Investigating the interaction of waves and river discharge during compound flooding at Breede Estuary, South Africa

Recent studies have drawn special attention to the significant dependencies between flood drivers and the occurrence of compound flood events in coastal areas. This study investigates compound flooding from tides, river discharge (Q), and specifically waves using a hydrodynamic model at the Breede E...

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Bibliographic Details
Published in:Natural hazards and earth system sciences 2022-01, Vol.22 (1), p.187-205
Main Authors: Kupfer, Sunna, Santamaria-Aguilar, Sara, van Niekerk, Lara, Lück-Vogel, Melanie, Vafeidis, Athanasios T
Format: Article
Language:English
Subjects:
Backwater effect
Backwaters
Climate change
Coastal flooding
Coastal zone
Coasts
Estuaries
Estuarine dynamics
Flood magnitude
Flooding
Floods
Hydrodynamic models
Impact assessment
Investigations
River discharge
River flow
Rivers
South Africa
Spring tides
Tidal waves
Tides
Water depth
Water discharge
Water levels
Waves
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Summary:Recent studies have drawn special attention to the significant dependencies between flood drivers and the occurrence of compound flood events in coastal areas. This study investigates compound flooding from tides, river discharge (Q), and specifically waves using a hydrodynamic model at the Breede Estuary, South Africa. We quantify vertical and horizontal differences in flood characteristics caused by driver interaction and assess the contribution of waves. Therefore, we compare flood characteristics resulting from compound flood scenarios to those in which single drivers are omitted. We find that flood characteristics are more sensitive to Q than to waves, particularly when the latter only coincides with high spring tides. When interacting with Q, however, the contribution of waves is high, causing 10 %–12 % larger flood extents and 45–85 cm higher water depths, as waves caused backwater effects and raised water levels inside the lower reaches of the estuary. With higher wave intensity, the first flooding began up to 12 h earlier. Our findings provide insights on compound flooding in terms of flood magnitude and timing at a South African estuary and demonstrate the need to account for the effects of compound events, including waves, in future flood impact assessments of open South African estuaries.
ISSN:1684-9981
1561-8633
1684-9981
DOI:10.5194/nhess-22-187-2022