Journal of Irrigation and Drainage Engineering

Scour is a natural phenomenon in alluvial streams around hydraulic structures due to the removal of bed material and often leads to their failure. Scour due to jets are the most prevalent form of scour seen downstream of hydraulic structures. This paper presents a detailed review of scour processes with respect to the effect of various parameters on scour under different jet conditions. Different aspects of the scour hole characteristics under various applications of jets have been reviewed, which include (1) scour process; (2) the effect of parameters such as impinging height, jet impact angle, aeration, size of sediment particle, and sediment gradation; (3) flow characteristics within the scour hole; and (4) temporal variation and time taken to reach an asymptotic state of scour depth. Moreover, the experimental findings of various researchers on the development of the scour profile geometry and their applicability to large-scale conditions have been summarized.

Abstract

Waterlogging and high salinity levels have been largely due to poor agricultural drainage management. The productivity of agricultural lands could be greatly increased if agricultural drainage systems are properly monitored. This study was conducted in the Bontanga irrigation scheme in the Guinea Savannah Ecological Zone of Ghana to evaluate the performance of the drainage system using drainage performance indicators. Mapping of the components of the drainage system using GPS coordinates and GIS and installation of six (6) observation wells to account for waterlogging intensity and water-table fluctuations with time was done. Three (3) composite soil samples were taken two (2) times during the cropping season at depths of 0–20, 20–40, and 40–60 cm. Drainage coefficients values were computed using a water-balance approach. The findings indicated that the current drainage network conforms with the components of an agricultural drainage system. Electrical conductivity of the soil in the scheme ranged from 0.025 to $0.039\mathrm{dS}/\mathrm{m}$ before planting and 0.065 to $0.098\mathrm{dS}/\mathrm{m}$ after harvesting. Mean sodium values of the scheme ranged from 5.31% to 6.68% before sowing and 6.53% to 10.98% after harvesting. Waterlogging intensity ranged from 155 to 235.5 cm.days for April and 140–240 cm.days for May. Drainage coefficients were found to range from 5.1 to $5.7\mathrm{mm}{\mathrm{day}}^{-1}$ for April and 6.6 to $7.4\mathrm{mm}{\mathrm{day}}^{-1}$ for May. Scheme managers should collaborate with the Water Users’ Associations to enforce bylaws prohibiting the cultivation in the drains, ensuring every farmer maintains the drains and adhere to good water management strategies.

Practical Applications

The study was conducted to investigate the drainage system at the Bontanga irrigation scheme in Ghana. The research looked at the components of the drainage system, salinity levels of the soil, waterlogging situation, sodium levels in the soil, and drainage coefficients of the scheme. The findings on the salinity, sodicity, and waterlogging levels of the soil were within acceptable limits. Worth noting is that, though the salinity and sodicity levels were in acceptable ranges, there has been an increase with time. After computation of the drainage coefficient of the scheme using a water balance approach, it was found to be within the range for rice cultivation. The scheme has the components that should be in an agricultural drainage system. However, there are challenges with regards to the maintenance of the drains by the farmers. To ensure proper management of drainage system in irrigation schemes, management should integrate drainage as a key component of the irrigation system and ensure collaboration with water users association at scheme level.

Water scarcity, the intensification of agricultural nonpoint pollution, and continuous deterioration of the ecosystem are serious problems in arid areas. Optimal allocation of water resources is the key way to achieve sustainable and efficient development of irrigated agriculture. An integrated multiobjective optimization model considering water-balance processes was developed under shallow groundwater environments to enhance comprehensive objectives and obtain optimal irrigation solutions. A simulation module of the physical processes of water movement among crop root zones, soil water, and groundwater aquifers, and a multiobjective optimization module of irrigation water allocation were incorporated into a general framework. It has the following advantages in terms of (1) illustrating variations of agricultural hydrological parameters (e.g., soil water content, groundwater depth, groundwater-based evaporation, and so on) in water movement processes; (2) obtaining a set of noninferior decision-making solutions through a modified nondominated sorting genetic algorithm (NSGA-II), which can maximize the interests for multiple parties; and (3) generating optimal solutions of irrigation water allocation and alleviating water scarcity, improving irrigation water productivity, and reducing negative environmental effects. To demonstrate its applicability, it was applied to optimize irrigation water allocation in the Jiefangzha Irrigation Subarea (JIS), China. It was firstly split into 44 irrigation subsystems, and each subsystem was assumed to be a homogeneous unit in meteorology, soil texture, and groundwater. Under the water competition between subsystems and rigid constraints of water availability, optimized results enhanced net economic benefits by 14.7%, saved 7.74% of irrigation water amount, and improved irrigation water productivity by 13% compared with status quo. Meanwhile, it can reduce graywater footprint of grain production by 58% compared with the average level of Hetao Irrigation District, China.

Infiltration galleries are constructed near surface waters to induce recharge for water supply and irrigation diversion projects. Technical guidance for the hydraulic design of bed-mounted infiltration galleries is limited. We review the gallery yield equation presented by Driscoll, which appears to be an ad hoc application of the Thiem equation. Driscoll’s results provide a relatively crude approximation of the flow conditions within a typical gallery. New yield equations that better represent typical gallery flow geometries are then developed by complex analysis and presented as dimensionless design charts. Comparison with the new solution shows that the Driscoll equation provides conservative results, underestimating yield by factors of approximately two; Driscoll’s equation should be used with caution. The new yield equations are modified using the method of fragments to include the effects of a filter layer at the stream bed and skin losses at the drain, extending their use and providing a more rational basis for analysis and design of bed-mounted infiltration galleries.

This study aimed to assess the effect of time on local scour development downstream of parallel sluice gates in different operations. The results revealed that the time scale of local scour development is a function of symmetric and asymmetric operations of the gates. By reducing the gate opening to a channel width ratio, the maximum scour depth and accuracy of the power-law equation increase and decrease, respectively, compared with classic hydraulic jump conditions. Finally, a new equation with high accuracy is proposed.