A Call for Permeable Paving

with permeable paving, stormwater doesn't all become surface runoff

With permeable paving, all stormwater doesn’t become surface runoff
Image Source: Flickr

I’ve said it before and I’ll say it again: urban dwellers have an obsession with paving every possible open space.

Housing society compound?
Pave it — we need to park our cars!

Open area where social interactions take place?
Pave it — our clothes get muddy!

Barely-used internal road?
Pave it — we get stuck in the monsoon and it’s hell on the tyres!

If we Must Pave, Let it be Permeable

Some of this paving may well be justified but, because it is done indiscriminately, it leads to a boatload of problems related to the water table, the health of the city’s trees and even the heat we’re subjected to. I’ve written all this in greater detail elsewhere on this site but this particular post is about a type of product that could help in such situations.

In late 2015, there was a buzz in the construction world as Lafarge UK showcased a super-porous asphalt that could guzzle an incredible 4000 litres of water in about a minute. Media started calling it “thirsty concrete” and truly, if you watch the video below, it does look like the water is vanishing into desert sands.

Permeable Concrete Video

I have never been a great fan of the wasteful use of concrete but, when it is required, the least we can do as architects is to try and use it correctly.  Unfortunately, at least as far as I can tell, this product and others like it are not readily available in India. In fact the only case I know of permeable concrete being used, is for a parking lot at Jaipur railway station.

Unless architects and engineers specify such products and create a market for them, there is no way that companies will manufacture them here. I do hope some of my brethren in the industry take up the call.

Reduce Hard Paving

In our urban environment we see numerous examples of open spaces with hard paving all over them. One of the reasons for this is our insatiable hunger for parking. The earth in our cities is starved of air and water — sacrificed at the altar of our rubber-shod tin cans.

“Ah”, but I hear you say, “we really do need that parking space!”.

Of course, if our city fathers were more enlightened and aimed for better public transportation instead of caving in to the cult of the car, we wouldn’t have reached this impasse in the first place. However, this page is not a rant about ineffective urban planning but about the effects of indiscriminate paving and what we can do about it.

When we pave over open spaces, a number of things happen.

The Water Table Drops Dramatically

This one is pretty obvious and hardly needs an explanation. If the ground is paved, there is no way that any more than a tiny fraction of rainwater will ever reach the soil. In Bombay, there was a time when one could dig a well and hit water not far below the surface. These days, the only reliable wells are the ones that adjoin large green spaces — like the maidans for example.

Other cities are not so lucky and those who live where borewells are common will tell you that the wells need to be dug deeper every year. The water they reach is also an increasingly fickle seam. The demand on the groundwater is constantly on the rise but all that paving never allows it to get recharged.

Egress of Saline Water in Coastal Areas

too much paving leads to a drop in the water table which allows egress of saltwater

Freshwater is lighter than saline water

Saltwater is denser than freshwater and forces its way inland below the latter. If the (fresh) water table drops, the boundary between them is pushed deeper inland. Salinity in the soil is not merely bad for plant life but also for construction.

Trees Find it Difficult to Survive

For plants — and especially trees — paving is doubly detrimental. Not only is there very little water in the soil to help them grow but their roots are also unable to breathe. As a result, the trees develop a weak rooting system; it is no wonder so many of them topple over during the monsoons. That many of the avenue trees in our cities are fast-growing exotics, doesn’t help very much either.

Drainage Systems are Overwhelmed

Kalyan Station under water July 2005

Kalyan Station under water
Image source: Wikipedia

When it rains in an urban area that is excessively paved, the runoff has to go somewhere! That somewhere, is the storm-water system which is frequently unable to cope. This leads to the all-too-familiar floods we see every year.

At best, flooding is an inconvenience but, as the last few years have shown us, it can also be deadly. Corrupt builders, politicians, and bureaucrats are responsible for the rampant encroachment on natural drainage channels in many of our cities. This results in the kind of devastation and loss of life we saw in Bombay (2005), and Madras (2015).

No doubt, in both cases there had been uncommonly heavy rainfall. We must remember, however, that climate change is causing an increased frequency of such extreme events, so it would be foolish to brush them aside as a freak events.

Worsening of the Urban Heat Island Effect

urban heat island

Temperatures are significantly higher in cities
Image source: Wikipedia

Paving is one of the major factors leading to the heat island effect — that phenomenon where an urban area is significantly hotter than its surroundings.

