· · · Repository Hydraulic Engineering Reports

The Administracao dos Portos do Douro e Leixoes is confronted with the fact that future expansion of the port area of Leixoes is limited by the surrounding hills and urbanization. One of the alternatives for future expansion might be the creation of port facilities in the Douro estuary, where a relatively large, flat area is available. However, the river entrance is rather unstable from a morphological point of view, so that regular dredging is required to maintain an access channel. In order to eliminate the risk of unexpected morphological changes in the Douro estuary, due to harbour works in thee Douro estuary, APDL has decided to study the morphology of the Douro bar thouroughly, and to make a design for a mathematical model to investigate the influence of harbour works in the area. The study consists of: (1) wave penetration study (2) calculation of longshore transport (3) calculation of tidal prism (4) sediment transport measurements (5) morphological evaluation (6) set-up of a mathematical model. (Note: Hydronamic report 708-8 and 708-9 report on follow-up)

The research output describes the results of – analysis of factors of river capacity problems along the Middle-Tisza section, – scenario analysis of intervention options to raise the flood conveyance capacity of the flood bed, – scenario analysis of partial floodplain reactivation with controlled inundation. Individual and combined effects of river capacity improvement, selected detention basins as well as combined effect of river capacity improvement and flood detention was investigated. Results of modelling are summarised and form important input of the design and implementation of the flood hazard reduction programme of the region called Update of the Vásárhelyi Plan.

The dissertation we proposed to develop comprises, besides an intense bibliographic search, a strong fieldwork component. For the Douro mouth sand spit actual evolution knowledge we had resorted to GPS, technology that allows to obtain precise facts, whose analysis and interpretation have permitted us to infer about the behaviour of this sandy structure during the observation period. The morphodynamic evolution of the Douro river mouth sand spit is related with several factors, which interfere on the Portuguese coast line, detaching natural and anthropic actions. The Douro mouth region where, after a sinous and long course, the river contacts with the ocean, is endowed with self-proper dynamic, morphology and evolution. The Douro river sand spit located on the left margin of this estuary is close to N/S direction, being genetically considered as a result of a fluvial-marine commitment. Through the years, the Douro mouth problems, in general, and the sand spit problems, in particular, have showed difficult resolution or even unavoidable. The analyse of some historical details, namely the floods, the shipwrecks, the navigation difficulties, the implementation of several works and the countless proposals for improvement of the approach to Douro bar are the proof of that difficulty. The necessity of making security commercial changes culminated in the Leixões artificial harbour building, which seems to practise, cumulatively with other anthropic conditionants, some influence on sand spits morphodynamics. The deposition on this place is due to the decrease of solid material transport, related, obviously, with a flow velocity reduction, which results, by its turn, from the reciprocal and counterwork between the fluvial current, the tidal flow and the swell, without despising the wind action. The alluviums carried by the river, in time floods basically, and deposited in the terminal part of its course carries to sandbanks formation which, through the year, the marine action drags away to the open sea or to the continent, thickening or thinning the sand spit. The terminal part of this sandy structure, by the action of fluvial flow, as well the tide and wave, bends then, to upstream or downstream, acquiring rebellious and capricious shapes. The sand spit morphology reveals oneself, by consequence, unsteady and its variability constitutes a conditioning of the major or minor facility of the bar transposition. The sand spit was mapped since the last XVI century. Till our days, when it's possible to use scientific and technologically advanced methods, many cartographic works were made, whose elaboration obeyed, basically, to the demands from the socio-historic context of each epoch.

The first three chapters of this report offer introductions, each from their own viewpoint. In the first chapter, the focus point is the river landscape in general. Amongst others the history of human interference in the river landscape, theories on the ecological functioning of rivers and summaries of hydrological and morphological processes are treated here. Because of its general nature the reference list of this chapter is somewhat longer than that of the other chapters, offering a number of entries for those interested in further reading. The second chapter gives an overview of relevant policy documents for the river landscape in the Netherlands. The third chapter deals with some aspects in which the interrelations between the different rehabilitation measures (treated in more detail in chapters 4 to 10) come to light. These aspects are the ecological coherence in ecological networks, the effects of measures on design river water levels and aspects of dealing with polluted soils. Chapters 4 to 10 each deal with one of the measures that might be considered in floodplain rehabilitation projects. In all of these seven chapters, first the measure and its reference situation are described; then attention is paid to the functioning of the area in which the measure is implemented, from hydrological, morphological and ecological viewpoints. Finally an overview of the suitability of the river stretches to the measure and a number of guidelines and recommendations for the implementation of the measure are given. For all of these chapters a similar structure was chosen, in order to secure easy access for users trying to find specific information quickly. The last chapter deals with grazing management, the choices that must be made there, and the consequences these choices have for the further development of the area. This last chapter to some degree is relevant for all preceding chapters dealing with specific measures, but this time from the viewpoint of terrain management.

During the dry season shipping between Mongu and Kalabo is impossible, therefore this project was started to improve the situation by dredging. Dredging was started at Mongu harbour, where a new dredger was delivered, assembled and launched. Due to the urgency of the project dredging had to be started before a profound survey concerning the topography and hydrography of the total area was made. This is one of the reasons why it was not possible to make a detailed time and production planning. This report is based on a field survey, carried out from May 29th until June 29th, 1978. The survey can be divided into two parts, first the topographical survey, reSUlting in a 1:20,000 map of the Luanika-Waterway, and second the hydrographic and morphological survey. The purpose of the surveys was to give an advice for the planning of the dredging works in the Luanika-Waterway.

