Data analysis and integrated modeling of compound flooding impacts on coastal drainage infrastructure under a changing climate

• Published in: Journal of hydrology (Amsterdam) 2023-01, Vol.616, p.128823, Article 128823
• Main Authors: Sangsefidi, Yousef, Bagheri, Kian, Davani, Hassan, Merrifield, Mark
• Format: Article
• Language: English
• Subjects: Climate change; Coastal areas; Compound flooding; Groundwater infiltration; Sea-level rise; Stormdrain system
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2022.128823

•Adverse impacts of sea-level rises are not limited to a landward shift in shoreline.•Shallow groundwater can impact inland infrastructure kilometers from the coastline.•About 2/3 of the stormdrain length is subject to seawater & groundwater intrusion.•Coastal stressors can increase flood magnitude, frequency, and duration.•Compound flooding volume increases up to 6 times by a 2 m sea-level rise. Low-lying coastal areas are susceptible to multiple types of flooding from marine, subsurface, and surface sources. The co-occurrence of a rainfall event with high sea level, which raises coastal groundwater tables conjointly, may result in a compound flooding event, which could be much more widespread and dangerous than that of an individual flooding source. Focusing on Imperial Beach as a low-elevation coastal community in California, this paper provides a generalized methodology to determine the vulnerability of coastal stormdrain systems to compound seawater, groundwater, and stormwater flooding under a changing climate. Although marine inundation by itself is expected to flood only 7% of the study area by 2100 under the most pessimistic scenario (i.e. 2 m rise), our results show that more than 20% of the study area's subterranean stormdrain system is already at the risk of subsurface flooding at current sea levels. While marine inundation is a concern near the coastline as sea level rises, the results show that seawater intrusion into the stormdrain system can impact areas kilometers away from the coastline. The consequences of sea-level rise (SLR) can be exacerbated by an under-resourced stormdrain system, caused by groundwater infiltration through system defects. As such, by a 2 m rise in current sea-level, the flooding volume may double in an ideal system (i.e., no defects) while this ratio can increase six fold in a slightly defective stormdrain system (with 0.25 % porosity systemwide). The continuous simulations of the stormdrain system performance indicate that flood events will be more destructive and frequent under these circumstances.