Unlike soil which cools off rapidly when the sun goes down, paving retains heat for longer and then emits it slowly through the night. One of the only ways to reduce this effect is to increase the area under plantation (including on roof terraces). However, as we have seen earlier, that is rather hard to do, when everything has been paved over. It’s a bit of a vicious cycle.

What We Need to do

Of course the very best thing to do is to avoid paving as far as possible. However, there are many situations when we really have no choice. At such times, the least we can do is to use materials and systems to mitigate the problems we cause.

Pervious Concrete Paving

permeable concrete

Permeable Concrete
Image Soure: Wikipedia

This is a type of concrete where the fine aggregate (sand) is missing so that the concrete becomes porous enough for water to percolate through. This means, of course, that it is not as solid as other concretes and cannot sustain the same heavy-duty usage. On the other hand, it is perfectly usable in areas where traffic density is low or, for example, in parking lots.

Some cities like Portland, Oregon in the USA have experimented quite extensively with permeable paving. Unfortunately, there is little sign of anything even remotely close being done here.

Perforated Paving Block or Grass Paver

grass paver blocks

Grass Pavers
Image Soure: Wikipedia

These are easily available here but not as commonly used as I wish they were. They are easy to lay and, to my eye, they make a space look much nicer than if were completely covered with a hard surface.

Permeability is excellent but, like porous concrete, it can only be used for low-traffic areas or parking lots.

Tree Guards

tree guard

Tree Guards
Image Soure: Flickr

If all else fails — and even if not, it is wise to have tree guards which allow the soil around the roots to breathe. This is something that is conspicuously lacking in our cities.Instead, we see a low brick wall made as close to the trunk as possible. Apart from being undersized and ugly, these are also tripping hazards for pedestrians.

It would be so simple, instead, to embed a cast iron tree guard that is level with the pavement. If the city authorities feel that the iron will be pilfered, they can do something similar in ferro-crete. It won’t look half as nice but at least it will be effective.

Green Roofs

green roof

Green Roof
Image Source: Wikipedia

While a green roof can’t do very much for the surface runoff and the storm-water systems, it can certainly be help reduce the urban heat island effect.

Planted roofs haven’t caught on too well here as yet. That will not change until waterproofing systems become much more reliable. People who have running battles with monsoon leakage are unlikely to tempt fate.

Conclusion

The situation is far from ideal but it isn’t a lost cause just yet. Given enough awareness and pressure from the general public, things can improve. Organisations like depave, for example, have done this very effectively. They have not only raised awareness in Portland but have even forced the local government to reverse past mistakes.

Maybe it’s time to start something like that in all our cities here as well.

The Architect and the Plantsman

This Wall Street Journal article on the collaboration between reclusive Swiss architect Peter Zumthor and ascetic Dutch landscaper Piet Oudolf made me think about my own (much less famous) interaction with A.Y. Retiwalla for the Karjat Resort a decade ago. Unlike the collaborators here, neither of us had heard of the other before and were brought together by the client, Dr. Beramji. Still, the mutual respect and acceptance of ideas was similar and it ultimately led to something that was appreciated by all.

The restaurant, shortly after construction

The restaurant, shortly after construction

The restaurant about five years later

The restaurant about five years later

No egos were bruised during our meetings — they were left outside

Mr. Retiwalla was already well established in his line and it is to his credit that he discussed things with a relative youngster like myself, purely on merit. Ideas flowed freely between us and, with Dr. Beramji taking a keen interest in every aspect of the project, the tripartite meetings were very enjoyable.

Planting for Birds & Butterflies

Plants that you should consider

There are a number of things you can do to attract butterflies and birds to your garden. Here is a basic list that may be useful as a starting point for people living in peninsular India. Please remember that this list is neither complete nor comprehensive because habitats vary so dramatically across our country. I’ve tried as far as possible to list local species but some, like the Lantana, have naturalised in our country and have therefore found a mention.

Grasses

A number of butterfly species lay their eggs on grasses – but not of the cultivated kind. Unless you have a very large plot, it is unlikely you’d want to allow these to grow. However, if the possibility exists, it is nice to let a patch of garden in a corner somewhere actually grow wild.
Bamboos are food for some butterfly species and refuge for many birds and other creatures. Keep them a little distant from your house if you’re petrified of snakes, though.

Shrubs and Creepers

Trees

Even if you live in the heart of a city like Mumbai, you will be surprised by the variety of birds you can see if there is enough greenery around. I’ve seen the beautiful Paradise Flycatcher in Breach Candy which is, barring a couple of tiny green pockets, as concrete a jungle as you can get.

