On Higher Grounds

Whatever happens, at least one thing is always reaching higher levels: the ground level. As we know from archaeology, the ground we are living on is a big history book. We are surprised by everything appearing in excavations. It is amazing to see how deep everything is hidden. It is a strange thing that the city of the past lies a few meters deeper than the city of today. By the way, we might ask ourselves: where did all the dirt come from?

The construction of a new sewer in Dharavi reveals how quick the level is rising here. The whole package is about 75 cm thick and comprises sand, gravel, grit, pieces of glass, and other non-degradable matter. Under the package lies the floor of what once were the marshes. The layered structure shows that only every now and then a layer of grit and debris was added. Over time, dirt and sand whirled down. Dharavi once was marsh land and as people are inhabiting this area since about 50 year, the ground level is rising 1,5 cm per year.

Water piping has to be rearranged for this sewer reconstruction. This as well shows the growth of the soil package. Older pipes lie deeper now than when they were put there. The highest pipes are the most recent. Like the rings in the stem of a tree, the pipes in the ground tell the history of this neighbourhood.

In countries with a less warm climate, water piping is laid deep in the ground to protect them against freezing. In the Netherlands the typical frost-free depth is 60 centimetre. In countries with a more explicit continental climate, depths of 1 meter and more are common. In Mumbai, where midwinter temperatures do not drop below 20°C, it is no use indeed to lay pipes that deep. In addition, many inhabitants do not hold formal property rights over their house or the land they live on. There is a real risk of being expelled today or tomorrow. To dig a trench and cover the water piping is an investment that is quite risky in such a setting. Therefore, many water pipes in Dharavi run over ground. Of course, it is less convenient for pedestrians and of course, there is a risk of damage and subsequent leakage, but that does not outweigh the costs of digging. In the end, it all is covered by dirt and stones anyway.

Demolition waste is very useful in fighting floods. Especially brick and concrete debris get a good destination from it. Dharavi sits, as mentioned, on former marshlands and for that reason, the soil is soft. It cannot bear heavy loads and as a result, houses gradually sink, which is inconvenient in case of flooding. In addition, the rising street level as we saw above makes every ground floor end up as a basement some day. During monsoon, the downpour can be that heavy that drainage cannot cope with it. The lower areas of Dharavi get flooded. Houses with a floor level notably higher than street level are better of in such days. There are many advantages in keeping the debris on the location when demolishing a house. The ground floor level of the new house is on an attractive level from the start. A second advantage is cost saving on transportation. Debris is heavy and in most cases, it is impossible to get a truck near the site. The alleys and even the streets are too narrow for trucks. Manual disposal of that much material over such distances is undoable and uneconomic. Debris can only be used as road fill or land fill and that leaves it unprofitable. Balanced against the advantages of a higher ground floor, the choice is easy.

The unprofitability of transportation can also be seen at the feet of power line masts. These masts are often screened off with walls, thus providing excellent dumping grounds. By now, these masts stand sturdy up to their knees in stone. The masts themselves are used as laundry racks.

The ground level of Dharavi is on a permanent way up. Houses and streets gradually sit higher and higher. History goes deeper and deeper.

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