Drainage issues - Can someone please help....

Hi

We recently bought a house which is around 2 years old (NSW, Liverpool Area). We are in a difficult situation with drainage. Not familiar with this topic (first time buying a house) so feeling overwhelmed and thrown from one corner to another when discussing with others to solve this issue (Different people giving different opinion when consulted).

We noticed water pooling in the backyard. It takes a while to get the water to recede. But even then, the soil is wet. Can feel the water when we step on it (water squeezes out when pressure is applied) . It takes a good amount of time to get the water completely dry. Our house sites at a lower level than our neighbors.The soil is reactive (H1) clay so water doesn't drain easily.

When searching this forum, noticed many highly experienced people (Insider, BE etc.. thanks to all ) mentioning that water & dampness could damage the foundation. We are planning to put AG-pipe so that the water drains properly. This is being discussed with the plumbers now.

Another thing noticed is something very particular. During the heavy rain, water bubbles (sorry, not sure I used the correct term) from the storm-water pit. This goes on until the rain eases. I have attached a video here. - https://gofile.io/?c=atkinw

Just wondering what might be causing this? Something I need to be concerned?

Thanks.... and really appreciate your help.

You don't say if the area is old or new.

If it is a well established area its probably likely that either; the council owned surface water pipes are either blocked and/or have inadequate capacity.

Generally I have found that a lot of areas were originally developed with smallish 3 bedroom houses on blocks of 1/4 acre or larger. The drains only had to take the roof water.

As people have built extensions and subdivided blocks the amount of roof area going to the drains has at least doubled so there is much more water trying to get down the same sized pipes.

I have also found in many areas the surface water drains have been constructed to a poor standard resulting in cracked pipes and root penetration( check this link; SEWER ROOTS)

Being on H1 is indeed a concern as are the low finished surface levels.

Did you contact someone who specialises in drainage or is it just an everyday plumber?

From what I see in the video, you have either stormwater surcharge or a flow restriction which is the prime reason for the flooding and the inability for the surface water to drain during rain.

If it is an inability of the main stormwater system to handle the flow, I would expect the onsite surcharge to be greater given that your site is lower. Do you know if the neighbours also have similar issues? I suspect not.

Can you also post a photo of the 'bubbling drain' when there is no surface water thanks? Is the top cover round? I need to eliminate a 'possibility' but if the bubbling drain was an additional issue, the plumbers certainly should have noticed.

The probability is that it will be an obstruction in your onsite stormwater pipe. This should be the first thing checked and is done by a plumber feeding a CCTV indrain camera along the pipe to look for any obstruction which will usually be tree roots.

Has the plumber done a camera inspection?

Also, at the bottom of the downpipes, there could be a plastic adaptors (I don't know the downpipe sizes). If there are adaptors, do you see water coming out of them when the drain is bubbling?

Information about the Liverpool Council's stormwater system is in the link below.

https://www.interflow.com.au/wp-content ... cil-JM.pdf

Thanks @ bashworth. This is a new area but have houses around. (most of them are 4 bed, double storey house)

I found a grill-opening (?) near by curb. Not sure if the stormwater pipe is directly connected to it. Is there any option for the residents to get the plan/layout of the drainage system from the council?

Thanks @SaveH2O : This house was built by Rawson homes and completed in Dec-2016. I contacted a plumber when I noticed it with the recent rain. I think he is just everyday plumber. I was given a quote of around $8000-$9000 to put AG around the 3 sides of the house. Considering this is $$$$ expense, I thought of getting another quote. As you guessed - different people , different different opinions. 1 person was thinking in the same way you mentioned - he said probably due to water from retaining wall (our plot is below the neighbours- all 3 sides), or due to slope issue (pipe laying problem). He mentioned that a builder consultant service is required and probably a camera inspections as well.

Do you know any Drainage specialist in Sydney / Liverpool area that I can contact who has experience with these sorts of things? Thanks.

I couldn't find any adapters at the bottom (or was I looking at a different thing?, sorry). I have attached a few photos.

I also noticed the round-grill kind of thing (overflow relief gully ?), which is buried in the pebbles connecting the pipe coming from the storminwater pit, is missing at the side where the water is bubbling. The picture is from the other side.

Also put that plumber on your blacklist of who never to use. Not all plumbers have CCTV drain cams, maybe he was one of them. There are many good honest plumbers around but also a lot of characters who should be run out of the business. When you find a good plumber, treat him like gold.

