Water as Leverage- Setting the scene for a call for action

Water as Leverage for Resilient Cities Asia
Semarang
Organizing a City below
Sea Level
The city center of Semarang is a
low-lying area, pressured by sea
level rise and vulnerable to frequent
tidal floods, especially in the
tropical season.[1] Its coast used
to be lined with long stretches of
mangrove forest, capturing sediment
flows and extending the city’s
land on sea.[2] The combination
of natural sedimentation and
human land reclamation has led
Semarang to expand seawards.[3]
However, these weaker clay-layered
sediments are not ideal for building
upon, causing problems of land
subsidence.[4]
Additionally, insufficient freshwater
supply forced the city to extract
groundwater from deep aquifers,
speeding up the process of land
subsidence.[5] Semarang is a
sinking city, subsiding by an average
of about 6 to 7 centimeters and a
maximum of 14 to 19 centimeters
in the most-affected areas. By
comparison, sea level rise due to
climate change amounts to about
2 millimeters each year. While the
informal settlements in the lowestlying
areas of the city are the most
vulnerable, this phenomenon causes
severe damage to housing and
infrastructure throughout the city.
In the future, parts of the city will
lie below sea level, increasing its
vulnerability to flooding during high
tide.[6]
Semarang’s city planners are
presently debating the locations
and heights of prospective building
developments in relation to where
land subsidence occurs.[7] Can
this process only lead to a very
restrictive form of urban planning or
could the issue of sinking become an
opportunity to develop amphibious
activities and functions – urban or
otherwise – that benefit from the
direct and seasonal presence of
water?
Though the causes of land
subsidence are currently being
addressed, it will take many years
before the process comes to a
standstill. Even in the best scenario,
the land will still sink by 1.6 meters.
The mangrove restoration programs
are believed to have positive
effects on land subsidence, but the
mangroves alone are incapable of
mitigating the sinking process as a
whole. The challenge is therefore
twofold: one the one hand, what
could be a systematic strategy that
solves the problem of sinking in the
long term, and, on the other hand,
what planning strategy should the
city endorse in the meantime? For
example, is it sustainable to build a
hard coastal defense infrastructure
in a place that is drastically sinking;
or is it eventually more feasible to
retreat and [partially] move the city of
Semarang to higher ground?[8]
[5]
[4]
[2]
[7]
[3]
[6]
[8]
[1]
110 Call for Action
PART 1 / From Global Water Issues to a Call for Action
111