Journal of Irrigation and Drainage Engineering

Saint-Venant equations are accurately solved by a fully implicit solution, and a numerical model for furrow water flow is proposed with unconditional stability. Furthermore, this numerical model is extended to furrow networks. There are continuous hydraulic connections among multiple furrows by network junctions, thus the surface water flows of all furrows in a furrow network are simultaneously simulated. Then, a fully hydrodynamic coupled model with unconditional stability is constructed for furrow networks. The dam-break problem with an analytical solution is first used to test the proposed model, and a good performance with different time steps is obtained. Meanwhile, two field-scale experiments for a furrow network are selected to validate the proposed model. The validated results show that the proposed model can well simulate water flows of a furrow network and presents good mass conservation ability. Meanwhile, the computational efficiency of the proposed model can satisfy the requirement of irrigation application.

Mathematical and numerical models are used to simulate the transport of pollutants released into a water body. Such simulations can be computationally burdensome, however. One approach to overcome computational burdens associated with the simulation of pollutant transport is to use data-mining tools. The aim of this study is to simulate the concentration of methyl tertiary butyl ether (MTBE) at various locations within a river-reservoir system using the support vector regression (SVR) data-mining tool. The SVR tool is optimized by means of a genetic algorithm (GA). This paper’s results indicate that the developed and optimized SVR tool is more accurate than artificial neural networks (ANN) and genetic programming (GP) when judged by the correlation coefficient of regression analysis ($R^2$).

Floods are the most devastating natural hazards in the United States, and these events lead to significant economic consequences. Estimation of damages and losses at different parts of the floodplain can be used to identify the vulnerable areas susceptible to flood. Floodplain maps combined with damage assessment could identify high-flood-risk areas and present a platform to develop guidelines and zoning resolutions for proper land use, building new infrastructures, and placing and retracting residential areas. In this study, a risk-based methodology is proposed to quantitatively assess damages. For this purpose, a geographic information system (GIS)–based approach is used as an alternative to more complex software packages. The system is called a flood-damage estimator (FDE) and utilizes empirical synthetic depth-damage functions, land-use data, digital elevation model (DEM), raster maps (for featuring the characteristics of the properties at flood risk areas), and floodplain extent for the region in order to estimate flood damage. The results from this model are compared with the results of flood hazard analysis module in the FEMA HAZard United States (HAZUS) software. This model uses different characteristics, such as ground elevation and storm surge elevations to estimate flood damages and losses. In both models, a 100-year floodplain proposed by the FEMA flood insurance studies (FISs) of 2007 and 2013, as well as floodplain developed by the gridded surface subsurface hydrologic analysis (GSSHA)–distributed hydrologic model, are used to determine the flood water depth at different locations. This hydrologic model provides input from simultaneous consideration of inland and coastal flooding to the damage estimation model. The proposed methodology is applied to Manhattan. The results show the significant value of combining GIS-based models with damage-risk analysis to provide a flexible and simple platform for damage estimation as an alternative to the HAZUS model. Flood-risk maps created based on the damage estimation are of great use and importance in proper planning for land use and setting priorities for allocation of financial resources in recovery and reconstruction plans.

