Long-term effects of longitudinal training walls: a numerical study

Le Thai Binh, Alessandra Crosato, Wim S.J. Uijttewaal

Tuesday 30 june 2015

17:33 - 17:36h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics, Poster pitches

Parallel session: Poster pitches: 7B. Sediment - River

Recently, engineers propose building longitudinal training walls instead of traditional transverse groynes to enhance river navigation or free water inlets at low flow conditions and at the same time maintain the channel conveyance during high flows. For example, the main low-flow stream of the Tra Khuc River in the middle of Vietnam, does not follow the same route year after year causing problems to the inlets of irrigation channel systems along this river. Engineers would like to build longitudinal training walls to stabilize the main stream during low flows without affecting the flood conveyance on rainy season. Another example is along the well-trained Waal River, Dutch authorities are considering substituting the old groynes with longitudinal training walls to obtain an improved navigation channel, while preserving the river conveyance capacity during floods. However, whether longitudinal training walls are indeed effective in achieving the goals and whether they may also produce some undesirable effects is still not clear. This investigation analyses the stability of a system of parallel channels that is formed after the construction of a longitudinal training wall. The analysis is based on the application of a numerical model (Delft3D). The model is applied to a river channel with alternate bars or point bars (as most rivers do). The results show that with a single training wall along one side or two training walls along both sides of the river the parallel channel(s) may become unstable. In addition, starting with a flat bed (to consider the case in which all bars dredged before side wall construction) does not change the unstable character of the channel system. In general, the position of the training wall with respect to a bar plays an important role for the subsequent morphological developments