Restoring in-stream spawning habitats in degraded rivers has received increasing attention as a tool for mitigating local wild fish population declines, notably in response to the European Water Framework Directive (WFD). However, spawning gravel placements are far too often designed without accurate knowledge of the morphodynamic river processes, resulting in a limited efficacy and longevity of the artificial spawning ground. To address the combined effects of bedload transport and fine sediment clogging processes on the sustainability of artificial spawning gravel habitats, we examined the effects of such rehabilitation actions on six degraded river reaches in Wallonia, Belgium. The monitoring scheme was based on the evolution of the thickness and clogging of the spawning gravel (using wooden stakes driven into the gravel layer to measure the depth of the anoxia) and on the PIT-tagged tracking of gravel dispersion over a period of 3.6–8.5 yrs. On the one hand, the results highlighted that several artificial spawning grounds were quickly clogged because of improper sizing of the spawning material. Gravel that was too coarse to be mobilized by the river and that had a narrow grain size range favoured fine sediment accumulation within the interstices of the gravel layer. On the other hand, one spawning gravel placement was rapidly scoured (after 2.2 yrs) because of an undersizing of the gravel with respect to flow competence. In the end, one gravel placement presented adequate gravel sizing, allowing periodic gravel transport over short distances (the mean annual travel distance was ~3 m). The longevity of a gravel placement and the ability of the displaced gravel to form new spawning grounds downstream were strongly dependent on the distance that the placed gravel was likely to travel, which in turn depended on several hydromorphological parameters, such as unit stream power, channel morphology and bed texture. The key parameters highlighted in this study need to be acknowledged when designing spawning gravel placement projects.

作为缓解当地野生鱼类种群减少的一种工具，恢复退化河流中的产卵栖息地已受到越来越多的关注，特别是对欧洲水框架指令（WFD）的回应。然而，产卵砾石的放置过于频繁，而没有对河床形态动力学过程的准确了解，导致人工产卵场的效力和寿命受到限制。为了解决床载运输和细沙淤积过程对人工产卵砾石生境可持续性的综合影响，我们研究了此类恢复行动对比利时瓦隆大区六个退化河道的影响。监控方案基于产卵砾石厚度和堵塞的演变（使用被驱动到砾石层中的木桩来测量缺氧深度），以及在3.6倍的时间内用PIT标记的砾石弥散跟踪8.5岁。一方面，结果突出表明，由于产卵材料的尺寸不正确，几个人工产卵场被迅速堵塞。砾石太粗糙而无法被河流调动，且粒度范围狭窄，有利于在砾石层空隙中的细小沉积物堆积。另一方面，一个产卵砾石的放置被迅速地冲刷了（2.2年之后），这是因为砾石在流动能力方面的不足。最后，一个砾石位置显示了足够的砾石尺寸，允许定期进行砾石短距离运输（平均年行进距离约为3 m）。砾石放置的时间长短和被置换的砾石在下游形成新的产卵场的能力在很大程度上取决于所放置的砾石可能行进的距离，而距离又取决于几个水形态参数，例如单位水流功率，河道形态和床的质地。在设计产卵砾石放置项目时，需要确认本研究中突出显示的关键参数。而这又取决于几个水形态参数，例如单位流功率，河道形态和床构造。在设计产卵砾石放置项目时，需要确认本研究中突出显示的关键参数。而这又取决于几个水形态参数，例如单位流功率，河道形态和床构造。在设计产卵砾石放置项目时，需要确认本研究中突出显示的关键参数。