Howdy all. This is my first post, and I'm looking forward to being a participant on this forum. I completed my PDC earlier this year, and I'm pretty excited about buying a property to design and develop.
That said, I have a question about a property that I'd like to buy.
The property has a history of being water rich. Historically, it has had two or three "seep" springs that produce enough water year-round to keep three decent-sized ponds full despite less-than-ideal catchment and a lot of direct sun (in Brazil). Over the past 5-10 years, however, these springs are becoming less and less productive. This diminishing-spring trend isn't uncommon in the region I'm in. Most people think the reduced rain totals (and in some cases drought) are responsible for this trend. But a few have noticed that springs drying up seems to be corresponding to the increase in eucalyptus farming. (Massive Eucalpytus monoculture.)
Either way, the property I'm considering sits adjacent to a large Eucalyptus farm, and the springs are about 75 m from the property line where the Eucalpytus begin. (***EDIT: I deleted the comment about the difference in elevation between the Eucalpytus farm and the springs -- it was inaccurate. The bulk of the farm is several meters higher than the springs in elevation, but the closest trees are about even with the springs in elevation.)
An ideal place to put a swale on this property is (roughly) somewhere between 20-35 meters uphill from the springs. My questions:
(1) Is this distance between the springs and the swale acceptable? Basically, is it close enough to benefit the springs rather than (somehow?) harm them? Is a different distance between them and the swale better? If so, why?
(2) Is the Eucalyptus farm close enough to the springs to be responsible for their reduced productivity? If so, even if I were to swale this area, would I be fighting a losing battle?
(3) Is a swale even the best way to deal with this situation? The prior owner has already planted trees around and uphill from the spring in an effort to protect it. Is that the right strategy? Should that be used in conjunction with a swale? Etc.
I look forward to hearing what all of you have to say. I've been lurking here for a while, and I admire you folks.
To me it seems that your questions are not all that easy to answer, maybe that's why you did not get a reply so far. I don't know for sure, but my best guess would be that the springs dry up for a number of reasons. The eucalyptus farming might indeed be one of them, around here whole swamp areas have been dehydrated in the past using these trees. Added to that probably the land is dehydrated more because of drainage and loss of topsoil, vegetation cover etc. Then finally if your local climate is getting dryer, it probably also means that rains fall further apart in time and that rainfall is more extreme, meaning that relatively few heavy showers lead to more runoff than a lot of mild showers. Still all of that together means basically only one thing: the soil holds less water and looses too much of the rains that do fall, because a lot of it simply runs off and disappears.
Are swales the solution? It depends I think. Only one swale above the springs probably won't make a big difference. If the whole area above the spring gets swales maybe it helps more. Planting trees also helps, getting a thick layer of leaves and vegetation under these trees will also help. Basically anything that stops the runoff and gets the water to infiltrate in the ground helps. Even if it would not be enough to get the springs flowing again, it still helps the land.
In answer to your questions:
1. I don't see how a swale above the spring will harm the spring. I think it will always have some positive effect.
2. See above, you might fight a loosing battle with regard to the spring, but your swale will still have positive effects.
3. Both planting trees and swaling have a good effect and they can easily be combined. Swales are 'meant' to be tree growing systems as well.
Make sure you estimate correctly how much water your swale will catch in heavy rain events, so you dig it the right size. Also make sure that if it receives excess water that you have a spillway to let that water go without doing damage.