Although the links above all point to wikipedia, a very good resource I have found for Indian plants is Flowers of India. The site aims at having comprehensive information about Indian flowering plants with their common names (especially in Indian languages), pictures and details of habitat and distribution.

Preventing Soil Erosion

Erosion of soil is a very real problem that can crop up when we encounter sloping land on a site. In this article, I’ll outline the measures taken on two different sites where erosion needed to be controlled. The first was done entirely via plantation and the second (where the foundation of a building had to be supported) involved terracing of the land — in conjunction with plantation of course.

Slope Stabilisation with Vetiver

In the year 2003, a client of mine wanted to buy an 11 acre plot of land along the Narmada river. It was a lovely location but the soil was very soft and powdery and the land was scarred by deep fissures where rainwater flowed down to the main river. What made it downright dangerous was that these steep gullies were collapsing at points and something needed to be done before parts of the plot got cut off and became inaccessible.

At the time, I suggested reducing the angle of the slopes and planting local reeds that grew along the riverfront to hold the soil. The first part worked but the second did not. The wild plants refused to grow where we wanted them to and something else needed to be found. That’s when she decided to try growing Chrysopogon zizanioidesVetiver (also called Khus).

What happened next was almost miraculous. The Vetiver took hold of the soil and bound it in a way that not only stopped erosion but allowed rainwater to seep into the soil instead of letting it all run off to the river. As a result, even the trees growing in the gullies got healthier and what looked like an almost barren landscape then, is now a great example of how working with mother nature is far more productive than trying to fight her. And plantation costs a fraction of what it would if we used “man-made” solutions.

What makes Vetiver different from other grasses is the fact that it’s roots do not form a horizontal mat like the others but grow downwards as far as 4m (13 feet). Another good thing is that it propagates in a way that makes it easy to control – so it doesn’t become an invasive weed.

To know more about Vetiver and how to use it for erosion control, go to the Vetiver International Network Website and download their manuals, videos and presentations.

Terracing the Land

Now, while I’ve been extolling the benefits of natural solutions, there are times when we simply have to use brick and mortar solutions when structural demands have to be met. The [RaBV] bungalow at Nasrapur was built on steeply sloping land and we not only had to prevent erosion but also make sure that the building’s foundations had rock solid support even if an earthquake struck. In such a situation, simply planting Vetiver, or any other vegetation for that matter, would never have been sufficient.

The first thing to do in the design was to follow the slope of the land as closely as possible. The main floor level was split with the living room sunk by about 0.6m (2 feet) from the rest of the house. Then, the verandah which projected by 2.4m (8 feet) beyond the house line was almost 1.8m (6 feet) above surrounding ground level so instead of filling it up, a little earth was excavated and an extra level – like a basement – was created below the verandah. Not only did this reduce loading on the peripheral foundation wall in a big way but is also served as a space for garden implements, a separate room for rainwater harvesting tanks and parking for a motorcycle.

The verandah effectively then, became the first terrace. Then, to buttress the foundation, a second terrace was created just in front of the basement. Here, we planted only shrubs and bushes – nothing with strong roots that might weaken the stone wall at some future date. Finally, we built a retaining wall to support the second terrace.

Maybe it was unnecessary to go so far but, when there is going to be no second chance to correct a mistake, you tend to err on the side of caution. Around the bungalow, on non-critical slopes, local vegetation has been allowed to grow naturally and has taken root well enough to protect against erosion.

Appropriate Plantation

There is a raging debate among naturalists about the desirability of cultivating exotic plant species and there are no easy answers. My own view is that we should try our best to avoid introducing any new species into an existing ecosystem but there is no need to get worked into a froth if a species has naturalised over a substantial period of time. Yes, there are places where exotic species have become very invasive at the cost of the local varieties and there may be a case for culling them – but such a discussion is beyond the scope of this article. Instead, we are going to focus on the use of exotic and native species in the context of what is appropriate landscape architecture in a predominantly hot country like India.

Improving Comfort Levels

Trees are often the first line of defence when it comes to passive cooling of a bungalow or other low-rise structure. They provide shade which prevents the build-up of heat not only on the ground but also on the walls of the building. Shade on the ground means the breeze coming in through your window is cooler and shade on the walls means less heat gets transferred indoors. Aside from shading, trees also cool by transpiration to the extent that they can, if properly located, reduce ambient temperatures by as much as 5° compared to the surroundings.

