sistem irrigasi

SISTEM IRRIGASI

Didik Suprayogo

Bahan Bacaan:

http://www.fao.org/docrep/R4082E/r4082e06.htm

IRRIGASI

Penyiapan tindakan yang memungkinkan petaniuntuk menyediakan kecukupan air bagi

tanamannya yang dikumpulkan dan disalurkanuntuk menyediakan kecukupan air bagi

tanamannya yang dikumpulkan dan disalurkandari tempat lain

FUNGSI IRIGASI

Fungsi utama:

Memenuhi kebutuhan air tanaman

Fungsi spesifik:

1. mengambil air dari sumber (diverting)1. mengambil air dari sumber (diverting)

2. Membawa/mengalirkan air dari sumber ke lahan pertanian (conveying)

3. mendistribusikan air kepada tanaman (distributing)

4. mengatur dan mengukur aliran air (regulating and

measuring)

SISTEM IRRIGASI?

The irrigation system consists of:

• Diverting: a (main) intake structure or (main) pumping station, station,

• a conveyance system,

• a distribution system,

• regulating and measuring:

• a field application system, and

• a drainage system

SISTEM IRRIGASI

� The (main) intake structure, or (main) pumping station, directs water from the source of supply, such as a reservoir or a river, into the irrigation system.

� The conveyance system assures the transport of water from the main intake structure or main pumping station up to the field ditches.

� The distribution system assures the transport of water through field ditches to the irrigated fields.

� The field application system assures the transport of water within the fields.

� The drainage system removes the excess water (caused by rainfall and/or irrigation) from the fields.

Pumping stationconveyance system

distribution system field application system

MAIN INTAKE STRUCTURE

� The intake structure is built at the entry to the irrigation system (see Fig. 70). Its purpose is to direct water from the original source of supply (lake, river, reservoir etc.) into the irrigation system.

PUMPING STATION

In some cases, the irrigation water source lies below the level of the irrigated fields. Then a pump must be used to supply water to the irrigation system (see Fig. 71).

PUMP

There are several types of pumps, but the most commonly used in irrigation is the centrifugal pump.

The centrifugal pump (see Fig. 72a) consists of a case in which an element, called an impeller, rotates driven by a motor (see Fig. 72b). Water enters the case at the center, through the suction pipe. The water is immediately caught by the rapidly rotating impeller and expelled through the discharge pipe.

BENDUNGAN URUGAN TANAH DAN

WADUK PERTANIAN (EMBUNG)

Sumber gambar : http://www.flickr.com/photos/erensdh/4025394008/

KEGUNAAN BENDUNGAN URUKAN TANAH DAN


� Penyediaan air untuk irigasi

� Mengendalikan atau mengontrol kelebihan air

� Rancangan ditentukan integrasi anatara prinsip fisika tanah

dan mekanika tanah sebagai rancangan dan penerapan prinsip dan mekanika tanah sebagai rancangan dan penerapan prinsip

prinsip konstruksi keteknikan

� Tinggi konstruksi tidak lebih dari 15 m.

� Bendungan dikonstruksi dari tumpukan tanah dimana bahan

tanah ditimbun merata secara berlapis dan dilanjutkan dengan

pemadatan pada kondisi kelembaban yang optimum untuk

mencapai kepadatan maksimum yang ditargetkan.

RANCANGAN BENDUNGAN URUKAN TANAH DAN


� Rancangan untuk mengontrol air diprediksi atas

dasar: � Sifat pondasi, yaitu: stabilias, kedalaman pada lapisan yang kedap air,

permiabilitas tanah, dan kondisi drainase

� Kondisi setempat dan ketersediaan bahan konstruksi� Kondisi setempat dan ketersediaan bahan konstruksi

� Macam Konstruksi:

� Embung sederhana

� Lapisan kedap air terpusat (core / Zoned type)

� Tipe diafragma / pancang

Blanket di perpanjang = 8 s/d 10 kali kedalaman waduk

Dasar waduk:

70% pasir, 20 s/d 25 % liat, dan cukup debu,

Tanah diurug 0.3 m di padatkan

Paling tidak 0,6 m harus ada tanah diatas batuan

Bila tidak ada bahan tsb, dapat dilakukan

campuran bentonit dg tanah dengan

minimum mengandung 10 s/d 15% pasir,

Atau dg polyphosfate, atau bahan kimia

lainnya, atau film plastic atau butyl

Tebal Blanket = 10% kedalaman waduk, minimum 1m

Blanket di perpanjang = 8 s/d 10 kali kedalaman waduk

Dari bahan plastik, butyl, beton, logam, kayu

PERSYARATAN PONDASI

� Untuk bendung kecil cukup dengan bor tanah bila lebih besar perlu mengkaji

kondisi bawah tanah dan kondisi geologi, untuk uji mekanika tanah:

� Distribusi ukuran partikel tanah

� Indek plastis dan cair

� Kekuatan geser tanah,

� Kompressibilitas

� Permiabilitas� Permiabilitas

� Macam Pondasi:� Batuan pejal; kadang ada malahan bahaya bocor, untuk itu perlu sementasi / injeksi

bahan semen

� Pasir halus yang seragam, bila dibawah “kepadatan kritis” (void ratio dimana tanahmengalami deformasi walupun tanpa merubah volume), maka pondasi ini harusdikonsolidasi untuk mencegah aliran akibat beban penggenangan

� Pasir kasar dan kerikil, pada saat penggenangan akan mengaalami konsolidasi, pelapisan bahan kedap air di bagian muka diperlukan untuk mencagah kebocoran,

� Liat yang plastis, tekanan geser yang diakibatkan oleh berat bendungan harus lebihkecil dari pada ketahanan geser bahan pondasi, side slope yang lebih mendatardiperlukan untuk mengurangi tekanan geser

RANCANGAN YANG DISESUAIKAN BAHAN YANG TERSEDIA

� Ranacangan ditetapkan pada keguanaan secara ekonomis

yang paling murah yang didasarkan dari bahan yang tersedia

di tempat bangunan

� Rancangan Penampang melintang tergantung kondisi pondasi

dan ketersediaan bahan urukan, contoh: kombinasi lapisan dan ketersediaan bahan urukan, contoh: kombinasi lapisan

kedap air dan Lapisan kedap air terpusat dilakukan untuk

pondasi yang tidak kedap air yang dalam.

� Untuk pemadatan dan kapasitas penahanan air:

� Kerikil : pasir: debu: dan liat untuk kepadatan maksimum = < 20% kerikil, 20-

50% pasir, < 30% debu dan 15-25% liat

� Tanah yang mudah mengembang dan mengkerut hanya di gunakan pada yang

tergenang,

� Bahan organik tanah harus di kelupas dari konstruksi

AIR REMBESAN MELALUI BENDUNGAN

� Air rembesan tergantung pada karakteristik bahan tanah baikuntuk pondasi dan urukannya.

� Pemahaman dan pengetahuan posisi garis rembesan pentinguntuk mengontrol rembesan.

� Garis rembesan adalah garis diatas rembesan: diatas garis ini� Garis rembesan adalah garis diatas rembesan: diatas garis initidak ada tekanan hidrostatis, dibawah garis ini ada tekananhidrostatis

� Garis rembesan dipengaruhi: (1) permebilitas bahan urukandan pondasi, (2) posisi dan aliran air bawah tanah, (3) tipe danrancangan bendungan, (4) penggunaan perangkat drainaseuntuk menampung rembesan dibagian bawah bangunan.

� e = h / 3

� q = (K(h – e)/L)*((h + e)/ 2) = (K/2) * ((h2 – e2)/L) = (4Kh2/9L) � q max

q = (4Kh2/9L)

e = 23/3 = 7.6 m

L = (2Z + h – e/2) cot α + W + 0.3M

L = (2X3 +23 – 7.6/2) x 1 +6+6.9 = 38.1 m

q = (4 x 0.0176 x 23 x 23)/ (9X 38.1)

q = 0.1086 m3/ d per lineal meter of length

PERLAKUAN PONDASI

� Macam pondasi: (1) batu, (2) material bertekstur halus (liat

dan debu), material bertekstur kasar (pasir dan kerikil).