Surface water has to drain to a silt pit which then drains through a raised outlet to a stormwater connection. This is to prevent silt draining from numerous properties into the council stormwater pipe and then transported to creeks and other waterways. The pit in the above photos is a silt pit and the single pipe is the raised overflow. If ag pipes are fitted around the property, they also have to drain to a silt pit but as you know, the current pit cannot drain the water already in it.

If ag pipe is put in, it would connect to the current pit but before ag pipe can be installed, the silt pit's discharge pipe has to be working.

I am surmising that the pipe is obstructed but not totally blocked and the pipe's slope is allowing air on the other side of the blockage to travel upstream and percolate into the silt pit, hence the bubbling from amalgamated smaller bubbles which indicates very slow water velocity through a sloped pipe. A pipeline air pocket also presents a physical obstruction.

If there is no obstruction, then it is an overloaded council storm water system but the bubbling indicates otherwise.

Note that my advice cannot be guaranteed because I am not on site but the pipe does needs investigation as the first step towards remedy.

NO, sorry. Just Google search for a plumber who has a CCTV drain camera and does mostly drainage.

It looks like a 90mm pvc downpipe and it will be sealed...no adapter.

Yes, it's an Overflow Relief Gully (ORG) which is part of the sewer system. I just had to make sure that the bubbling wasn't coming from an ORG.
Correction in post further below...it is NOT an ORG.

The ORG should be 75mm above the finished ground surface to prevent surface stormwater from flowing into the sewer system. The landscaping stones fill a lot of that clearance space, does surface water flow into the sewer system?

Is that ORG? . The round with the black grate.

I thought its just a storm water inspection point.

I'm building right. And the storm water inspection point look exactly like that.

While me ORG actually looks like a mushroom shape cap with grate on top.

Thanks for that....You are correct of course. I should have looked closer, I thought that it was domed.

Not an ORG!!!

An update on this - I got a good plumber, with camera and have been doing drainage work, to look at this issue. He said this is due to the way the pipe was laid. Not enough slope for the water to flow through to the kerbside. He showed me the water in the pipe. I will get the report tomorrow.

looks like a $$$$ job.

First time getting into a situation. Can I please ask

1) This house is just 2 years and 2 months old. I dont know if the builder is going to say 2 years warranty is over and cant help. But I am sure the warranty covers and this is a major work.
2) I am ready to talk and fight to the max extend the law permits. What are the legal avenues I have (and legal keywords that I can use) - Fair Trading / my statutory rights? Who should be my go-to if things are not that smooth.

Thanks all for the direction. Don't have enough words to express my gratitude.

I don't know where you stand with the builder, it's not my field. It appears that the slab (and site cut) is too low, did you have the house built or buy established?

An inadequate head is effectively a flow restriction and the one I was fearing you had.

1. Does the pit connect to a common pipe that the downpipes also drain to?

If the pipe only drains the pit, it should drain at many hundreds of litres per minute even if the pipe is flat.It looks like there is at least 200mm above the pipe's invert to the top of the pit and this should give a flow of +370 litres per minute.

2. Have you ever stood at the pit when it is full and watched the water? If so, do you see a surface whirlpool extending down to the pipe?

3. Do you know the course of the pit's pipe?

I will wait for an answer to my questions and then look for a hydraulic solution that won't cost too much. At this stage I am thinking that the pit shares a common pipe with the downpipes which have a head positive to the pit during heavy rain.

Thanks SaveH2O

I have attached the stormwater drainage plan here. I noticed some deviations and have marked it.

1) The pit and the overflow are connected to the same Pit-to-Kerbside pipe. The water-tank overflow, that is connected to the pit's pipe is around 1.5m from the ground. (3000L capacity)

2) I don't remember seeing any whirlpool in the pit. If it rains in Sydney, I will pay close attention to it,

3) This house was bought from the first owner after its was fully completed.


Thanks Again

.

Just wondering instead of connecting the watertank overflow pipe to the stormwater pipe, just connect that to the Pit (probably increase the size of the pit). Or use a 2nd pit for the watertank overflow pipe and then to the stormwater pipe?

Thanks for the diagram, exactly what I needed.

I can see the problem, it's what I suspected and it fails to meet the performance requirements in the NCC by a huge margin. Whoever did the storm water plan has no clue about hydraulic design.

I will post some calculations for you tomorrow when I have time but do you (approximately) know your roof area...just the plan area (as seen from above) to the gutter extremity? I have it guesstimated at about 225 sq m. Once you see the figures, you will understand why the problem exists and how it can be fixed.

