Analysis of coarse sediment connectivity in semiarid river channels

Coarse sediment in river channels influences the channel morphology but channel morphology also influences the supply, sediment transfer and sedimentation. Coarse sediment is mainly stored on bars: lack of bars in a reach may reflect lack of supply, lack of storage availability, or high competence. A conceptual model of sedi­ment connectivity has been developed and is applied to two channel systems in the semiarid area of southeast Arizona, USA. Detailed evidence of sediment sources was collected from field mapping and aerial photographs. Sediment size was sampled at intervals down the channel and competence was calculated from surveyed cross-sections and hydraulic data. The spatial patterns of sediment transfer and storage were shown to be related to a complex combination of sediment supply, valley morphology and channel gradient. Deposits and sediment segregation in such systems can reflect recessional flows. The implications of spatial variability in coarse sediment transfer and storage are discussed.