As a continuation of the initial study on the morphology of the Douro mouth, performed by Hydronamic in 1982, the Administracao dos Portos de Douro e Leixoes commisioned Hydronamic bv to construct a mathematical hydro-morphological model of the Douro mouth. Within the framework of the study an analysis of old charts, available in the archivas of A.P.D.L. has been made. The charts cover the period between 1860 and 1983. Both a statistical as a visual analysis of the charts has been made. The purpose of the visual analysis id to get a better insight of the morphological processes as they appeared in the past. Studying these charts gives a very good feeling on the real behaviour of the river. With such a more profound insight a more realistic mathematical model can be developed. In chapter 5 the visual analysis is discussed. The purpose of the statistical analysis is to provide data for the calibration of the mathematical model. The data obtained from the charts are put into the computer and analysed.

The river Douro debouches into the Atlantic Ocean near Oporto (Portugal) with a funnel-shaped mouth, partly closed from the ocean with a sand spit. Both the wave-induced longshore sediment transport as the sediment yield of the river are limited by the available quantity of sediment (non-alluvial conditions). The results of some sediment transport measurements are presented. The morphology of the river mouth is discussed in relation to the geology of the area, the river discharge and the wave climate, based upon data from the field survey as well as upon some additional calculations

Occasional flows of the river Nyabage cause floods in the river valley, flooding bridges and buildings, amongst others a small hospital of MsF. The flow is a mixture of water and debris and causes severe damage. The report describes the phenomena and the damage in the area. Some proposals for improvements are given

The Lower Mekong River area is a zone with plenty of natural resources and it has the highest agricultural production in Vietnam. The river passes though six provinces in the Southern patt of Vietnam, with more than 16 million in habitants in total. However, serious riverbank erosion problems occur and there is no master plan or mitigation strategy to prevent this problem. Given these conditions, the first objective of this Master of Science study was to study bank erosion prediction by means of both empirical methods and numerical methods. The second objective is to study possible mitigation measures, especially the use of revetments, bend cut-off, and permeable groynes. Based on a number of satellite images (1987, 1996, 2000), old map (1937, 1966) and the observed topography data at some locations, empirical methods to predict riverbank erosion were studied, tested and modified. It appeared not possible to derive an empirical method which in generally applicable in the Lower Mekong River. A numerical model was developed amongst others to make of riverbank erosion predictions. This model was properly calibrated and verified against data from measurements. In an early state of numerical model development, riverbank erosion prediction along the Lower Mekong River was tested with the model. In this testing, the sensitive of parameters in the bank erosion module of MIKE21 C were checked for the Tan Chau -Hong Ngu reach. To prevent (predict and mitigate) riverbank erosion is a very challenging task in river engineering. The mitigation measures were studied by a comprehensive approach, which reviewed the existing mitigation measures in the lower Mekong river, and subsequently fare an overview of possibility preventive measures in this area. Finally, one case study, notably the critical reach near Tan Chau, was taken considering three kinds of measures: a revetment, a bend cut and permeable groynes. The numerical model was used to predict (i) the scour hole in front of revetment, and (ii) the effect of the bend cut. Also the application of the permeable groynes was studied, but these appear to be less suitable for the specific conditions at Tan Chau.

Overview report of the final design of the Feni closure dam in Bangladesh

Overview of sediment transport formulas and comparison with measurements in Waal and Rijn river in the Netherlands.

Observations were made of temperature, salinity, currents and meteorology in the ocean off the northern coast of South America, during autumn 1970 and spring 1971. The observed salinity distributions in the surface layer reflect the seasonal variation in the trade winds. Besides, very strong vertical current shear waS found over the layer between surface and halocline. A rough estimate for the horizontal lateral exchange-coefficient is 1. 4 to 2 X_ 105 m2 s-1 being of the same order of magnitude as the values reported for the Gulf Stream. Large scale movements of the water have been traced by drift bottle experiments; recoveries were reported from the northern coast of South America, from Central America and from North America. An estimate is made of the fresh water flux of the Amazon that passes along the coast. There are no indications to conclude to an intermittent fresh water flow.

If we plot the discharges of natural water-courses measured under all manner of circumstances against the water levels measured at the same time, the points obtained win give us what is called the stage-discharge relation curve. But it should be noted that the relation win only be a true one ifthere is no backwater effect (due, for exampIe, to a dam or a tributary debouching downstream from the measuring point) at the points at which the discharges and levels are measured. The stage-discharge relation will also change with any changes in the depth of the bed of the water-course, and discharges and levels will then have to be measured at regular intervals to ensure that the stage-discharge relation curve gives a faithful picture of the actual situation. Once the stage-discharge relation has been established, a glance at the water-level indicator win suffice to enable the Controller to determine the discharge at any particular moment.

In deze publicatie worden enkele resultaten van projecten in Bangladesh gepresenteerd met aandacht voor een mogelijke toepassing in alternatieve ontwerpen van kribben. Deze resultaten betreffen hoofdzakelijk doorlatende palenrijen en falling aprons. Een falling apron kan worden vergeleken met een toplaag zonder zinkstuk.

This report is part 2 of the economic analysis of the project ‘Space for the Rivers’, which aims at improving the safety against flooding along the river Rhine. It is a Cost-Effectiveness Analysis (CEA) of proposed measures and packages. A method has been developed for evaluating measures and packages with more than one effect at the same time. Progress in safety, growth of the number of hectares with desired nature, and value judgements on spatial and recreational quality are the elements in the CEA. Combining progress in safety with the development of nature in one measure does not reduce costs in general. The choice of measures along the river Nederrijn-Lek does not seem efficient, both in the base package as in the alternative package. The alternative for the passage Veur-Lent deserves serious consideration.