STUDI TINJAUAN KELAYAKAN EMBUNG GROJOGAN DESA

PLANDAAN KECAMATAN PLANDAAN KABUPATEN

JOMBANG

SKRIPSI

TEKNIK PENGAIRAN KONSENTRASI PENGETAHUAN DASAR

TEKNIK SDA

Ditujukan untuk memenuhi persyaratan

memperoleh gelar Sarjana Teknik (S.T.)

TOMY DWI HARTANTO

NIM. 115060407111005

UNIVERSITAS BRAWIJAYA

FAKULTAS TEKNIK

MALANG

2018

DAFTAR ISI

KATA PENGANTAR .............................................................................................. i

DAFTAR ISI ............................................................................................................ iii

DAFTAR TABEL .................................................................................................... v

DAFTAR GAMBAR ................................................................................................ vii

RINGKASAN .......................................................................................................... xi

BAB I PENDAHULUAN

1.1 Latar Belakang Masalah....................................................................................... 1

1.2 Identifikasi Masalah ............................................................................................ 2

1.3 Batasan Masalah ................................................................................................. 2

1.4 Rumusan Masalah ............................................................................................... 3

1.5 Tujuan dan Manfaat ............................................................................................ 3

BAB II TINJAUAN PUSTAKA

2.1 Embung..................................................................................................... 5

2.1.1 Tipe Embung Berdasarkan Tujuan Pembangunan.............................. 5

2.1.2 Tipe Embung Berdasarkan Penggunaannya ....................................... 5

2.1.3 Tipe Embung Berdasarkan Jalannya Air ............................................ 6

2.1.4 Tipe Embung Berdasarkan Material Pembentuknya .......................... 6

2.2 Kestabilan Lereng ..................................................................................... 7

2.3 Ketersediaan Air Embung .......................................................................... 8

2.3.1 Prediksi Debit Sungai Dengan Metode NRECA ................................ 9

2.3.2 Curah Hujan dan Curah Hujan Efektif ............................................... 10

2.4 Kebutuhan Air Irigasi ................................................................................ 12

2.4.1 Evapotranspirasi................................................................................ 13

2.4.2 Harga Koefisien Tanaman ................................................................. 17

2.4.3 Penggunaan Konsumtif ..................................................................... 18

2.4.4 Penggantian Lapisan Tanah ............................................................... 18

2.4.5 Kebutuhan Air Selama Penyiapan Lahan........................................... 18

2.4.6 Perkolasi .......................................................................................... 19

2.4.6 Analisis Neraca Air ........................................................................... 19

2.5 Analisis Manfaat ...................................................................................... 20

2.5.1 Manfaat Irigasi .................................................................................. 20

2.5.2 Manfaat Proyek ................................................................................. 21

2.6 Analisis Biaya Proyek ................................................................................ 22

2.6.1 Biaya Modal ..................................................................................... 22

2.6.2 Biaya Tahunan .................................................................................. 24

2.7 Analisis Ekonomi ..................................................................................... 24

2.7.1 Rasio Manfaat dengan Biaya (B/C Ratio) .......................................... 24

2.7.2 Selisih Biaya Manfaat (B-C) ............................................................. 25

2.7.3 Tingkat Pengembalian Internal (IRR) ................................................ 25

2.7.4 Periode Pengembalian ....................................................................... 25

2.7.5 Analisis Sensivitas ........................................................................... 26

2.8 Analisis Lingkungan ................................................................................. 26

BAB III METODOLOGI KAJIAN

3.1 Deskripsi Embung Grojogan ...................................................................... 27

3.2 Pengumpulan Data ..................................................................................... 29

3.3 Langkah Pengerjaan................................................................................... 30

3.3.1 Menganalisis Studi Kelayakan Awal ................................................. 30

3.3.2 Menganalisis Neraca Air ................................................................... 30

3.3.3 Menganalisis Manfaat, Biaya, dan Ekonomi ...................................... 30

3.3.4 Menganalisis Kelayakan Lingkungan ................................................ 31

3.4 Diagram Alir Kajian .................................................................................. 32

BAB IV HASIL DAN PEMBAHASAN

4.1 Keadaan Embung Grojogan ............................................................. 33

4.2 Dampak Lingkungan Pembangunan Embung ............................................. 33

