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Malvik overvann

Flomfrekvensanalyse for Malvik kommune

I avrenningsområde Sandmarkbekken i Malvik kommune har det gjentatte ganger oppstått flom. Malvik kommune har henvendt seg til DHI for å beregne dimensjonerende vannmengder i feltet og flomgjentaksintervall for dagens system. I den øvre delen av sonen i nord klarer ikke fellesledningen på 300 mm å ta imot overflateavrenningen. Her skulle det avklares om kapasiteten var utilstrekkelig eller om inntaket var underdimensjonert. I den nedre delen oppstår det regelmessig oppstuvning i kulverten som går under gamle E6 og jernbanen. Hele avrenningen fra feltet, inklusive bekker blir samlet her. Det er i tillegg undersøkt hvordan en videre utbygging av sonen vil påvirke avrenningsforholdene.

Nedslagsfeltet for Sandmarkbekken er på 261 ha. Størrelsen av tette flater (hus og veier) i sonen er på bare 4,56 ha, altså under 2 %. Avrenningskarakteristikken er dermed sterk preget av overflate- og grunnvannsavrenning fra bratte jordbruks- og skogsarealer. RDII modulen i MIKE URBAN er benyttet til å simulere de ulike andeler avrenning. For flomfekvensanalysen er modellen kjørt med en tidsserie på 37-år. Ledningsnettet og bekker er også modellert i MIKE URBAN.

Det var mulig å gjenskape den observerte flommen med MIKE URBAN modellen som er satt opp for den historiske nedbørsperioden 1967-2004. Avrenningen i kulverten viste seg å være begrenset av tilbakestuvning fra sjøen ved flo. En oppdimensjonering av kulverten ville dermed ikke redusere flomhyppigheten, men heller fordrøyningstiltak foran kulverten. Den simulerte flomfrekvensen for kulverten er ved jernbanelinjen på 1,3 år. I den nordlige delen er flomfrekvensen beregnet til 3 år og fellesledningen her viste seg å være underdimensjonert i denne situasjonen.

En utbygging av avløpssonen førte til hyppigere, men ikke større flommer. De største hendelser er fortsatt preget av avrenningen fra permeable flater. Flomfrekvensen i den nordlige delen økte til 1-års intervall med den eksisterende 300 mm ledningen.

Gjennom modellen og simuleringene var det mulig å analysere de ulike årsakssammenhengene for flom og dermed å planlegge målrettete tiltak for de forskjellige deler av ledningsnettet.

The capability to understand and investigate the motion of liquids and gasses in detail is of high importance in a wide range of engineering disciplines. Today this is done primarily using CFD.

DHI has applied CFD for the last fifteen years and developed an in-house code named NS3. A recent NS3 application includes a study of the Kapar power plant cooling water intake. This involves a combination of free surface flow and internal pipe flow modelling. The NS3 model was used as an efficient design and optimisation tool.

The Kapar Power Plant, Malaysia
The power plant is located at the western coastline of Malaysia at the Malacca Strait. The power plant applies seawater as cooling water. Due to the close proximity of the outlet from the Selangor River large sedimentation issues are seen at the existing intake. To resolve this it was decided to move the intake head approximately 250m offshore and carry out a re-design.

The NS3 system has been applied to model the flow in the new pump structure including evaluation of head loos through the new arrangement of pipes, free surface, study of potential resonance, sediment transport, and deposition in the pumping house.

Results
The NS3 simulations of the entire system did reveal that with the original design surface elevation in the pumping house would be very close to a critical level during pump start. Hence the layout of the pipes had to be redesigned in order to minimise the head loss and obtain an acceptable water level in the pumping house.

For further details please see here.

– Experience from Horns Rev I Wind Farm

During recent years a significantly increasing number of offshore wind farms have been developed. The offshore wind farms have become attractive as larger turbines become available and not least due to the difficulties of finding new good locations onshore. The wind farms are often located nearshore in shallow waters, where they in many cases are exposed to strong currents and large breaking waves. Under these conditions around 30% of the total construction costs are related to the foundation and a significant part of this is the cost of the scour protection.

In Denmark Vestas, Dong Energy and DHI have recently finished an evaluation of the scour protection implemented at the Horns Rev I Wind Farm. The Horns Rev is located off the North Sea coast of Denmark. The wind farm is founded on mono-piles located at 6.5 m to 13 m water depth. The seabed consists of sand and the scour protection consists of a filter layer and an armour layer of stones.

The construction of the wind farm took place in the summer of 2002 and the scour protections were surveyed shortly after installation. A control survey was made in 2005. Comparison of the bed level in 2002 and 2005 shows a lowering of the seabed around the edge of the scour protection, but not to a critical level. However, close to the foundation relatively large scour holes had developed, often 1 m to 2 m deep, in some cases more.

Calculations showed that the failure of the scour protection was caused by the loss of sand through the scour protection proper, especially close to the foundation. For this reason special care must be taken in the design of future scour protections.

