灌溉排水系统工程

Physical infrastructureassets are essential to provide a specific service, which may change over time, according to service needs, challenges and life style. 40-100 years old water and wastewater pipes were installed to provide a service ? conveying water for consumption for the former, carrying away storm and sanitary water for the latter - to a given number of customers under assigned external conditions, and were designed according to technologies and rules existing at the time of installation. As the conditions and the population to serve vary over time and during infrastructure lifetime, performance is likely to suffer as the physical condition of the pipes deteriorates, if timely remedial action is not taken. Talking of performance, what is expected from the pipes may change over time (the loading may increase for instance), and the reliability with which they can perform these functions may decrease.

Human activities require more and more resources- among them water is certainly the most precious. Modern agriculture consumes almost two thirds of the water pumped in United States. For this reason, more and more people are seeking ways to conserve it. In the quest for improving water conservation in soils during irrigation, the United States Department of Agriculture (USDA) conducted studies on various materials in the early 1960s. As a result, a resin based on the grafting of acrylonitrile polymer onto the backbone of starch molecules (starch-grafting) was developed, which was known as ?Super Slurper?. At the time, the USDA gave the basic technology to several USA companies for further development. As the Japanese companies were excluded from participating, they started independent research using starch, carboxy methyl cellulose (CMC), acrylic acid, polyvinyl alcohol (PVA) and isobutylene maleic anhydride (IMA). The hydrolyzed product of the hydrolysis of this starch-acrylonitrile co-polymer gave water absorption greater than 400 times its weight and did not release water as fiber-based absorbents do. Could super absorbent polymer (SAP) be the future of irrigation water conservation?

Fluctuations in cotton (Gossypium hirsutum, L.) yield in the Tennessee Valley of Alabama are common and usually related to drought or irregular rainfall. A sprinkler irrigation study was established from 1999 to 2004 to evaluate the minimum design flow rate to produce optimum cotton yields and economic gain. A replicated randomized block design consisting of four irrigation treatments ranging from one inch every 12.5 days (equivalent to 1.5 gpm acre-1 design flow rate or system capability) to one inch every 3.1 days (6.0 gpm acre-1) and a control, rainfed treatment. Daily plant water requirement was determined using soil moisture sensors and a spreadsheet-based scheduling program (MOISCOT) developed by Alabama Cooperative Extension engineers. Significant yield differences between irrigated and rainfed cotton were noted during the study period, with rainfall variability and treatment effects accounting for most of the yield response. The minimum design flow rate (1.5 gpm acre-1) increased mean seed cotton yield by more than 500 lb acre-1 over rainfed yields. The most economically efficient design flow rate (4.5 gpm acre-1) increased mean seed cotton yield by more than 996 lb acre-1. A positive relationship was observed between cotton yield and total seasonal irrigation depth during dry years. Across all six years of the study, irrigated treatments produced significantly higher yields than rainfed cotton. The highest six-year cotton lint yield and net economic returns were obtained with the 4.5 gpm acre-1 irrigation treatment. This result provides a rule of thumb for estimating the extent of irrigated area based on available water supply rate.

Irrigation systems need to be selected and designed on a new paradigm, a total system cost approach. The true costs associated with new systems are often boiled down to the tangible fixed and variable system outlays. In many cases, alternative decision metrics are employed, but there are times this fails to adequately account for ostensibly intangible costs that are necessary to be both competitive and responsible. This problem is compounded when water is undervalued, or the true costs associated with the withdrawal are obscured, deferred, or even subsidized.

The study of droplet evaporation is applied to many and varied fields: the present approach is oriented to sprinkler irrigation. This paper examines a parametric study on the evaporation in air of a single droplet, with the aim of highlighting the influence of each parameter alone on the evaporative process. Four parameters are investigated:air temperature, droplet initial velocity, droplet initial diameter, diffusion coefficient of vapour in air. Droplet evaporation is studied through numerical-CFD simulation employing STAR-CCM+ version 5.04.012 software, which treats the evaporative phenomenon hypothesizing quasi-steady conditions, given the interface low liquid-gas vapour concentration gradients. The results are provided as time- and space-dependent in-percentage evaporation rates, the latter ones after defining a specific distance, from the injection point, to be covered. Apart from a qualitatively predictable effect of air temperature and diffusion coefficient of vapour in air, droplet initial velocity and above all droplet initial diameter prove not at all to be negligible when managing an irrigation process, the latter being inversely proportional to droplet mass evaporation. These results prove that droplet evaporation is a complicate fluid dynamic effect and cannot be simply regarded as a diffusive process. The final discussion provides some practical remarks useful to irrigation operators.