Journal of Irrigation and Drainage Engineering

Surface drip irrigation is an efficient system for delivering water to crops; however, conditions at the soil surface affect evaporation rate and efficiency. A method is proposed, sand tube irrigation (STI), to increase the efficiency of drip irrigation systems. This method is specific to permanent tree crops where soil is not tilled or turned. The STI method consists of removing a soil core beneath the emitter and filling the void with coarse sand. The SWMS _2D model, implemented in a 3D axisymmetric form, was used to simulate infiltration, water redistribution, evaporation from the soil surface, and rise of water inside the sand tube. Model simulations were compared with laboratory measurements determined from a weighing lysimeter. The simulated values of water height inside the sand tube and temporal position of the wetting front in both lateral and upward directions closely matched the experimental measurements. The advancement of the wetting front in the downward direction and evaporation estimates was predicted with less accuracy. Experiments showed that relative to surface drip irrigation, the STI method reduced evaporation by approximately 26% over a 4-day period.

Irrigation schemes in the central clay plains of Sudan represent a major irrigated area in Africa. Annual irrigation requirements may approach 10¹⁰/m³. The main irrigation season extends for 9 months (mid-June to mid-March). Off-season irrigation requirements mainly for sugarcane and orchards have to compete with the water supply and hydropower for the usually scarce water resources available in the Blue Nile at this time of the year. Accurate estimates of off-season irrigation requirements become critical for such conditions. A prerequisite for this is to estimate reference evapotranspiration (ET) from meteorological and other data. In this paper four forms of the Penman combination equation were compared with measured ET data from a clipped grass lawn. The Penman-Monteith method gave the best agreement with measured data, followed by the FAO-Penman (used with the original Penman wind function) and Penman-Watts-Hancock methods, which gave almost identical results. The Penman 1963 method was the least satisfactory among the methods tested; however, its performance improved significantly when the saturation vapor pressure was calculated as the mean value at maximum and minimum air temperatures. The results of this study lend further support to the recommendations of “Evapotranspiration 1990” and “The FAO Panel of Experts—1991”: Both documents recommended the Penman-Monteith method for general use.

An analytical model, known as RISK-N, is developed to simulate nitrogen cycling in soils, and nitrate transport and fate in soils and ground water. The soil is separated into upper-root, lower-root, and intermediate-vadose zones, each with uniform properties. Transport in each soil zone is modeled on the basis of complete mixing. Transport in the aquifer, however, is modeled using a two-dimensional advection-dispersion transport equation. A simulation is made with a hypothetical corn plot, using meteorological, soil, hydrologic, and hydrogeological data for the South Platte River region of northeastern Colorado. Sensitivity analyses are performed on model parameters. This study shows that the RISK-N model is capable of simulating nitrate leaching rates, as well as ground-water concentrations, that are consistent with those obtained by numerical models, while requiring fewer input variables.

Schuurmans et al. (1995a) presented a model for the design of water level controllers for irrigation and drainage canals that describes the essential characteristics of the processes relevant for canal control (such as water movements and control structures). This paper evaluates the accuracy of this model in two ways: (1) by comparing its frequency response with a model based on a finite difference approximation of the linearized St. Venant equations, and (2) by comparing simulation results with data from field experiments. Using these results, we characterize the accuracy of the model and discuss how these results can be taken into account in controller design.

This paper presents an evaluation of the potential of an optimization approach in improving real-time irrigation water management in systems with complex distribution networks. The optimization approach is based on quadratic programming. The operational objective is to maximize crop production through appropriate water allocation, while maintaining equity between different irrigation schemes and units within schemes. The approach has been evaluated through application to the irrigation system in the Lower Ayung River Basin in Bali, Indonesia. A simulation model of this irrigation system was available, and it has been possible to measure the effectiveness of the optimization approach by comparing the results of simulation runs incorporating optimization with the results of runs representing existing water allocation practice. The results indicate that the optimization approach does have potential and can significantly improve crop production at the basin scale. This paper presents a preliminary assessment of the potential of the approach and describes the development of a more sophisticated optimization approach based on real-time evaluations of crop water requirements. Considerations for practical implementation are discussed.

The adjusted factor G_a is a generic friction loss correction factor for pipelines with multiple outlets. The adjusted factor G_a can be applied to pipelines with or without outflow at the downstream end. Furthermore, this factor can be applied to a pipeline where the first outlet is at a full outlet spacing or a fractional outlet spacing from the pipeline inlet. When the outflow at the downstream end is reduced to zero, the adjusted factor G_a reduces to the adjusted factor F_a. If the first outlet is positioned one outlet spacing from the pipeline inlet, the factor G_a reduces to G. Finally, if both the outflow is zero and the first outlet is one outlet spacing from the pipeline inlet, the adjusted factor G_a reduces to a close approximation of the well-known factor F. The adjusted factor G_a is a function of the number of outlets along the pipeline, the location of the first outlet from the pipeline inlet, the outflow ratio, and the velocity exponent of the head loss formula.

The drainage infrastructure constructed by the Inca at ancient Machu Picchu represents a significant public works achievement. The difficult site constraints associated with the nearly 2,000 mm per year of rainfall, steep slopes, landslides, and inaccessibility posed drainage challenges that were met successfully by the Inca. The technical analysis of the Inca drainage works demonstrates that the drainage criteria used were reasonable and the implementation exceptional, and that the Inca were good engineers even though they labored without the benefit of a written language or the use of a wheel. Proof of the Inca success with drainage rests with the fact that Machu Picchu lay in the rainforest for 400 years without failure. There is no better example of successful ancient civil engineering than Machu Picchu. It was built by Native Americans before the arrival of the Spanish Conquistadors, was essentially abandoned in 1540 A.D., and endured for 4 1/2 centuries under a thick rainforest until the 20th century. Scientists, engineers, and laymen alike continue to marvel at the wonders of Machu Picchu.

Seepage effects on the stability, mobility, and incipient motion of sand-bed particles are experimentally investigated. Seepage through a sand bed in a downward direction (suction) reduces the stability of particles, and it can even initiate their movement. The bed erosion is increased with the increased rates of suction. Whereas the seepage in an upward direction (injection) increases the stability of bed particles, it does not aid initiating their movement. The rate of bed erosion is reduced or even stopped by the increased injection rates. Hydrodynamic conditions leading to the so-called “pseudoincipient motion” with suction (for the initiation of particles movement that are otherwise at rest under no-seepage conditions), and with injection (for only arresting the particles movement that are otherwise moving initially) are evaluated. The conventional Shields curve cannot be used to predict such pseudoincipient motion conditions with seepage. The concepts thus developed are useful for a better understanding of the sediment transport mechanics and in the design of stable alluvial channels affected by seepage.

Roadway sanding is a common practice in cold regions because sand increases the roadway friction when mixing with snow. However, after snow melt, sand imposes potential hazards to traffic. Recovery of sand from highways has become an increasing concern not only for the reason of traffic safety, but also for being nonpoint pollution sources to nearby wetlands and streams. In this study, a snow storage element is introduced to the renascence project of a mountainous highway that is running through an environmentally sensitive forest area in Colorado. Recovery of winter sanding material from the highway is designed to be a joint effort of surface runoff and sweeping machines. As a tradeoff exists between sand recovery and the size of a snow storage area, this study also presents a maximization methodology by which the size of the snow storage area can be determined by the diminishing return of sand recovery.