much irrigation water needs to be applied. The irrigation scheduling was
determined by equations (2) and (3).
3.2.1. Depth of irrigation application
The first component of irrigation schedule is gross irrigation depth, which highly depends
on the irrigation methods and its flexibility, perceived net application depth, and
application efficiency. Ideally, at the beginning of the growing season, the amount of
water given per irrigation application, also called the irrigation depth, is small and given
frequently. This is due to the low evapotranspiration of the young plants and their
shallow root depth. During the mid season, the irrigation depth should be larger and given
less frequently due to high evapotranspiration and maximum root depth. Thus, ideally,
the irrigation depth and/or the irrigation interval (or frequency) varies with the crop
development.

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When sprinkler and drip irrigation methods are used, it may be possible and practical to
vary both the irrigation depth and interval during the growing season. With these methods
it is just a matter of turning on the tap longer/shorter or less/more frequently. When
surface irrigation methods are used, however, it is not very practical to vary the irrigation
depth. With surface irrigation, variations in irrigation depth are only possible within
limits. Irrigating cane fields by varying the depth of application based on the growth
stage is not also practiced in the Ethiopian sugar industries due to its difficulty for
management. It is difficult to control the flow and the cutoff of time for furrow irrigation
in which the water delivery method is bank breaching (opening a cut in the banks of a
field canal to discharge water into the field). Therefore, it is often sufficient to estimate or
roughly calculate the irrigation depth and to fix the most suitable depth; in other words, to
keep the irrigation depth constant over the growing season.
The net depth of application based on 90cm rooting depth (rooting depth at full growth of
cane), design application efficiency of 80% and furrow length of 100m were estimated
and presented below.
Soil types Net depth (mm) Gross depth (mm)
Clay 122 152
Silty clay 111 139
Sandy loam 86 107
Sandy clay 65 81
Table 6: Net and gross depth of application
For best control of irrigation application depth, selection of inflow rate and cut off time combinations is
vital; the implementation requires flow and time measurement. Later in the field use, these combinations
of flow rate cut off time are converted to cut off ratio. Cutoff ratio is a time required for water to advance
to the end of the field to the total set time. This is because our volume control mechanism is based on
advance distance of water front. However, cut off ratio has not been determined for the area

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3.3 Procedure ofCROWAT
1. Calculation of ETo: by using metrological data ETo is calculated as following table:
Figure 1: ETo of sugarcane at Beles
When this ETo shown by chart/graph, it look like as follow:

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Figure 2: Graph representation of ETO
2. Calculating Effective rain fall:
Figure 3: Effective Rainfall of pawi station
3. Calculating crop coefficient:

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Figure 4: description of sugarcane coefficient
4. Calculating soil moisture content and available water content:
Figure 5: soil moisture content and available watercontent of Beles

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5. Check CWR table:

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Figure 6: CWR representation
Figure 7: Graphical representation of irrigation required
6. Check irrigation scheduling table from CROP WAT:

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Figure 8: irrigation scheduling
Figure 9: Graph Representation of irrigation scheduling

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4. CONCLUSIONS ANDRECOMMENDATION
Based on the results obtained the following recommendations are drawn, total net irrigation
required is 567.2mm and total gross irrigation required is 810.2mm.
As we determine by CROPWAT Irrigation water Intervalof Tana Beles sugar development
project is 10days (table 8). Another output data for this paper
I. No Description Result remark
1 ETo 2.94 mm/day
2 Total annual eff. rainfall 749.1mm
3 Planting date 21/09/19
4 Harvesting date 12/01/2014
5 Total life age ofsugarcane 480days
6 Average Height ofsugarcane 3m
7 Irrigation itervals 10days
Figure 10: summery of report