A preliminary palaeohydraulic model applied to late Quaternary gravel dunes: Altai Mountains, Siberia

The morphology and granulometry of large ‘fossil’ late-Quaternary gravel dunes at Kuray in Siberia are used to estimate the hydraulic conditions associated with dune building and stabilization. To accomplish this, an algorithm is tested which provided reasonable predictions of the flow characteristics measured above small gravel dunes in the Toutle River, Washington State. Palaeoflow depths and velocities above the ‘fossil’ dunes as the bedforms finally stabilized are estimated using a simple force balance for initial motion and the partitioning of the flow resistance between the drag owing to the duneform and grain resistance. Flow parameters for peak discharge conditions when dunes actively developed are assessed with respect to the dune-upper plane bed transition and the entrainment of over-passing blocks. These data, coupled with an assessment of the lateral extent of the flood, provide estimates of the discharge magnitude of the glacial out-break flood which was responsible for the dunefield. Sensitivity analyses indicate the stability of the estimates and demonstrate that the dunes were initiated and finally stabilized when the flood was of the order of 5 × 10 4 m 3 s −1 and 2 × 10 4 m 3 s −1 respectively. The flood peak need not have exceeded 750 000 m 3 s −1 with a maximum depth of a few tens of metres.