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Perhitungan Luas

Contoh Perhitungan di petak Tersier

Skala 1 : 25.000

1 cm : 25.000 cm

1 cm : 250 m

1 cm2 : 2502 m2

1 cm2 : 62500 m2

1 cm2 :6250010000

ha

1 cm2 : 6,25 ha

- W3 . Ki

Berdasarkan perhitungan luas petak = 6.71 cm2

L = 6.71 x 16 = 107.36 ha

- B3 . Ka


L = 6.12 x 16 = 97.92 ha

- B9.Ka


L = 6.29 x 16 = 100.64 ha

Perhitungan NFR

Contoh pehitungan NFR

- Bulan Nopember Periode 1

ET0 : 5,20 mm/hr

P : 2,00 mm/hr

T : 31 hari

S : 300 mm

Re : 1,37 mm/hr

M = (1,1 ET0 + P)

= (1,1 (5,20) + 2)

= 7,72 mm/hr

k = M .T

S

= 7,72 x 31

300

= 0,798

IR = M .ek

ek−11 mm/hr =0,001 m x10000 m2

24 x3600

= 7,72 x e0,798

e0,798−11 mm/hr = 0,000116 m3/dt/ha

= 14,36 mm/hr 1 mm/hr = 0,116 l/dt/ha

NFR = IR - Re

= 14,36 – 1,37

= 12,99 mm/hr ( 0,116 )

= 1,503 l/dt/ha

- Bulan Desember Periode 1

ET0 : 4,20 mm/hr

P : 2,00 mm/hr

c : 1,27 (koef. Rata-rata tanaman)

WLR : 1,10 mm/hr

Re : 3,84 mm/hr

ETc = ET0 x c

= 4,20 x 1,27

= 5,334 mm/hr

NFR = ETc + WLR + P - Re

= 5,334 +1,10 + 2,00 – 3,84

= 4,58 mm/hr (0,116)

= 0,53 l/dt/ha

- Bulan April Periode 1

ET0 : 4,30 mm/hr

P : 2,00 mm/hr

c : 1,27 (koef. Rata-rata tanaman)

WLR : 1,10 mm/hr

Re : 4,86 mm/hr

ETc = ET0 x c

= 4,30 x 1,27

= 5.461 mm/hr

NFR = ETc + WLR + P - Re

= 5,461 +1,10 + 2,00 – 4,86

= 3,687 mm/hr (0,116)

= 0,427 l/dt/ha

( Jadi, NFR yang dipakai yaitu NFRmax = 1,50 l/dt/ha )

Diagram Pola Tanam

NOP DES JAN FEB MAR APR MEI JUN JUL AGS SEP OKT1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2

Tabel Kebutuhan Air Netto (NFR)

BulanPeriod

eNFR

(l/dt/ha)DR

November1 12.990 1.5032 11.210 1.297

Desember1 4.580 0.5302 8.890 1.029

Januari1 6.914 0.8002 6.040 0.699

Februari1 12.810 1.4832 7.470 0.865

Maret1 9.140 1.0582 7.060 0.817

April1 3.687 0.4272 2.270 0.263

Mei1 8.090 0.9362 3.330 0.385

Juni1 0.000 0.0002 0.898 0.104

Juli1 0.000 0.0002 4.180 0.484

Agustus1 3.809 0.4412 2.583 0.299

September 1 3.920 0.454

2 0.000 0.000

Oktober1 1.522 0.1762 1.481 0.171

Perhitungan Debit Saluran

Contoh perhitungan debit saluran Tersier

- Saluran W3 . Ki

NFR : 1,503 l/dt/ha

Luas : 107.36 ha

et : 0,8

Q = A x NFR

= 107.36 x 1,503

= 161,362 l/dt

Qt = Qe t

= 161,362

0,8

= 201,703 l/dt

- Saluran B3 . Ka

NFR : 1,503 l/dt/ha

Luas : 97,92 ha

et : 0,8

Q = A x NFR

= 97,92 x 1,503

= 147,174 l/dt

Qt = Qe t

= 147,174

0,8

= 183,967 l/dt

- Saluran B9.Ka

NFR : 1,503 l/dt/ha

Luas : 100,64 ha

et : 0,8

Q = A x NFR

= 100,64 x 1,503

= 151,262 l/dt

Qt = Qe t

= 151,262

0,8

= 189,077 l/dt

( Perhitungan selanjutnya disajikan di tabel )

