irrigation engineering ii · irrigation engineering ii 1. irrigation system( 5 hours lecture and 6...

Irrigation Engineering II

1. Irrigation system( 5 hours lecture and 6 hours home study or tutorial sessions)

i. Characteristics, adaptability

ii. Irrigation system design, layout and their components

iii. Land leveling

iv. Efficiency v. Uniformity

2. Surface irrigation methods ( 6 hours lecture and 10 hours practical or tutorial sessions)

i. Furrowii. Basiniii. Border

3. Pressurized irrigation methods ( 6 hours lecture and 10 hours practical or tutorial sessions)

i. Sprinklerii. Dripiii. Pressure and flow regulationiv. Water hammer

4. Pumps for irrigation ( 6 hours lecture and 8 hours practical or tutorial sessions)

i. Types of pumpsii. Operation characteristics of pumps

iii. Pump selectioniv. Operation and maintenance of pumps

5. Operation and maintenance of irrigation systems ( 3 hours lecture and 5 hours practical or tutorial sessions)

i. Operation of irrigation systemsii. Maintenance of irrigation systems

• Global irrigation development– Throughout the world 1.2 billion people have to survive on

income levels of less than 1 US$ per day– Three quarters of those live in rural areas and most of them

depend on agriculture– Spatial expansion of HH agriculture production is limited– worldwide agricultural production of about 7 million

hectares could be intensified through small-scale irrigation (SSI) alone and benefit approx. 40 million smallholders

– 10% of this potential is located in Sub-Saharan Africa (SSA), 700,000 ha and up to 4 million beneficiaries respectively

• Small-scale irrigation are development initiatives which are undertaken by small farmers who “own and manage an individual plot or are part of a community managed irrigation scheme”.

• The term “small-scale irrigation” therefore fits a wide range of irrigation activities ranging from bucket and drum kits with low-cost drip lines of individual farmers to irrigation schemes of several hundred hectares in which individual small farmers participate as users.

• A Water Users Association (WUA) is defined as “a group of registered farmers, within a given geographical location, who have come together for the purpose of utilizing a common water resource for irrigation and drainage development. The members are bound together by agreed by-laws, which specify the membership, functions and management of the association”

• Type of irrigation schemes – Scale in size - small, medium and large scale irrigation

schemes– Source of water – surface, lakes /geologic depressions with

underlying clayey strata that prevent seepage, which during the rainy season fill up with runoff from the surrounding plains/, ground water and waste water

• Water abstraction – Gravity– Engine driven Pump, hand operated pump, treadle pump

TYPOLOGY OF

IRRIGATION SCHEMES

IN ETHIOPIA

TRADITIONAL IRRIGATION SCHEME

Stream diversion - Water works are simple and temporary, reconstructed every season

Water abstraction and distribution

Implemented, operated and maintained by farmers

Implementation, operation, maintenance

Traditional water users associations led by elected chiefs

Organization

Has been practiced for many centuries

Historic background

Small-scale: 50 ha to 100 haAverage size of schemes

60 000 haTotal area in Ethiopia

Inadequate water control at the head works: chronic shortageWeeds, pests: shortage of farm inputs, inadequate farm equipmentWeak on-farm water management

Main problems and issues

Low irrigation efficiencyLow productivitySustainability (traditional organization)

Performances

Flooding irrigationUse of chemical inputs Mechanization of land works (animal traction)

Farmers’ practices

Cereals, pulses, oil crops, coffee, enset, vegetable, sugarcane, fruit

Main crops

Implemented by government (or NGO) with involvement by beneficiaries (in principle)O&M supported in practice by zonal government departments (instead of farmers association)


Water users associations initiated by government

Organization

Started after 1974 land reformsHighly encouraged after 1983 devastating drought

Historic background

Small-scale: 20 ha to 200 haAverage size of schemes

30 000 haTotal area in Ethiopia

MODERN COMMUNAL IRRIGATION SCHEMES

Low irrigation efficiencyLow productivitySchemes little used or abandoned

Performances

Flooding irrigationUse of chemical inputs Mechanization of main works (animal traction)


Food crops (corn), fruits, vegetables, sugar cane

Main crops

Stream diversion - Water works are simple and temporary, reconstructed every season


Weeds, pests: shortage of farm inputs, inadequate farm equipmentWeak on-farm water management


Owned, built and operated by private entrepreneurs (in principle)


Capitalistic enterprises Organization

Sugar estates by the Dutch in the 50s, cotton in the 60s. Nationalized in the mid 70s and Re-emerged with adoption of market based economy in the 90s

Historic background

0,5 to 2000 ha Average size of schemes

6 000 ha Total area in Ethiopia

MODERN PRIVATE IRRIGATION SCHEMES

Low irrigation efficiencyProductivity over 50% of potentialSlow emergence of these schemes

Performances

Furrow irrigation but low land leveling + some pressurized distribution systems. Intensive use inputs (fertilizers, improved seeds)


