Author(s): Janek Laanearu
Linked Author(s): Janek Laanearu
Keywords: No Keywords
Abstract: This study focuses on the hydraulic analysis of low-head dams in two of Estonia’s rivers, where the shape of the riverbed has substantially changed: 1) the Nehatu site weir rebuilding project, implemented on the Pirita River, and 2) the Sindi site weir/rapids rebuilding project, executed on the Parnu River. The hydraulic analysis is based on the solution of specific energy functions and momentum equations, which both make use of a centroid of a non-rectangular cross-sectional area of flow. The quadratic-type channel hydraulic framework is used to determine the energy losses due to the formation of hydraulic jump; where two controls along the river channel are required for the free-surface flow, jumping between super- and sub-critical flow conditions. It is shown that barrier overflow-boundaries modifications are responsible for the locally turbulent mixing conditions, resulting from riverbed changes gained within the weir rebuilding projects. A novel methodology is introduced within the open-channel hydraulic framework, allowing the use of some geometrically non-isolated solutions for the sequent heights, due to the river-channel control acting downstream from the low-head dam locations. The rapidly varying flow processes at weirs and rapids are discussed to explain some hydraulic-modelling aspects in river environments for future studies. Explicitly selected annual maximum discharges for two of Estonia’s rivers correspond well with the flood conditions at lowland sites near the weirs and are used to estimate the hydraulic parameters of the pre- and post-rebuilding hydraulic structures.
Year: 2024