Journal of Irrigation and Drainage Engineering

Drop manhole structures are used in steep, sloped, urban areas to achieve an acceptable flow velocity inside the gravity network by reducing the slope in sewer pipes and dissipating energy. The energy dissipation is governed by manhole geometry, inflow conditions, and generated flow regimes. The experimental design parameters and the hydraulic performance of drop manholes have been extensively studied, whereas numerical studies are very limited. In this study, the authors have shown how the Flow-3D version 11.2 software package was used to onduct a three-dimensional (3D) computational fluid dynamic (CFD) simulation of rectangular stacked drop manholes (SDMs) to assess the impact of the geometric configuration and flow conditions on the energy dissipation efficiency. It was concluded that an economical cross section of an SDM is a ($3D\times 3D$) square, and that the total drop height should not exceed ($10D$) for one SDM unit, where ($D$) is the diameter of the inlet pipe. The maximum energy dissipation ranged from 78% to 90%, which was achieved when the first chamber’s drop height, ($H1$), ranged between 60% and 75% of the total SDM drop height, ($H$).

Estimations of Penman-Monteith reference evapotranspiration (${\mathrm{ET}}_{\mathrm{oPM}}$) in greenhouses can benefit the operation of these intensive agricultural production systems. Meteorological variables required to calculate ${\mathrm{ET}}_{\mathrm{oPM}}$ within greenhouses are seldom available. In this study, meteorological data for two years from two weather stations (one inside a polycarbonate greenhouse and one outdoors) were used to derive relationships between greenhouse ${\mathrm{ET}}_{\mathrm{oPM}}$ and outdoor ${\mathrm{ET}}_{\mathrm{oPM}}$ plus outdoor solar radiation (measured and extraterrestrial). The results were validated in another greenhouse at a different location in a different year. The two locations represent two different climatic conditions (a coastal subhumid climate and an inland semiarid climate). The results show that ${\mathrm{ET}}_{\mathrm{oPM}}$ in ventilated greenhouses can be predicted from the outdoor ${\mathrm{ET}}_{\mathrm{oPM}}$, extraterrestrial solar radiation, and the ventilation rate within the greenhouse; it can also be predicted from measured solar radiation and the square root of greenhouse transmissivity using an equation developed herein. Under typical ventilated conditions, greenhouse ${\mathrm{ET}}_{\mathrm{oPM}}$ was found equal to 60% of outdoor ${\mathrm{ET}}_{\mathrm{oPM}}$, with solar radiation accounting for more than 90% of the variance. Under unventilated conditions, the relationship is more complex; however, ${\mathrm{ET}}_{\mathrm{oPM}}$ can still be estimated satisfactorily from outdoor solar radiation $R_s$ and greenhouse transmissivity measurements. These findings have potential applications in terms of providing guidelines for predicting greenhouse ${\mathrm{ET}}_{\mathrm{oPM}}$ from outdoor climate variables or from outdoor ${\mathrm{ET}}_{\mathrm{oPM}}$. The estimations could enhance climate-smart agriculture applications in subhumid and semiarid environments while minimizing in-greenhouse meteorological data requirements.

The temporal-spatial distribution of agricultural water requirements constitutes an important basis for the optimal allocation of regional irrigation water resources. The primary crops (rice, maize, and soybeans) of 12 cities in Heilongjiang Province, China, were used as a case study, and reference evapotranspiration, crop water requirement, effective rainfall, irrigation requirement, and irrigation requirement index for these crops were calculated for a period of 10 years (2006–2015). The indexes of homogeneity and stability were used to reveal the characteristics of the temporal and spatial distributions based on a cloud model, i.e., a mathematical representation of qualitative concept—including expectation, Ex, entropy, En, and hyperentropy, He—that integrates the homogeneity and stability of the explored water use terms. Path analysis was used to determine the most pertinent factors influencing the irrigation requirement. The results showed a wide range in annual effective rainfall. The trends of the annual irrigation requirement and irrigation requirement index were similar, with the maximum irrigation requirement occurring in 2007. The distribution of the annual irrigation requirement was widely dispersed and that of the annual effective rainfall displayed the lowest degree of cohesion. The ranges of the various agricultural water requirement indicators between crops except for the effective rainfall were greater in the southwest than in the northeast. The distributions of the annual reference evapotranspiration, effective rainfall, irrigation requirement, and irrigation requirement index were most discrete and unstable in the Xiaoxing’anling Mountains, whereas the distributions of the annual crop water requirement, effective rainfall, and irrigation requirement index in the Sanjiang Plain were uniform and stable. Compared with the temporal distribution, the spatial distribution of each indicator was discrete and nonhomogeneous. Temperature and precipitation were the primary factors that influenced the irrigation requirement.

In this study, 10 test cycles of fertigation with urea using muddy water were performed to examine the anticlogging performance of inline nonpressure-compensating emitters. The potential causes of emitter blockage were proposed from the adsorption behavior of urea on sediments, the morphology and components of the clogging materials, and the total number of microorganisms. The results showed that drip irrigation (DI) with muddy water led to the sedimentation of various minerals (e.g., illite, montmorillonite, calcite, and quartz) in the clogging materials and accelerated the risk of emitter clogging. The weak adsorption of urea (7.4% at an equilibrium time of 6 h and a pH value of 7.9) exhibited a negligible effect on the flocculation, agglomeration, and settlement of sediment particles. The addition of 2% urea inhibited the number of bacteria and fungi in the lateral sediment and induced a 1,000-fold increase in the total number of actinomycetes. The discharge reduction rate (Drr) of emitters exhibited a high correlation ($r=0.9892$; $\mathrm{p}<0.01$) with the dry weight ($\mathrm{DW}$) of solid particles. The clogging mechanisms of emitters with urea muddy water fertigation were the result of the agglomeration of solid particles via the crosslinking of actinomycete secretions and the precipitation of calcite phase (${\mathrm{CaCO}}_3$). These research findings can serve as an essential scientific basis for selecting proper management strategies of urea muddy water fertigation in the Yellow River irrigation area.