Reservoirs experience siltation due to total or partial sediment trapping of the materials that come from upstream (incoming load). Reservoir siltation affects hydrology, ecology and socioeconomics, as for instance loss on storage capacity and flood regulation, damage of dam components (e.g. sluice gates, water gates), limitation of the recreational use of the reservoirs, propensity to eutrophication and sediment starvation downstream from the dam. Problems are being solved by total or partial drawdown of the reservoirs, through the releases of flow and stored sediments). Drawdown has being consolidated as an effective management tool, but it impacts the fluvial system downstream. This study analyzes the hydrosedimentary dynamics of the Sant Llorenç de Montgai reservoir associated to a partial drawdown (Segre River) in a 40 km reach downstream from the dam. For this, the flow discharge and suspended sediment transport was monitored in four sections to study hydrosedimentary dynamics and built the mass balance of the drawdown. Recorded discharges at the dam were similar to those registered during flood events. Most of the evacuated sediment was trapped in the weirs located immediately downstream from the dam. Consequently, suspended sediment registered downstream the weirs came mostly from the river channel and it was the result of the flow's sediment transport capacity. Results highlight the key role of the infrastructures located downstream from the dam and how these infrastructures modify water and sediment transport during the drawdown, mitigating its ecological impacts and maximizing sediment availability for subsequent competent events. Results also show how coordinate management of downstream infrastructures needs to be considered to optimize the longitudinal continuity of suspended sediment transport.