Water Profile over an Ogee-Shaped Crest and the Reynolds Fractional Equations

Weir crest must have the correct shape in the concave side of an ogee-shaped crest to diminish erosion. This shape can be obtained using an approximation of the fractional Reynolds equations when the water interacts with the surface. A model is introduced for the Reynolds stresses complemented with a closure relation of fractional origin. A power type solution is obtained for the main velocity and stress. Velocity profile is found based on the assumption of a steady flow and the energy conservation equation. A Froude number and the cubic equation of the weir are built. The dimensionless upstream velocity head is also determined which allow graphically showing the exponent and coefficient of the water-profile over an ogee-shaped crest. It is possible to estimate the occupied-space index trough an exponents＇ ratio of profile over the velocity head.

The Mexican Environmental Flow Standard:Scope,Application and Implementation

With the implementation of the Official Mexican Standard NOM-011-CONAGUA-2000 [1], the water balance of 730 basins has been calculated and its water availability agreement is published. This rule points out to allocate water for the environment only as an annual volume since methods for estimating environmental flows were not standardized in the country. For this reason, The Water Agency (CONAGUA) issued the standard NMX-AA-159-SCFI-2012 [2], to assess environmental flows needed both, at the strategic level in Integrated Water Resources Management (IWRM), or as part of the Environmental Impact Assessment (EIA) of large hydraulic projects. For over ten years, this standard was developed and finally published in September 2012 [3]. It explains different methods from hydrological to holistic approaches, with examples for the country. Its application will cover the urgent need to preserve water for ecosystems in watersheds with high ecological importance and low stress for water use. In this paper, an analysis of the environmental flow standard and examples of the suggested hydrological methods are presented. For its implementation, some steps are taking place, mainly establishing environmental water reserves and building capacities. In addition, environmental allocations are becoming a common practice for all water projects, as well as setting limits to hydrological alterations by hydroelectric dams. The standard promotes the use of technical integration tools to analyze the responses of ecosystems to changes in the flow regime and adaptive management under different scenarios of water use. Although the main steps have been taken, its implementation as mandatory rule will take time.

Environmental Approaches during Planning and Construction Stages of Hydropower Projects in Mexico

During the Environmental Impact Assessment procedure (EIA) for hydropower projects, apart from the compliance with environmental standards and regulations, important environmental and ecosystem changes are foreseen from planning and construction stages. In Mexico, the EIA and environmental standards are being systematically applied and fulfilled at planning and construction stages for hydropower projects. These are mainly related to control air emissions, solid and hazardous wastes, water discharges and deal with protected species. In addition, due to land use changes, forestry compensation procedures have already been established. To comply with project approval conditions, an Environmental Management Plan (EMP) is carried out during construction;it includes mitigation measures, standards, regulations and approval conditions resulting of project review and in some cases requests from the public audience. Monitoring is carried out in the area of influence that is in the works and where it is expected that natural processes are modified. However, indicators to track these changes are minimal. This paper analyzes the regulatory and organizational frameworks to address environmental management during the planning and construction of hydropower facilities in Mexico and gives recommendations to expand the scope of the supervision and management of ecosystem changes.

Evaluation of Sunlight and Humidity Protection of a Bioherbicide for Eichornia crassipes Biocontrol

C. piaropi （Cercospora piaropi） and A. zonatum （Acremonium zonatum） have proved to be effective in reducing water hyacinth growth. However, efficacy of these fungi in field is limited by the effect of solar UV （ultraviolet） light and desiccation. In this study, three compounds used as sunscreens and one seed plant that produce mucilage were tested for their effects on the infection produced by C. piaropi and A. zonatum inoculum under laboratory and field conditions. In laboratory conditions, TiO2 （titanium dioxide） and metamucil did not inhibit C. piaropi and A. zonatum viability. Moreover, the addition of TiO2 and metamucil to the inoculum suspension increased fungi infection. The protective effect of TiO2 and metamucil was more evident when the inoculum suspension was applied 4 h before sunset. These results suggest that addition of TiO2 and metamucil provides necessary humidity and solar protection for increasing C piaropi and A. zonatum infection on water hyacinth plants.

