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Assessment of flood damage risk for engineering structures in river floodplains

IWRA World Water Congress 2008 Montpellier France
4. Development of Water Resources and Infrastructure
Author(s): Borris Gjunsburgs
Roberts Neilands
Elena Govsha
Water Engineering and Technology Department, Riga Technical University

Keyword(s): Flood, risk, engineering structures, scour
Article: Poster:

AbstractWater flow regime in rivers is changing because of the climate, but it means that impact is not only on nature, economy, and urban infrastructure, but also strongly influences the transport infrastructure – roads, bridges, dams, and also water supply system, irrigation systems and canals. Frequency and intensity of flood events with high water levels and considerable discharges becomes frequent and increases the load on engineering structures in rivers and possibility to be damaged. The objective of this research is to study erosion processes developing during the multiple floods and work out methods that allows estimating stability and safety of engineering structures in river floodplains. Existing methods and formulas do not take into account multiple floods impact on scour process near structures, floods probability, floods duration and sequence, computing only equilibrium stage or temporal development of scour at the flood peak. In the present study, a differential equation of equilibrium of the bed sediment movement for clear water was used and a new method for computing the scour development at engineering structures in river floodplain during multiple floods was elaborated. The method was verified by experimental data. A new method for computing equilibrium stage of local scour at engineering structures in river floodplain was also developed. Using two mentioned methods we propose to estimate possible damage of engineering structures caused by multiple floods. The parameters of scour hole computed during multiple floods can be compared with its equilibrium parameters by equations suggested, and the flood damage risk factor for engineering structures can be determined as a ratio hs/hequil, where hs is a scour depth developed during/after multiple floods, and hequil is a equilibrium scour depth. The closer current depth value of the scour hole is to the equilibrium value of the scour hole, the more is risk factor and less is the stability of the structure. By risk factor we can estimate the current stability of the structure in the period of maintenance or predict/compute it’s stability at the design stage. For critical conditions, as flood management measures, when the developed scour hole is close to the equilibrium conditions, emergency protection measures (for example, riprap, rock riprap, sand/cement filled bags, etc.) should be fulfilled. In this paper are presented new method how to forecast and estimate floods impact on engineering structures in river floodplains.
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