Journal of Irrigation and Drainage Engineering

Water-saving technologies have been gaining interest as a way of saving water while minimizing crop production losses. This study aims to introduce a new technique for reducing the vertical infiltration rate through clay and sandy loam soil surfaces by using soil compaction and oil-based liquid (palm oil) treatment. A two-factorial experiment of a randomized complete block design with three replications was conducted for each soil type. The compaction factor had levels of zero-, three-, and five-time compaction passes performed by a plate compactor. The oil factor had two levels, namely, 0 and ${1.0\mathrm{L}/\mathrm{m}}^2$ palm oil, which was applied to the soil surface prior to compaction. The soil infiltration rate, bulk density, moisture content, and penetration resistance were recorded. The results showed that the soil bulk density for both soils increased with increasing compaction as well as the application of palm oil. The maximum bulk densities reached for clayey and sandy loam soils were 1.7 and ${1.8\mathrm{g}/\mathrm{cm}}^3$, respectively. Additionally, increasing compaction and treating the soil with palm oil resulted in decreasing the infiltration rate generally. The infiltration depth versus time nonlinear curves fitted well based on the Kostiakov infiltration model. The infiltration dynamics profile of the noncompacted surface was higher than that of the compacted soil for all compaction treatments. On average, compaction had a reduced infiltration rate of 86% and 73% in sandy loam and clayey soil, respectively. The associated reductions by palm oil treatment on respective soils were 22% and 25%. This finding suggests that the oil factor provided an additional effect on compaction when reducing the vertical infiltration rate through the soil surface, and thus could be exploited in constructing the bottom of the furrow for selected crop productions under a raised bed system. The reduced vertical infiltration forces the water to move laterally into the plowed and noncompacted beds of the furrow. The increased lateral water movement physically increases the amount of water stored within the root zone, thereby improving the irrigation efficiency and crop productivity of the raised bed furrow crop system. The raised bed is generally good in controlling the soil moisture content for the growth of aerobic paddy and the majority of vegetables.

Weirs are commonly used for making discharge measurements in irrigation canals. There are several types of weirs that are categorized based on their geometric shape or hydraulic properties. A gabion weir is a porous weir that can pass flow through its body in addition to the flow that passes over the weir. This study focuses on determining the discharge coefficients ($C_d$) for rectangular broad-crested gabion weirs using fabricated physical models. Dimensional analysis was carried out for finding the most effective parameters that govern the flow. Results show that the $C_d$ of gabion weirs is 10.5% greater than that of similar solid weirs. In addition, the $C_d$ for porous weirs in free flow conditions is 17.2% greater than that for submerged flow. For $H/L>0.45$ (where $H$ is the water depth over the weir crest and $L$ is the weir length) a porous weir acts similar to a solid weir and the effect of porosity ($n$) nearly vanishes. For a specified value of $H/L$, the ratio of submergence ($S_r$) for a solid weir is higher than that for porous weirs. Porous weirs with 50% porosity have lower values of $S_r$ compared with solid weirs and weirs with lower porosities, of 45%, 41%, and 30%. Regression equations for the flow through gabion weirs were generated for free and submerged flow conditions. The derivations of equations were carried out using multivariable nonlinear regression and genetic programming (GP). Finally, a comparison of $C_d$ in the present study with the other studies was carried out.

Earth’s surface net radiation ($R_n$) governs sensitive and latent heat fluxes, plant photosynthesis, and the terrestrial carbon cycle. However, $R_n$ records are scarce in China. The accurate quantification of $R_n$ is therefore of great importance. The $R_n$ is the difference between net shortwave (incoming) and net longwave radiation (outgoing), and the Food and Agricultural Organization of the United Nations (FAO) 56 Penman-Monteith (FAO-56 PM) method has been widely used to estimate $R_n$. However, site-specific calibrations of parameters are required for the FAO-56 PM method. Thereby, an improved $R_n$ estimation in China was done by (1) quantifying the spatial and temporal variations of surface albedo to better estimate net shortwave radiation and (2) recalibrating the parameters of FAO-56 PM method based on in situ observations to better estimate net longwave radiation. Results indicate that the monthly value of surface albedo over the course of a year is U-shaped, and the minimum value appears in the boreal growing season (April to September). The monthly surface albedo during the nongrowing season was best fit by a latitude-dependent quadratic function. By better accuracy in the estimation of net shortwave and longwave radiation, results at 31 validation stations indicated that the improved FAO-56 PM method enhanced the accuracy of estimated $R_n$ by 33% (the median Nash-Sutcliffe coefficient increased from 0.6 to 0.8) when compared to the default FAO-56 PM method. The improved method developed in this study has universal applicability in data-scarce regions in China and elsewhere, which is valuable for various practical applications including evapotranspiration simulation, hydrological modeling, and agricultural crop planning and management.

This study aims to construct the multiple time-scale joint distributions of drought duration and severity using two-dimensional copulas and compare the drought characteristics in India’s two contrasting climate regions: the arid Rajasthan and humid, tropical Kerala. The drought occurrences were defined by the standardized precipitation index (SPI) with a threshold below $-0.8$ at time scales of 3, 6, 12, and 24 months for 1900–2016. Significant correlations were noted between the drought severity and drought duration in both regions. The Clayton copula gave a better fit than other copulas for modeling the dependence among the observed drought duration and severity. The results indicate that the probability of short-term droughts (SPI-3 and SPI-6) is more significant than those of long-term droughts (SPI-12 and SPI-24) for an identical drought event in both regions. Also, the probability of severe drought events with greater duration and severity for long-term droughts (SPI-12 and SPI-24) is higher in Kerala than that in western Rajasthan. For all the time-scale SPIs, the conditional probability of drought severity for a given duration exceeding a threshold showed an increasing trend in both regions. Furthermore, the conditional probability of the drought duration given the severity for short-term droughts is greater than that of the long-term droughts for the same drought event. For short-term droughts, the conditional return period of an identical drought event is lower in Kerala than in western Rajasthan. In contrast, the conditional return period of long-term droughts is lower in western Rajasthan. Additionally, copula-based nonexceedance conditional distributions for the major crops were established based on rainfall.

In many applications, the adjustment of a gate opening to a specific value is crucial for the passage of a defined outflow or to maintain an upstream water level that serves upstream turnouts. Previous work used trial-and-error and interpolation methods to calculate the opening of sluice gates. This study concentrates on the development of a way to estimate the opening of sluice and radial gates to achieve the desired discharge or upstream water level. In addition to energy and momentum (E-M) principles, this paper develops relationships to determine the openings of sluice and radial gates under free- and submerged-flow conditions. Based on experimental data, the mean absolute relative errors for calculating the opening of sluice and radial gates under different flow conditions using the previously proposed methods, as well as dimensional analysis, were 4.3% and 7.1%, respectively. In this study, the calculated relative errors in employing E-M principles were reduced from 3.6% to 2.9%, in which the effects of energy loss were overlooked, and the gate’s energy coefficient was introduced.