M.Sc. Thesis – Handling river floating debris for dam safety – inventory, scenario descriptions and risk judgements

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M.Sc. Thesis – Handling river floating debris for dam safety – inventory, scenario descriptions and risk judgements

Reference: RD. Ex-jobb Drivgods

Production and transport of floating debris in regulated water courses forms a risk for dam safety during high floods and must be handled properly, so that the spillway discharge capacity of a dam is guaranteed. The project reviews the research and projects carried out within the area, both in Sweden and abroad, with the purpose of inventorying state of the practice, evaluating the safety risks and identifying the research needs.

Project description:


Extreme river floods may give rise to floating debris in form of trees, bushes and many other types of lumber. There have been no problems with debris at our spillways during high floods that so far have occurred in the regulated rivers. In some countries, however, it is a known problem, sometimes already during normal floods, and counter-measures are investigated or undertaken.

The requisite of floating debris production is the trees in the water, on the river banks etc. Whether or not floating debris will occur depends on factors like the steepness of the river sides, trees in areas that would be inundated during high flows, water velocity etc. Landslides in river bluffs could also cause debris in the river during a short time.

In Scandinavian countries like Sweden, the debris would consist of spruce and pine trees of varying size. Floating debris accumulating in a reservoir during an extreme flood could block the spillway and reduce its discharge capacity. What one tries to avoid is the obstruction of the spillway openings. Should this happen, it could lead to overtopping.

Although no noticeable incidents caused by floating debris have been experienced or reported in Sweden, there is an example where a heavy rainfall led to a high flood causing serious erosion that in turn produced up to 10 000 m3 trees in a small river catchment. Here the area was very steep and the rainfall most extreme and the area comparatively small. Studies indicate that many dams in Sweden could experience floating debris problems during extreme floods. Even if the probability for such floods is extremely low, this should be dealt with through proper engineering measures.

Handling of floating debris does not simply refer to how to deal with it at the spillways; one should have a handling strategy for the whole catchment. This include identification of potential debris production, inception upstream in the river including tributaries, etc.


In many dams owned by Vattenfall, floating debris may occur in a situation with high river floods, which constitutes a risk for dam safety if any measures are taken. The project aims to disseminate the knowledge of floating debris in hydropower reservoirs, to understand the risk and to summarize and evaluate potential measures for risk reduction. This is achieved by:

1. Examination of debris production amount in a catchment

2. Handling strategy

3. Spillways are operated in a safe manner.

4. Spillway modifications if necessary.


During the past two decades, studies of debris behaviors and counter-measures, though limited, have been performed in Sweden and abroad. Those include laboratory tests, small-scale field tests and prototype observations (including Energiforsk and CEATI). Separate projects were also made with the purpose to identify debris potential and review countermeasures.

The project consists of the following aspects.

1. Background and literature collection

2. Interview of owners and consultants

3. Review of studies in Sweden

4. Inventory of studies abroad

5. Summary of the state of the practice

6. Looking into the research needs and possibly proposing research projects

7. Report writing


• Strong interests in hydropower, dam safety and hydraulic engineering

• The project corresponds to a 30 hp diploma work

• It is to be performed by one student or two. You should find a cooperative partner yourself if conducted by two students

• Proper background is university education in civil (hydraulic) engineering, engineering physics or similar disciplines

• The time of execution must be within four (4) months, completed during 2020

• Fluent written English is required

• You should have found an examiner at your university (and even ämnesgranskare if needed).

• Vattenfall pays out a standard gratitude upon project completion with distinction.

More information:

• Start of assignment: 2020-08-15 or by agreement

• Location: in the first place at Vattenfall R&D in Älvkarleby or at a location per agreement,

• Your application should comprise a cover letter in which your motivation is stated, CV, and grades. Specify project reference RD. Ex-jobb Drivgods. An incomplete application is not handled.

• The complete contact information for the examiner should be specified in the application

• Deadline for application is 2020-08-10.

• Potential candidates should directly send their applications to James Yang (E-mail: james.yang@vattenfall.com), contact person and project supervisor. For inquiries a phone call is preferred, 070-2723 200.

Note: Applications are processed on a running basis and the vacancy is filled as long a suitable candidate is found and the announce is then removed. This is the reason why you should not wait to the deadline to send in your application.

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M.Sc. Thesis – Handling river floating debris for dam safety – inventory, scenario descriptions and risk judgements

Vattenfall AB