Posted: Mon Feb 12, 2007 5:20 pm
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.
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.