Rain Variability and Population Growth to Explain Historical Levels of the Patzcuaro Lake in Mexico

The height variability of Lake Patzcuaro, in central Mexico, remained constant for several decades, and during that period, the lake maintained its functionality and environmental services. However, in the last twenty years, there has been a significant decrease in the variability range. In order to estimate the water balance, in this work, an approach was developed to understand how water moves in time and space, and to determine possible inherent thresholds to lake variability. The historical Lake Patzcuaro height above 2035 masl was correlated with several climatic variables. The correlation with monthly rainfall shows that there is a delay of three months, indicating that the lake volume depends on three factors: precipitation, surface runoff and underground contribution, of which precipitation over the lake surface is the least significant. In the long term, using annual data, there is a remarkable memory of precipitation extending beyond five years, seen as a correlation with the accumulated precipitation anomaly (r2 = 0.76). This behavior should be explained by understanding relationship between the lake and its aquifer. Also important is the population growth, which affects the lake level in two ways: water extraction and water discharge. The models pointed out a nonlinear relationship between water level and the aforementioned variables, and suggest that the carrying capacity of the basin is around 90 thousand people, under current patterns of water consumption. It also indicates that, in order to allow lake recovery or to maintain system resilience, the anomaly of precipitation accumulated during several years should exceed 1000 mm. Although a correlation with land use was attempted, historical data do not reflect a trend that could be associated with water balance.

Theoretical and Experimental Analysis of Vortex Origin

Several investigations refer to the issue of creation and identification of vortices in flows with different regime and presence of obstacles. Reasons have to do with the crucial role that vortices play in nature and industrial processes （sediment transport, mixing, radiation, noise, etc.）. Despite the contributions, further work is needed in order to perform more analysis of the mathematical arguments used to explain this phenomenon. In this idea order, the paper presents some advances in mathematical analysis and experimental results. In the first section, we do a description of the fluid motion from a fractional view through a sequence of three steps： Darcy＇s law, Navier-Stokes equations and Reynolds equations. Next, a representation of the temporal change of kinetic energy is found, which allows the possibility of the two signs. We obtain a description of the process of vortex creation. A length that represents the transition between flow and vortex intensity is found; then a succession of lengths is established that allows scaling from micro to macro. In the second section, experimental results are present; we consider vortex creation and its detection upstream of a bed form similar to that found in rivers, installed in an open channel, equipped with a water circulation system. For vortex detection, a methodology based on the particle image velocimetry PIV technique is proposed. So, we fulfill two objectives： vortex identification and its passage frequencies behind the bed form installed in the channel. Such procedure allows a computer process time reduction in vortices identification task.

Mechanical and natural ventilation systems in a greenhouse designed using computational fluid dynamics

The aim of this study was to analyse air exchange and temperature distribution in a greenhouse with combined mechanical and natural ventilation and to design more efficient mechanical ventilation systems.For this purpose,a computational fluid dynamics(CFD)model of the greenhouse was used.Three configurations were considered:Configuration 1(mechanical ventilation and closed roof ventilators),Configurations 2 and 3(mechanical ventilation and roof ventilators open 30%and 100%,respectively).After validation,the CFD model was used to improve the design of the greenhouse mechanical ventilation system in each of the three configurations analyzed.Four greenhouse lengths,28 m,50 m,75 m and 100 m,were used in the simulations.Compared to fan ventilation only,roof ventilation improved the climate of fan-ventilated greenhouses in terms of the air exchange rate(22%)and climate uniformity because the internal air was mixed better than with mechanical ventilation only.As the greenhouse length increased,more advantages were achieved with natural ventilation compared to mechanical ventilation.For most configurations,there was a strong linear correlation between temperature gradient and greenhouse length.The greenhouse whose regression line had the steepest slope was the one with closed roof ventilators.Increasing the fan capacity produced a general reduction in temperature,but the effect was less intense for the greenhouses with open roof ventilators.Compared to box inlet ventilators,an enlarged continuous inlet in the wall opposite the fans increased overall system performance because it eliminated backflow recirculation zones,which are prone to produce high temperatures.