� Bahan batu harus hati hati melihat sambungan, patahan

geologi, lapisan permiabel.

� Bahan bertekstur halus: penglupasan bahan organik, buat � Bahan bertekstur halus: penglupasan bahan organik, buat

galian profil sedalam 0.6 s/d 1 m dengan lebar bawah 4 s/d 6

m

� Bahan bertektus kasar: dibuat profil hingga kedalaman lapisan

kedap air, atau batuan, lebar bawah minimum 3 m s/d 6 m

� Tinggi minimum lapisan kedap air sebagai penyumbat air adalah setengah

dari tinggi bendungan, side lope kurang dari 1:1,

� Minimum lewbar bagian atas lapisan kedap air 1.2 m

Drainase:

SIDE SLOPE AND BERMS, TOP WIDTH

� Kurang 15 m < tajam dari 3:1 bagian depan dan 2:1 bagian

belakang,

� Bahan urukan kasar 3:1 atau 4:1

� Top width bendungan < 5 m = 2.4 m,

� Top width > 5 m � W = 0.4 H + 1� Top width > 5 m � W = 0.4 H + 1

Freeboard h = 0.014 (Df) 1/2

Net and gross freeboard embung 0.6 ha, dimana panjang permukaan air = 183 m, asumsi

frost depth = 0.15 m, dengan periode ulang 25 th Q max = 4.00 m3/detik, dengan

kedalaman aliran spillway =0.3 m

H = 0.014 (183)1/2 = 0.19 m, flood storage depth = 0.6m

Net freeboard = 0.15 + 0.19 = 0.34 m

Gross freeboard = 0.34 + 0.3 + 0.6 = 1.24 m

Mechanical Spillways

CONVEYANCE AND DISTRIBUTION

SYSTEM

The conveyance and distribution

systems consist of canals

transporting the water through the transporting the water through the

whole irrigation system. Canal

structures are required for the

control and measurement of the

water flow.

OPEN CANALS

An open canal, channel, or ditch, is

an open waterway whose purpose

is to carry water from one place to

another. Channels and canals refer

to main waterways supplying to main waterways supplying

water to one or more farms. Field

ditches have smaller dimensions

and convey water from the farm

entrance to the irrigated fields.

CANAL CHARACTERISTICS

According to the shape of their cross-section,

canals are called rectangular (a), triangular (b),

trapezoidal (c), circular (d), parabolic (e), and

irregular or natural (f) (see Fig. 73).


The most commonly used canal cross-section in irrigation and

drainage, is the trapezoidal cross-section. For the purposes of

this publication, only this type of canal will be considered.

The typical cross-section of a trapezoidal canal is shown in

Figure 74.


The freeboard of the canal is the height of the bank above the

highest water level anticipated. It is required to guard against

overtopping by waves or unexpected rises in the water level.

The side slope of the canal is expressed as ratio, namely the

vertical distance or height to the horizontal distance or width.

For example, if the side slope of the canal has a ratio of 1:2 (one

to two), this means that the horizontal distance (w) is two times

the vertical distance (h) (see Fig. 75).

A BOTTOM SLOPE OF A CANAL

EARTHEN CANALS

Earthen canals are simply dug in the ground and the bank is

made up from the removed earth, as illustrated in Figure 77a.

The disadvantages of earthen canals are the risk of the side

slopes collapsing and the water loss due to seepage. They also

require continuous maintenance (Fig. 77b) in order to control

weed growth and to repair damage done by livestock and

rodents.

LINED CANALS

Earthen canals can be lined with impermeable materials to

prevent excessive seepage and growth of weeds (Fig. 78).

Lining canals is also an effective way to control canal bottom

and bank erosion. The materials mostly used for canal lining are

concrete (in precast slabs or cast in place), brick or rock

masonry and asphaltic concrete (a mixture of sand, gravel and

asphalt).

