Rainwater Harvesting

darkpool

ehhmmm SuDS built in the 1970s? i'm not convinced you really know what suds are all about. could you tell me what suds features you know about that were built in the 1970s? it's possible that your part of the country is 30 years ahead of everywhere else regarding suds, but i doubt it.

ehhmm the local water board knock on your door to see if you want to look down some sewers? be honest at the very least that is unusual.

regarding sewer flooding it is the intensity that is important. this is because roofs shed rainwater very quickly. if you have 10mm of rain in 15 minutes (a fairly typical 5 year return event) that would mean 1.3l/s for a 120m house. Your 133mm over two days means an average flow of 0.09l/s. You honestly think sewers can't cope with each house discharging 0.09l/s into them? that's little more than a dripping tap.

The two day 133mm storm flooding was for a river catchment. a short storm on agricultural land doesn't cause problems as the ground acts like a sponge and soaks up the water. it's prolonged rain that generally causes flooding in rivers.

so in short, a sewerage system will generally flood due to short term high rainfall events. a river floods due to long term persistent rainfall.

so if you do your calcs again with 10mm of rain what reduction in sewer flow do you get? i suspect if you do the calc you will see a massive drop in sewer flow.........

if you want to do some more "research" on google type in time of concentration

PS i bet a lot of people would be able to "engineer" a tower that could hold a 5 tonne weight how about something crazy like some old railway sleepers? at my work we balanced a 1000tonne bridge on some old sleepers

darkpool

zeupater wrote: »

Finally, regarding the reference to the BS standard on rainwater harvesting. Of course, I agree with what they say, they are the experts and I am not.

Z

yes we can agree upon that.

zeupater

darkpool wrote: »

ehhmmm SuDS built in the 1970s? i'm not convinced you really know what suds are all about. could you tell me what suds features you know about that were built in the 1970s? it's possible that your part of the country is 30 years ahead of everywhere else regarding suds, but i doubt it.

ehhmm the local water board knock on your door to see if you want to look down some sewers? be honest at the very least that is unusual.

regarding sewer flooding it is the intensity that is important. this is because roofs shed rainwater very quickly. if you have 10mm of rain in 15 minutes (a fairly typical 5 year return event) that would mean 1.3l/s for a 120m house. Your 133mm over two days means an average flow of 0.09l/s. You honestly think sewers can't cope with each house discharging 0.09l/s into them? that's little more than a dripping tap.

The two day 133mm storm flooding was for a river catchment. a short storm on agricultural land doesn't cause problems as the ground acts like a sponge and soaks up the water. it's prolonged rain that generally causes flooding in rivers.

so in short, a sewerage system will generally flood due to short term high rainfall events. a river floods due to long term persistent rainfall.

so if you do your calcs again with 10mm of rain what reduction in sewer flow do you get? i suspect if you do the calc you will see a massive drop in sewer flow.........

if you want to do some more "research" on google type in time of concentration

PS i bet a lot of people would be able to "engineer" a tower that could hold a 5 tonne weight how about something crazy like some old railway sleepers? at my work we balanced a 1000tonne bridge on some old sleepers

Hi

You're probably correct. The term SuDS seems to be one of those useless modern acronyms created to describe something which has been around for a long time. I can assure you that surface water drainage systems which are specifically designed to alleviate potential flooding from exceptional rainfall events dating from the 1970s exist locally. However, these systems are not rainwater harvesting systems, they are surface drainage floodwater control systems.

Regarding "ehhmm the local water board knock on your door to see if you want to look down some sewers? be honest at the very least that is unusual." ... yes they do. If you take time to check what I actually posted you would note that the access chambers are on my property. Even if there is a right of access granted in order to inspect or maintain sewerage systems it is considered courteous to seek permission prior to commencing inspection. The surface and foul water drains which cross my 1/4 acre front garden are the large concrete deep main drains, so of course they will need inspection, and of course, if someone is going to open up the chamber for a look after courteously requesting permission to access I'll look down the hole at the same time. Courtesy is not unusual, neither is the inspection of underground drainage.

You now seem to have changed tact. According to your latest post a heavy 15 minute downpour delivering 10mm of water is the equivalent of 1.3l/s on a 120sqm catchment, an event which the drainage system could easily cope with .... so why, if the existing drainage system could cope with this 5 year return event is there the risk of surface water causing foul water overflow/flooding which you originally postulated that rainwater harvesting systems would prevent ?

