Optimising water distribution systems using a weighted penalty in a genetic algorithm

Genetic algorithms (GAs) have become the preferred water system design optimisation technique for many researchers and practitioners. The main reason for using GAs is their ability to deal with nonlinear complex optimisation problems. The optimal decision in terms of designing, expansion/extending, addition or rehabilitation of water supply systems has to review possible options and select a cost-effective and efficient solution. This paper presents a new approach in determining a penalty value depending on the degree of failure, of the set pressure criteria, and the importance of the link supplying a specific node. Further modifications are also made in the cross-over and mutation procedures to ensure an increase in algorithm convergence. EPANET, a widely used water distribution network simulation model, is used in conjunction with the proposed newly developed GA for the optimisation of water distribution systems. The developed GA procedure has been incorporated in a software package called GANEO, which can be used to design new networks, analyse existing networks and prioritise improvements on existing networks. The developed GA has been tested on several international benchmark problems and has proved to be very efficient and robust. The EPANET hydraulic modelling software as well as the developed GANEO software, which performs the optimisation of the water distribution network, is freeware. The software provides a tool for consulting engineers to optimise the design or rehabilitation of a water distribution network.Keywords: optimising, water distribution system, genetic algorith

Investigating the bottom free surface nappe (ogee profile) across a sharp-crested weir caused by the flow in an asymmetrical approach channel

The shape of an ogee spillway is based on the shape of the lower nappe of water flowing over an aerated sharp-crested weir. At the design discharge, this shape minimises the possibility of sub-atmospheric pressure occurring on the spillway and maximises the discharge across the spillway. The formulae that are currently in use to approximate the ogee profile consider only two-dimensional flow parameters, being the depth of flow over the spillway crest, the inclination of the upstream wall face, and the pool depth upstream of the spillway. The current formulae for the ogee shape, does not consider the influence of three-dimensional flow. The most significant three-dimensional flow parameters that could affect the shape of the lower nappe are the flow velocity distribution upstream of the spillway, the orientation or angle of the water approaching the spillway, the asymmetrical cross-section of the approach channel, and the curvature of the dam wall. This paper reflects the influence of asymmetrical flow in the approach channel. The investigation was based on a physical model constructed at the Department of Water and Sanitation (DWS). The inclination of the model’s sidewalls of the upstream approach channel was varied to cause a change in the symmetricity, while the lower nappe profile was routinely measured. It was found that the flow in the asymmetrical approach channel caused a variation from the theoretical estimated ogee profile. A comparison between the measured nappe profile and the currently used formulae was investigated. It can be concluded that the symmetricity of the approach channel influences the shape of the bottom nappe, which differs from the shape as proposed by the current ogee formulae. It is recommended that three-dimensional flow should be examined when designing an ogee spillway.http://www.journals.co.za/ej/ejour_civileng.htmlam201

What do near-term observations tell us about long-term developments in greenhouse gas emissions? A letter

Long-term scenarios developed by integrated assessment models are used in climate research to provide an indication of plausible long-term emissions of greenhouse gases and other radiatively active substances based on developments in the global energy system, land-use and the emissions associated with these systems The phenomena that determine these long-term developments (several decades or even centuries) are very different than those that operate on a shorter time-scales (a few years) Nevertheless, in the literature, we still often find direct comparisons between short-term observations and long-term developments that do not take into account the differing dynamics over these time scales In this letter, we discuss some of the differences between the factors that operate in the short term and those that operate in the long term We use long-term historical emissions trends to show that short-term observations are very poor indicators of long-term future emissions developments Based on this, we conclude that the performance of long-term scenarios should be evaluated against the appropriate, corresponding long-term variables and trends The research community may facilitate this by developing appropriate data sets and protocols that can be used to test the performance of long-term scenarios and the models that produce the

A review of low head hydropower technologies and applications in a South African context

This paper provides a review of available low head hydropower technologies, followed by the identification of sites where the technologies can be implemented, applied specifically to a South African context. The potential sites where low head hydropower can be installed in South Africa are grouped as follows: dams and barrages (retrofitting); rivers; irrigation systems (canals and conduits); and urban areas (industrial and urban discharge, storm water systems and water distribution systems). Keywords: low head hydropower, review, hydropower potentialWater Research Commission (WRC).http://www.elsevier.com/locate/rser2016-10-30hb201

A Methodology and Implementation of Automated Emissions Harmonization for Use in Integrated Assessment Models

Emissions harmonization refers to the process used to match greenhouse gas (GHG) and air pollutant results from Integrated Assessment Models (IAMs) against a common source of historical emissions. To date, harmonization has been performed separately by individual modeling teams. For the hand-over of emission data for the Shared Socioeconomic Pathways (SSPs) to climate model groups, a new automated approach based on commonly agreed upon algorithms was developed. This work describes the novel methodology for determining such harmonization methods and an open-source Python software library implementing the methodology. A case study is presented for two example scenarios (with and without climate policy cases) using the IAM MESSAGE-GLOBIOM that satisfactorily harmonize over 96% of the total emissions trajectories while having a negligible effect on key long-term climate indicators. This new capability enhances the comparability across different models, increases transparency and robustness of results, and allows other teams to easily participate in intercomparison exercises by using the same, openly available harmonization mechanis

Evolution of anthropogenic and biomass burning emissions of air pollultants at global and regional scales during the 1980-2010 period

Several different inventories of global and regional anthropogenic and biomass burning emissions are assessed for the 1980-2010 period. The species considered in this study are carbon monoxide, nitrogen oxides, sulfur dioxide and black carbon. The inventories considered include the ACCMIP historical emissions developed in support of the simulations for the IPCC AR5 assessment. Emissions for 2005 and 2010 from the Representative Concentration Pathways (RCPs) are also included. Large discrepancies between the global and regional emissions are identified, which shows that there is still no consensus on the best estimates for surface emissions of atmospheric compounds. At the global scale, anthropogenic emissions of CO, NOx and SO2 show the best agreement for most years, although agreement does not necessarily mean that uncertainty is low. The agreement is low for BC emissions, particularly in the period prior to 2000. The best consensus is for NOx emissions for all periods and all regions, except for China, where emissions in 1980 and 1990 need to be better defined Emissions of CO need better quantification in the USA and India for all periods; in Central Europe, the evolution of emissions during the past two decades needs to be better determined. The agreement between the different SO2 emissions datasets is rather good for the USA, but better quantification is needed elsewhere, particularly for Central Europe, India and China. The comparisons performed in this study show that the use of RCP8.5 for the extension of the ACCMIP inventory beyond 2000 is reasonable, until more global or regional estimates become available. Concerning biomass burning emissions, most inventories agree within 50-80%, depending on the year and season. The large differences between biomass burning inventories are due to differences in the estimates of burned areas from the different available products, as well as in the amount of biomass burned

The discontinuity required at an air valve or vent for effective pipeline de-aeration

The location and sizing of air valves to ensure effective de-aeration of pipelines and to provide vacuum break capability was researched. Based on these findings, software was developed to evaluate gravity and pumping systems. A sound understanding of the factors affecting the hydraulic transportation of air in a pipeline is paramount for locating air valves. When air is hydraulically transported to the position of release from the pipeline, it is necessary that the free air should be intercepted by a discontinuity and expelled via an air valve or vent arrangement. Research information on the layout and dimensioning of the discontinuity to ensure the interception of air in pipelines is lacking. This paper discusses experimental and numerical model assessments undertaken to compile provisional guidelines for determining the dimensions of the required discontinuity.The Water Research Commissionhttp://www.journals.co.za/ej/ejour_civileng.htm