Finding the optimum groin layout for the Konaweha river banks protection via 2D numerical modeling

River bank erosion has become a critical issue, especially for river bends with an alluvial soil type. Mostly, river bank erosions have caused structural failures because many national roads in Indonesia are placed near the river bend areas. Groins can reduce flow velocity, thereby increasing riverbank stability. However, most groins were installed in the river without impacting the river flow due to the improper design. This paper analyzes the use of groins placed at the river bend of the Konaweha River to protect the river bank with a length of 250 m from erosion. The evaluation employs 2D numerical modeling using MIKE21 FM to observe the influence of the groin on the river velocity, flow distribution pattern, and water level. Sixteen model scenarios with four groin configurations were tested for 25-year discharge, 2-year discharge, normal discharge 600 m3/s, and low discharge 197 m3/s to achieve the most effective plan. Based on the simulation results, Scenarios with five groins are recommended to reduce the flow velocity along the outer river bank from 2 to 0.3 m/s, thus minimizing the erosion. In addition, the spacing of groins being twice the groin length is recommended.

ANALYSIS OF CHARACTERISTICS OF SEVERAL BENDS ON SIDOAN RIVER

Researching the behavior of the river. Especially at the bend, where the morphology of the river is not always straightforward. Flow velocity high water and grinding at river bends occur at different points. This research was conducted on five adjacent bends on the Sidoan River section. This study examined the condition of riverbed sediment, knowing the stability of riverbed sediment granules based on shearing velocity, and stability of riverbed sediment granules based on shear stress. The method used in this study is geometric measurement. Q50 discharge calculation. produces hydraulic simulation. d50 sediment diameter. HEC-RAS software simulation and Shields graphs analysis. The results of the study on five bends for Q50 discharge are the condition of the riverbed in five bends all moving, the critical shear velocity relationship and flow depth are directly proportional, the highest condition at bend 2, otherwise the lowest condition at bend 3. The relationship between particle dimensions and shear velocity is inversely proportional to the value of sliding velocity. if the particle dimensions are small then the large shear stress occurs at bend 5 and vice versa, the dimensions of large particles then the small shear velocity occurs at bend 4, sliding velocity is directly proportional to the shear stress. The highest critical shear stress at bend 2, while the lowest condition at bend 4, the greater the radius of the bend the scouring was deeper.

Analysis on The Effect of Groyne Type Impermeable Placement on Sediment Distribution in Lariang River Bend

Sedimentation and erosion caused by differences in discharge is a problem that often occurs at river bends. One of the functions of placing the groyne is to reduce the river flow velocity along the riverbank, accelerate sedimentation, and ensure the embankment or river bank's safety against scouring. This study aimed to determine the distribution of current velocity, distribution of riverbed shear stress, and sediment distribution to the effect of groyne placement. There are 7 (seven) simulation models used to get the most effective groyne placement. From the model simulation results by adding a groyne building on the river's outer bend for the simulation model scenario 2 to scenario 7, the largest sedimentation production is in scenario 3, namely the height of riverbed sediment deposits 230 hours of 1.094 m. Furthermore, the groyne building's effective placement is determined based on a maximum change in the riverbed scenario. In scenario 3, the placement and dimensions of the groyne length of 17.5 m; distance between groyne 24.4 m; the groyne is inclined upstream in the direction of flow 10°