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Posted: Tue Jan 31, 2006 5:13 am
by knightwatch
We have a winter spring that has surfaced in our new indoor riding arena. It is not huge, but enough to cause standing water when the water table is high. Wondering what type of drain would be best for this- any ideas? Thanks!
Posted: Tue Jan 31, 2006 3:51 pm
by TheRobster
Some sort of filter drain would seem appropriate. Filter drains are basically trenches in the ground that are filled with gravel and are wrapped in a permeable geotextile membrane to prevent the gravel becoming clogged with fine silts. There's also usually a perforated pipe running along the base on the trench which acts to convey the water away.
Alternatively, if you have the space you could always build a swale, which is basically a small (usually grassed) depression in the ground that acts as a channel to convey the water away.
Another issue is what you do with the water. If you are in the UK, it is highly unlikely to can drain to an existing sewer system because sewerage undertakers very rarely accept what they see as "land drainage" into their system. It sounds as though this would be classed as land drainage and so you may have legal problems connecting to existing systems. If there is a convenient nearby watercourse that you can drain to you should have less problems. Alternatively, you could drain it to another area of your own land and into a soakaway (assuming ground conditiond are suitable for this to work).
There is further information on all of these techniques located on this website somewhere if you need more information. 
Posted: Tue Jan 31, 2006 5:02 pm
by knightwatch
Thanks!
Posted: Wed Feb 01, 2006 1:46 am
by Suggers
Ingrid-
Would be interested to know your surface finish - sand, re-con rubber ? Also, base and sub-base of ground under surface of school.
As you know , horses constantly training over same line of run, produce incredible force.
I feel that any drain-run crossing the horses path, should be deep and probably reinforced above.
Good news - at least you're inside!!
Posted: Wed Feb 01, 2006 7:01 am
by knightwatch
We have not installed the base or footing yet- we just put up the arena this fall. We had been waiting for the arena area to dry out before working on the base, and footing. The subbase is clay, slick and long to dry! We live in Oregon, USA, and have been having incredible rain in a short period of time- I think 11 " in the month of January (our normal is about 5). I spoke with my footing guy tonight- we are going to go ahead with putting in the base and footing- he will take out any soft spots, and we will see what we have. The "spring - like " area is pretty mild (so far!) for a spring, but we should know more once we are in, I think. His concern was if we put a drain in now, his compaction machine would crush any pipe. I also agree with what you stated, about forces generated by 1300 # + animals- drains need to be deep if present!
We shall see how it goes!
Thanks-
Posted: Wed Feb 01, 2006 10:13 pm
by TheRobster
Yes I should have mentioned that. If you need to put in a land drain in an area that's going to be used by the horses then you need to take the additional load into account. Alternatively you could use a design that doesn't have a pipe. The filter drains I mentioned previously could be adapted so that they don't use pipes, although they ideally should as it allows the water to drain away more efficiently.
However, if pipes are out of the question then you could just dig a trench in the ground through the problem area and fill it with gravel that is wrapped in a permeable geotextile membrane. The water will flow into the gravel trench via the membrane and through the pore spaces in the gravel. You would have to lay the trench in such a way that there is a gradient along the structure and the water will flow downhill through the trench. You can lead the water away to another area using this method, although obviously you will have to create some kind of outfall from the trench once it is safely away from the arena area.
You will also need some cover on the trench...probably at least 900mm of backfill above the top of the gravel filled trench. This will spread the load from any horses running about on top.
It's just an idea though.....it's hard to be more specific without actually seeing the site!
Posted: Wed Feb 01, 2006 10:17 pm
by TheRobster
Another problem I can think of would be ground compaction. With horses running around on the surface the ground is likely to become heavily compacted and this will retard the flow of water. In this case, if you do build a land drainage trench, it would probably be a better idea to build several small ones spaced at regular intervals rather than one large one.
Posted: Thu Feb 02, 2006 12:02 am
by Suggers
I think the Robster's cracked it - a herringbone lay-out is the way to go. Quite a standard solution when building a menege here in the UK. 11" in a month? - bloody hell, I thought it was wet here - and you're in clay....
Posted: Thu Feb 02, 2006 5:33 am
by knightwatch
Yes, we have lots of clay...the building went up in the rain, so we had lots of clay mud....it is finally starting to dry....I may actually get to ride in the arena sometime this year.... 
Thanks for your help!
Posted: Fri Feb 03, 2006 9:52 am
by Suggers
Just a quick note - have remembered there's an interesting thread on building schools, in the forum archive, under Drainage. Worth a look.