4.2.1 Lingkungan Fisik…………………………………………… ............. 33

4.2.2 Lingkungan Biologi .......................................................................... 35

4.2.3 Lingkungan Sosial ............................................................................ 35

4.3 Stabilitas Lereng ..................................................................................... 36

4.3.1 Aliran Filtrasi (Rembesan) ............................................................... 37

4.3.2 Bidang Longsor ................................................................................ 40

4.4 Ketersediaan Air Embung .......................................................................... 42

4.5 Debit Andalan Embung ............................................................................. 51

4.6 Kebutuhan Air Irigasi ................................................................................ 52

4.7 Analisis Neraca Air Embung Grojogan ...................................................... 57

4.8 Biaya Proyek Pembangunan Embung Grojogan ......................................... 60

4.8.1 Biaya Modal (Capital Cost) ............................................................. 60

4.8.2 Biaya Tahunan (Annual Cost) .......................................................... 62

4.9 Manfaat Proyek (Benefit) .......................................................................... 62

4.10 Analisis Manfaat-Biaya ........................................................................... 66

4.10.1 Rasio Manfaat-Biaya (B/C) ............................................................ 67

4.10.2 Tingkat Pengembalian Internal (IRR) ............................................. 68

4.10.3 Periode Pengembalian (Payback Period) ........................................ 68

4.10.4 Analisis Sensitivitas Proyek ............................................................ 68

BAB V KESIMPULAN DAN SARAN

5.1 Kesimpulan ............................................................................................... 73

5.2 Saran ......................................................................................................... 74

DAFTAR PUSTAKA

LAMPIRAN

DAFTAR TABEL

No Judul Halaman

Tabel 2.1 Faktor Keamanan Stabilitas Lereng dalam Kondisi Tanpa Gempa ............. 7

Tabel 2.2 Faktor Keamanan Stabilitas Lereng dalam Kondisi Dengan Gempa ........... 8

Tabel 2.3 Hubungan suhu (t) dengan nilai ea, W, dan f (t) ........................................ 15

Tabel 2.4 Besar Nilai Angot Untuk Daerah Indonesia ............................................... 16

Tabel 2.5 Besaran Angka Koreksi (c) Bulana ............................................................ 16

Tabel 2.6 Harga Koefisien Tanaman Padi.................................................................. 17

Tabel 2.7 Harga Koefisien Tanaman Palawija dengan Metode Penman ..................... 17

Tabel 3.1 Data yang digunakan dalam Studi .............................................................. 29

Tabel 4.1 Koordinat Rembesan Aliran Filtrasi Kondisi Muka Air Normal ................. 38

Tabel 4.2 Koordinat Rembesan Aliran Filtrasi Kondisi Muka Air Banjir ................... 40

Tabel 4.3 Perhitungan Bidang Longsor Kondisi Muka Air Normal ............................ 42

Tabel 4.4 Perhitungan Bidang Longsor Kondisi Muka Air Banjir .............................. 43

Tabel 4.5 Curah Hujan Rerata 10 harian di Embung Grojogan .................................. 44

Tabel 4.6 Hubungan temperatur (t) dengan nilai ea, w dan f(t) .................................. 45

Tabel 4.7 Nilai Angot (Ra) ....................................................................................... 46

Tabel 4.8 Koefisien Reduksi Penman ........................................................................ 46

Tabel 4.9 Hasil Perhitungan Evapotranspirasi Potensial ............................................ 47

Tabel 4.10 Parameter NRECA .................................................................................... 48

Tabel 4.11 Debit aliran air di Embung Metode NRECA .............................................. 50

Tabel 4.12 Hasil Perhitungan Debit Andalan Embung ................................................. 51

Tabel 4.13 Perhitungan Kebutuhan air untuk Penyiapan Lahan tanam Padi ................. 53

Tabel 4.14 Rangking Curah Hujan .............................................................................. 55

Tabel 4.15 Hasil Perhitungan Curah Hujan Efektif ...................................................... 56

Tabel 4.16 Neraca Air dengan Simulasi Embung Grojogan ........................................ 59

Tabel 4.17 RAB Proyek Embung Grojogan ................................................................. 60

Tabel 4.18 Biaya Tidak Langsung Embung Grojogan ................................................. 62

Tabel 4.19 Keuntungan Tanam Padi Musim Hujan per Hektar Sawah ......................... 63

Tabel 4.20 Keuntungan Tanam Padi Musim Kemarau 1 per Hektar Sawah ................. 64

Tabel 4.21 Keuntungan Tanam Jagung Musim Kemarau 2 per Hektar Sawah ............. 65

Tabel 4.22 Proyeksi keuntungan pertanian dari irigasi Embung Grojogan ................... 66

Tabel 4.23 Hasil perhitungan IRR ............................................................................... 67

Tabel 4.24 Hasil Perhitungan analisis sensitivitas biaya naik 20% ............................... 68

Tabel 4.25 Hasil Perhitungan sensitivitas Biaya tetap manfaat turun 20% ................... 69

Tabel 4.26 Hasil Perhitungan sensitivitas Biaya tetap naik 20, manfaat turun 20% ..... 70