For further details please see here

A number of publications on modelling of wave-structure interaction using different methods and technologies have recently been published, e.g.:

• Numerical simulation of ship motion in offshore and harbour areas by Erik Damgaard, Bjarne Jensen, Simon Brandi Mortensen, Hans Fabricius Hansen and Jens Kirkegaard.

A method for simulating the motions and mooring forces of a moored ship subject to wave forcing has been further developed and validated for both the open water case and inside harbour areas. The simulation tool solves the equations of motions in the time domain. Examples from both open waters and enclosed waters in harbours are presented.

• Numerical modelling of wave run-up on a wind turbine foundation by Anders Wedel Nielsen, Simon Brandi Mortensen, Vagner Jacobsen and Erik Damgaard Christensen.

The paper presents the results of a CFD model of the wave run-up on a mono-pile. The mono-pile is widely used as the foundation unit for offshore wind turbines. The aim for the calculations is to make a detailed investigation of the effect of three-dimensional (3D) waves on the run-up and to determine the maximum wave run-up. The CFD results are compared with the results of physical model tests conducted under the same conditions. The model tests were conducted under idealized conditions: The tests were carried out on a horizontal bottom using phase and directional focused waves to obtain a 3D effect and at the same time being able to control the breaking. The key objective of this part of the numerical analysis is to develop a model capable

For further details please see here.

The Okavango River and Delta comprise a phenomenon virtually unique in the world. The river, with an average annual inflow of 7,500Mm3 per annum, terminates in the semi-arid Kalahari in a delta with an area of 30,000km2. Virtually the entire inflow evaporates and transpires from the perennial and seasonal swamps, while a small percentage infiltrates to ground water.

The Okavango Delta possesses remarkable biodiversity, and in 1997 was listed as a Ramsar site. An Integrated Hydrologic Model of the delta has been established using MIKE SHE, with integrated layers representing the atmospheric waters, surface waters (channels and swamps), and ground waters (unsaturated and saturated).

A presentation of the project is available here

Across Europe EU member states and local authorities are required to develop river basin water management plans. A key element of the basin plans is a programme of measures (POM) for each river basin district. The POM outlines the most cost effective management measures and their application to meet the objectives of good ecological status. The measures shall remedy conflicts between economic benefits from water use and associated pollution. The Water Framework Directive (WFD) states that POM must be implemented by 2012.

An example of this is the basin water plan for the Susaa basin, Sealand, Denmark, where the local EPA representative is responsible for developing a plan. The EPA experienced challenges in formulating consistent methodologies and tools to develop POM and associated basin plans.

To meet these challenges the EPA in partnership with DHI has developed a comprehensive Water Framework Directive (WFD) planning tool. This easy to use toolset allows users to pose questions and obtain answers to support in water management decision making.

For further details please see here

The discharge of hospital waste water into the community was just one of the critical problems in a project on hospital waste in northern Vietnam. Another serious difficulty was the shortage of water resources. The problems were obvious: hospital waste dumped beside streams and on the hospital grounds; no sharp-boxes for used syringes; reuse of culture discs; poor sanitary conditions, etc.

Hospital waste water discharged directly into the rice fields and the environment may contain hazardous chemicals and contagious microorganisms. These not only constitute a current problem to the environment and to humans but may also contain active pharmaceutical substances such as antibiotics. In the long term this may lead to the development of antibiotic resistant bacteria.

Focus on straightforward measures
The project, which included 12 hospitals, began in 2006 with a preliminary environmental and health assessment. From the very start the assessment focused on four main areas: solid waste, effluent waste, control of infections, and training of hospital staff. The overall objective was to reduce health hazards, not only for staff and patients but for the local community as well.

DHI has recommended a number of measures, including purchase of equipment for storing syringes, needles, etc. Other measures included installation of washbasins on the hospital grounds and storage rooms for contagious waste. The most important task, however, was to train the hospital staff in handling and segregation of hospital waste.

For further details please see here.

REACH changes the treatment of chemicals and goods in Europe. At DHI we have developed a number of the EU guidance documents and provide REACH assistance to industrial companies.

Right now companies who import or produce chemical substances in bulk or as part of other products should be aware of the pre-registration window, which is open until 1 December 2008. It is possible to apply for a so-called “bulk pre-registration” using the IUCLID-5 facility to pre-register several substances in one go. The IUCLID-5 bulk pre-registration facility makes it easier to conduct a quality check before submission and if needed to allow easy handling of the pre-registration by different legal entities of the same company.

Read more on our website http://reach.dhigroup.com

DHI hosts and participates in a wide range of events worldwide. A list is available here

Training, capacity and institution building – DHI courses around the globe
For a number of years DHI have offered a variety of courses worldwide. The courses range from short and intensive standard software and vocational training courses to dedicated, specialised training matching individual clients' specific needs and requests.

For further information on courses and training activities please contact DHI International Course Secretariat (courses@dhigroup.com) or consult our websites.

Vocational training http://www.dhigroup.com/Consulting/VocationalTraining.aspx
Software training http://www.dhigroup.com/Software/Training.aspx

DHI has offices around the global. For contact details please see here