Ship‐lock–induced Surges in an Impounded River and Their Impact on Subdaily Flow Velocity Variation

Abstract

The majority of large rivers are fragmented by dams, and navigation is often supported by the installation of ship locks. Despite their ubiquitous existence, the effect of ship locks on river basin hydrodynamics is rarely considered in an environmental context. Ship-lock operation induces single-wave crests or troughs called surges, which propagate along the basin and are subject to reflection at the up-and downstream impoundments. We used pressure sensors and acoustic Doppler current profiler measurements to investigate the effects of up-and downstream ship locking on the water level and the current velocity dynamics in a 12.9-km-long basin of the impounded river Saar (Germany).Ship lifting at the lower dam and the associated water export from the basin results in a negative surge propagating upstream, whereas a descending ship-lock operation at the upper dam of the basin creates a positive surge propagating downstream. Both types of waves are subject to positive reflection at the opposing dams. Frequent lock operations lead to a complex pattern of multiple superimposing surges. The resulting water level fluctuations are comparable in magnitude with those associated with discharge variations due to hydropower peaking but occur at much shorter timescales. Associated with the water surface displacement during wave passage is a corresponding increase or decrease of the longitudinal current velocity. The magnitude of wave-induced velocity fluctuations can exceed mean flow velocities by a factor of three and, depending on wave type and direction, can result in a reversal of the main flow direction of the river. Because of their longevity of several hours and superposition effects, ship-lock-induced surges govern 66.3% and 45.4% of the subdaily variations in flow velocity and water level, respectively. This article concludes with a discussion of the potential effects of lock-induced flow dynamics in impoundments on oxygen dynamics and methane ebullition.

Short-term and seasonal variability of oxygen fluxes at the sediment–water interface in a riverine lake

“…The flow velocity and resulting near-bed turbulence are potentially affected by anthropogenic activities in many aquatic systems, e.g., by the damming of river basins (Friedl and Wüest 2002), ship navigation (Maeck and Lorke 2014), and increasing population pressure on surface waters (Prigent et al 2012). Alterations of the hydrodynamics of rivers and lakes on the global scale could therefore generate an additional perturbation of the biogeochemical cycling in inland waters (Regnier et al 2013).…”

“…In impoundments, filling and emptying of lock chambers generate propagating surges, which are subject to reflection at the dams located up-and downstream. They persist over several hours and can dominate sub-daily velocity variations in impounded rivers (Maeck and Lorke 2014). Ship locks are located about 5 km upstream and 15 km downstream of the study area.…”

Eddy‐correlation measurements of benthic fluxes under complex flow conditions: Effects of coordinate transformations and averaging time scales

“…2a). As analyzed by Maeck and Lorke (2013) in greater detail, current velocities are predominantly influenced by the operation of ship locks. Surges are generated as the result of down-and upstream ship locking, which are reflected back and forth within the impoundment and superposition of these waves result in a series of distinct periods of flow variation between 12 and 68 min.…”

“…Spectral variance within this frequency range is not affected by the applied coordinate transformations. Separated by a narrow spectral gap around 3⋅10 -3 Hz (≈ 5 min), the original data show a series of distinct spectral peaks with corresponding periods of, e.g., 769, 1264, 1970 s (12.8, 21.2, 32.8 min), which can be attributed to lock-induced surges reflected at the dams and traveling back and forth along the impoundment (Maeck and Lorke 2013). According to their long wave length of 4-5 km, these surges can be considered as shallow water waves and associated orbital velocities in the vicinity of the bed are predominantly horizontal.…”

Untitled

“…The measurements were obtained near the sloped river bottom and under highly variable man-made flow conditions due to the operation of ship locks (Maeck and Lorke 2013). Based on this data set, Lorke et al (2012) have analyzed the effect of ship locking on the sediment-oxygen uptake rates in this impoundment.…”