River deltas are densely populated regions of the world with vulnerable groundwater reserves. Contamination of these groundwater aquifers via saline water intrusion and pollutant transport is a growing threat due to both anthropogenic and climate changes. The arrangement and composition of subsurface sediment is known to have a significant impact on aquifer contamination; however, developing accurate depictions of the subsurface is challenging. In this work, we explore the relationship between surface and subsurface properties and identify the metrics most sensitive to different forcing conditions. To do so, we simulate river delta evolution with the rule‐based numerical model, DeltaRCM, and test the influence of input sand fraction and steady sea level rise (SLR) on delta evolution. From the model outputs, we measure a variety of surface and subsurface metrics chosen based on their applicability to imagery and modeling results. The Kullback‐Leibler (KL) divergence is then used to quantitatively gauge which metrics are most indicative of the imposed forcings. Both qualitative observations and the KL divergence analysis suggest that estimates of subsurface connectivity can be constrained using surface information. In particular, more variable shoreline roughness values and higher surface wetted fraction values correspond to increased subsurface connectivity. These findings complement traditional methods of estimating subsurface structure in river‐dominated delta systems and represent a step toward the identification of a direct link between surface observations and subsurface form.
Climate change is raising sea levels across the globe. On river deltas, sea‐level rise (SLR) may result in land loss, saline intrusion into groundwater aquifers, and other problems that adversely impact coastal communities. There is significant uncertainty surrounding future SLR trajectories and magnitudes, even over decadal timescales. Given this uncertainty, numerical modeling is needed to explore how different SLR projections may impact river delta evolution. In this work, we apply the pyDeltaRCM numerical model to simulate 350 years of deltaic evolution under three different SLR trajectories: steady rise, an abrupt change in SLR rate, and a gradual acceleration of SLR. For each SLR trajectory, we test a set of six final SLR magnitudes between 5 and 40 mm/yr, in addition to control runs with no SLR. We find that both surface channel dynamics as well as aspects of the subsurface change in response to higher rates of SLR, even over centennial timescales. In particular, increased channel mobility due to SLR corresponds to higher sand connectivity in the subsurface. Both the trajectory and magnitude of SLR change influence the evolution of the delta surface, which in turn modifies the structure of the subsurface. We identify correlations between surface and subsurface properties, and find that inferences of subsurface structure from the current surface configuration should be limited to time spans over which the sea level forcing is approximately steady. As a result, this work improves our ability to predict future delta evolution and subsurface connectivity as sea levels continue to rise.
more » « less- NSF-PAR ID:
- 10372640
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 127
- Issue:
- 9
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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