Easy. From a bit of 1/4″ hardboard or something like that, cut a shape that marries up to the profile of the cladding about 6 feet off the deck. This piece is a pattern. Now using the first one for a pattern, cut out as many pieces as there are “hollows” along both sides of the building. Along the sides of the building fasten a 2×4 with 1/4″ per foot fall towards one end of the building. The 2x with obviously span the hollows. Mark its intended location on the building by using a string and a water level. In 200 feet you need a difference in elevation of 50″, call it four feet, so at one end the 2x is 6 feet off the deck, at the other 2 feet. Before you fasten the 2x to the building, bevel the top edge so it will be horizontal after the 2x is mounted.
Mount with lag screw from the inside. Now mount all the little parabolas in all the little hollows by screwing them to to top bevelled side of the 2x with countersunk wood screws. Then lay a 4″ glass tape half on the hardboard, half on the cladding and resin in place with polyester resin (“lay-up resin” as used for boats). Mount a regular gutter on the vertical outboard side of the 2x. Then, overlapping the tape and the mounting lip on the gutter, lay down a light glass cloth such as “PowerVeil” and resin in place. Make sure you get “total wet-out”. Then, when the lay-up resin has cured, give it a coat of gel-coat resin. The gelcoat is not inhibited by air, the lay-up resin is, which means that the gel coat is required to get a tack free surface. There you go. Collect the water in a cistern at the low end. Don’t forget a pump – 200 x 80 feet can yield a lot of water in a hurry :-)
I was wanting to mount the gutters along the ground. If it’s along the ground, some flashing could be slipped under the bottom edge of the corrugated building tin to channel the water into the gutter. But I can’t think of a way to keep the dirt out of the gutters. Keeping dirt out is a big thing – isn’t it? The dirt blows like crazy around here. Or, could the dirt/mud run into the sump, then be pumped out during the first few minutes of rainfall? The 1/4″/ft. slope mentioned seems like a lot. Is the 1/4″/ft. a pretty firm rule? Maybe I could work from both ends towards the middle and put the sump there. That would give me a 2′ difference in height, but even that would be difficult to manage if running the gutter along the ground. What kind of gutter could I use for a ground level setup? Don’t think Home Depot or Lowes gutters would do. Maybe some sort of 1′ or 2′ diameter drainage pipe cut in half lengthwise?? Anything else out there you know of? Keep those ideas coming. I’d like to put this thing in this Spring.
This is for irrigation water? Will you be able to place the top of your storage tank below ground level at your collection building? Or, do plan to pump into your storage tank? The two ideas for attaching gutters to the sides of your building sound good to me and will keep your water cleaner. You can consider slightly sloping the tank and putting a drain valve on the low side and taking your supply out of the high side. Then, your tank could serve as a settling basin. If your are going to pump into the tank and need a sump, then that sump can serve as a settling basin. The sump could be as simple as an un-covered hole in the ground, perhaps with plastic lining.
I don’t think that there are any hard rules for gutter parameters: 1) gutter size 2) gutter slope 3) gutter lengths (between collection points) The better you do on each parameter, the more rain you can capture during an intense rain event. But, minimal parameter values can capture all the rain during light rainfall events. I have seen numbers like 4″ gutters, 1/4″ per foot slopes, and 40′ gutter lengths as “rules of thumb”. Living in a 30″ annual rainfall area and having more roof area than I need, I chose to to use almost no slope, 3″ gutters, and downspouts spaced at 60′. I lose rain to gutter overflow during heavy rain, but still catch far more than I need. I guess in west Texas, you want to catch everything you can. You can decrease the total drop of your gutters while maintaining slope by having shorter gutter runs (more collection points). My guess is that 3″ PVC stand pipes under gutter downspouts leading into a 4″ PVC collection system is good for up to about a 10,000 square foot building. I further guess you might want to have a stand pipe collection point for about every 500-1000 square feet of roof area.