Physical Modeling and Its Importance in SHP Development

PMSP, S. B. Thapa , Hydro Lab Pvt. Ltd

Hydraulic modeling is the art of creating a scaled down topographical model of the region where a Small Hydro Power facility is being considered.The model is then used by the researcher to study the natural behavior of the river.The researcher is able in a very short time to test various scenarios without the risk of life or equipment.The data collected from these tests can be used to further determine the feasibility of a site and to ensure that the proper structures / systems are designed for the project.

The model is built to accurately reproduce the behavior of the situation being modeled.There are different laws to be followed to fix the model scales for various parameters. Consideration must be given to the similitude of Froude's number (Fr), Reynold's number (Re) and Euler's number (Eu), to mention a few.Attention must also be paid to the conflicting scale ratio arising for kinematic and dynamic variables.Taking these things into consideration it is apparent that not more than one of these similitude criteria (or dimensionless number) can be tested at a time in a model. Consequently, it is important to establish which forces are of paramount importance to the researcher and to set the scales in accordance with the appropriate forces ratio. Experience shows that Froude's model law is almost sufficient for civil engineering works.

Why Physical Model Study?

It is a useful tool for collecting technically data and determining economically optimal solutions to engineering problems. In this context experimental work on scale models is often the most efficient, cost effective and sometimes the only method of solving the problem.Model studies provide possibilities for answers to problems that cannot be solved through theoretical or numerical analyses. Physical model is a highly effective tool to visualize projects to decision makers, funders, managers, and other stakeholders who may not have training in water engineering. With the model it is possible to verify the field data and clarify river processes. The model study allows for rapid and economic comparison of alternative solutions to river problems.

The cost of hydraulic model studies varies according to the scope of work, the scale of the model chosen and the accuracy of the study required.In general the investment made in model studies is usually recovered by optimum solution derived from the model studies. In the developed countries, the model study is a very common tool applied in combination with theory to design and solve the hydraulic problems.

Physical Modelling and Small Hydropower Development

Hydraulic design of headworks for small hydropower plants in steep rivers, have proven to be equally difficult and some times more challenging than for medium sized hydropower plants. The river flow varies largely and it responds rapidly to heavy rains. Super critical flow may occur in the intake area. Sediment transport patterns are complex and the bed-load may be significant during floods both in terms of transport rates and in terms of sizes of the transported material. Ice, trash and floating debris may cause severe operational challenges and reduced regularity of the power generation. The performance of small hydro power plants during the wet season are therefore not guided by the availability of water in the river, but by the headworks ability to withdraw water constantly from the river to maintain regular power generation.

Physical hydraulic modelling has proven to be an important and efficient tool in conceptual as well as detailed hydraulic design of headworks for run-of-river hydropower plants. The costs of hydraulic modelling have, however, limited this tool to large and medium sized power plants which can carry the costs of engineering services relatively better. The need for a hydraulic model study may, however, be more prominent for small hydropower plants than the larger ones.

Some studies have been carried out by M.Sc. student S.B.Thapa (Nepal) under the supervision of Prof. Haakon Stole at NTNU, Norway in 2004 in order to reduce the model study-cost for smaller schemes. A general test rig was developed at IVM-NTNU laboratory, Trondheim and different methodologies have been suggested to reduce the volume of work and consequently the cost. The findings of this research were promising.

For further information on Hydraulic modelling please contact:

Surendra Bdr. Thapa at: sbt@hydrolab.org

Hydro Lab. Pvt. Ltd.

Hydro Lab Pvt. Ltd, an independent laboratory with permanent facilities and the first and only hydraulic research center in Nepal was established in 1999 through the support of the Norwegian Agency for Development Cooperation (NORAD) and in close co?operation with the Norwegian University of Science and Technology (NTNU), and the International Centre for Hydropower (ICH) in Trondheim, Norway. The availability of the services for hydraulic model studies at Hydro Lab in Nepal has provided opportunity to local developers and investors to conduct such tests at affordable price which if it had to be done abroad could have cost quite a lot. The current activities going on in the lab are:

• Physical Hydraulic model studies
• Sediment and flow measurements
• Performance testing
• Education and training
• Applied research