A water balance approach to assessing the hydrologic buffering potential of an alluvial fan

The hydrologic connectivity of a catchment determines the efficiency with which runoff is moved through the catchment and hence opportunities for runoff storage. Potential storages include valley floors and alluvial fans. Monitoring results from a small alluvial fan indicate that alluvial fans can be significant hydrologic buffers, Between 20% and 100% of surface runoff delivered to the study fan from a 26-ha catchment was slowed and/or stored during the monitored events. Interevent differences in buffering response are attributed to antecedent moisture conditions. In one event, when catchment conditions were very wet, only 20% of incoming runoff was absorbed by the fan. Under dry conditions, smaller proportions of total rainfall were delivered to the fan head as surface runoff, of which >60% was absorbed by the fan. Because sediment storages can modify surface runoff delivery, because of their distinctive morphologic and sedimentologic properties, it is suggested that their distribution through a catchment will influence catchment hydrologic connectivity hence runoff and sediment delivery through catchments.