The construction cost is much higher than for earthen canals. The construction cost is much higher than for earthen canals.

Maintenance is reduced for lined canals, but skilled labour is

required.

CANAL EROSION

Canal bottom slope and water velocity are closely related, as the following example will show.

A cardboard sheet is lifted on one side 2 cm from the ground (see Fig. 79a). A small ball is

placed at the edge of the lifted side of the sheet. It starts rolling downward, following the

slope direction. The sheet edge is now lifted 5 cm from the ground (see Fig. 79b), creating a

steeper slope. The same ball placed on the top edge of the sheet rolls downward, but this time

much faster. The steeper the slope, the higher the velocity of the ball.

Water poured on the top edge of the sheet reacts exactly the same as the ball. It flows

downward and the steeper the slope, the higher the velocity of the flow. downward and the steeper the slope, the higher the velocity of the flow.

Water flowing in steep canals

can reach very high velocities.

Soil particles along the bottom

and banks of an earthen canal

are then lifted, carried away by

the water flow, and deposited

downstream where they may

block the canal and silt up

structures. The canal is said to

be under erosion; the banks

might eventually collapse.

DROP STRUCTURES AND CHUTES

Drop structures or chutes are required to reduce the bottom

slope of canals lying on steeply sloping land in order to avoid

high velocity of the flow and risk of erosion. These structures

permit the canal to be constructed as a series of relatively flat

sections, each at a different elevation (see Fig. 80).

Drop structures take the water abruptly from a higher section

of the canal to a lower one. In a chute, the water does not drop

freely but is carried through a steep, lined canal section. Chutes

are used where there are big differences in the elevation of the

canal. canal.

DISTRIBUTION CONTROL

STRUCTURES

Distribution control structures are

required for easy and accurate water

distribution within the irrigation system

and on the farm:and on the farm:

1. Division boxes

2. Turnouts

3. Checks

DIVISION BOXES

Division boxes are used to divide or direct the

flow of water between two or more canals or

ditches. Water enters the box through an

opening on one side and flows out through

openings on the other sides. These openings

are equipped with gates (see Fig. 81).

TURNOUTS

Turnouts are constructed in the bank of a canal.

They divert part of the water from the canal to

a smaller one.

Turnouts can be concrete structures (Fig. 82a),

or pipe structures (Fig. 82b).

CHECKS

To divert water from the field ditch to the

field, it is often necessary to raise the water

level in the ditch. Checks are structures

placed across the ditch to block it

temporarily and to raise the upstream water

level. Checks can be permanent structures

(Fig. 83a) or portable (Fig. 83b).

CROSSING STRUCTURES

It is often necessary to carry irrigation water

across roads, hillsides and natural depressions.

Crossing structures, such as flumes, culverts and

inverted siphons, are then required.

1. Flumes

2. Culverts

3. Inverted siphons

FLUMES

Flumes are used to carry irrigation water across

gullies, ravines or other natural depressions.

They are open canals made of wood (bamboo),

metal or concrete which often need to be

supported by pillars (Fig. 84).

CULVERTS

Culverts are used to carry the water across

roads. The structure consists of masonry or

concrete headwalls at the inlet and outlet

connected by a buried pipeline (Fig. 85).

INVERTED SIPHONS

When water has to be carried across a road

which is at the same level as or below the canal

bottom, an inverted siphon is used instead of a

culvert. The structure consists of an inlet and

outlet connected by a pipeline (Fig. 86). Inverted

siphons are also used to carry water across wide

depressions.

WATER MEASUREMENT STRUCTURES

� The principal objective of measuring irrigation water is to

permit efficient distribution and application. By measuring

the flow of water, a farmer knows how much water is

applied during each irrigation.

� In irrigation schemes where water costs are charged to the

farmer, water measurement provides a basis for estimating

water charges. water charges.

� The most commonly used water measuring structures are

weirs and flumes. In these structures, the water depth is

read on a scale which is part of the structure. Using this

reading, the flow-rate is then computed from standard

formulas or obtained from standard tables prepared

specially for the structure.

