The Brew Cabin

Hi Just discovered this (fantastic) forum and web site and have a real challenge for you guys that I really hope you can help me with.

We live in an old (350 years) stone built house (no dpc). Water supply is from a well (important for later) and drainage to a septic tank and a stream for rain water. The stream flows in winter months only and runs through the garden. An extension was built on the property - about 30 years ago I think – which extends to within about 5 feet of the stream (the ext. has dpc). As the stream flows past the extension, it passes through a calvert for 40 feet or so. The calvert starts approx. where the extension is.

Ok, so that’s the layout, here is the problem. We have some damp issues throughout the property with extensive problems at the front (where ground levels are higher) and minor problems at the back where the extension is. I had some specialists inspect the damp and they all suggested that to start with I need to lower the ground levels outside as they were too high. This made sense so I hired a mini-digger and dug a trench around the entire property including the extension. I intended to fill this trench with shingle to improve drainage.

This was last August and over the following winter months, as the stream started to flow, I was concerned to see a moat forming in the trench around the extension near the stream. Its still like that now with water standing against the brick foundations of the extension up to a few inches below the French windows door cill – pretty much ground level before I dug the trench. I don’t know whether the moat is due to the stream seeping through its banks or the water table. If I were to pump the water away and its there because of the water table, then could this affect the adequacy of the water supply from my well? And presumably, the pump would be running nearly all the time and would eventually fail anyway. Do you have any suggestions? I know this is tricky as I had the environmental health officer (responsible for waterways etc) around to give advice and he couldn’t think of a way to resolve the problem. I suggested extending the culvert back another 40 feet to eliminate problems with the stream but their opinion was that this probably wouldn’t make any difference as the water would penetrate from further up the stream ….but to be honest, they seem unsure.

I know I’m in danger of writing a book here as its difficult to describe and I have so many questions of this nature but any help you can give me with this one would be really gratefully received. I have pictures of the problem but am not sure whether I could post those. I could email them if it would help.

Ta muchly, Tim.

have you thought about frence draining with terram,say half way through you garden between the stream and moat(house)this can soak up water and re direct it?im no pro but it's a idea??or a soak away chamber ?

The fact that you use a leach field to deal with the output from the septic tank suggests that you must have ground that is reasonably amenable to drainage and isn't a heavy clay. This being the case, it follows that the moat effect could only be caused by an elevated water table.

So, is the level of the moat higher than that of the culverted stream? The natural groundwater regime would, under natural circumstances, use the stream to carry away any "excess", but I wonder if by culverting the stream, the ability of excess groundwater to enter the stream has been restricted or even denied?

If you converted your 'moat' into a large collector drain which was then connected to the culverted stream, or had its outfall further downstream, beyond the culverted section, would this reduce the groundwater level adjacent to the property?

Obviously, I'm working at a disadvantage because I can't see the site to assess ground levels and potential gradients, but, from what information I have, it seems that culverting the stream may have had a detrimental effect on the water table level in that area and, by extending the culverted section, you would possibly exacerbate the problem. The most obvious solution, given that un-culverting the stream is not feasible, would be to provide ingress to the culverted stream at one or more points along its length.

Does that make sense?

Hello again,
Thanks both for your responses. I don’t know what terram is – I seem to recall reading about it somewhere (maybe even this site) but I’ll find this out anyway and look into it. I did think about a soak away but I thought there would be nowhere for the water to flow away – presumably, as soon as I dug a soakaway, it would fill with water to the same level as the moat.

Regarding your comments about the ground you are right, its not heavy clay – though there appears to me to have a significant clay content; but from a visual inspection of water levels, it appears to me that the moat is slightly lower than the current level of the stream and as heavy clay is not present, does this not suggest that water could be seeping through the stream banks to fill the moat?

It’s really interesting what you say about the possibility of the culvert restricting drainage of excess water into the stream, I hadn’t thought of it that way but I did think of draining the excess water into the stream further downstream. The only problem with this is that the gradient is slight and to drain the moat would mean laying pipework starting about 18 inches down and applying a fall of, say, 1 in 60 or 80 would mean a long pipe laid under garden and stone patio or alternatively a pump. I don’t fancy either of these solutions much but if that’s the only way…...

What are the problems with leaving the water where it is – up against the brick foundations? Should I refill the moat? – presumably, the problem has been there for years but I just didn’t see it until I dug the trench.

Finally, if I do manage to get rid of the moat, do you think it would have an effect on the adequacy of the water supply to my well – it actually dried up during the long dry spell over the summer and running out of water is no fun – believe me! The well is some 50 metres away from the moat.

Thanks loads for any more ideas/comments you may have.

Tim.

Terram is a brand of geo-membrane that has a thousand and two uses (at the last count). However, I'm not sure a soakaway will work - if the ground is already saturated, there is nowhere for the water to soak away.

The flow pattern of the groundwater, whether it's moving from moat to stream or stream to moat, could be ascertained by using tracing dyes, but my guess is that it's a two-way affair, with water moving in both directions depending on water table level at any given time. Consequently, I would regard any finding from a tracing exercise with caution, as it only reveals the regime flow direction at the particular time.

With regard to falls on possible pipelines, you can get away with much shallower falls than 1:60. You could, possibly, use a fall as shallow as 1:150, depending on site layout. Basically, as long as there is some fall between the moat and the proposed outfall, then any pipeline installation would provide a useful escape route for any excessive build-up of water in/around the moat.

Backfilling the moat does not prevent groundwater lodging against your walls. It means there is less space for groundwater, but it will still be there unless you backfilled to 100% compaction with an impervious material. And losing the moat should have no effect on the performance of your well. If the water is moved out of the wmoat, it has to go somewhere else, and, assuming that the water level in the well follows that of the water table, then backfilling the moat should have no effect. It's not unusual for your well to run dry during prolonged dry periods - this is a result of the local geomorphology, the shape and make-up of the ground around your patch, and nowt to do with whether there's an open trench near your walls. :)

If you were to install some form of drainage at a level of, say, 750mm below ground level, then there's no way the water level in the well or the moat could rise above that level to compromise your foundations, but, just as importantly, there's no way the drain could empty the well, as it's effects are restricted to that upper 750mm layer: it has no effect on anything deeper.

I think I'd be a little worried if (local) groundwater was getting into the well. Surely one of the advantages of wells is that the water is coming from an aquifer, and therefore has a degree of filtering. Indeed there is a lot of fuss shold an aquifer become polluted as they are very difficult to clean.

I think the only answer is a long trench or pipe from the lowest point of the moat to a lower downstream point in the stream.

Welcome to the family of moated property owners however!

Thank you to everyone for your comments and suggestions. I have a structural surveyor coming soon to look at the situation too but it seems like I'd better start digging up the garden (even more) and start laying that pipe. The wife will be pleased!!! :)

Thanks again.

Let us know if the surveyor comes up with owt.