Sand dynamics is an important issue in harnessed gravel-bed rivers where sand deposits can locally impact river management for ecological or safety purposes. However, sand flux is very complex to evaluate continuously in such rivers because of the strong spatial and temporal variability of the sand concentration throughout a river cross-section and along the river, and also because of the supply-limited aspect of sand. Sand transport capacity formulas are not applicable for such rivers. This paper introduces some methods easy to apply and based on the concentration index, i.e. assuming a possible relationship between the sand concentration at a specific position of a river cross-section and the section averaged concentration. These methods that use regular pump samplings and turbidity measurements are applied on the Lower-Isère, France, downstream of a series of dams during a flushing event. During this 2 week-event, we estimated a sand flux between 1.3 and 1.7 Mt depending on the method and site used. The concentration index method appeared robust and so very useful for a continuous evaluation of sand fluxes but the index concentration must be measured at a location where the turbulence intensity is high enough so that sand suspension can be observed and it must validated with regular sand gaugings. Eventually, we showed that the sand supply allowed the system to reach its sand transport capacity for approximately 3 days after a delay of 2 days after dam openings.

沙动态是治理砾石河床河流中的一个重要问题，其中沙沉积物可能会局部影响出于生态或安全目的的河流管理。然而，由于整个河流断面和沿河的沙子浓度具有很强的空间和时间变化性，而且沙子的供应有限，因此在这些河流中连续评估沙子通量非常复杂。输沙能力公式不适用于此类河流。本文介绍了一些易于应用的基于浓度指数的方法，即假设河流断面特定位置的沙浓度与断面平均浓度之间可能存在的关系。这些使用定期泵采样和浊度测量的方法适用于法国下伊泽尔省一系列水坝下游的冲水事件。在为期 2 周的活动中，我们估计沙通量在 1.3 至 1.7 公吨之间，具体取决于所使用的方法和地点。浓度指数方法显得稳健，因此对于连续评估沙通量非常有用，但指数浓度必须在湍流强度足够高的位置测量，以便可以观察到沙悬浮液，并且必须通过定期沙计量进行验证。最终，我们表明，在大坝开放后延迟了 2 天后，沙子供应使系统能够在大约 3 天内达到其输沙能力。