Field research was conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory (SCAL) located near Clay Center, NE, in the growing seasons of 2011 to 2014. A partial economic analysis was conducted for maize (Zea mays L.) at nitrogen (N) fertilizer treatments of 0, 84, 140, 196, and $252\mathrm{kg}{\mathrm{ha}}^{-1}$ under full irrigation (FIT), limited irrigation (75% FIT), and rainfed settings for all growing seasons and then compared to crop water productivity (CWP) measured as crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE). Nitrogen fertilizer increased CWUE and IWUE in all growing seasons. The CWUE values ranged from 0.90 to $2.81\mathrm{kg}{\mathrm{m}}^{-3}$ and the IWUE values ranged from $-1.01$ to $3.24\mathrm{kg}{\mathrm{m}}^{-3}$. Operational costs and net income varied among treatments and across years. Irrigation and N fertilizer rate had an interacting effect ($P_{0.05}<0.05$) on both gross and net income in 2011, 2012, and 2013. Net income was maximized under rainfed settings with a N fertilizer rate between 140 (dry year) to $196\mathrm{kg}{\mathrm{ha}}^{-1}$(wet year); in contrast, the optimal N fertilizer rate under irrigated conditions was $196\mathrm{kg}{\mathrm{ha}}^{-1}$. Positive relationships were observed between relative net income (RNI) and CWUE with $R^2$ values of 0.72, 0.87, and 0.84 for rainfed, 75% FIT, and FIT, respectively, as well as between RNI and IWUE with an $R^2$ value of 0.96 for 75% FIT and 0.86 for FIT. Lower CWUE and IWUE values were associated with lower RNI. With consideration to CWUE, IWUE, and partial factor productivity of N, full irrigation management is recommended under non-water-limiting conditions and limited/deficit irrigation management strategies (e.g., 75% FIT) under water-limiting conditions, with N fertilizer rate not exceeding $196\mathrm{kg}{\mathrm{ha}}^{-1}$ to achieve a high economic return for the study area.

This study experimentally investigates the influence of color on the evaporation rate of a Class A evaporation pan. Two Class A evaporation pans, one in the original galvanized metal color and the other painted white, are placed in the same meteorological station for 18 months. Since the wind speed, air temperature, and vapor pressure deficit are the same for both pans, the color and the resulting net radiation are the only causes for differences in the evaporation rate. The results reveal that the average net radiation of the white pan is about 90% that of the metal-colored pan. This leads to the annual evaporation rate of the white pan ($\mathrm{1,041}\mathrm{mm}{\mathrm{year}}^{-1}$) being only 75% of the evaporation rate ($\mathrm{1,392}\mathrm{mm}{\mathrm{year}}^{-1}$) of the metal-colored pan. In addition, the prediction error of the daily evaporation rates by the energy budget method is lower than that of the Penman-Monteith type models. The differences between the measured evaporation rates of the two pans are analyzed to examine the role of irradiance on the pans’ evaporation rate. The results indicate that the irradiance absorbed by the pan wall can affect the energy budget and evaporation rate of the pan.

Normal depth is a key parameter occurring in open-channel hydraulics. For all practical canal sections, open-channel resistance equation involves implicit form for normal depth. Therefore, the determination of the normal depth involves the tedious method of trial and error. Presented in this paper is the good approximate explicit equation for normal depth in parabolic open-channel sections.

A representative curve number (CN) of a catchment is often calculated from the area-weighted average of CN values of unique land use and soil combinations. While convenient for implementation, this method is known to underestimate direct runoff depth. This paper investigates the mathematical mechanism of the expected underestimation and proposes alternative CN averaging methods called the quadratic and exact averaging methods, to handle the underestimation problem. Results suggest that the quadratic method could reduce the level of underestimation in direct runoff depth; further, the exact method could provide the same direct runoff depth as that of the area-weighted direct runoff depth averaging method. A representative CN is found to be a function of rainfall size and catchment landscape, and the underestimation is relatively large for small and mid-sized storm events. The improvement in runoff estimation with the newly proposed averaging methods is particularly beneficial to stormwater management, flood controls, and erosion controls upon small return-period events.

Side weirs are frequently used for water-level control in irrigation systems, sewer networks, and flood protection. Researches on side weirs have generally focused on determining the hydraulic characteristics of sharp-crested side weirs. A common type of this weir, which has larger capacity to pass the flow, is the circular-crested weir. To the authors’ knowledge, investigation of hydraulic features of this weir as side weir has been ignored in literature. Based on an experimental model for subcritical flow conditions and under the hypothesis of constant specific energy, the hydraulic characteristics of the circular-crested side weir with various weir heights, widths, and downstream slopes are taken into account to formulate an expression for the discharge coefficient. The results indicate that the upstream Froude number, the weir height to weir length, specific energy to the weir radius, and downstream slope of the weir are the important variables that affect the discharge coefficient of circular-crested side weirs. A comparison between circular-crested and sharp-crested side weirs confirms that circular-crested side weirs are more economical and efficient than sharp-crested side weirs, due to the greater discharge coefficient.