Water and sediment flux interactions are examined in Magela Creek, an alluvial (anabranching) sand-bed river in the northern Australian tropics. Dense riparian vegetation stabilises the channels and floodplains thereby preventing erosional instability at flow depths up to 6.2-times bankfull and discharges up to 15-times bankfull. Narrow anabranching channels characterise >92% of the alluvial reach and transport bedload more efficiently than short reaches of wide single-channels, yet overall 29 ± 12% of the bedload is sequestered and the average vertical accretion rate is 0.41 ± 0.17 mm/y along the 12 km study reach. The most effective discharge for transporting sediment (40–45 m³/s) is consistent at all 5 stations (10 channels) examined and is equivalent to the channel-forming discharge. It has an average recurrence interval ­­­­­of 1.01 years, occurs for an exceptionally long 13–15% of the annual flow duration and averages a remarkable 2.1-times bankfull. The high flow efficiency (i.e., bedload transport rate to stream power ratio) of the anabranches is facilitated by low width/depth channels with banks reinforced by vegetation. Colonnades of bank-top trees confine high-velocity flows overbed (i.e. over the channel bed) at stages well above bankfull. At even larger overbank flows, momentum exchange between the channels and forested floodplains restrains overbed velocities, in some cases causing them to decline, thereby limiting erosion. Magela Creek exhibits a complicated set of planform, cross-sectional and vegetative adjustments that boost overbed velocities and enhance bedload yield in multiple channels while restraining velocities and erosion at the largest discharges.