Also, I need to know the distance from the bottom of the pipe in the pit to the top of the pit. Just measure from the top of the pipe, I know that the pipe's diameter is 90mm. I have guesstimated the distance as being about 240mm from the bottom of the pipe (the invert) to the top of the pit.

Also, what size pipe is the water tank's overflow? I am assuming 90mm which is an outside diameter which makes it a 283mm circumfrence. Is there just the one overflow pipe coming out of the tank? Has the tank ever overflowed during heavy rain? Also, do you have an external or submersible pump? If it is external, could you post a photo of the outlet valve that supplies the pump thanks.

The water tank has sub standard installation issues but that is normal unfortunately. Practically every photo of a water tank installation that I see on Homeone shows a sub standard installation.

EDIT: Typo.

The tank is part of the stormwater system and it also needs attention.

If the diagram is correct, the tank's overflow pipe communicates with the stormwater pipe via a junction that merges the water into the pipe in the direction of flow which boosts the flow rate. At least they got that right!

If you diverted the tank's overflow pipe to the pit, you would lose that boost plus some additional head pressure and the situation would be much worse.

A second pit would just fill and contribute nothing to the flow rate as it would operate with the same head as the first pit.

Thanks SaveH2O.



1) Roof Area : Not quite sure but the floor area is around 225 m2 with a roof 23 deg. Which roughly calculates to 250 m2. Considering we have AG pipe also brining water, 285 sqm is a proper estimate.

2) The storm water pipe is 100mm. The water tank inlet and overflow outlet also are 100mm. I have attached a diagram just created using the MS paint.

3) we havent noticed the tank overflowing.

4) I can see 2 inlets and 1 overflow. Just took some photos ( My dog decided to pose for the photo, she is not ready to move from there )

5) The pump is submersible pump.

I should have enlarged the photo that showed the pit's pipe, that would have shown me that it wasn't a thin (1.9mm) walled 90mm stormwater pipe. Aah! The perils of not being on site.

It looks like water could seep through around the pipe. I would be sealing around it.

It is good that all pipes are 100mm Drain Waste Vent (DWV) pipes which have 4mm thick walls, an internal diameter of 104mm and have a volume of 8.5 litres per metre..

I'll do calculations for the roof area being 230 sq m.

The roof slope uses a slope based multiplier to calculate the individual roof harvest areas draining to each downpipe during wind driven rain but we only need to use the plan area to calculate the rainfall on the total roof area for this exercise.

I surmise that the house was (most probably) handed over after construction with stormwater drainage that didn't include the connecting pipe shown as red in the diagram but which did include the water tank.

Your area probably has a 1:20 Average Recurrence Interval (ARI) of 200 mm/hr. The ARI is based on an average 5 minute rainfall intensity and 200 mm/hr = an average 3.33 mm/min of rain intensity over a five minute duration. A region's 1:20 ARI is used to determine compliance for the eaves gutter cross sectional area, downpipe size, the maximum roof harvest areas and the stormwater pipe sizes.

Downpipes draining a 230 sq m roof during a 200 mm/hr 1:20 ARI would collectively drain 230 x 3.33 = 766 litres per minute (lpm). This is a velocity of 1.5 metres per second through a DN 100mm DWV pipe. AS/NZS 3500.3.5.4.11.2(d) states that the full pipe velocity is recommended to not exceed 1.5 m/s and shall not exceed 2.0 m/s.

The house has 6 downpipes and for this exercise, I will treat all downpipes as harvesting equal roof areas of 38.33 sq m each. This equates to 128 lpm during a 1:20 ARI. In reality, downpipes do not harvest equal roof catchments.

I also surmise that the pit was installed after handover which invariably is the case.

I will refer to the downpipe at the garage as dp1 and so forth.

Using the above and assuming that the diagram is accurate, the 100mm stormwater pipework was originally designed to:

1. Plumb the downpipe connections to merge with and assist the stormwater flow rate.

2. Have four downpipes (dp1, dp2, dp3 & dp4) connected to a charged (wet) system that discharged into the tank via a vertical riser. The downpipes were not fitted with leaf diverters and the available head from the top of the horizontal wet system pipe above the tank to the gutter's sole looks to be at most 0.7 m.

3. The 4 downpipes would have drained 512 lpm (128 L x 4) to the tank during a 1:20 ARI. A 100mm DWV pipe has a volume of 8.5 litres per metre. 512 L/min = 8.53 L/sec or a velocity of fractionally more than 1 m per sec.

