Drainage advice sought for a soft and wet field.

J

jonjo

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Can any one offer advice on this conundrum.

In the near future I plan to build a house. Someone looked at the land and said it was very soft under foot and very wet. This may make it difficult to provide an adequate treatment system and also standard foundations may not be adequate. I was told the ground conditions should improve if the land was sufficiently drained.

I therefore have a number of options:

Should I proceed with percolation tests and a trial hole?

Should I drain the land before any such tests? If so what area needs draining? The field is about 10 acres, but of course the house will only be on a very small area. So do I need to drain the whole field or just the area the house will be built on and the area surrounding the sewerage/septic tank area.

Thirdly, what does it mean to drain the land and how much does it normally cost per acre?

Any information would be gratefully received!
jonjo
 
Hi Jonjo,

Not sure if this thread will give any advice but worth a read.

This might be of interest also.

Best of luck with the new house.
 
Hi jonjo,

Draining the field may help to dry the ground out a bit but this probably will make little or no difference to any problems you may have with your house.

The fact that the field is wet may be due to many reasons such as
  • the aspect of the field (i.e. is it low lying). If there is high ground surrounding it then all the rainfall may be naturally accumulating in the lowest point ie your field
  • the outflow potential from the site may be poor. That is you may drain the field but unless there is the potential to get the drained water off the site (into a main drain/ stream or river) then your drains may be useless. You may need to clean out a main drain to achieve this which may mean the cooperation of your neighbouring landowners is required if the main drain runs through their land.
  • the soil may have poor percolation to start with. In very heavy soils (with high clay content) the soil will act as a sponge for water and may not release this water that easily. It will be difficult to improve drainage in this case without spending a lot of money.
  • the water table (level of ground water under the soil- you tap into this if you are digging a well) maybe high. Drainage may help here insome cases.
For the percolation test if your soil has poor percolation or the water table is high then this will be picked up when the trial hole is dug from looking at the soil itself (the soil will show this through colour changes & water lines)- I doubt if having it drained will have any great influence on the results.
For your foundations again the soil and its load bearing capacity will determine how deep you need to go to get solid ground for the founds.
If the proposed site of your house is wet it would be advisable to dig a drain around the proposed site boundary to try and minimise the amount of water coming onto the site (important at foundation stage and right throughout the build). Again the effectiveness of this drain will be influenced by the points above. There is no point pulling drains through the proposed site itself as you will only end up breaking them when you dig your foundations.

My advise would be to get a local site clearence expert/ diggerman out on site and get his opinion. Talk to neighbouring farmers and get the name of a drainage contractor and get him out on site for a second opinion.

The cost of drainage is a 'how long is a piece of string' question but I would reckon that taking into account the price of hiring a tracked digger+ operator (+ one other person (you??)) , land drainage pipe, drainage stones you would be talking about €500- €800 per acre. Then if you drain the whole field you will need to reseed it - further costs.

Hope this helps,

laragh
 
Thanks for taking the time to reply. Both replies are very informative.

Laragh - The field actually backs onto a lake with a climb from the lake for about 100 metres. I plan to build the house at this point. From there the hill slopes very gently and the land is almost horizontal at the road a further 300m away. There is no connecting land that is higher. There is also a ditch inside one side of the field that could be used to channel water to the lake from cross drains.

I think therefore points one and two should not be problematic. As to your other points I will have to find out the clay content and the level of the water table.

Another point that has come to mind is that I will have to make sure access is adequate to the site for lorries and heavy machinery. So I will have to deal with the soft and wet ground from the road all the way to the site!

I have heeded the advice.
best
jonjo
 
sueellen said:
Hi Jonjo,

Not sure if this thread will give any advice but worth a read.

This might be of interest also.
Click to expand...

Brilliant site Sueellen
Once heard of a fellow who dug his test holes a bit deep put in some stone and topped it off with clay soaked great on day of test, but it could have went the other way and drew the water into the hole, I'd say drain it now and keep the drains deep,
 
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