Journal of Irrigation and Drainage Engineering

In this study, a new structure named a rotary gate is introduced to control and measure the flow in canals having a semicircular or semielliptical cross section. A pivot rod, connected to the centerline of the gate and to its frame, holds the gate in place and acts as a hinge for the gate rotational movement. The gate is easy to maneuver and requires a rather small force for its movement, which makes it appropriate for network automation. The hydraulic properties of the rotary gate were investigated during an intensive experimental study and presented in this paper. Influences of the gate opening angles on the flow depths, discharge measurements, and discharge coefficients in free flow were studied using different approaches, and the results of developed relationships were evaluated. Finally, a relationship to determine the relative head loss of the gate according to the relative opening and the relative discharge was proposed.

Drip irrigation is an efficient water-saving irrigation technique. However, the clogging of emitters is a major problem for drip irrigation systems that adversely affects the uniformity of water distribution and lowers the water use efficiency. The irrigation water with high sand content, if not properly treated, will cause physical clogging of emitters. To meet the requirement of drip irrigation, irrigation water of high concentration of sand particles should be filtrated in advance. In this paper, experiments on sandy water filtration by using two kinds of natural soils, sandy loam soil and sandy soil, and subsurface PVC drainage pipes were carried out. The filtration performance by using these two soils was investigated and compared. In addition, impact of sandy water filtration on physical properties of sandy loam soil and sandy soil were analyzed. Results show that both the sand content and filtration velocity of the filtered water decrease exponentially with time. The impact of sandy water filtration on physical properties of the two soils was also evaluated and the main reasons for clogging of soil pore space were analyzed.

The development of irrigated agriculture in northwest China is restricted by shortages of fresh water and groundwater salinization. Saline water irrigation may cause salt accumulation in the soil, which results in salt stress to roots. The effects of water salinity and irrigation amount on wheat root distribution and yield, as well as soil salt distribution, were evaluated in field experiments conducted in 2014 and 2015 at the Shiyanghe Experimental Station of the China Agricultural University (102°52′E, 37°52′N), located in the Liangzhou District, in the city of Wuwei in northwest China. A total of 12 treatments including 4 levels of irrigation water salinity as indicated by electrical conductivity (0.65, 3.2, 5.2, and $7.1\mathrm{dS}{\mathrm{m}}^{-1}$) and 3 levels of irrigation amount (205, 280, and 355 mm), were established using a randomized block design. Freshwater with an electrical conductivity of $0.65\mathrm{dS}{\mathrm{m}}^{-1}$ and an irrigation amount of 355 mm was used as the control for salinity and irrigation level. The results showed that the influence of irrigation amount and water salinity on root distribution was mainly in the top 40-cm. Irrigation amount had no statistically significant ($p>0.05$) effects on the average root length density (RLD) in the 2-year experiment. A decrease in irrigation amount reduced root biomass (RB) at maturity when water salinity ranged from 0.65 to $5.2\mathrm{dS}{\mathrm{m}}^{-1}$. Water salinity less than $3.2\mathrm{dS}{\mathrm{m}}^{-1}$ stimulated root growth in the soil layers 10–40-cm at the heading stage without obvious yield reduction or salt accumulation. However, water salinities of 5.2 and $7.1\mathrm{dS}{\mathrm{m}}^{-1}$ led to decreases in RLD in the 0–10-cm layer and RB at the maturity stage, and a significant decrease in yield ($p<0.05$) in both years. The interaction effects of irrigation amount and water salinity had no statistically significant ($p>0.05$) effects on root parameters and yield. In the absence of rainfall, a regime with irrigation amounts between 205 and 355 mm and water salinity between 0.65 and $5.2\mathrm{dS}{\mathrm{m}}^{-1}$ can ensure a 70% yield.

Spatiotemporal information on historical peatland drainage is needed to relate past land use to observed changes in catchment hydrology. Comprehensive knowledge of historical development of peatland management is largely unknown at the catchment scale. Aerial photos and light detection and ranging (LIDAR) data enlarge the possibilities for identifying past peatland drainage patterns. Here, our objectives are (1) to develop techniques for semiautomatically mapping the location of ditch networks in peat-dominated catchments using aerial photos and LIDAR data, and (2) to generate time series of drainage networks. Our approaches provide open-access techniques to systematically map ditches in peat-dominated catchments through time. We focused on the algorithm in such a way that we can identify the ditch networks from raw aerial images and LIDAR data based on the modification of multiple filters and number of threshold values. Such data are needed to relate spatiotemporal drainage patterns to observed changes in many northern rivers. We demonstrate our approach using data from the Simojoki River catchment ($\mathrm{3,160}{\mathrm{km}}^2$) in northern Finland. The catchment is dominated by forests and peatlands that were almost all drained after 1960. For two representative locations in cultivated peatland (downstream) and peatland forest (upstream) areas of the catchment; we found total ditch length density ($\mathrm{km}/{\mathrm{km}}^2$), estimated from aerial images and LIDAR data based on our proposed algorithm, to have varied from 2% to 50% compared with the monitored ditch length available from the National Land survey of Finland (NLSF) in 2018. A different pattern of source variation in ditch network density was observed for whole-catchment estimates and for the available drained-peatland database from Natural Resources Institute Finland (LUKE). Despite such differences, no significant differences were found using the nonparametric Mann-Whitney $U$ test with a 0.05 significance level based on the samples of pixel-identified ditches between (1) aerial images and NLSF vector files and (2) LIDAR data and NLSF vector files.

In designing infiltration trenches or basins, the focus is usually on runoff conveyance and water quality, with less attention to optimizing infiltration and seepage to increase stormwater management efficiency. Four infiltration model conditions, applied as constituents of water balance in infiltration trenches and basins of a trapezoidal cross-section, were compared with the results of field studies. In the first two, infiltration rates conditions were constant and equal to native soil saturated hydraulic conductivity or to half of it along the side slopes. New analytical solutions for filling and emptying times based on the water balance equation were presented. The third model condition was a compilation of the inverse hodograph method with a simplified seepage function. The fourth model condition was based on Richards’ calculations solved numerically using the HYDRUS computer code. Among the analytical models, the authors recommend in-basin and trench designs using the concept IIIb. It predicts that the relative rate of infiltration from linear basins of trapezoidal cross-sections increases with the ratio of the water depth to the bottom width up to 0.8–2.4, depending on their side slopes. For higher relative water depth values, the relative infiltration rates stabilize, exceeding 20%–42% of the saturated hydraulic conductivity of the native soil. The relative infiltration rates from trenches or basins of trapezoidal cross-sections are less sensitive to the relative water depth than those from similar controls of a rectangular cross-section. Equations and procedures for the calculation of filling and emptying times are provided. The numerical model (HYDRUS 2D) gave satisfactory results, excluding the case of the filling of a trapezoidal trench without fill material.