4. All fittings, elbows etc create friction loss that is calculated as equivalent pipe lengths, for example, a 100mm 90 degree elbow has an equivalent pipe length of 3.7 metres friction loss and there are two 90 degree elbows and eight 45 degree elbows plus the junctions and pipe length in the wet system fed by dp's 1-4.

It is very difficult to calculate flow rates when there are four charged downpipes at different positions along the wet system. Regardless, I can calculate that a 104mm internal diameter pipe with 0.7 m of head will flow at 512 L per minute with friction losses measured as 77.7 metres of equivalent pipe length.

I am very interested to know the actual head but note that the original drainage calculations also needed to include the roof slope multiplier that allows for additional wind driven rain. For a 23 degree slope, the multiplier is 1.21.

5. Dp 5 was also diverted to the tank through another charged pipe, making a total of 640 lpm diverted to the tank during a 1:20 ARI.

6. The tank has a single high fitted 100mm overflow pipe with in practical terms no mitigation above the top of the overflow.

7. Dp6 connects to the stormwater pipe.

UNDERSTANDING ISSUES THAT WOULD HAVE BEEN FIRST EXPERIENCED

Depending on the actual head and the effect of wind blown rain during a 1:20 ARI, the single nominal diameter 100mm charged DWV pipe may not have been able to cope during a 1:20 ARI, resulting in the gutters overflowing. I consider this scenario to have been most likely.

A mistake often made is to calculate the head as being between the tank's top meshed inlet and the gutter's sole whereas for a pipe diverting flow at a good velocity, it should be from the top of the vertical riser to a minimum 50mm below the gutter's sole to allow for bubbles which lower the water column's atmospheric pressure at the top of the column. For your installation, the difference would have been nearly 200mm optomistic if the distances were incorrectly calculated.

Regardless of the above, the tank's 100mm overflow pipe could not have possibly coped with the inflow during rainfall much heavier than one mm/min.

Flow out of a side hole is calculated by using Torricelli's Theorem but AS/NZS 3500.1 has a convenient table (Figure 8.2) that shows flow rates through a short horizontal outlet at different heights above different size pipe's inverts. While it doesn't show a 104mm internal diameter pipe, it does show that a 100mm pipe with 100mm of water above the invert will discharge at 4.67 L/s or 280 lpm which is a long way short of our example of 640 lpm.

A significant additional point to consider is that Torricelli's Theorem and the figures in Figure 8.2 do not factor a tank having a meshed overflow outlet which presents a flow restriction and which can also clog.

Because the tank was part of the stormwater system, the installation was not compliant by a huge margin.

FIXING THE TANK OVERTOPPING PROBLEM FOR THE FIRST OWNER

As it wouldn't have taken long for the tank to fill from five downpipes, the new home owners were sure to have experienced overtopping and associated flooding very early and this was almost certainly the reason why the additional (red) connecting pipe was added.

It is really impossible to know how much would discharge into the tank now from dp's 1-4 during different rain intensities but with the significant flow restriction presented by the vertical riser, a lot of water would now drain through the new pipe marked in red as it is the path of least resistance and the reason why the tank does not overflow. I would not expect much if any water to flow into the tank during light to medium rain apart from the diversion from dp5.

CURRENT PLUMBING

A pit has been added to drain surface water but the pit's discharge pipe runs with minimal slope to the junction and the small amount of head provided by a full pit is negative to any head from the tank and dp6 as well as the other pipe connecting to the junction. This makes the pit a new path of least resistance, adding to the saturation in that area. The effect will be much greater during heavier rain than shown in the video.

The very low head of water in the pit will never win the battle against the water flowing from the additional pipe connection which itself is velocity retarded by the direction of slope and intersecting flow from dp's 1-4.

FIXING THE PROBLEM

The stormwater system needs less water flowing through the pipes on the tank side and the water from the pipe currently supplied by dp 1-4 needs to flow faster to the kerb.

Is the following possible with your landscaping?

Connect dp5 to the stormwater pipe with the direction of flow heading downstream.

Have the existing tank's overflow connected to a new detention tank sited inline with the existing tank. A detention tank provides mitigation by discharging a limited flow of water through a small outlet fitted near the bottom of the tank. This will reduce the flow of water to the stormwater pipe when the 3,000 L tank is full. The detention tank would need to be a minimum 2,000 L and have a 32mm bottom outlet connected to the stormwater drain to provide a sufficient high velocity flow into the stormwater pipe.

Only plumb dp 3 & 4 to the tank and cap the pipe at dp3.

Reverse the direction of discharge and slope from dp 1 & 2 towards the kerb so that the stormwater flows faster.

