Abstract In irrigation districts, water distribution satisfaction directly affects service quality. This study constructed an irrigation scheduling model that considers both demand-driven and supply-driven modes, along with supply uncertainty, irrigation method diversity, response time, and water level effects. Applied to a large Chinese irrigation district, the model successfully allocated water to 45 channels under fixed supply, with upstream channels achieving maximum flow diversion and downstream Channel 10 requiring a 4.7-h response time. Under variable supply (40, 30, and 50 m 3 / s ), the model dynamically adjusted flows, with Canal 21 requiring three separate irrigation sessions. The rotational grouping module divided 17 tertiary channels into 3 groups, achieving end-time differences of only 0.48, 1.14, and 0.92 h, reducing management workload. Under demand-driven conditions, the model prioritized flow-rate satisfaction, delivering 102.6 m 3 / s against a main canal capacity of 60 m 3 / s , meeting all flow demands while downstream irrigation time demands remained unmet due to supply constraints. This study provides a practical modeling framework for improving water-use efficiency and reducing scheduling conflicts in large-scale irrigation systems.
Straw returning to the field enhances crop yield and cultivated land quality while presenting risks of water quality degradation, particularly during the soaking period. In this study, a barrel planting experiment was used, three treatments (CK: no straw returning, ST: straw returning, SO: straw returning + micro-nano aeration irrigation) were set up to study the dynamic changes of surface water, soil solution (0-10, 10-20, and 20-30 cm), and key water quality indices [total nitrogen (TN), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), total phosphorus (TP), chemical oxygen demand (COD), dissolved oxygen (DO), pH] in the rice soaking period. The results showed that (1) straw return significantly increased the contents of TN, COD, and TP in paddy field water. Micro-nano aerated irrigation effectively improved water quality after straw return, reducing the average concentrations of TN, TP, and COD by 5.14%-13.54%, 2.08%-37.14%, and 6.07%-43.44%, respectively. (2) During the whole soaking period, there was a significant positive correlation between TN, NH4+-N and NO3--N (p<0.01). However, DO showed a significant negative correlation with COD, TN, and TP only in the middle of immersion, indicating that the increase of pollutant concentration in this stage was accompanied by a continuous oxygen consumption process. (3) The structural equation model showed that DO was the key driving factor for regulating water quality. DO had a strong negative direct effect on COD (lambda=-0.713, p<0.001) and TN (lambda=-0.051, p<0.001) and indirectly inhibited COD accumulation by regulating the morphological transformation between NH4+-N and NO3--N. This study uncovered the underlying mechanisms of straw incorporation and aerated irrigation on water quality during the soaking period, identified critical determinants driving water quality variations, and provided a more comprehensive and in-depth theoretical foundation for the precise and effective mitigation of water quality degradation caused by agricultural straw return.
The relationship between soil suction and soil water content in unsaturated soil mechanics is important but can be difficult to measure. The objective of the research described herein was to develop soil water characteristic curves (SWCC) from relative humidity values by incorporating the use of glycerin-water mixtures. Glycerin-water mixtures can be used to achieve different relative humidity levels by varying the concentration of glycerin within the mixture. The relative humidity created by each mixture was measured with a relative humidity sensor, and the relative humidity values and Kelvin's equation were used to compute the total suction. Soil water characteristic curves were then developed using the relationship between the applied total suction and the measured gravimetric water content of a 15-bar high air entry stone and four soils, including: illite, red clay, kaolinite, and Donna fill. The soil SWCCs, obtained using glycerin-water mixtures, were compared with the SWCC developed using a chilled mirror hygrometer and the filter paper method. For the red clay and kaolinite, the water-glycerin method effectively developed the portion of the SWCC at low water content and high suction values (R2 values of 0.87 and 0.96, respectively). For the soils that behaved as cohesive materials, there was sufficient data to establish the SWCC using the relative humidity method for suction values greater than 1,000 kPa. At lower suction values, there was a lack of suction data, requiring data from other methods to complete the curves. For the soil that behaved as a cohesionless materials, the relative humidity method resulted in all data residing along the residual water content, making the development of the SWCC difficult. Based on the results, the inexpensive and simple relative humidity method may be used to develop SWCC for cohesive soils for the drying path at low water contents and high suction values.
Vertical drop structures typically dissipate energy through a hydraulic jump formed immediately downstream of the drop toe, where strong aeration, splashing, and free-surface unsteadiness make conventional measurements difficult. This technical note evaluates the capability of an Intel RealSense D435if depth and color (red, green, blue) (RGB-D) depth camera, operating at 90 fps, to characterize the free surface of a hydraulic jump downstream of a 0.50 m vertical drop in a 0.80-m-wide laboratory flume. Experiments were conducted for unit discharges q=0.089-0.127 m3/s/m, corresponding to inflow Froude numbers Fr1=4.55-5.19. Mean free-surface profiles derived from the camera were validated against the characteristic depths y associated with local void fractions C=0.5 and C=0.9, denoted y50 and y90, respectively, obtained from single-tip conductivity-probe measurements along the channel centerline. Within the main roller region, the camera-derived profiles remained between the y50 and y90 envelopes, indicating that the RGB-D sensor can resolve the mean aerated free surface under highly disturbed conditions. An auxiliary comparison between single-tip conductivity-probe and conductivity wire gauge measurements of the equivalent clear-water depth yielded agreement within 7.3%, supporting the internal consistency of the intrusive validation data. Three-dimensional reconstruction of the hydraulic jump revealed marked transverse nonuniformity in the free-surface fluctuation field. Peak fluctuations did not occur systematically along the channel centerline; instead, the largest values were found at off-centerline locations and reached up to 8.9% above the corresponding centerline peaks. These findings show that centerline-only measurements may underestimate the governing fluctuation envelope and that RGB-D imaging provides a practical basis for assessing free-surface variability, freeboard requirements, and sidewall design in stilling regions downstream of vertical drops.
Sluice gate jamming occurs simultaneously during gate closure, seriously jeopardizing the safe operation of irrigation and drainage systems. This paper aims to identify the primary causes of gate jamming in submerged discharge by the combination of model tests and computational fluid dynamics (CFD) simulation, and analyzes the relationship between gate jamming and hoisting force. The results indicated that the high friction coefficient is a major reason for the nonclosure of a sluice gate under the premise of appropriate gate geometry. The permissible friction coefficient for a sluice in submerged discharge is influenced by the submerged weight, available areas of the panel and beam, and water level difference. An increase in the friction coefficient induces a static-dynamic friction transition during gate descent, causing the hoisting force to increase instantaneously and oscillate repeatedly. Increasing the counterweight or adding a convex lip facilitates gate closure but does not contribute to the reduction of hoisting force. Reducing the friction coefficient of the support structure and employing a stop log gate not only promote gate closure but also effectively mitigate hoisting force.
