JWSS - Journal of Water and Soil Science

Labyrinth weirs are the economic structures to increase the weir output efficiency in limited widths, which can be seen in the plane f trapezoidal and triangular forms. These weirs with a hydraulic load and fixed width pass the more discharge in comparison to other type of weirs. In this study, labyrinth weirs trapezoidal in plane form were investigated. The experiments were performed on 27 laboratory models with 9 different discharge rates and a total of 243 tests. The results showed that, in all of the composite trapezoidal labyrinth weirs, the ratio of discharge coefficient to H_t/p (H_t: Total hydraulic load and p: weir length) weir length was increased at first; after reaching the maximum rate, it started to decrease. According to the suggested general relation, the utmost impact on discharge coefficient resulted from the cycle number and  H_t/p relation. Creating new labyrinth on the wing of the weir led to the increase of the effective length; as a result of it, the discharge rate increased in a specific amount of H_t/p. Also, the discharge through a trapezoidal labyrinth weir with the semicircular planform was better than the square; the square, in turn, was better than the simple trapezoidal weirs.

Nonlinear weirs are regarded as important hydraulic structures for water level adjustment and flow control in channels, rivers and dam reservoirs. One example of non-linear weirs is shaped as curved-zigzag. The crest axis of these weirs is non-linear. At a given width, the crest length is greater than that of the conventional linear weirs. Thus, they achieve a higher flow rate for an identical hydraulic load. This research experimentally focused on the discharge coefficient and flow rate of curved weirs with three different curve radii in two triangular linear and zigzag shapes. The discharge coefficients of these weirs were comparatively explored in terms of the hydraulic performance as a function of the total hydraulic load to weir crest height ratio (hd/P) and curvature angle (θ) (or curve radius). The results indicated that for the same hydraulic load, the increase of θ (the decrease in curve radius) led to a lower discharge coefficient; this was first because of the increased topical rise of water level, and then the more indirect path with a greater curvature through which the flow had to transport. Both factors could negatively affect the water discharge coefficient. In practice, the runoff coefficient at a weir with a curve radius of R/w=1.25 was approximately 8.5% greater than that of a weir with a curve radius of R/w=0.75 under a hydraulic load of 0.2.