Tabel Perhitungan Debit pada petak tersier

SaluranLuas Petak

(ha)NFR

(l/dt/ha)et

Q (l/dt)

Qt (l/dt)

W1.Ka.1 86.4 1.503 0.8 129.859 162.324W1.Ka.2 92.8 1.503 0.8 139.478 174.348W1.Ki 89.6 1.503 0.8 134.669 168.336

W2.Ka.1 94.4 1.503 0.8 141.883 177.354W2.Ka.2 92.8 1.503 0.8 139.478 174.348W2.Ki 94.4 1.503 0.8 141.883 177.354

W3.Ka.1 98.56 1.503 0.8 148.136 185.170W3.Ka.2 102.08 1.503 0.8 153.426 191.783W3.Ki 107.36 1.503 0.8 161.362 201.703

W4.Ka.1 105.6 1.503 0.8 158.717 198.396W4.Ka.2 102.08 1.503 0.8 153.426 191.783W4.Ki 109.12 1.503 0.8 164.007 205.009

W5.Ka.1 97.92 1.503 0.8 147.174 183.967W5.Ka.2 78.88 1.503 0.8 118.557 148.196W5.Ki 97.92 1.503 0.8 147.174 183.967

W6.Ka.1 106.4 1.503 0.8 159.919 199.899W6.Ka.2 89.68 1.503 0.8 134.789 168.486W6.Ki 109.44 1.503 0.8 164.488 205.610

W7.Ka.1 103.36 1.503 0.8 155.350 194.188W7.Ka.2 91.2 1.503 0.8 137.074 171.342W7.Ki 91.2 1.503 0.8 137.074 171.342

W8.Ka.1 100.8 1.503 0.8 151.502 189.378W8.Ka.2 86.4 1.503 0.8 129.859 162.324W8.Ki 82.08 1.503 0.8 123.366 154.208B1.Ka 109.44 1.503 0.8 164.488 205.610

B1.Ki 103.68 1.503 0.8 155.831 194.789B2.Ka 97.28 1.503 0.8 146.212 182.765B2.Ki 94.08 1.503 0.8 141.402 176.753B3.Ka 97.92 1.503 0.8 147.174 183.967B3.Ki 92.16 1.503 0.8 138.516 173.146B4.Ka 95.36 1.503 0.8 143.326 179.158B4.Ki 93.44 1.503 0.8 140.440 175.550B5.Ka 89.6 1.503 0.8 134.669 168.336B5.Ki 97.28 1.503 0.8 146.212 182.765B6.Ka 86.4 1.503 0.8 129.859 162.324B6.Ki 106.56 1.503 0.8 160.160 200.200B7.Ka 72.6 1.503 0.8 109.118 136.397B7.Ki 84 1.503 0.8 126.252 157.815B8.Ka 98.56 1.503 0.8 148.136 185.170B8.Ki 92.16 1.503 0.8 138.516 173.146B9.Ka 100.64 1.503 0.8 151.262 189.077B9.Ki 66 1.503 0.8 99.198 123.998

Contoh Perhitungan debit saluran sekunder

- Saluran RW 1

NFR : 1,503 l/dt/ha

Luas : 2041,68 ha

et : 0,8

es : 0,85

Q = A x NFR

= 2041 x 1,503

= 3068,645 l/dt

Qs = Q

et x es

= 3068,6450,8 x0,85

= 4512,713 l/dt

- Saluran RW 5

NFR : 1,503 l/dt/ha

Luas : 860,56 ha

et : 0,8

es : 0,85

Q = A x NFR

= 860,56 x 1,503

= 1293,422 l/dt

Qs = Q

et x es

= 1293,4220,8 x0,85

= 1902,091 l/dt

- Saluran RB 8

NFR : 1,503 l/dt/ha

Luas : 166,64 ha

et : 0,8

es : 0,85

Q = A x NFR

= 166,64 x 1,503

= 250,460 l/dt

Qs = Q

et x es

= 250,46

0,8 x0,85

= 368,323 l/dt

Tabel Perhitungan Debit pada saluran sekunderSaluran Wukir

Luas Petak (ha)

