COMPARISON OF BATHTUB MODELING WITH SIMULATION OF SEA LEVEL RISE INDUCED GROUNDWATER INUNDATION

Among many of the world’s coastal municipalities, rising sea levels will produce more frequent tidally induced flood events and chronic inundation within the century. Groundwater inundation (GWI) will be a particularly challenging consequence of sea level rise (SLR), as groundwater progressively inundates infrastructure located above and below the ground surface. Because paths of flooding by GWI differ from other types of SLR induced flooding (i.e., wave overwash, storm-drain backflow) in that it is more difficult to impede, GWI will require a separate set of highly innovative adaptation strategies to manage. The flood component was recognized only recently by Rotzoll and Fletcher (2013), and thus has not been widely considered in adaptive planning or infrastructure design. The Honolulu area has served as a testing ground for techniques to simulate SLR induced GWI. To date, three main approaches have been employed: the hydrostatic, 1D analytical (Rotzoll and Fletcher, 2013), and 3D numerical (Habel et al., 2017) methods. Here we test the skill of the methods and find that, while each has unique strengths, the simplistic hydrostatic approach produces results that are highly comparable to those of the more dynamic methods when referencing the local mean higher high water tide datum (generally typical of flood studies), and when considering regions featuring shallow hydraulic gradients and limited well extraction/injection. The results indicate that the hydrostatic modeling method offers a simplistic alternative approach towards simulating GWI under particular hydrologic conditions. In municipalities where identification of GWI related vulnerability is limited by a lack of resources, these findings have the potential to influence progress towards accomplishing such efforts.