Journal of Irrigation and Drainage Engineering

Taro [Colocasia esculenta (L.) Schott] is a major root crop widely distributed in the tropics and subtropics. However, little information is available on its water stress tolerance under different soil textures. Therefore, this study aimed to evaluate the effects of five water regimes (20%, 60%, 100%, 140%, and 180% ${\mathrm{ET}}_{\mathrm{c}}$—crop water requirement) and three soil textures (clay, sandy clay loam, and sandy soil) on the growth, yield, and water-use efficiency (WUE) of taro. The experiment was conducted in a greenhouse, and two harvests of taro were analyzed. In both harvests, leaf number (LN), leaf area (LA), and corm yield (${\mathrm{Y}}_{\mathrm{c}}$) were lower at 20% and 60% ${\mathrm{ET}}_{\mathrm{c}}$ when compared with 100% ${\mathrm{ET}}_{\mathrm{c}}$, and higher at 140% ${\mathrm{ET}}_{\mathrm{c}}$ and 180% ${\mathrm{ET}}_{\mathrm{c}}$ when compared with 100% ${\mathrm{ET}}_{\mathrm{c}}$. Sandy soil (SS) exhibited higher LN at all water regimes than clay soil (CS) and sandy clay loam (SCL) soil. For LA, the values found in SS were higher at lower water regimes (20% and 60% ${\mathrm{ET}}_{\mathrm{c}}$). In the three types of soil, WUE was significantly higher at 20% ${\mathrm{ET}}_{\mathrm{c}}$, $1.00$ and $0.51\mathrm{kg}{\mathrm{m}}^{-3}$, respectively, in the first and second harvests compared with the other water regimes. In the second harvest, WUE and ${\mathrm{Y}}_{\mathrm{c}}$ were significantly higher in SS compared with CS and SCL, indicating that SS has greater potential to improve the WUE of taro under limited water availability conditions.

In this paper, the hydraulics of a central baffle flume (CBF) were experimentally studied. Extensive experimental runs were carried out to highlight the effects of different geometrical parameters such as baffle length, contraction ratio, and the length of upstream and downstream guide walls. Two different approaches, i.e., the Π theorem of dimensional analysis coupled with the incomplete self-similarity theory and the energy balance equation, were applied to deduce the stage–discharge formula of a CBF characterized by different geometrical parameters. The stage–discharge relationship deduced by the dimensional analysis approach was more accurate than that obtained by the energy approach. Furthermore, the dimensional analysis approach has the advantage of calculating discharge values explicitly. The measurements demonstrated that the flow capacity of a CBF decreased with increasing values of the central baffle length. The experiments also showed that a central baffle flume with an apex angle of 75° for upstream guide walls provides suitable hydraulic conditions at the flume entrance. The existence of downstream guide walls did not affect the stage–discharge relationship. In order to distinguish between the free and submerged flow conditions and to determine the modular limit of the flume, the dimensional analysis approach and the momentum balance method were used to formulate the submergence threshold. The analysis showed that the best model to describe the submergence threshold condition was obtained by dimensional analysis.

River restoration refers to the environmental and ecological aspect of river engineering and aims to improve the natural habitat of a river system using eco-friendly methods. This paper introduces a new river restoration technique for bank protection and restoration of meander bends by combining a permeable groin with a triangular vane. Nine different combinations of permeable groins with triangular vane including three different effective lengths and three angles of vane were investigated in a 180° mild laboratory flume bend in clear water conditions. Based on experimental tests, scour geometrical patterns were analyzed, classified, and compared with each other. This analysis showed that a triangular vane dramatically enhances the performance of the permeable groin to protect the outer bank from erosion. Then, using Buckingham’s theorem of the dimensional analysis and the incomplete self-similarity (ISS) condition, generalized functional relationships for estimating scour main characteristics around an enhanced permeable groin (EPG) were deduced. This analysis showed that scour patterns depend on the upstream densimetric particle Froude number ($A_{50}$) and the ratio between the effective lengths of the triangular vane and the permeable groin ($L_t/L_p$). The results showed that scour geometric characteristics estimated by the proposed equations agree reasonably well with the experimental values.

This note presents the results of a laboratory study on surface hydraulic jumps, which form immediately downstream of sharp-crested rectangular weirs for a certain range of submergence. These surface jumps appear to share some characteristics with classical hydraulic jumps generated in horizontal rectangular flumes. Correlations have been developed for many of their characteristics, in term of the relative submergence, equal to the ratio of the tailwater depth above the weir crest and the head on the weir. This study appears to be the first on surface hydraulic jumps.