NFR (l/dt/ha)

Et esQ

(l/dt)Qs

(l/dt)

RW1 2041.68 1.503 0.8 0.85 3068.645 4512.713RW2 1760.08 1.503 0.8 0.85 2645.400 3890.294RW3 1452.08 1.503 0.8 0.85 2182.476 3209.524RW4 1135.28 1.503 0.8 0.85 1706.326 2509.303RW5 860.56 1.503 0.8 0.85 1293.422 1902.091RW6 555.04 1.503 0.8 0.85 834.225 1226.802RW7 269.28 1.503 0.8 0.85 404.728 595.188

Saluran Bangun

Luas Petak (ha)

NFR (l/dt/ha)

Et es Q (l/dt) Qs (l/dt)

RB1 1464.04 1.503 0.8 0.85 2200.452 3235.959

RB2 1272.68 1.503 0.8 0.85 1912.838 2812.997RB3 1082.6 1.503 0.8 0.85 1627.148 2392.864RB4 893.8 1.503 0.8 0.85 1343.381 1975.561RB5 706.92 1.503 0.8 0.85 1062.501 1562.501RB6 513.96 1.503 0.8 0.85 772.482 1136.003RB7 357.36 1.503 0.8 0.85 537.112 789.871RB8 166.64 1.503 0.8 0.85 250.460 368.323

Contoh perhitungan debit saluran primer

- Saluran RP 1

NFR : 1,503 l/dt/ha

Luas : 3987,64 ha

et : 0,8

es : 0,85

ep : 0,9

Q = A x NFR

= 3987,53 x 1,503

= 5993,423 l/dt

Qp = Q

et x es xe p

= 5993,423

0,8 x0,85 x 0,9

= 9793,175 l/dt

- Saluran RP 2

NFR : 1,503 l/dt/ha

Luas : 1677,16 ha

et : 0,8

es : 0,85

ep : 0,9

Q = A x NFR

= 1677,16 x 1,503

= 2520,771 l/dt

Qp = Q

et x es xe p

= 2520,771

0,8 x0,85 x 0,9

= 4118,908 l/dt

Tabel Perhitungan Debit pada saluran primerSaluran

PasirLuas Petak

(ha)NFR

(l/dt/ha)Et es ep

Q (l/dt)

Qs (l/dt)

RP1 3987.64 1.503 0.8 0.85 0.9 5993.423 9793.175RP2 1677.16 1.503 0.8 0.85 0.9 2520.771 4118.908

Desain Dimensi Hidrolik Saluran Tersier

Contoh perhitungan dimensi saluran tersier

- Saluran M3. Ki

A : 107,36 ha

Q : 161,362 l/dt

Qt : 201,703 l/dt = 0,202 m3/dt

Dengan nilai Q diatas, maka didapat nilai-nilai sebagai berikut

m = 1 n = 1 k = 35 I = 0,0005 (direncanakan)

Tinggi Saluran ( h )

h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 0,202 .(1+2√1+12)23

(1+1 )53 . 35.0,0005

12 )

38

= 0,546 m

Lebar Saluran ( b )

b = n . h

= 1 . 0,546

= 0,546 m

Luas Penampang Saluran (A)

A = ( b + m.h ) h

= ( 0,546 + ( 1. 0,546)). 0,546

= 0,595 m2

Keliling Basah Saluran (P)

P = b + 2h√1+m2

= 0,546 + 2.(0,546)√1+12

= 2,088 m

Jari – jari Hidrolis (R)

R = AP

= 0,5952,088

= 0,285 m

Kemiringan Saluran (I)

I = 0,0005 (direncanakan)

Kecepatan Aliran (V)

V = QA

= 0 ,2020,595

= 0,339 m/dt

- Saluran B3. Ka

A : 97,92 ha

Q : 147,174 l/dt

Qt : 183,967 l/dt = 0,183 m3/dt




h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 0,183 .(1+2√1+12)23

(1+1 )53 . 35 .0,0005

12 )

