To simplify the complex hydrological variability of flow conditions, experiments on delta evolution are often conducted using a representative channel-forming flood flow and results are related to field settings using an intermittency factor, defined as the fraction of time in flood. Although this factor provides an approximation of dominant flow conditions and makes modeling deltas easier by turning their complex hydraulics into a single representative value, little is known about how this generalization affects delta processes. We conducted experiments with periodic flow conditions to determine the effects of intermittent discharges on fan deltas. For each run, the magnitude of floods was held constant, but the duration changed, thus varying the intermittency factor, between 1 and 0.2. Floods consisted of higher water and sediment discharge, while base flow periods had lower water discharge and sediment input ceased, causing the system to become erosional during these periods. We find that as the duration of floods decreases, the delta topset is larger in area with a shallower slope due to reworking on the topset during base flow conditions. During base flows, the experimental system adjusts toward a new equilibrium state that in turn acts as the initial condition for subsequent flood periods. These results suggest that the adjustment timescale is a factor in determining the behavior of deltas and their channels. We conclude that both periods of flood when most of the sediment is supplied to the system and periods of base flow when topset sediment is reworked contribute to delta dynamics.
Bibliographical noteFunding Information:
The authors would like to thank Anastasia Piliouras and Brandon Minton for their assistance in the lab, as well as John Buffington, Ton Hoitink, Brad Murray, Kyle Straub, and two anonymous reviewers for their valuable comments that strengthened this paper. We would also like to acknowledge John Shaw for providing survey data from the Wax Lake Delta. This work was made possible by funding from NSF EarthCube RCN award 1324760. Data have been made publically available on the Sediment Experimentalist Network Knowledge Base at http://sedexp.net/catalog/delta‐ experiments‐investigating‐flow‐ intermittency‐0.
All Science Journal Classification (ASJC) codes
- Aquatic Science
- Water Science and Technology
- Soil Science
- Geochemistry and Petrology
- Earth-Surface Processes
- Atmospheric Science
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science