Auel, Christian
Abrasion in a concrete-lined sediment bypass tunnel is estimated using a Japanese state-of-the-art prediction model and validated by measured invert abrasion data at Asahi Reservoir, Japan. The model is described in detail, certain shortcomings are disclosed, and a revised version is proposed. The model consists of a kinetic energy term accounting for the impact by saltating particles, and a friction work term accounting for the grinding stress. It is found that the latter term yields concrete abrasion values being consistently a multiple compared to its kinetic term contradicting other research. Based on that, and a possible particle impact angle inconsistency, it is proposed to omit the friction work term. It is shown that the calculated abrasion is overestimated by 138% on average compared with that measured, if both terms are accounted for. However, promising results are obtained with only 30% overestimation by neglecting the friction work term.
Field Investigation on Hydroabrasion in High-Speed Sediment-Laden Flows at Sediment Bypass Tunnels
(2020)
Wear due to sediment particles in fluid flows, also termed hydroabrasion’ or simply ‘abrasion’, is an omnipresent issue at hydraulic structures as well as in bedrock rivers. However, interactions between flow field, particle motion, channel topography, material properties and abrasion have rarely been investigated on a prototype scale, leaving many open questions as to their quantitative interrelations. Therefore, we investigated hydroabrasion in a multi‐year field study at two Swiss Sediment Bypass Tunnels (SBTs). Abrasion depths of various invert materials, hydraulics and sediment transport conditions were determined and used to compute the abrasion coefficients kv of different abrasion models for high‐strength concrete and granite. The results reveal that these models are useful to estimate spatially averaged abrasion rates. The kv‐value is about one order of magnitude higher for granite than for high‐strength concrete, hence, using material‐specific abrasion coefficients enhances the prediction accuracy. Three‐dimensional flow structures, i.e., secondary currents occurring both, in the straight and curved sections of the tunnels cause incision channels, while also longitudinally undulating abrasion patterns were observed. Furthermore, hydroabrasion concentrated along joints and protruding edges. The maximum abrasion depths were roughly twice the mean abrasion depths, irrespective of hydraulics, sediment transport
conditions and invert material.
The Gaulwerk hydropower plant (HPP) has a design discharge of 3.5 m3/s and generates about 6.5 GWh per year. The HPP has been in operation since 1963 and uses the flow of two alpine streams. The HPP impounds a 300 m long reservoir with a 6.50 m high weir. The storage is completely filled with sediments and is classified as a valuable habitat for fauna and flora. Due to the sedimentation, the area upstream of the reservoir head inundates about two to three times per year during small flood events, leading to complaints from affected landowners and adjacent municipalities. To investigate sustainable solutions, a study of alternatives has been carried out in which three alternatives to im-prove both the sediment and flood situation are being investigated. In addition, the residual flow release will be adjusted and fish facilities realized in all alternatives. The paper will summarize the analysis of the alternatives encompassing the (1)
flood situation, (2) sediment management, (3) reha-bilitation measures of the hydraulic structures and their costs and (4) the environmental impact.