38

= 0,527 m

Lebar Saluran ( b )

b = n . h

= 1 . 0,527

= 0,527 m


A = ( b + m.h ) h

= ( 0,527 + ( 1. 0,527)). 0,527

= 0,555 m2


P = b + 2h√1+m2

= 0,527 + 2.(0,527)√1+12

= 2,018 m


R = AP

= 0,5552,018

= 0,275 m




V = QA

= 0 ,1830,555

= 0,331 m/dt

- Saluran B9. Ka

A : 100,64 ha

Q : 151,262 l/dt

Qt : 189,077 l/dt = 0,189 m3/dt




h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 0,189 .(1+2√1+12)23

(1+1 )53 . 35 .0,0005

12 )

38

= 0,532 m

Lebar Saluran ( b )

b = n . h

= 1 . 0,532

= 0,532 m


A = ( b + m.h ) h

= ( 0,532 + ( 1. 0,532)). 0,532

= 0,567 m2


P = b + 2h√1+m2

= 0,532 + 2.(0,532)√1+12

= 2,038 m


R = AP

= 0,5672,038

= 0,275 m




V = QA

= 0 ,1890,555

= 0,333 m/dt

Desain Dimensi Hidrolik Saluran Sekunder

Contoh perhitungan dimensi saluran sekunder

- Saluran RW 1

A : 2041,68 ha

Q : 3068,645 l/dt

Qs : 4512,713 l/dt = 4,513 m3/dt


m = 1,5 n = 2.7 k = 40 I = 0,0003 (direncanakan)


h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 4,513 .(2,7+2√1+1,52)23

(2,7+1,5 )53 .40 .0,0003

12 )

38

= 1,305 m

Lebar Saluran ( b )

b = n . h

= 2.7 . 1,305

= 3.523 m


A = ( b + m.h ) h

= ( 3.523 + ( 1,5. 1,305)). 1,305

= 7.152 m2


P = b + 2h√1+m2

= 3,523 + 2.(1,305)√1+1,3052

= 8,228 m


R = AP

= 7,1528,228

= 0,869 m




V = QA

= 4,5137,512

= 0,631 m/dt

- Saluran RW 5

A : 860,56 ha

Q : 1293,422 l/dt

Qs : 1902,091 l/dt = 1,902 m3/dt


m = 1,5 n = 2.0 k = 40 I = 0,0004 (direncanakan)


h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 1,902.(2+2√1+1,52)23

(2+1,5 )53 . 40 . 0,0004

12 )

38

= 1,02 m

Lebar Saluran ( b )

b = n . h

= 2 . 1,02

= 2,04 m


A = ( b + m.h ) h

= ( 2,04 + ( 1,5. 1,02)). 1,02

= 3,641 m2


P = b + 2h√1+m2

= 2,04 + 2.(1,02)√1+1,022

= 5,718 m


R = AP

= 3,6415,718

= 0,637 m




V = QA

= 1,9023,641

= 0,522 m/dt

- Saluran RB 8

A : 166,64 ha

Q : 250,460 l/dt

Qs : 368,323 l/dt = 0,368 m3/dt


m = 1 n = 1,2 k = 35 I = 0,0005 (direncanakan)


h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 0,368.(1,2+2√1+12)23

(1,2+1 )53 . 40 .0,0004

12 )

38

= 0,652 m

Lebar Saluran ( b )

b = n . h

= 1,2 . 1

= 1,2 m


A = ( b + m.h ) h

= ( 1,2 + ( 1. 1)). 1

= 0,936 m2


P = b + 2h√1+m2

= 1,2 + 2.(1)√1+12

= 2,628 m


R = AP

= 0,9362,628

= 0,356 m




V = QA

= 0,3680,936

= 0,393 m/dt

Desain Dimensi Hidrolik Saluran Primer

Contoh perhitungan dimensi saluran primer

- Saluran RP 1

A : 3987 ha

Q : 5993,423 l/dt

Qp : 9793,175 l/dt = 9,793 m3/dt


m = 1,5 n = 3,8 k = 42,5 I = 0,000225 (direncanakan)


h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 9,793 .(3,8+2√1+1,52)23

(3,8+1,5 )53 . 42,5 . 0,000225

12 )

