Meeting the challenge of rising water levels
Sea levels that are increasing faster than predicted leave ports with costly risk mitigation decisions to make, explains Stevie Knight
According to a recent study looking at 25 years of NASA and European satellite data, sea level rise is actually accelerating. If it carries on at this pace, there is a good chance the global sea level will have risen 65 centimetres by 2100 from a 2005 baseline. The same calculation signals a 21 centimetre increase by 2050, within the span of a 35-year terminal concession.
This might not sound like much; Miguel Esteban of Tokyo University says “because so far it has been slow – 1.7 millimetres a year for most of the 20th century and only 3 millimetres now – ports have generally not responded and treated it as a problem”. However, he points out that the issue of sea level rise is compounded by storm surges along with increased hurricane and typhoon intensity “which are harder to predict”, making it difficult to anticipate the tipping point between inaction and action.
There is little comfort for those taking a longer 'wait and see' approach as these estimates seem to be getting worse, not better. “Generally, the sea level projections have risen over the last 10 years,” says Patrick King of Jacobs (CH2M). “Polar ice melt is a multiplier, the estimates before were more conservative and we just hadn't seen the acceleration.”
Of course, concern rises sharply in areas that have suffered: “We had a meeting in the Caribbean last year on sea level changes and other climate-related issues, some engineers came... but there was no sense of urgency,” says Dr Esteban. “Then a couple of hurricanes hit the region and at the next meeting the heads of the ports and transport authorities all turned up – suddenly it wasn't 'the future' anymore.”
However, Jason Giffen of the Port of San Diego admits that the uncertainty is part of the challenge: “I wish someone could come out and say, we know what the rise will be.” While forecasts for the near future are pretty solid “once you get to 2050, the predictions start to diverge, and beyond 2050, we have to consider a very wide range of possibilities”.
Sketching out a strategy for long term assets can be tricky: take San Diego's multipurpose Tenth Avenue Marine Terminal, which is the beneficiary of $24m of investment. “Obviously we want to maintain its integrity for the future,” says Mr Giffen. “Our current plan goes to 2036 and we believe the terminal's elevation is high enough to withstand sea level rise and storm surges until then, but... we are probably going to have to do some re-evaluation on what happens after that.”
The Port of San Diego has a lot more than its cargo and cruise terminals to consider: it also manages 34 miles of waterfront which ranges from open coast to urban areas. According to Mr Giffen's colleague, Phillip Gibbons, the port's been developing “a suite of strategies, from hard end infrastructure, raised pads to elevate buildings and so on... to natural breakwaters incorporating oysters and recreating salt marsh that we believe will act as a sponge in flood events”. The point is, it's a very broad approach that has been embarked on early enough to retain flexibility – and also have some room for experimentation.
“We will know a lot more about sea level rise after 2050 in a few years,” says Mr Giffen, “but we have to initiate a planning framework now which can be adjusted as time goes on.”
As Mr King adds: “It's difficult to nail down, although the longer the duration of monitoring, the more accurate we are becoming, and the more concrete our projections.” He concurs that what is needed is a realistic, 'adaptable' response; however, a pragmatic, sliding scale needs to fit the lifetime of the asset: “Something with just 20 years of life left you might not bother too much about -– judicious neglect is reasonable if a port is outside the urban environment.”
However, this changes if a port is in a populated area: “The potential impact, the risk of loss of life, is so much greater,” he says.
“During Hurricane Katrina the storm surge inundated the Port of Gulfport, Mississippi, on the Gulf of Mexico and washed the boxes and other infrastructure inland, into the city,” he explained, with disastrous consequences. “We had to stop that happening again, but while we could make the infrastructure stronger, the boxes left us with just two choices, either evacuate them, or raise the operating level by 4.3 metres.”
Evacuation looks, initially, like the most appropriate reaction but on examination, it isn't that clear: “A storm surge might be forecasted, but when do you shut down the port and make the evacuation?” he asked. “Eventually the port decided it was better just to put in the investment.”
It wasn't an easy job. “Every elevation has to change, a challenge by itself. But then you have to re-join the links, for example with the on-dock rail, the extra height can mean you're faced with working around an unacceptable gradient. You also need to modify the intermodal system as this also changes the normal operating heights; there's things like the crane's interaction with the ship, as now you have a sea level that could be 3 metres lower.”
All this isn't exactly cheap: in fact, the overall investment, including the associated redevelopment, came to around $500m, “but the port decided that the potential costs of getting it wrong made it worth it”.
There's another issue with a price tag. Some facilities will see a growing number of extreme weather events. The resulting downtime, explains Dr Esteban, could undermine the region's resilience and even a country's economy. The sensible answer is to build up port handling capacity to allow a faster rebound.
However, while the sea level rise may be 21 centimetres at 2050 for most ports, there are areas facing more dramatic issues.
Dr Esteban explains that due to groundwater extraction, some ports in Jakarta are subsiding at a rate of between 15 centimetres to 20 centimetres per year. The authorities have a range of responses: “In Sunda Kelapa, for example, as the water level increases, they construct a kerb, and every year they raise a section of wharf by a metre or two.” It helps that it's a fairly low tech facility and believes it can keep this strategy up indefinitely. Other ports in the area are likewise suffering from subsidence and have undergone one or two rounds of elevation, but in some cases, these facilities are now considering floating wharves.
There's even more of a problem in Japan where it would cost hundreds of times the amount spent to raise per metre at Sunda Kelapa, mainly because these quays also need anti-earthquake measures. “The problem with ports around Tokyo Bay is that a lot of them are facing inundation from the combined effects of the water level rise, tropical cyclones and associated storm surges,” says Dr Esteban. It doesn't help that the area's typhoons could also increase in scale.
Again, elevation is one answer, but there are a number of ports around the bay that would require this kind of protection with combined costs of over Yen120bn ($1.13bn), without including the expense of reconstructing buildings and other installations. More, he says: “You still have to ask, can the cranes take the winds, can the breakwaters take the waves – and sometimes you are at the limit of traditional port engineering.”
One alternative could be the construction of a gigantic storm surge barrier, a kind of lock, at the entrance of the bay which might allow some control over water levels although it would also slow down the passage of ships into the ports. It also comes at a very hefty price: “It becomes a question about priorities, and how much money you want to spend,” says Dr Esteban.
SEEKING OUT HIDDEN WEAKNESSES
In the climate change and rising sea level quagmire, global ports may have overlooked hidden vulnerabilities.
Tokyo University’s Miguel Esteban points out that port breakwaters, “are often in use long after their expected lifetime”. It is possible that a recalculation is overdue.
However, according to Jacobs’ (CH2M) Patrick King, there is a less obvious problem to address. While most quay structures are built to resist downward and lateral pressures, “more frequent storm surges on top of a sea level rise will generate tremendous hydraulic forces, making for significant uplift”, he explains.
“So now, when we are considering repairs on existing seabed structures, we are also looking at incorporating elements that can take these upward loads. Most facilities do not need to be flood or storm proof, but they do need to be resilient and adaptable to this fast-changing climatic environment.”
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