Bridge Scour : Basic Mechanisms and Predictive Formulas

This report aims at presenting basic knowledge on bridge scour and the processes governing its evolution as well as summarizing the most common formulas used to calculate scour depth at bridges. Design procedures concerning bridge scour in several different countries are also discussed, including United States, Australia, and the United Kingdom. The situation in Sweden with regard to bridge scour is briefly reviewed and several case studies are presented where marked scour holes have been detected at bridges. Two cases of bridge failures in Sweden are included where local scour was the main reason for the collapse.Bridge scour is typically separated into pier, abutment, and contraction scour, where each mechanism is controlled by different physics and governing parameters. Each type of bridge scour is discussed separately in the report with sections on basic mechanisms, governing parameters, common predictive formulas, and concluding remarks.The report also includes a brief summary on the expected influence of climate change on bridge scour. Larger and more intense rainfalls in the future imply larger flows in the rivers with increased bridge scour as a result.The report deals only with scour induced by bridges; other types of scour, such as general scour due to longitudinal transport gradients in the river, scour related to secondary flows in river bends, or scour downstream hard bottom, are not discussed. Most of the formulas included to estimate bridge scour are valid for friction material and only a few examples are given that are applicable to cohesive sediment, mainly related to recommended design procedures from different countries. Also, the objective of bridge scour analysis is often to estimate the maximum scour depth, occurring at equilibrium conditions under a certain flow, implying that most of the formulas are valid for such conditions

Laboratory Investigation of Beach Scarp and Dune Recession Due to Notching and Subsequent Failure

Analytical models to calculate notch development and subsequent mass failure of dunes are presented. The notch evolution model is based on a transport equation for sediment from the dune and the sediment volume conservation equation, whereas the models of mass failure are derived using elementary engineering statics and soil mechanics. An empirical transport coefficient in the model describing the notch growth rate is found to be related to the hydrodynamic forcing at the dune normalized by geotechnical parameters describing the resistive strength of the dune. Two modes of mass failure are modeled whereby the overhang generated by the removal of material from the dune foot (notching) slides downward or topples over following the development of a tensile crack some distance shoreward of the maximum notch depth. The accuracy of the notch evolution and mass failure models are assessed by comparing calculated recession distances against measurements from a small-scale laboratory experiment

Estimated Future Production of Desalinated Seawater in the MENA Countries and Consequences for the Recipients

Seawater desalination constitutes an important source for water supply to the population bordering the Arabian Gulf, the Mediterranean Sea, and the Red Sea. Desalination has advantages and disadvantages which may depend on the region, location, technology, impact and amount of fresh water production. Desalination may also have other impacts. For example, chemicals added in the pre-treatment stages could harm the fish production as well as the marine life in general.The total land area in the three regions represents about 11.8% of the world land area and the countries host approximately 9% of the world population in the three years 1950, 2008 and 2050. Population statistics for a 100-year period has been used inclusive a prognosis from 2010 to 2050. Data on desalination plant capacity covering 12 years from 1996 to 2008 has been summarized and a prognosis of the increase in desalination for the three regions until 2050 developed. The results obtained for desalination capacity in the study area were 62%, 58%, and 60% of the world capacity for 1996, 2008, and 2050, respectively. This study also included estimates of the desalination capacity in cubic meter per capita of fresh water in the years 1996, 2008, and 2050: this capacity is about 1.2, 2.5, and 4.7 m3/capita/yr in the world compared to 7.7, 15.6, and 30 m3/capita/yr in the study area. The increase in the recovery ratio is considered as one important factor in this study. In 1996 this ratio was about 30 to 35%, and in 2008 it was 40 to 45%, yet in some plants reaching up to 50%. Brine discharge will increase the salinities of the Arabian Gulf, Mediterranean Sea and Red Sea, with respectively some extra 2.24, 0.81 and 1.16 g/l in the year 2050

Morphological development of a small-scale beach nourishment in a non-tidal area

Combining hard and soft costal protection solutions can be an appropriate measure to enhance structure lifetime. This study aims to quantify the morphological evolution of the nourished stretch and adjacent coastlines. A small-scale beach nourishment has been performed in front of a rock revetment at site in Faxe Ladeplads in Zealand, Denmark. The overall objective is to learn more about the dynamics of small-scale nourishments in low energy environments. Monitoring techniques include repeated topographic (Trimble RTK-GPS, drone surveying) and bathymetric (single beam) measurements. To measure the hydrodynamic conditions two surface acceleration buoys deployed at -4 and -7 m water depth were used. Sediment volumes from nourishments of size 70,000 m3 and 20,000 m3 redistributed relatively quickly. The nourished material built up the cross-shore profile and a longshore bar in this area, and distributed sediments in the direction of the dominant littoral drift (SW). Results suggest that the morphological evolution of the nourishment is dependent on local hydrodynamic conditions and local geomorphology. These findings have implications for the main objectives of preventing wave overtopping onto an adjacent coastal road during extreme events and restoring a beach for recreation

What is technology adoption? Exploring the agricultural research value chain for smallholder farmers in Lao PDR