WEIRS

In its simplest form, a weir consists of a wall of timber, metal or concrete

with an opening with fixed dimensions cut in its edge (see Fig. 87). The

opening, called a notch, may be rectangular, trapezoidal or triangular.

PARSHALL FLUMESThe Parshall flume consists of a metal or concrete channel

structure with three main sections: (1) a converging section at

the upstream end, leading to (2) a constricted or throat section

and (3) a diverging section at the downstream end (Fig. 88).

Depending on the flow condition (free flow or submerged flow),

the water depth readings are taken on one scale only (the

upstream one) or on both scales simultaneously.

CUT-THROAT FLUMEThe cut-throat flume is similar to the Parshall flume, but

has no throat section, only converging and diverging

sections (see Fig. 89). Unlike the Parshall flume, the cut-

throat flume has a flat bottom. Because it is easier to

construct and install, the cut-throat flume is often

preferred to the Parshall flume.

PENGUKURAN

DEBIT AIR

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DEBIT AIR

Pengertian Dasar

• Debit air adalah Jumlah air yang mengalir pada suatu luasan persatuan waktu tertentu misalnya:

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misalnya:

(liter/detik) atau (liter/menit), (liter/detik) atau (m3/menit)

Peralatan Pengukuran

�Peralatan yang dapat digunakan untuk mengukur debit air harus disesuaikan dengan kondisi aliran air yang akan diukur

�Debit aliran yang kecil (1 s/d 5 lt/dt) cukup digunakan alat sederhana misalnya ember

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digunakan alat sederhana misalnya ember untuk mengukur volume dan arloji, jam tangan untuk mengukur waktu

�Untuk debit yg sedang dan besar

( > 5 lt/det) maka diperlukan alat ukur yang lebih baik dan lebih teliti

�Peralatan tersebut antara lain dinamakan current meter, yakni alat yang berfungsi

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current meter, yakni alat yang berfungsi mengukur kecepatan aliran air dg sangat teliti.

Dasar Perhitungan

• Rumus dasar:

• Q = A x V

Dimana :

Q = debit aliran (m3/det)

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Q = debit aliran (m3/det)

A = Luas penampang aliran (m2)

V = Kecepatan aliran air (m/det)

PENGUKURAN AIR DI PIPA

FAKULTAS PERTANIAN

UNIVERSITAS BRAWIJAYA

Debit Aliran Melalui Pipa

�Debit aliran yang melalui pipa dapat diukurdebitnya dengan cara meletak suatu alat yang disebut meter air.

�Q =C A (2gh)1/2 C= 0.6

�Prinsip kerja alat ini adalah merubah kecepatanaliran air menjadi putaran baling-2 (propeller) dankemudian dirubah dalam satuan debit.

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kemudian dirubah dalam satuan debit.

�Alat elektrik, singnal listrik, solar panel, transmisiradio

Meteran air

Mengukur debit air yang keluar dari Pipa

�Untuk debit kecil dapat diukur dg peralatan

ember dan jam tangan

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Q = A x V atau

Q = Vol / waktu

Ember

Contoh perhitungan

• Volume ember 6 liter:

• Waktu pengambilan air = 2 detik

• Maka debit aliran adalah

• Q = 6/2 = 3 liter/detik

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Pengambilan air harus dilakukan minimal 5 kali agar didapatkan hasil yg cukup teliti, dengan cara diambil harga rata-rata dari semua nilai yg didapat

Memperkiraan debit yg

lewat Pipa tertutup

Q = A x V

A = Luas penampang pipa (cm2 atau inc2)

V = Kecepatan aliran lewat pipa (m/dt)

Contoh perhitungan :

Kondisi Pipa dianggap penuh air, maka

A = ¼ µ d2, , d = diameter pipa ( 4 inci=10 cm)

A = ¼ x3,14 x(10) 2 = 78,5 cm2

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A = ¼ x3,14 x(10) 2 = 78,5 cm2

