Octria Adi Prasojo, Trevor B Hoey, Richard David Williams, Amanda Owen

Paleodischarge estimation is largely undertaken within fluvial settings, and there are limited paleodischarge estimates specifically from delta deposits, despite their significance globally. Making water paleodischarge estimates for deltas using catchment-based approaches developed using data from fluvial settings requires estimation of parameters from the rock record (e.g. paleotemperature, paleoslope, paleorelief) that may be difficult to determine, and may lead to under- or over-estimation of paleodischarge values due to differences in process-form relationships between alluvial rivers and deltas. When a sediment-conveying fluvial channel starts to debouch into a standing body of water, delta lobes develop through repeating mouth bar deposition due to flow deceleration, forming a deltaic morphology with distributary channel networks that differ morphologically from those developed in unidirectional flowing alluvial rivers. This study provides empirical relationships determined across five climate regions, using 3823 measurements of distributary channel width from 66 river deltas alongside their bankfull discharge, by applying the concept of hydraulic geometry. Empirical relationships are developed from the global delta dataset between bankfull discharge and catchment area (Qb-A) and also bankfull discharge and distributary channel width (Qb-w). These empirical relationships produce very strong statistical correlations, especially between Qb and w, across different climate regions (Qb = 0.34w1.48, R2 = 0.77). However, both Qb-A and Qb-w relationships have outliers that may be explained by particular hydrological or geomorphic conditions. These new empirical relationships derived from modern systems are applied to Cretaceous outcrops (Ferron Sandstone, Dunvegan and McMurray formations). The comparatively simple scaling relationships derived here produced paleodischarge estimates within the same order of magnitude as the paleodischarge values derived from existing, more complex approaches. Our study contributes to source-to-sink investigations by enabling paleodischarge estimates that intrinsically account for climate impacts on channel geometry at the time of deposition, using measurements of channel width or catchment area of a deltaic outcrop.