© 2019, Springer Nature B.V. A common and driving assumption in agricultural research is that the introduction of research trials, new practices and innovative technologies will result in technology adoption, and will subsequently generate benefits for farmers and other stakeholders. In Lao PDR, the potential benefits of introduced technologies have not been fully realised by beneficiaries. We report on an analysis of a survey of 735 smallholder farmers in Southern Lao PDR who were questioned about factors that influenced their decisions to adopt new technologies. In this study, we have constructed measures or states of adoption which identify key elements of an adoption decision-making nexus. Analysis was conducted to statistically group explanatory factors of adoption. The key explanatory factors represented attributes of the farmer, the factors considered when undertaking production decisions and elements of the agricultural value chain that present as opportunities or constraints. We describe the combination of farmer’s personal attributes, perceptions of the value chain, and the introduction of new technologies by external actors as an “agricultural research value chain”, where agricultural research activities intervene to derive greater benefits for local farmers. A generalised linear model, via Poisson (multiple) regression analysis on the identified explanatory factors, was applied to explore how they influence adoption measures and we found several significant relationships

Stormfloder - en kunskapsöversikt av metoder för att identifiera och kvantifiera extrema havsvattenstånd

Stormfloder är tillfälligt förhöjda vattennivåer orsakade av meteorologiska fenomen som kan ge upphov till översvämningar utmed kusten. När havsnivån stiger till följd av klimatförändringarna och befolkningen utmed kusten ökar, leder det till en ökad översvämningsrisk. Risk kan beskrivas som en kombination av sannolikhet och konsekvens. För att kunna bestämma var som är säkert att bygga och hur befintlig bebyggelse kan skyddas behövs kunskap om hur höga vattenstånd som kan uppstå, hur stora vågorna kan bli och hur länge en storm varar. Vanligtvis utgår man från en sannolikhetsnivå, till exempel att ett område kan tillåtas att översvämmas i genomsnitt vart hundrade år, och bestämmer sedan vilken vattennivå det motsvarar genom extremvärdesanalys av tillgängliga mätdata. För att göra en så säker förutsägelse som möjligt behövs en lång tidserie (i förhållande till den beräknade frekvensen). Det är även viktigt att veta om observationerna är representativa även för framtida förhållanden. Vid stadsplanering och dimensionering av kustskydd är planeringshorisonten i storleksordningen 25 – 200 år, och känsliga byggnader, till exempel vattenverk, kärnkraftverk, och sjukhus dimensioneras för långa återkomsttider, i storleksordningen 200 – 10 000 år. I dagsläget är det svårt att med rimlig säkerhet bedöma konsekvenserna av så ovanliga händelser och hur de kommer att utvecklas i framtiden. Problemet är att mätserierna av stormfloder ofta är för korta för att göra en robust analys. I den här rapporten undersöks hur analyser av stormfloder kan förbättras genom att ta hänsyn till händelser som inträffade innan vattenståndsmätningarna började samt hur de påverkas av klimatvariationer och klimatförändringar.Genom en internationell litteraturstudie undersöks vilka metoder som kan användas för att utöka dataserierna genom att studera historiska dokument, geologiska undersökningar, samt hydrodynamisk modellering. Vidare studeras hur olika statistiska modeller kan användas för att inkludera dessa faktorer i extremvärdesanalys. En fördjupad studie görs av utvalda länder runt Nordsjön och Östersjön (Danmark, England, Schleswig-Holstein och Nederländerna). Analysen visar på stora skillnader, både mellan de studerade länderna och i jämförelse med Sverige, avseende dimensionerande händelser, metoder för extremvärdesanalys, samt hur historiska stormfloder beaktas i riskanalyser.Om översvämningsrisker underskattas, föreligger risk för stora materiella skador och i värsta fall människors liv och hälsa. Om översvämningsrisker å andra sidan överskattas innebär det en suboptimal markanvändning i kustnära områden och att översvämningsskydd överdimensioneras med negativa samhällsekonomiska och miljömässiga effekter till följd. För att möjliggöra en hållbar utveckling av kustnära områden är därför korrekta bedömningar av översvämningsrisken en nyckelfaktor. Metoderna som presenteras i den här studien kan appliceras på Sveriges kuster för öka kunskapsunderlaget om stormfloder och möjliggöra mer robusta riskanalyser och dimensioneringsunderlag för kustskydd

Suspension by regular and groupy waves over bedforms in a large wave flume (SISTEX99)

Suspended sand concentrations and bedforms under waves were measured in the controlled environment of a large wave flume. Three suspension conditions are discussed here; those occurring with regular (monochromatic) waves of height 0.55m over anorbital ripples, regular waves 1.0m high over orbital bedforms, and repeating wave groups (with a significant wave height of 0.6m) also over orbital-scale features. In all cases the wave-to-wave variability in suspended load was high (∼30%). Patterns of suspension were dependent on the bedform type and on instrument location relative to the bedform. Regular waves suspended an order of magnitude more sediment than groupy waves with a similar significant wave height illustrating,the importance of sequences of high waves in pumping-up sediment concentration into the water column

A Bayesian network model to explore practice change by smallholder rice farmers in Lao PDR

© 2018 A Bayesian Network model has been developed that synthesizes findings from concurrent multi-disciplinary research activities. The model describes the many factors that impact on the chances of a smallholder farmer adopting a proposed change to farming practices. The model, when applied to four different proposed technologies, generated insights into the factors that have the greatest influence on adoption rates. Behavioural motivations for change are highly dependent on farmers' individual viewpoints and are also technology dependent. The model provides a boundary object that provides an opportunity to engage experts and other stakeholders in discussions about their assessment of the technology adoption process, and the opportunities, barriers and constraints faced by smallholder farmers when considering whether to adopt a technology