38

= 1,62 m

Lebar Saluran ( b )

b = n . h

= 3,8 . 1,62

= 6,158 m


A = ( b + m.h ) h

= ( 6,158 + ( 1,5. 1,62)). 1,62

= 13,917 m2


P = b + 2h√1+m2

= 6,158 + 2.(1,62)√1+1,52

= 12 m


R = AP

= 13,917

12

= 1,16 m




V = QA

= 9,793

13,917

= 0,704 m/dt

- Saluran RP 2

A : 1677,16 ha

Q : 2520,771 l/dt

Qp : 4118,908 l/dt = 4,119 m3/dt


m = 1,5 n = 2,5 k = 40 I = 0,0003 (direncanakan)


h = (Q .(n+2√1+m2)23

(n+m )53 . k . I

12 )

38

= ( 4,119 .(32,5+2√1+1,52)23

(2,5+1,5 )53 . 40. 0,000225

12 )

38

= 1,290 m

Lebar Saluran ( b )

b = n . h

= 2,5 . 1,29

= 3,224 m


A = ( b + m.h ) h

= ( 3,224 + ( 1,5. 1,29)). 1,29

= 6,652 m2


P = b + 2h√1+m2

= 3,224 + 2.(1,29)√1+1,52

= 7,874m


R = AP

= 6,6527,874

= 0,845 m




V = QA

= 4,1186,652

= 0,619 m/dt

PERENCANAAN GORONG-GORONG

Elevasi hulu R. W. 1

El.Talud = + 113.220

El.MA = + 112.620

El.MTA = + 115 El.Dasar Sal

Elevasi pada R.M.5 hulu Gorong – gorong

El.Muka Tanah Asli = + 110 + (

400800 . (115 – 110))

= + 112,5

El. Muka Air = + 112,380 + (0.0003 x 357)= + 112,5

El. Dasar Saluran = + 112,5 - h = + 112,5 – 1,305= + 111,195

El. Talud = + 112,5 + w= + 112,5 + 0.6= + 111,795

Kelas jalan II dengan lebar lajur ideal 3.5 m sehingga lebar jalan 7 m.

Elevasi Pada R.W.5 hilir

El.Muka Tanah Asli = + 110 + (

393800 . (115 – 110))

Dimensi R. W. 1

Q = 4,513 m3/dt

V = 0.631 m/dt

b = 3,523 m

h = 1,305 m

I = 0,0003

m= 1.5

n = 2,7

w = 0.6 m

L = 800 m

BM. 4

BW. 5

RW. 1

800 m

400 m

= + 112,456

El. Muka Air = + 112.380 + (0.0003 x 393)= + 112,497

El. Dasar Saluran = + 112,497 - h = + 112,497 – 1.02= + 111,192

El. Tanggul = + 112,497 + w= + 112,497 + 0.6= + 113,097

(Kelas jalan II dengan lebar lajur ideal 3.5 m sehingga lebar jalan = 7 m)

Analisa Perhitungan

1. Kecepatan rencana ditetapkan 1,50 m/dt – 2,00 m/dt

Direncankan Va = 2.00 m/dt

Dimana:

Q = A x Va

A = Q / Va

=

7 .152 m3 /dt2

= 3,576 m2

2. Jika direncanakan bentuk penampang persegi

B = n.h

= 2,7 h

A = b x h

7.152 m2 = 2,7h x h

h2 = 2,648 m2

h = 1,627 m

Maka,

b = n.h

b = 2,7 x 1,627 m

= 4,39 m

P = b + 2h

P = 4,39 + 2 (1,627)

P = 7,64 m

R = AP

R =

7 .152 8. 228

R = 0.869 m

3. Menghitung Kehilangan energi

Va = 2.00 m/det

V = 0.631 m/det

Sepanjang gorong – gorong akibat gesekan

dimana :

P = 8,228 m

A = 7,152 m2

R = 0,869 m

C = k x R1/6

= 40 x (0.869)1/6

= 39,074

Dhf = Va2 xLC2 xR

=

2 .002̂ x 839,074 2̂ x 0,869

= 0.024 m

Dh masuk = 0 .50

(Va−V )2

2 g

= 0 , 50

(2. 00−0 .631 )2

2 (9 , 81)= 0.04 m

Dh keluar = 1 .00

(Va−V )2

2 g

= 1 .00

(2 . 00−0 , 631 )2

2(9 , 81 )

= 0.09 m

Total kehilangan energi :

hf = hfgesekan + hfmasuk + hfkeluar

= 0.024 + 0.04 + 0.09

= 0.154 m

tugas irigasi sp

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