What needs to be taken into context is that the 15 minute/10mm rainfall events which you refer to are often a component part of more prolonged rainfall events, effectively a peak event within a storm. The point you seem to be missing now is that heavy rainfall prior to the peak event is likely to have already pre-filled any rainwater harvesting system, so when the peak arrives there is no storage capacity remaining and all of the 10mm will enter the drainage system. The Harvesting system will have little/no effect on potential flooding when this happens.

As interesting as this discussion is, I can see no way that you are open to logic, only postulation on narrow focus theory. There is no way on earth that you have supplied any logical point which would make me consider my position, so I can't see where this is going. I agree that rainwater harvesting is good from the point of view of reducing the requirement for reservoir storage, treated water, treatment works, treated water storage etc ... also it can save money, it could even show a payback without need for incentive if the capital investment is minimised, but there is little chance that it could be considered as providing a significant contribution to the prevention of foul water system flooding for the reasons given. Putting this in context .... I'd place any claim of a significant reduction in foul water flood risk resulting from installing domestic RWH alongside 'rent-a-roof' 3kWp solar pv systems saving £1000/year on electrity bills, a single panel solar thermal system satisfying 100% of annual hot water demand or a placing a magnet on my fuel feed pipe allowing my car to achieve 100mpg ...... not all 'green' people in terms of being ecological are 'green' in terms of gullibility.

Z

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Edit: Referencing the previous post, if you do attempt to be personal, please do so within context without clipping relevant text. The full context to be considered was ......
"Finally, regarding the reference to the BS standard on rainwater harvesting. Of course, I agree with what they say, they are the experts and I am not. However, looking at what you have quoted, what does it really say in the text which you have highlighted ? ... "It can also provide benefits for theattenuation of surface water run-off" ... I agree, it will, but they have not quantified the benefit, whereas I have by roughly calculating a 6% benefit ..... are you able to provide a link to any peer reviewed study or any other source which provides a domestic rainwater harvesting system benefit on surface water drainage from a domestic property which results in a quantifiable percentage greater than 6% in flood causing rainfall conditions, ie a months rainfall in 2 days ?"

.... which certainly changes the meaning !!

darkpool

zeupater wrote: »

Hi

You now seem to have changed tact. According to your latest post a heavy 15 minute downpour delivering 10mm of water is the equivalent of 1.3l/s on a 120sqm catchment, an event which the drainage system could easily cope with .... so why, if the existing drainage system could cope with this 5 year return event is there the risk of surface water causing foul water overflow/flooding which you originally postulated that rainwater harvesting systems would prevent ?

What needs to be taken into context is that the 15 minute/10mm rainfall events which you refer to are often a component part of more prolonged rainfall events, effectively a peak event within a storm. The point you seem to be missing now is that heavy rainfall prior to the peak event is likely to have already pre-filled any rainwater harvesting system, so when the peak arrives there is no storage capacity remaining and all of the 10mm will enter the drainage system. The Harvesting system will have little/no effect on potential flooding when this happens.

---

Edit: Referencing the previous post, if you do attempt to be personal, please do so within context without clipping relevant text. The full context to be considered was ......
"Finally, regarding the reference to the BS standard on rainwater harvesting. Of course, I agree with what they say, they are the experts and I am not. However, looking at what you have quoted, what does it really say in the text which you have highlighted ? ... "It can also provide benefits for theattenuation of surface water run-off" ... I agree, it will, but they have not quantified the benefit, whereas I have by roughly calculating a 6% benefit ..... are you able to provide a link to any peer reviewed study or any other source which provides a domestic rainwater harvesting system benefit on surface water drainage from a domestic property which results in a quantifiable percentage greater than 6% in flood causing rainfall conditions, ie a months rainfall in 2 days ?"

.... which certainly changes the meaning !!

where have i changed tact? you started saying that 2 day period storms caused the most flooding in sewerage systems. then i pointed out that most/ every person that actually knows what they are talking about would agree that shorter storms (typically under 1 hour) cause the most flooding in sewerage systems. if you think a two day storm causes the most flooding in sewers you're wrong. using YOUR figures of 83mm over 2 days for a 120m3 house means an average flow of 0.06l/s.

ehhhmmmm i do think 10mm of rain in 15 minutes can cause flooding in sewers. where did i say otherwise?

you really think a 15 minute storm/ 10mm event is part of a longer term storm? again this sounds like another "fact" pulled out of thin air. i would say that the ability for air to "hold" moisture is limited. if the air temperature drops suddenly you get an intense 15 minute storm. if it drops slowly you get a longer less intense storm. yet you think you get a 2 day storm that can also suddenly have the intensity of a 15 minute storm? that's an interesting theory.

i'm just surprised you admit that you are not an expert yet you still seem to think you know better than the experts. You even doubt anyone can build a tower that can hold a two tonne weight. I'm sorry if you find this personal, but I think your knowledge of drainage/suds and hydrology is limited to what you have picked up on google. but obviously you will come back and tell me if you have actually studied the subject or had any involvement in it?

darkpool

just to show no hard feeling. using your example.