Cotton, maize, oil crops, vegetables, cut flowers, fruits

Main crops

Low-lift pumping, run-of river diversion. Distribution through earth channels


Schemes are few in number and not operating at full capacity, despite state incentives (tax holidays): huge investment, long pay-back period, lack of market, poor infrastructure


Owned, operated and maintained by the State


Centralized management Organization

Development, notably through nationalization, during socialist area (70s). Scaled-down since adoption of a market economy (abandon & less often privatization)

Historic background

Large-scale: > 3000 ha

Alwero, Gode, Weito, FinchaaAverage size of schemes

60 000 ha Total area in Ethiopia

PUBLIC IRRIGATION SCHEMES

Variable irrigation efficiencyHigh productivityProblem of financial viability High decrease of irrigated areas

Performances

Furrow irrigation, except one sugar estate with sprinkler irrigationAppropriate inputs and adequate cultural practices


Cotton, sugar cane, horticultural crops

Main crops

Abstraction with masonry weirs and pumps from rivers or lakes. Distribution through gravity canals


Seasonal flooding, salinity & drainage. Problem of cash flow and cost effectiveness, inadequate management. Difficulties of transport & marketing (cotton).


Tip for discussion:

� Typology per the scale of the scheme, source of water for irrigation and method of abstraction� Small-scale, medium scale, large scale

� Surface water (Rivers, lakes, spring), ground water, Waste water, mixed water

� Degree of water control (total and partial water control)

� Gravity, pump, pressurized and gravity network

Chapter one

Irrigation system

i. Characteristics, adaptability

ii. Irrigation system design, layout and their components

iii. Land levelingiv. Efficiency v. Uniformity

DEFINITION AND SCOPE OF IRRIGATION

• “Irrigation is the artificial supply of water for agriculture, the systematical distribution of this water over the fields and the drainage of this water from the fields to natural drains after as much benefit as possible has been derived from it.”

• Generally the following are some of the factors that necessitateirrigation.– inadequate rainfall– uneven distribution of Rainfall,– increasing the yield of the crops,– growing a number of crops,– insuring against drought,– growing perennial crops.

• Irrigation is not confined to application water to the land. It includes watershed, hydrology, river engineering, design and construction of hydraulics and irrigation structures, drainage system…

GENERAL DESCRIPTION OF IRRIGATION AND DRAINAGE SCHEMES

• Irrigation and drainage schemes are constructed and operated to create favorable conditions for crop growth.

• This means that in a good scheme equitable, adequate, reliable and flexible water supplies

should be delivered to all water users to enable them to irrigate their crops in an optimal manner,

• and that an adequate drainage system exists that removes any water that is not needed or wanted

• Irrigation and drainage schemes are constructed and operated to create favorable conditions for crop growth.

• Irrigation system – composed of technical part of measures that are needed for proper water management in irrigated agriculture including lay out

• Irrigation scheme comprises all aspects including those of operation and management

Six ‘levels’ of interested parties can thus be distinguished in general in the planning, design,

construction and operation of irrigation and drainage schemes:

1. Beneficiaries of the irrigation schemes;

2. Water Users, usually organized in groups (such as Water Users Associations);

3. Water Management Boards (such as Drainage Authorities and Irrigation Authorities);

4. Provincial or State Governments;

5. Central Governments; and6. Neighboring countries, global interests.

Some elements of an irrigation and drainage system (adapted from Bos, 1982)

Maps and data are required for the technical planning and design of water control projects.

These have to cover the following:(a) the physical, economic and human conditions to such a scale/detail that the actual situation and future changes can be studied to a sufficient extent;(b) topographical maps and/or aerial photographs and/or GIS data, on a scale according to level of needed detail:– general plans: scale 1/250,000 till 1/50,000 (military map)

with contour intervals of 2.5 to 1.0 meter;– construction plans: scale 1/20,000 to 1/5,000 with

contour intervals of 1.0 to 0.2 meter for alignments;– detail construction drawings and/or land leveling plans

would need other scales and intervals;(c) soil maps and/or land classification and land capability

maps to appropriate scales; information on soil properties and on soil conservation;

d) climatological data: rainfall, temperature, humidity, wind and radiation are the more important ones;

(e) agronomic data: actual and possible crops and cropping patterns; crop water requirements, irrigation and drainage requirements;

(f) hydrologic data: surface runoff, river flow and stage, aquifer characteristics;

(g) economic and financial data: expected costs and benefits, at all levels mentioned previously;

(h) sociological data, such as population statistics, available labor and available management at the various levels;

(i) administrative data: organizations, laws; and(j) construction conditions and materials in the project area.• The irrigation network,• Types of water control structures- fixed, open (closed),

stepwise adjustment, gradual adjustment and automatic,• Upstream and down stream water control

Irrigation network

LAND LEVELING AND FIELD LAYOUT

• Land grading is reshaping of the field surface to a planned grade -suitable field surface to control the flow of water, to check soil erosion and provide surface drainage.

