Putting some notes together for the MDCA proposal to the TSC on Thursday to take the sale of the causeway off the table, out of consideration, I came across this amazing elevation map provided by the Parliamentary commissioner for the environment in conjunction with its recent report on certainty and uncertainty in regard to sea level rise
Take at the map and look at the pruple shaded areas – all less than 50cm above mean spring high tide (mean, not max) . The South east boundary of the major area of purple in the mapua lagoon/inlet “is” the causeway. Any dutchman looking a this map would say, oh, you’ve built a dyke to keep the sea out. Well, yes. In fact , that casueway is a major element in stormwater flood control for mapua, and the flood gates in the culvert under it close off water moving out as well as in to the upper reaches of the Mapua lagoon.
A dyke is a classic example of a public good – every inch of dyke height, every kg of dyke mass benefits many people. That’s why when many benefit and yet only one (a private landowner) bears the cost, an inefficient height and mass of dyke is likely to be constructed. But construction isn’t the only issue. That parliamentary report predicts that many thousands of km of seawall around the country will be abandoned. The decisions that lead to this abandonment however, if left in the hands of a single private land owner, will only reflect that land owners’ net benefits, not the net benfits to the man others upstream of that dyke. This is the classic argument for collective and coordinated public sector management and ownership.