V = kecepatan air misal = 1 m/det=100 cm/dt, maka

Q = 78,5 x 100 = 7850 cm3/det= 7,85 lt/dt

1 hari = 24 jam=60 menit=86400 detik

Q = 7,85 x 86400 =678240 lt/dt=678,24 m3/hari

• Harga 1 m3=Rp 100,- = 67800,-/hari

• Harga 1 bln=30 hari = 30 x 67800 = Rp. 2.034.000,-/bln

PENGUKURAN AIR DI SALURAN

TERBUKA

FAKULTAS PERTANIAN

UNIVERSITAS BRAWIJAYA

Debit Air pada Saluran Irrigasi / Sungai

Untuk debit pada saluran irrigasi /sungai kecil

dapat diukur dengan cara sbb:

• Dengan menggunakan pelampung/gabus yang

diletakkan pada permukaan air yg sedang

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diletakkan pada permukaan air yg sedang

mengalir dan dicatat waktunya menempuh jarak

tertentu

• Mengukur kedalaman air dan lebar saluran

/sungai dengan meteran

Contoh Gambar

1 2

10 m, t =…..det? Misal t = 10 det

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V = 10 m/10 det = 1 m/det

Bila rata aliran = 80% aliran pelampungb = 2 m

h = 0,5 m A = b x h = 2 x 0,5 = 1 m2, maka

Q = A x V = 1 x 1 x 0.8 = 0.8 m3/det

Gambar Current Meter

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PERSYARATAN PENGUKURAN DEBIT DI SUNGAI

Persyaratan yang di maksud antara, lain

meliputi :

1. Lokasi pengukuran;

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1. Lokasi pengukuran;

2. Jumlah dan waktu pengukuran;

3. Peralatan, tenaga pelaksana dan dana.

1. Lokasi Pengukuran

� Mempunyai pola aliran yang seragam, kecepatan alirannya tidak terlalu lambat atau terlalu cepat.

� Pengukuran yang baik pada lokasi yang

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� Pengukuran yang baik pada lokasi yang mempunyai kecepatan aliran mulai dari 0,20 m/det sampai dengan 2,50 m/det;

� kedalaman aliran pada penampang pengukuran harus cukup, kedalaman aliran yang kurang dari 20 cm biasanya sulit diperoleh hasil Yang baik.

� Jangan Pada aliran turbulen/bergolak Yang

disebabkan oleh batu-batu, vegetasi,

penyempitan lebar alur sungai

� dilakukan pada alur sungai yang stabil atau lurus,

� lokasi pengukuran debit mudah didatangi, tidak

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� lokasi pengukuran debit mudah didatangi, tidak

tergantung dari keadaan cuaca khususnya pada

musim penghujan atau pada saat terjadi banjir;

2. Jumlah dan waktu pengukuran;

• Pelaksanaan pengukuran debit, hasilnya harus dapat menggambarkan sebuah lengkunng debit untuk sebuah penampang basah yang tidak tetap,

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basah yang tidak tetap,

• Jumlah pengukuran debit minimal 10 buah untuk sebuah lengkung debit yang datanya tersebar mulai keadaan aliran terendah sampai tertinggi

• Sedangkan periode pelaksanaannya tergantung daripada musim.

• Pada musim kemarau pada umumnya cukup satu sampai dua kali selama keadaan aliran masih tetap rendah.

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keadaan aliran masih tetap rendah.

• Pada musim penghujan memerlukan frekuensi pengukuran Yang lebih banyak, yaitu minimal 3 kali

Lengkung Debit

Tinggi air

1,4

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Tinggi air

(m)

Debit air

(m3/det)

0

1

2 5

3. Peralatan, tenaga pelaksana dan

dana

• Gabus, curret meter, arloji, meteran dll

• Mininal 1 -2 orang

• Tergantung situasi

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Bangunan Pengukur Debit pada

Saluran Irigasi

1.Bangunan Cipoletti

Berbentuk Segi empat H

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Berbentuk Segi empat

2.Bangunan Thomson

Berbentuk setitiga

Q = a Hb

H

H

B

www.themegallery.com

• Pintu Sorong

H

B

Bila sungainya besar?

Bagaimana cara mengukurnya?

• Misal lebar sungai = 20 meter

• Kedalaman air 2 meter

• Berapa debit nya?

74

• Berapa debit nya?

b = m ?

h =…m?

FIELD APPLICATION SYSTEMS

� There are many methods of applying water to the field. The simplest one consists of bringing water from the source of supply, such as a well, to each plant with a bucket or a water-can (see Fig. 90).

� This is a very time-consuming method and it involves quite heavy work. However, it can be involves quite heavy work. However, it can be used successfully to irrigate small plots of land, such as vegetable gardens, that are in the neighbourhood of a water source.

� More sophisticated methods of water application are used in larger irrigation systems. There are three basic methods:

� Surface irrigation

� Sprinkler irrigation

� Drip irrigation

SURFACE IRRIGATION

� Surface irrigation is the application of

water to the fields at ground level.

Either the entire field is flooded or the

water is directed into furrows or

borders. borders.

� Furrow irrigation

� Border irrigation

� Basin irrigation

FURROW IRRIGATION

� Furrows are narrow ditches dug on the field between the rows of crops. The water runs along them as it moves down the slope of the field.

� The water flows from the field ditch into the furrows by opening up the bank or dyke of the ditch (see Fig. 91a) or by means of syphons or spiles. Siphons are small curved pipes that deliver water over the ditch bank (see Fig. 91b). Spilesare small pipes buried in the ditch bank (see Fig. 91c).

BORDER IRRIGATION

� In border irrigation, the field to be irrigated is divided into strips (also called borders or borderstrips) by parallel dykes or border ridges (see Fig. 92).

� The water is released from the field ditch onto the border through gate structures called outlets (see Fig. 92). The water can also be released by means of siphons or spiles. The sheet of flowing water moves down the slope of the border, guided by the border ridges.

Perkiraan aliran (l/detik) pada siphons

H (cm) Diameter siphons (mm)

27 34 42 53 63 76

5 0.3 0.6 0.9 1.5 2.1 3.1

H

5 0.3 0.6 0.9 1.5 2.1 3.1

7 0.4 0.7 1.1 1.8 2.5 3.7

10 0.5 0.8 1.3 2.1 3.0 4.5

15 0.6 1.0 1.6 2.6 3.7 5.5

20 0.7 1.1 1.8 3.0 4.3 6.3

30 0.8 1.4 2.2 3.6 5.2 7.7

50 1.1 1.8 2.8 4.7 6.8 10.0

PANJANG MAKSIMUM IRRIGASI ALUR

(m)

Q

max

(l/s)

S

(%)

Rata-rata kedalaman air yang diterapkan (m)

75 150 225 30

0

50 100 150 200 50 75 100 125

Liat Lempung PasirLiat Lempung Pasir

6.0 0.1 340 440 470 50

0

180 340 440 470 90 120 190 220

1.2 0.5 400 500 560 75

0

280 370 470 530 120 190 250 300

0.3 2.0 220 270 340 40

0

180 250 250 340 60 90 150 190

BASIN IRRIGATION

� Basins are horizontal, flat plots of land, surrounded by small dykes or bunds. The banks prevent the water from flowing to the surrounding fields. Basin irrigation is commonly used for rice grown on flat lands or in terraces on hillsides (see Fig. 93a). Trees can also be grown in basins, where one tree usually is located in the centre of a small basin (see Fig. 93b).

SPRINKLER IRRIGATION

� With sprinkler irrigation, artificial rainfall is created. The water is led to the field

through a pipe system in which the water is under pressure. The spraying is

accomplished by using several rotating sprinkler heads or spray nozzles (see

Fig. 94a) or a single gun type sprinkler (see Fig. 94b).