• Land leveling operations may be grouped into three phases:– Rough grading -the removal of abrupt irregularities

such as mounds, dunes and rings, and filling of pits, depressions and gullies.

– Land leveling - land grading = land forming = land shaping – requires moving large quantity of earth over considerable distance

– Land smoothing-final operation of land leveling to form plane surface

• Criteria for land leveling -land leveling is influenced by – the characteristics of the soil profile, – prevailing land slope, – rainfall characteristics,– cropping pattern,– methods of irrigation,– other specific features of the site including the

preference of the farmer1. Land Grading Survey and Design

– Identify field boundaries considered for leveling,– Survey the area for land leveling design,– Establish a grid system over the field (general practice)– Set stakes at the grid points (refer the figure in the next

slide)– Usual grid spacing is 25 m in each direction, 15, 20, 30

m

Grid pattern for staking a field which is to be graded

Grid point elevation of the field marked with contour lines

60 – 150 5 – 10

30 – 602 – 5

15 – 301 – 2

6 – 15 0 – 1

Contour interval (cm)Land slope range (%)

To make the survey information more readily understood, contour lines are drawn at suitable intervals: Refer the table below:

Land leveling design methodsThe basic methods of land leveling design are:1. plane method, - deals with this method in detail2. profile method,3. plan-inspection method, and 4. contour adjustment method

Plane Method

• Determining the centroid of the filed– The centroid of a rectangular field is located at the point of

intersection of its diagonals. – The centroid of a triangular field is located at the intersection

of the lines drawn form its corners to the mid-points of the opposite sides.

– To determine the centroid of irregular fields, the area is divided into rectangles and right angled triangles. The centroid is located by computing moments about two reference lines at right angles to each other.

– The distance of the centroid of the field from any line of reference is equal to the sum of the products obtained by multiplying the area of each part times the distance from the line of reference to its centroid, divided by the area of the entire field.

– By computing the distance to the centroid from two lines of reference perpendicular to each other, the exact point of the centroid can be determined.

6115.058

1062.55212.59

927.55187.584750.058Total

975.06162.57975.06162.5G

962.57137.56962.57137.5F

787.57112.551012.59112.5E

612.5787.54787.5987.5D

437.5762.53562.5962.5C

262.5737.52337.5937.5B

87.5712.51112.5912.5A

ProductNo StakesDistanceLineProductNo StakesDistanceLine

The distance of the centroid from the reference line is then obtained by dividing the sum of the products by the total number of stakes, or

m81.89658

4750linereferencethefromcentroidofDistance ==

With the two dimensions, the centroid point is located at (105.603, 81.896).

b) Determining the average elevation of the field• This is obtained by adding the elevations of all grid points in the field and

dividing the sum by the number of points= 98.78/58=>1.703m, • the total of the 58 elevations on the grid corners is 98.78m

Example The topographic survey of a field gave the following elevations (m) at grid points

9.139.419.679.489.89D

9.489.659.9210.0810.32C

9.759.849.9510.4210.47B

9.679.6810.0710.4310.65A

54321

oCalculate the elevation of the centroid of the field. Stakes are to guide the leveling of this field into a play ground. oCalculate the cut and fill at the grid points. oCompare the quantities of earthwork in cutting and filling

Solutions:Total number of stations = 4 * 5 = 20Total elevations of 20 stations = 197.96

m9.89820

197.96

pointsgridofNumber

pointsgridtheofelevationstheofsumcentroidofElevation ===

•Since the field is to be used as a playground, it is to be leveled without any slope in any direction. •The cuts and fills at various grid points are obtained by subtracting the elevation of the corresponding grid point from the elevation of the centroid. •Thus, the cut/fill at grid point A1 is 9.898 – 10.65 = -0.752m. The –sign indicates the cut, while +sign indicates fill. The cuts and fills (in m) at the different grid points are computed which are tabulated below:

+0.768+0.488+0.228+0.418+0.008D

+0.418+0.248-0.022-0.182-0.422C

+0.148+0.058-0.052-0.522-0.572B

+0.228+0.218-0.172-0.532-0.752A

54321

Check: ∑ ∑ == mfillcut 228.3

Major irrigation methods

Irrigation Methods

Surface Irrigation Sub surface irrigation Pressurized irrigation

Border

Check basin

Furrow

Natural

Artificial

Sprinkler

Drip/Trickle

Considerations in irrigation system selection

Efficiency

• Irrigation consumptive use coefficient:

• Irrigation efficiency:

Uniformity

• Irrigation uniformity measures describes how the water infiltrated is distributed over a field.

• Uniformity needs to consider the scale of plant roots,• The definition also ignores the intercepted by canopy and

water consumed during the irrigation event itself

irrigation engineering ii · irrigation engineering ii 1. irrigation system( 5 hours lecture and 6...

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