120m2 house 10mm of rain = 1.2m3
storage available = 0.5 m3
runoff 0.7m3

so the rainharvesting means a 42% reduction in water going to the sewer.

zeupater

darkpool wrote: »

where have i changed tact? you started saying that 2 day period storms caused the most flooding in sewerage systems. then i pointed out that most/ every person that actually knows what they are talking about would agree that shorter storms (typically under 1 hour) cause the most flooding in sewerage systems. if you think a two day storm causes the most flooding in sewers you're wrong. using YOUR figures of 83mm over 2 days for a 120m3 house means an average flow of 0.06l/s.

ehhhmmmm i do think 10mm of rain in 15 minutes can cause flooding in sewers. where did i say otherwise?

you really think a 15 minute storm/ 10mm event is part of a longer term storm? again this sounds like another "fact" pulled out of thin air. i would say that the ability for air to "hold" moisture is limited. if the air temperature drops suddenly you get an intense 15 minute storm. if it drops slowly you get a longer less intense storm. yet you think you get a 2 day storm that can also suddenly have the intensity of a 15 minute storm? that's an interesting theory.

i'm just surprised you admit that you are not an expert yet you still seem to think you know better than the experts. You even doubt anyone can build a tower that can hold a two tonne weight. I'm sorry if you find this personal, but I think your knowledge of drainage/suds and hydrology is limited to what you have picked up on google. but obviously you will come back and tell me if you have actually studied the subject or had any involvement in it?

Hi

Your theory that a heavy rainfall event of 10mm in 15 minutes is flawed. This is a peak precipitation of 10mm within 15 minutes within a rainfall cell, and I actually believe that you know that this is the case yet are not prepared to accept that you position is unsupportable. On your latest figures you would need to accept that rainfall at a rate of 2.5mm for 30 minutes before peak would fill the rainwater harvesting system to overflowing and any peak reached after this would simply be dumped to drainage.

Please try to stop obfuscating around this subject by quoting a peak 1 in 5 year event threshold as being the total amount of rainfall in a storm condition ... it is the peak, with further precipitation either side of the peak. It would be very unusual for there to be no rain followed by exactly 10mm in exactly 15 minutes, followed by no rain. Also, why concentrate on a 1 in 5 year event, why not a 10,20 or 30 year event ?

If there is a vested interest in convincing readers that one side of the argument is correct and one isn't, believe me, it's not on my side of the debate. However, I'll leave it to others to decide whether someone who claims to be a Civil Engineer, has had direct involvement in SuDS and has recently been looking at a RWH system on a farm (? sales ?) would have any interest in convincing people on a 'Green & Ethical' forum that RWH would 'Save the Whale' (yes I am that old), or, more appropriately, at least the fish in our rivers !!

I agree, I am not an expert, however, I am basing my position on simple logic, reported events, and personal experience. The response always seems to be based on exact figures from a textbook or minimum standard specifications, out of context quoting, or misrepresentation of the content of previous posts which would suggest that the alternative view is also not being proposed by an expert, however, I believe that logic still stands well on my side of the debate.

Z

darkpool

zeupater wrote: »

Hi

Your theory that a heavy rainfall event of 10mm in 15 minutes is flawed. This is a peak precipitation of 10mm within 15 minutes within a rainfall cell, and I actually believe that you know that this is the case yet are not prepared to accept that you position is unsupportable.
Z

i'm sorry but i just don't understand what you are saying. what is a rainfall cell?

i work in road construction. have i ever said that i sell RH systems? tbh i doubt you would get many civil engineers selling RH systems. however i used to analyse sewerage systems for a well known english water company. my job was to design ways that would reduce flooding from sewers. i usually found that reducing the areas in the network would reduce flooding from sewage systems. that's why i can say with a fair degree of certainty that rainfall harvesting will reduce flooding. i can also assure you that short term storms cause the most flooding.

