Rising ground water level - Winter field flooding

[plantsman]

I have a real problem with rising water levels every winter. I am a specialist horticultural grower and was recently given permission to erect a commercial glasshouse in a new site which was previously agricultural land. The field is flat( there is a microscopic incline) as is the surrounding area and is located in what must have been a flood plain/river bed thousands of years ago. The river is about 3/4 mile away and floods into the ajoining fields every winter but we are far enough away to not get affected directly.The soil/subsoil has about 6-8" good loam topsoil then you hit sand with a touch of loam for about a foot then you hit a mix of pure sand and with small streaks of what looks like yellow/orange clay.It causes the sand to become viscous and gluey when wet and behaves like when you were digging holes on the beach as a kid.When it dries it is rock hard and greyish and needs a pic to get through it.The glasshouse( 20M x 30M) went up last year and i set about putting in a drain, T shaped across the diameter/centre of the G/house (20M the full width) by 15 M (half the length) at the wetter and very slightly lower end and used yellow soak away polypipe.I know i will need a soak away or perhaps i thought of pumping the water to a small pond/collection area with a liner if the gradient isnt enough for a soak away. The water level started rising dramatically in November/december after a month of heavy rain even when we pumped out the existing collection point. So now i have dug a 3.5 to 4ft deep & 2ft wide trench along the 3 outer glasshouse walls at the wettest end so that there is a protective drain for the soil inside the drain perimiter. This fills up with water daily and is pumped out using a gravity switch on the sub/pump.However if i dig a hole in the centre of the protected area end, the water fills it up within hours and is only six inches below the surface( & rising!). What worries me is that if i also dig a hole 1 metre from the drain inside the ring its also fills up but maybe 8 inches below the soil surface yet its only a few feet from the drain. After reading the site (superb) i thought that the water was trapped in the topsoil and prevented from draining through by the clay/sand mix layer some 3 ft below the topsoil surface but am now not sure if the water is coming up from deep below as well as from the sides.The whole glasshouse now looks like a bomb site and i am desperate to save many really rare breeding/production plants that have been planted directly into the ground. I am not a professional works engineer/landscaper like yourselves or a really accomplished Mr B&Q ( the wife wont let me put shelves up!) but am familiar with small commercial plant nursery and horticultural related works/ installations and am competant enough at some of these tasks. However i am out of my depth here and currently am not in a strong enough financial position to get a professional in. Either the volume of water is too great for the size of drains i have dug and the whole floor needs to come up and the classic french drain needs to be installed, but remember at the moment in a glasshouse 20 m wide by 30 m long which has a drain in the wetter end of 20 metres wide by 15 metres at each side along the inside glasshouse perimeter; Plus the original T shaped drain i installed last summer makes nowhere in the wetter end further than 5 metres from a drain.
I should have noticed the marsh grass with roots like rope as a bad omen when i looked the site over but it was dormant and the field was( and is every year) bone dry in June/July till Nov. Any help would be really great.

[flowjoe]

I think you should try www.kingcanute.com or stilts r us.com

I can`t see how laying drainage lower than the ground water level on a flat site will help you, and you may need one almighty pump dependant on the area you are draining and thats if you have an outfall to aim at.

You will have to get the site looked at by either a drainage expert or a local farmer who may have some knowledge of area that can help.

[lutonlagerlout]

you wont like this much guy,but if the water table is that high and the ground that flat then can the glass house not be elevated by say 300mm??
the fact that there is sand there indicates there has been a water course or flod plain there at some point
TBH i think you need to get some expert on site advice,better to lose a little money than lose it all
cheers LLL