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Irigasi dalam budidaya tanaman tebu di GMP : tujuan

• Menekan kejadian defisit air yang

dialami oleh tanaman tebu : durasi,

intensitas, dan luasan tanaman yang

menderita

• Menekan kehilangan hasil pasca

musim kemarau yang ekstrim hingga musim kemarau yang ekstrim hingga

sekecil mungkin

• Memantapkan tingkat produksi dari

tahun ke tahun dan mening-katkan

produktivitas secara sinambung

Irigasi dalam budidaya tebu di GMP :

pendekatan

• Pengembangan potensi sumber-daya air : pengukuran dan peme-taan; identifikasi karakter sumber air; reklamasi sumber/badan air

• Pemeliharaan dan pelestarian sumberdaya air : penghijauan DAS; sumberdaya air : penghijauan DAS; pengendalian erosi; pengendalian gulma air dan gulma terestrial

• Penguasaan teknik aplikasi irigasi : pengetahuan dasar, perhitungan, pemilihan sistem, penyediaan prasarana dan sarana

• Penyesuaian budidaya : bulan tanam, block system

Irigasi dalam budidaya tebu di GMP : pilihan

sistem aplikasi

• Perhitungan kebutuhan air tanaman

• Penentuan prioritas stadia pertum-

buhan tanaman yang diirigasi

• Irigasi curah vs irigasi tetes vs irigasi • Irigasi curah vs irigasi tetes vs irigasi

alur

• Irigasi curah : big-gun mobile

sprinkler vs travelling irrigator

DRIP IRRIGATION

� In drip irrigation, also called trickle irrigation, the water is led to the field through a pipe system. On the field, next to the row of plants or trees, a tube is installed. At regular intervals, near the plants or trees, a hole is made in the tube and equipped with an emitter. The water is supplied slowly, drop by drop, to the plants through these emitters (Fig. 95).

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DRAINAGE SYSTEM

� (A drainage system is necessary to remove excess water from the irrigated land. This excess water may be e.g. waste water from irrigation or surface runoff from rainfall. It may also include leakage or seepage water from the distribution system.

� Excess surface water is removed through shallow open drains (see Surface drainage, Chapter 6.2.1). Excess groundwater is removed through deep open drains or underground pipes (see Subsurface drainage, Chapter 6.2.2).

TUGAS KUALITAS AIR IRIGASI

1. Pemerintah telah mengeluarkan standar kualitas Air Irigasi, untuk itu dari standar tersebut, melalui studiliteratur deskripsikan teknik mengukur masing-masingstandar kualitas air irrigasi tersebut. Mengapa kualitastersebut penting bagi pertanian.

2. Kualitas Air di sepanjang Sungai Brantas telah di lakukanmonitoring secara periodik oleh Perum Jasa Tirta, monitoring secara periodik oleh Perum Jasa Tirta, tetapkan wilayah pengairan yang memenuhi standar air irrigasi dan wilayah pengairan yang tidak memenuhistandar air irrigasi, dari waktu kewaktu.

3. Melalui kajian literatur, beri rekomendasi bagaimana caraagar wilayah pengairan yang tidak memenuhi standarkualitas air irigasi menjadi air irigasi yang memenuhistandar kualitas air irigasi bagi usaha pertanian.

STRATEGI KONSERVASI AIR

� (1) REDUCE PLANT WATER DEMAND

� A. Plant selection

� B. Site landscape design

� C. Plant cultural practices

� D. Root zone depth� D. Root zone depth

� E. Mulching

� F. Soil amendments

� (2) MAXIMISE IRRIGATION APPLICATION EFFICIENCY

� (3) PRECISE CONTROL OF IRRIGATION

� (4) ADOPT NEW TECHNOLOGIES

� (5) OPERATOR SKILLS




� A. High uniformity

� B. Optimise hydraulic operating conditions for outlets

� C. Correct outlet selection� C. Correct outlet selection

� D. Effective outlet coverage

� E. Effective functioning of equipment

� F. Low head drainage








� A. Match irrigation to plant water demand

� B. Correct depth of irrigation� B. Correct depth of irrigation

� C. Hydrozones


� A. Weather stations

� B. Soil moisture sensors

� C. Smart controllers

� D. Alternative method of irrigation - Subsurface drip


TERIMAKASIHTERIMAKASIH

sistem irrigasi

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