(1990) who calculated similar statistics including a rise of between +16-19.3 cm throughout 1900–1988. Super storm Sandy of 2012 is an example of the devastating effects rising sea levels can cause when mixed with a perfect storm. Super storm Sandy sent a storm surge of 4–5 m onto New Jersey's and New York's barrier island and urban shorelines, estimated at $70 billion in damage. This problem could be overcome by further modelling and determining the extension of height and reinforcement of current seawalls which needs to occur for safety to be ensured in both situations. Sea level rise also will cause a higher risk in flooding and taller tsunamis. Hydrostatic water pressure Seawalls, like all retaining walls, must relieve the buildup of water pressure. Water pressure buildup is caused when groundwater is not drained from behind the seawall. Groundwater against a seawall can be from the area's natural water-table, rain percolating into the ground behind the wall and waves overtopping the wall. The water-table can also rise during periods of high water (high tide). Lack of adequate drainage can cause the seawall to buckle, move, bow, crack or collapse. Sinkholes may also develop as the escaping water pressure erodes soil through or around the drainage system. Extreme events Extreme events also pose a problem as it is not easy for people to predict or imagine the strength of hurricane or storm induced waves compared to normal, expected wave patterns. An extreme event can dissipate hundreds of times more energy than everyday waves, and calculating structures which will stand the force of coastal storms is difficult and, often the outcome can become unaffordable. For example, Omaha Beach seawall in New Zealand was designed to prevent erosion from everyday waves only, and when a storm in 1976 carved out ten meters behind the existing seawall, the whole structure was destroyed. Ecosystem impacts The addition of seawalls near marine ecosystems can lead to increased shadowing effects in the waters surrounding the seawall. Shadowing reduces the light and visibility within the water, which may disrupt the distribution as well as foraging capabilities of certain species. The sediment surrounding seawalls tends to have less favorable physical properties (Higher calcification levels, less structural organization of crystalline structure, low silicone content and less macroscale roughness) when compared to natural shorelines, which can present issues for species that reside on the seafloor. Other issues Some further issues include: