It’s wet, very wet. Ark Constructions Pty of Serangan are doing a roaring trade, ducks are getting new seals fitted to their nether regions and my dog is growing webbed feet.

Finally, after years of pretty feeble attempts at a wet season, we are now being treated to a more acceptable tropical monsoon experience. Who knows, with most of the major hotels out of action and, for the time being, not drawing gigalitres of water per second out of the ground to supply gold plated naughty bit washers, perhaps Bali’s poor beleaguered water table may even have a chance for a wee bit of recovery.

Meanwhile, sitting at home in the rain, we find new challenges. We are reminded of that roof leak we forgot to fix last year, or we find the spot where the Ginger Tom from next door has disturbed the tiles with his late-night fornications.

As the waters slowly rise, we start to make discoveries of a more serious nature. We suddenly find that the new house development down the street has blocked off the natural drainage and now lakes are forming where we haven’t seen them before.

The wet season is a good time to go and do some checking. First check your house to see if there are any roof leaks leaving telltale wet patches on your ceilings, take note of where they are so the leak can be found and repaired.

Next, go for a walk around your house and your neighbourhood during or immediately after very heavy rain to check out the lie of the land. Note where water is coming from, where the water flows and where it pools. You might be surprised where lakes are forming and where water is flowing. Once you understand the problems, you can start finding solutions.

You may find a problem that is affecting many people in the area (a flooded road or a large area of pooled water) in which case it is best to go and talk to the local Banjar, they can rally the community to arrange a team effort.

If the problem is confined to your house, it is best to find someone who knows what they are doing but take care, good plumbers are rarer than hen’s teeth in Indonesia.

Unfortunately, many drainage problems are caused by poor design and/or installation when a building is first designed. Drainage is below the ground, out of sight and out of mind, architects often don’t concern themselves with such trivia, and so the design and installation are often left to the last person to say “no” or to the pembantu’s second cousin twice removed.

Drawings of house plumbing systems are rare, so upgrading them may require some investigation and careful thought.

If you find yourself with drainage problems, or if you are building a new house and want a drainage system that works, the most important thing is to find someone who knows what they are doing.

To help us find solutions let us consider the key components of a well-designed drainage system:


1   A Discharge Point

This is a place where draining water can be reliably discharged, it might be into a river, a canal, a storm drain on a road, a soak pit or an area of permeable ground into which the water will effectively soak. The discharge point must be able to handle the amount of water during heavy rain. Also, it mustn’t back up or you may find your drainage system does the opposite of what you want and creates a lake in your garden

You will need to find somewhere that you can legally use. Do not discharge onto someone else’s land without their permission and certainly never discharge into a sewerage system.

If you don’t have a suitable discharge point perhaps you can create one by installing an absorption well (locally known as a resapan).


2   Drainage Conduits

Drainage conduits carry the water either as open drains (channels and gutters) or closed drains (pipes) from collection points to discharge points. The conduits must progressively slope downhill (surprisingly it is amazing how many people don’t understand this simple concept), 2% of slope is a good minimum for a drain.

Round bottom conduits are better than flat bottom conduits, they concentrate the flow of water and so have a “self cleaning” action.

These conduits must be large enough to cope with the amount of water to be drained and the size should progressively increase as you move downstream and the amount of water being carried increases.

Water is very heavy stuff and drainage conduits must be strong enough to hold the weight of the water they are carrying. This is particularly important for roof gutters where tukangs who learned their trade grilling satay simply cannot understand just how heavy a gutter is when it is full of water.


3 Collection points

These are places that collect the water and guide it into the conduits. Collection points usually consist of gently sloping concrete funnels set at low points in the ground where water pools in wet weather. The design and positioning of these points needs careful thought so that firstly, full drainage is achieved and secondly, earth or leaves are not washed into the drainage conduits.

In many countries steel grating is used to help prevent leaves or rubbish from being washed into drains.

Also small chambers may be set in the ground before the pipe entry these slow down the flow of water momentarily and gravel or sand in the water can settle to the bottom of the chamber before entering the pipe.

These are concepts widely used in more advanced countries but are generally not understood by the average Indonesian tukang.


4   Cleanouts

Your conduits may block up from time to time so you need to allow for this when designing a drainage system by including cleanouts. These are access points in the pipework that allow the conduits to be easily unblocked. Carefully positioned cleanouts along with the use of 45-degree rather than 90-degree bends can make it significantly easier to clean out blocked pipes.


A few things to bear in mind:

1   Levels, levels, levels. Water flow is all about levels, and these might not be obvious before it rains. For example, bathroom floors must slope to the drain. To check that a slope is correct, try pouring a pan of water onto a surface (such as those newly laid bathroom floor tiles) and see which way it flows.

2   A common mistake is to underestimate just how much water can be collected from even small areas in sustained heavy rainfall (this is especially the case with roofs). Think about it, 1 centimetre of rainfall on 1 are (100 square meters) of land will be a cubic meter of water.

3   Another very common mistake is to underestimate the weight of water, that cubic meter of water will weigh 1,000 kilograms or a metric ton (a tonne).

4   Tree roots have always been a problem growing into drains and blocking them. Tree roots follow water, so they find water leaks where pipes have been damaged or badly joined, they grow into the pipe and block it. These days, with modern PVC pipes, there shouldn’t be any leaks so tree roots should not be a problem unless the pipe is damaged or badly installed.

5   Modern PVC plastic pipes should be joined using solvent cement and not PVC glue, PVC glue doesn’t stick to the PVC very well while solvent cement melts the PVC, so you get a “welded” joint.

If you need some help give us a call.


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