Amrullah Mansida

Sedimentasi merupakan proses pengendapan material yang terjadi di sungai. Krib merupakan bangunan yang dibuat melintang sungai guna mengatur arus sungai dan mengurangi gerusan. Tujuan penelitian ini yaitu mengetahui pengaruh krib permeable terhadap karakteristik aliran dan mengetahui berapa besar laju angkutan sedimen dasar akibat krib permeable menggunakan metode Duboys dan Einstein. Penelitian ini dilakukan di Laboratorium Teknik Unhas menggunakan flume akrilik sepanjang 900 cm dengan krib permeable dari kayu bulat dan bahan uji tanah pasir lolos ayakan 20. Hasil penelitian ini diketahui bahwa terjadi penurunan bilangan Froude sekitar 18 % dan kenaikan bilangan Reynolds sekitar 14,56 % pada pengaliran menggunakan krib kerapatan (ak1) 0,9 cm. Laju angkutan sedimen dasar tertinggi ada pada Q3S3ak1 dan yang terendah pada Q1S1. Menurut Einstein didapatkan qb sebesar 7,564 m3/hari dan 0,358 m3/hari sedangkan menurut Duboys sebesar 0,4096 m3/hari dan 0,0058 m3/hari.

The phenomenon of turbulent flows becomes a virtual object in any changes in open channel flow hydraulics. Turbulent flow and shear stress have a role in the geometrical changes of bed channel and sediment movement. The dynamics of turbulent flow are consequences of hydraulic channel dynamics. Turbulent flow has excessive kinetic energy resulting in resistance force because the increase of friction effect and infraction in turbulent flow creates a complex phenomenon. Shear stress is in the eternal pressure of flow against the deformation of the primary basic form of channel. The research aims to analyze turbulent flow, shear stress, and bed scours’ phenomena and potential. Measurement of turbulent flows is by measuring the flow velocity in four segments at a distance of 100 cm each. The channel’s cross-section is divided into nine parts and five measurement points in the flow depth of inner and outer regions. There are three variations of channel discharge and slope, i.e., low discharge (Q1), medium discharge (Q2), large discharge (Q3), and downward slope (S1), medium slope (S2), and high pitch (S3). The parameter of turbulent flow analysis, shear stress includes flow velocity average (U), flow depth (h), channel slope (S), viscosity (φ), the mass density of the liquid (ρ), the characteristic length or hydraulic radius (L/R) by using an empirical equation approach. Turbulent flow analysis used dimensionless Reynolds’ number equation approach. The effect of hydrodynamic on turbulent flow causes the distribution of shear and scour stress, transport, and sediment deposition. The increase in the slope of the channel affects the increase in the values of shear stress.

Highly dynamic changes in flow regimes are caused by relatively high rainfall intensity, so that the excessive flood volume in the last ten years, and it is caused by watersheds experiencing a crisis or degradation due to conversion into economic and non-economic areas which ultimately impacts on river bank and beds by turbulent flow. The use of groin structure as a method of scouring prevention and channel flow control has not been able to fully meet the expectations of scouring prevention. We obtain the effect of changing the turbulent flow regime on the use of groins on the bent channel. Testing was conducted through laboratory experiments in artificial conditions to investigate the relationship between variables by providing certain treatments in several experimental groups with a comparative control of bend channel angle uses 60° with distance variations of groins and discharge; in addition, software Surfer used to describe scour contour pattern. Analysis of changes in flow behavior is done by using Froude (Fr) and Raynolds (Re) number approaches with the effect of turbulent flow on the bent channel scour. The results of the research indicate that the placement of the groins on the river bank channel bend causes a new phenomenon of turbulent flow with shear stress, resulting in local scouring around groin structure and the placement of looser permeable groin gives prevention 81% of river bank scour.