WATER TANK AND FIRST FLUSH DIVERTER

What you see near the top of the vertical riser is a first flush diverter. First flush is the dirtiest and most polluted water that first comes off the roof.

The original installation had sealed wet systems which means that the downpipes remained full of water to the overflow level into the first flush diverters.

There is an Inspection Outlet (IO) at the bottom of one vertical riser, this has been installed to flush built up crud from the underground pipe but it cannot drain the pipe.

Whether it rained after the water in the downpipes and the vertical risers was lowered to the bottom of the IO or whether the pipes were full to the level of the discharge into the first flush, the first flush diverters will not fill with the first flush. If by some miracle the first flush from all five downpipes managed to get to the head of the queue, the amount of water collected by each first flush diverter would be maybe 8 litres each but miracles like water jumping the queue don't happen.

The first flush diverters also have a dripper which usually wastes 4-5 litres each per hour.

Fitting the first flush diverters at the top of the vertical risers was imbicilic and a waste of money and yield for the original owner.

Current installation.

Because the pipe (dp 1-4) now drains through the additional pipe connection after every rainfall, each downpipe's first flush will now drain to the kerb. The first flush diverters (still) serve no purpose.

Keeping first flush diverters fitted to vertical risers on 'proposed' installation.

No purpose.

VERTICAL RISER.

The top of the vertical riser should have the elbow fitted lower to increase the head and it should also discharge through a flap valve to prevent mosquitoes and other pests from accessing the standing water. This is not compulsory in your area like it is further north but it is good practice. From egg to adult mosquito takes about 12 days.

A late note about the vertical riser on the downpipe 5 wet system.

None of the downpipes have leaf diverters and the underground section of dp5's wet system has been slowly building up crud. The 104mm internal diameter pipe has a volume of 8.5 litres per metre. Even when diverting 128 lpm to the tank during a 1:20 ARI, the velocity up the vertical riser will only be 0.25 metres per second (128 litres only fills 15 metres of pipe).

This is insufficient velocity to flush/carry anything except light suspended sediment. This wet system diversion is very much sub standard.

LEAF DIVERTERS.
Wet (charged) systems should be fitted with leaf diverters at the top of the downpipes but again, they are not compulsory in your area like it is further north but it is good practice. The ICON Leaf and Debris Controller is the best of the current offerings.

SUBMERSIBLE PUMPS.

Many submersible pumps draw water from the bottom (see first photo below) and it will be a term and condition of warranty to have the pump positioned above the sediment layer but this is rarely done. The result is dirty water being vacuumed from the tank's floor and supplied to cisterns and washing machines.

You should check your pump to see whether it is sitting on the tank's floor and whether the floor around the pump is clean. If the floor surface around the pump is dirty, then the water pick up will be higher up. If it is clean, then the pump will be vacuuming the floor like in the photo below.

I know that this hasn't answered your question about additional drainage but you cannot move to that stage until the stormwater system has the capacity to exceed anticipated demands.

Thanks SaveH2O. I really appreciate your effort and time providing details.

This is being discussed with the Builder now. I will use this info while talking to them. I will update this thread as I get more details as this could help others as well.

Once again... thanks a lot.

An additional fact that you need to know to understand the system is that the friction loss expressed as equivalent pipe length of the pipe between the pit and the intersecting junction is about 46m. A 250 mm water level above the pipe's invert in the pit will provide a maximum flow rate of about 390 lpm provided that the intersecting water through the junction has good velocity and (I think) not act as a flow restriction that the current slow flow from dp 1, 2, 3 & 4 does.

The real life pit to kerb figure will be less than this because of the flow restricting and volume reducing entrained air produced from jetting water in communication from dp5 and dp6 to the stormwater pipe (the same cause of the bubbling you have seen in the pit) and also from the additional intersecting water in the junction and the remaining pipe to kerb, the reason why achieving good stratified flow velocity from dp1, dp2 & dp3 will be vital.

There will be some minor pipe slope between the junction and the kerb.

There would be no air entrainment generated by the 32mm valve because it would operate under full flow conditions but fitting an air release valve further along the storm water pipe will need consideration.

There are also a couple of other but similar variations to my initial suggestion.

NOTE: The surface level at the junction is 200mm lower than at the pit but we don’t know what the pipe’s depth at the junction is. The plumber however has said that the cam showed ponding in the pipe and it would be expected that the pipe depth at the junction was not as deep as the pipe level in the pit. No allowance for any additional (unknown) pipe slope was made in the head/flow calculations but some minor additional head should be reasonably expected.