Sensitivitas alat ukur debit Cipoletti di saluran irigasi

PURBANINGTYAS, Daru, Prof.Dr.Ir. Budi Wignyosukarto, Dip.HE.,DEA

2006 | Tesis | S2 Teknik Sipil

Pembagian air irigasi yang memenuhi kriteria tepat waktu, jumlah dan kualitas, merupakan harapan banyak pihak khususnya para petani. Keberadaan bangunan/alat ukur debit menjadi penting dalam sistem pendistribusian air irigasi. Ketelitian dan sensivitas mempakan parameter penting dalam pemilihan alat ukur debit. Sensivitas menunjukkan kemampuan alat ukur mengukur setiap perubahan debit. Ketelitian alat ukur debit ditunjukkan dalam ketelitian persamaan debit- kedalaman aliran yang memberikan nilai debit untuk setiap kedalaman aliran yang temkur, baik pada saat aliran bebas maupun aliran terendam. Penelitian ini membuat evaluasi alat ukur debit Cipoletti berbentuk trapesium dengan variasi pada kemiringan sisi /tepi, yaitu m = 1:1, m = 1:2, m = 125, m = 1:3 dan m = 1:4. Masing-masing model diuji dengan lima atau enam besaran debit yang berkisar antara 1200 cm3/s sampai 4700 cm3/s. Kedalaman air di hulu dan di hilir model dicatat secara serentak dan menems dengan alat wave height meter dari kondisi aliran bebas sampai menjadi aliran tenggelam. Pembahan kedalaman air hilir diperoleh dengan menaikkan pintu belakang (tailgate) secara menerus dan perlahan- lahan. Hasil pengujian menunjukkan bahwa model dengan kemiringan sisi yang lebih tegak mempunyai sensitivitas yang lebih tinggi dibandingkan model yang memiliki kemiringan sisi lebih landai. Model 1 (M1, 1n = 1:1) memiliki sensitivitas terkecil dan memberikan nilai kesalahan debit submerged terhitung yang lebih besar dibandingkan keempat model lainnya. Model 2 (M2, m = 1:2), Model 3 (M3, m = 125), Model 4 (M4, m = 1:3) dan Model 5 (M5, m = 1:4) mempunyai sensitivitas yang eukup baik dan memberikan nilai kesalahan debit submerged terhitung yang cukup kecil. Pada saat terendam, dimana kedalaman air hilir lebih tinggi daripada batas modular, koreksi debit terhitung dipengamhi oleh perbandingan muka air hilir dan air hulu, serta batas modularnya (7 ), yang dapat didekati dengan persamaan eksponensial Q (1 e )Qcal )/τ h1 −(1− h2 = − (1 e )Qcal )/τ(RUMUS)

The distribution of irrigation water that meets criteria of appropriate time, quantity and quality, will satisfy the farmer’s needs. The existence of discharge measurement structure plays an important role in irrigation distribution system. The accuracy and sensitivity are the important parameter in choosing a measurement structure. The sensitivity of measurement structure indicate the capability of the structure measure any variability of discharge. The accuracy of discharge measurement structure is shown by the accuracy of discharge-flow depth equation of this structure in performing discharge of any measured flow depth either in free flow condition and submerged condition. This research evaluate the sensitivity and accuracy of trapezoidal Cipoletti that varied in side slope, m = 1:1, m = 1:2, m = 1:2.5, m = 1:3 and m = 1:4. Five or six discharge types were applied from 1200 cm3/s to 4700 cm3/s. Upstream and downstream depth were simultaneously and continuously recorded by means wave height meters, starting from free flow to submerged flow regime. Downstream depth change was controlled by operating the tailgate continuously and slowly. The result showed that the straighter side slope weir model gained higher sensitivity than the mild one. Model 1 (M1, m = 1:1) had the smallest sensitivity and yield bigger error number of calculated submerged discharge compared with the other four models. Model 2 (M2, m = 1:2), Model 3 (M3, m = 1:2.5), Model 4 (M4, m = 1:3) and Model 5 (M5, m = 1:4) gained fair sensitivity levels and yield error number of calculated submerged discharge. The correction of calculated discharge in submerged flow is function of the ratio of downstream and upstream depth, and the modular limit ( τ ), this can be expressed by this exponensial equation limit ( τ ), this can be expressed by this exponensial equation Q (1 e )Qcal )/τ h1 −(1− (FORMULA)

Kata Kunci : Irigasi,Pendistribusian,Alat Ukur Debit, Cipoletti, sensitivity, free flow and submerged flow