As I have mentioned previously I have designed SuDs. Typical suds features I have designed include filter drains/ swales and attenuation ponds. I also have extensive experience of drainage design using "windes" and "hydroworks"

Furthermore I also have an MSc in water resources. I think it fair to say out of all the posters, in this thread, I am the most qualified to discuss flooding from sewerage systems.

If you feel that the BS standard is wrong to state that RH reduces flooding I suggest you contact them and say so. If you are lucky they will send you some pens/ balloons/ posters and a t shirt to thank you for your contribution

zeupater

darkpool wrote: »

i'm sorry but i just don't understand what you are saying. what is a rainfall cell?

i work in road construction. have i ever said that i sell RH systems? tbh i doubt you would get many civil engineers selling RH systems. however i used to analyse sewerage systems for a well known english water company. my job was to design ways that would reduce flooding from sewers. i usually found that reducing the areas in the network would reduce flooding from sewage systems. that's why i can say with a fair degree of certainty that rainfall harvesting will reduce flooding. i can also assure you that short term storms cause the most flooding.

As I have mentioned previously I have designed SuDs. Typical suds features I have designed include filter drains/ swales and attenuation ponds. I also have extensive experience of drainage design using "windes" and "hydroworks"

Furthermore I also have an MSc in water resources. I think it fair to say out of all the posters, in this thread, I am the most qualified to discuss flooding from sewerage systems.

If you feel that the BS standard is wrong to state that RH reduces flooding I suggest you contact them and say so. If you are lucky they will send you some pens/ balloons/ posters and a t shirt to thank you for your contribution

Hi

I suppose it's time for me to turn the tables and advise you to Google storm cells and relate this to rainfall .... I'm actually quite surprised that you haven't already done so considering the relationship between rainfall, storm cells and water resources.

Regarding BS being wrong, I have not stated this. Again you are misrepresenting what has previously been posted, which related to there being no data provided by yourself to support a BS source text which you quoted. To ensure that you are fully aware of what you are referring to I will re-post the exact wording for a second, and hopefully last, time .....

"Finally, regarding the reference to the BS standard on rainwater harvesting. Of course, I agree with what they say, they are the experts and I am not. However, looking at what you have quoted, what does it really say in the text which you have highlighted ? ... "It can also provide benefits for theattenuation of surface water run-off" ... I agree, it will, but they have not quantified the benefit, whereas I have by roughly calculating a 6% benefit ..... are you able to provide a link to any peer reviewed study or any other source which provides a domestic rainwater harvesting system benefit on surface water drainage from a domestic property which results in a quantifiable percentage greater than 6% in flood causing rainfall conditions, ie a months rainfall in 2 days ?"

It must be quite easy for one as highly educated in this particular field to provide quantifyable data to support your position to someone who is obviously not, but simply relies on a logical approach, as some careers demand.

Z

darkpool

this is a money saving site. RH can save money in certain situations.

this is the "green" area. RH does reduce flooding, it also reduces water being taken from aquifers etc.

RH can also mean that you can flush the toilet when all your neighbours are queuing up at a water bowser.

i find your posts dull, i'm not going to respond to any more unless you find something interesting to say.

Poosmate

I was going to post but I can't be @ssed now but having gone through your (Zeup and Dark) stupid childish bickering I have to post in order to make it worth having read it!

Dark, I was with you on page one but alas even before all the arguing I knew it was only wishful thinking. Yes I believe that if every household in the country had a waterbutt in their gardens it may, just may, prevent the inevitable once in a blue moon when all the butts in the area were empty and the rainfall was just about enough to cause a minor flood. Any more prolonged rainfall (enough to cause a flood) would just mean that it happened 10 - 15 mins later than if there had been no water butts. Once all the butts are full the same amount of roof runoff goes into the sewers.

Regarding surface water sewers, they would be the responsibility of your local council not your waterboard. If there is a surface water sewer in your road the gullies in the road will be connected to them - it's the council's responsibility to (within reason) maintain the drainage of rainwater from the roads. If there is no surface water sewer, the gullies are connected to the foul sewer. Very often, localised flooding occurs (in older parts of towns or cities) because either the main foul sewer is blocked or lacks capacity.

I must get a waterbutt one day.

Poo

ETA: Gullies should be connected to surface water sewers but in the city I used to work many of the surface water sewers were not shown on any of the plans the council had access to so we'd occasionally find a surface water sewer (usually because a manhole had been stolen or damaged and we were trying to find out who was responsible for said sewer).