So what kind of trees should we plant, and where?

While the finer details vary across different parts of the country, broadly it is safe to say that the hottest sides are the South and West so, if you can concentrate on protecting these directions with dense evergreens, you’re good to go. On the East, you might want to have high-branching trees that won’t block your early morning sun and on the North – depending on whether you get direct sunlight penetration or not – you could grow colourful, possibly deciduous trees. You have to be careful during plantation that you leave enough distance between the tree and your foundation because many of the large trees have strong spreading roots.

Trees, even in urban areas (albeit to a lesser extent), are part of an ecosystem and need to treated at as such. If they are native, they will invariably be well integrated into that ecosystem along with the local fauna like the birds and butterflies. An introduced plant is unlikely to be so well assimilated and may therefore not contribute in a positive way. There are plants that have been naturalised over a long period of time but I’m referring to those that have been introduced because they are ornamental or because they grow rapidly. Usually the ornamental ones are fragile and drop their branches on your head at the beginning of the monsoon and the fast-growing varieties with their short life-spans often sap the soil so severely that nothing else grows there for years after they’re gone.

Usage of Water

This is a very important factor to take into consideration especially if you’re thinking of sustainable landscaping. Many ornamental trees and bushes are extremely high-maintenance and don’t even get me started on lawns. They may look very pleasing to the eye but, with few exceptions, they guzzle frightening amounts of water and are often heavily sprayed with chemical pesticides — which naturally leech into the groundwater.

Here, a very important argument for using native species is that they will, by default, survive with the naturally available moisture and precipitation. Of course they may need some amount of watering when they are saplings as also during the hot summer months but, in general, their water requirements are a small when compared to exotic ornamentals.

Trees, Landscaping & Microclimate

The microclimate of a particular location or site is controlled – to a great extent – by it’s landscape and terrain. In a predominantly hot country like India the plantation of trees plays a vital role in preventing the build-up of heat. They shade the ground (and the walls of low-rise buildings) with their canopy and, combined with their transpiration, trees can lower temperatures in their immediate surroundings by as much as 5°C. Also, in conjunction with shrubs they can help in channelling prevailing breezes and improve comfort levels indoors as well as outdoors.

It is important, from the point of view of sustainability, to preserve what we can of a site’s natural ecosystem. This includes not just the flora and fauna but also the natural drainage patterns. We all know how landscaping can transform the aesthetics of a place but not many of us realise that greenery does more than just look pretty. Out choices affect what birds, butterflies and other creatures will survive not just in our own property but in the immediate surrounding areas as well.

For example, if milkweed plants like the calotropis sp. grow commonly in the area and we say, “oh, they’re ugly – let’s get rid of them”, then we’re not merely removing a species of plant but also banishing a number of small creatures – many of them attractive – that depend on the calotropis for their survival. I am not for a minute advocating that one should allow one’s garden to grow wild but merely pointing out that landscaping involves more than just choosing pretty plants.

Plant Appropriately

It is not merely enough to know where you are going to grow something; it is equally important to know what you are growing and how it affects the local ecosystem.

The subject of exotic versus native trees has generated a lot of debate but my own personal opinion is that, whenever possible, it is better to plant a local tree instead of one that belongs to a different ecosystem.
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Reduce Hard Paving

City folk seem to have an obsession with paving every inch of land they see. This leads to a huge increase of rainwater runoff which, in turn, overloads the storm-water systems and results in flooding – sometimes with disastrous consequences. Soil, especially when well planted, allows a large percentage of the rain that falls on it, to penetrate the ground and recharge the water table beneath. This, in turn, allows plants to grow more naturally, gives us sweet water in the dry season and, in coastal areas, prevents the egress of saline water.
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Give Nature a Home

Nature’s creatures respond very quickly to favourable conditions, so if you want to attract birds, butterflies or other creatures, it is just a matter of finding out what they need. Only remember that nothing exists in isolation so if, for example, you plant flowers to attract butterflies, you’re going to have predatory creatures like spiders trying to eat them (the butterflies, not the flowers) and you’ll have to be grateful for both!
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Prevent Erosion

Sometimes you’re faced with a situation where erosion becomes a major problem. Usually, through landscaping, you should be be able to either eliminate the problem or, at the very least, bring it under control. In 2003, a client of mine bought a tract of land along the Narmada river where the soil was so powdery that even a little rainfall would create a channel in the ground. Today, that site is a great example of how to deal with soil erosion in a totally natural and eco-friendly way.
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