ditches/swales/furrows

My 2 acre plot drains towards the area I intend to cultivate and the area floods yearly. However in the summertime we can go weeks without rain. After learning about swales I started digging ditches during the last rainy period to direct the flow better.

I'm imagining having a network of ditches that allow the water to sit below the line of the cultivated soil during wet periods. During dry periods I'd like to fill them like furrows. How far apart should I place the "branches" of this ditch system to keep the raised areas watered? I've read that capillary action can only move the water around 12 inches reliably. I've read that swales can be like 20 feet apart however.

Dusty, welcome to Permies! Your situation sounds similar to my husband's and mine. We're doing something similar with a swale system to capture rain to keep our land hydrated during our annual dry spells. We're following Bill Mollison's guidelines. Here's a quote from his Permaculture: A Designer's Manual, page 168

"The distance between swales (the run-off or mulch-planted surface) can be from three to twenty times the average swale width (depending on rainfall). Give a useful swale base of 1-2 m (4-6 feet), the interswale space should be 3-18 m (12-60 feet).

He also mentions that the wicking action gradually extends its area of hydration over several years.

My lower 2 acre field is classified as a 1 foot flood plain.  It has a natural Z shaped swale pattern that fills every winter but dries out during 3 to 4 month summer dry season.  I begin filling the swale ponds with mown grass as the summer progresses so that the ground does not dry out completely.  When the swale is full during the winter I rake the soaked grass, that is starting to break down anaerobically, out and use it to mulch planting areas.  In the spring then the swales are open ponds for the frogs to propagate.  So I have almost no mosquitoes.   The depth of soil on the clay keeps increasing.  Even though it has been 4 months since the last soaking rain as I am cutting the dry grass there is some green grass beginning to come up.

I'm also not totally sure about swales, how to dig them, how far they should be, how they are related to hugelkultur. Could the berms of the swales be hugelkultur beds? Reading a book or 10 doesn't help as much as getting your hands dirty and learning from your mistakes OR having some experts with experience teach you in person, if you want to get it right the first time. There is an earlybird special on the Wheaton Labs PDC - ONLY until this Sunday, though.        
                                                         
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