I definitely have a lot more to learn about swales, keylines etc, but we're currently considering buying a property & I need to quickly get some idea about how the swales & access would be done before potentially putting in an offer. (I guess I'm pretty @*# scared about making the wrong decision here, never bought anything more than a laptop in my life & don't have much savings!)
The 9 acre property is a north facing slope starting from the dirt road at about 80m & steadily dropping over about 200m to 40m at the winter-creek (& then rising up the south facing slope from there - but most of the property is the north facing slope & the south facing is native bushland so we wouldn't touch it much, at least for quite awhile. Note we're in the southern hemisphere.) Currently most of what we'd 'develop' is in pasture, though there is a bit of light bush on the north side of the creekline that we would think about clearing.
A priority for us would be to swale the property (annual rain variable, 600-1200m), but I'm struggling a bit to see what the best way would be to retain access to the bottom of the slope should we want to get a bulldozer down there to make a dam or clear more trees or whatever (We probably won't have the spare money to even put in an application to dam the creek within the first 5 years, but it's always a possibility further down the track when regulations have changed/disappeared). Maintaining a grassed strip along the fenceline would of course be easiest, but doesn't seem like the best solution to me. What do other people think? If it's only for the occasional access rather than an everyday kind of road, might it be ok?
The only other way I can think of is for like, a hairpin road following the swales, but I don't think driving over the berm/mound at the bottom of the swale is a great either. Though perhaps for that very occasional access that's fine too? We would just have to do a bit of repair afterwards?
About how many swales would be put in over a 40m drop like this?
(Hmm - as another question, what do you think about the winter creek & dam situation? There is another dam not far downstream so we think that would create difficulties in getting permission. Would a dam just above the creek be almost as good?! Or would halfway down the slope be good? Obviously that would affect the access road as well... Or are dams completely superfluous with swales?)
I concur with Tyler's request for a satellite view or Google Earth coordinates. Many times a view from above will give clues to solutions/problems that are not seen on the ground.
In the mean time I will take a shot at answering some of your questions.
Holding water as high up in the landscape as possible should be your goal. Water soaked into the ground via swales is "in the bank" for all plants to access. Water stored in a pond may or may not be as accessible to "all" plants. If you could find a location for a pond that was not at the complete bottom of your landscape then you would not be forced to use some of your most valuable valley land for a pond. That would also eliminate the need for permits to dam the creek which you hinted might be difficult.
If you can fit a pond somewhere up on your slope, then you can potentially have swales designed that when full, overflow or "drain" into the pond to help fill it. Likewise, when the pond fills to a certain point, excess water can be diverted into swales to take it further down the slope on a gentle path.
Based on your land slope (dropping vertically 40m over ~200M horizontally) = 1:5 slope ratio. This is a fairly steep slope. Not scary steep, but enough that one would need to be careful going cross slope with equipment.
How many swales do you need? It will depend, but if you built one swale for each meter of vertical fall, you would need 40 swales. If you built one swale for each .5 meter of vertical fall, you would need 80 swales. You could start off building a swale for each 2 meters of vertical fall, and you would need 20 swales. Start from the top and work down. If you start at the bottom and work up, the bottom swale is inundated with all the runoff from the slope above it and tends to either blow out and wash away, or silt in with debris from above.
Also, you need to plan to gather the runoff water from the roadway into a swale as it will create more runoff than pasture grassed areas.
Swales can be placed on the land much less expensively than building a pond -- which typically requires an excavator or bulldozer. Another thing is that swale building can start and stop with budget constraints very easily -- a pond stopped at the wrong point in time due to budget constraints can become a disaster. I would start with swales and see if you even need to worry about a pond.
Hope these thoughts help you formulate a strategy.
Location: SE Australia
posted 3 years ago
Thanks for your comments so far Kevin.
I guess the only reasons I thought a dam at the bottom would be good is because it would be collecting from the creek - most of the water would come from outside the property so would increase the water available to us - & also being at or very close to the valley bottom it would be shaded to limit evaporation. I also thought having a body of water down there close to the native bush may also be useful for fighting bushfires before they run up into our orchard on the northern slope. Always a concern in Aus.
I was wondering how to handle runoff from the road, considering I assumed it would be easiest/cheapest to put all buildings just below the road (also as far from the eucalypts as possible for fire safety). Also don't know whether terracing a bit below the road before a flat building platform is a good way to go about it, or just build on a slope...
Hope this attachment works...
Location: SE Australia
posted 3 years ago
Think I stuffed up the attachment
Location: West Texas - near Big Bend National Park
Tell me more about the drainage easement shown in your drawing. Is it for the road drain? It is drawn like it just goes straight down slope.
Location: SE Australia
posted 3 years ago
Well, my partner spoke to the council briefly about the drainage easement... don't really see how it could drain the road as it shows it coming from behind the house which is in the middle of the section. They said we wouldn't be able to build over it but swales across it would be fine.
Beware of trying to dam a creek. Unless you have a really good dam builder who knows what he's doing, the dam can easily blow out in flood. In general I think putting dams in creeks is a bad idea. It can also make you unpopular with downstream neighbors who may worry that you're "stealing the water" or worry about your dam suddenly breaking and flooding their land.
What are your plans for the site? Looking at your aerial photo and with the slope that you have on your site, maybe it would be better suited to doing something other than swales. Or maybe doing as Tyler suggested (I think it was Tyler), put in one retention structure mid slope with swales catching to it.
I think with the slope you have, designing an access road would be best suited to maybe zigzag across the site. You would also need this in order to be friendly on your machines and your back when coming back up with a load of harvest! So maybe an option here is to map out a zig zag road and since it is going to be used so infrequently by vehicle traffic, you can make a broad foot path that barely fits your machine. Maybe a bulldozer could come grade it in for you a little bit. I would drop the road zig zagging down the hill side on like a 1:400 or 1:300 slope, maybe a little steeper (Tyler do you have a suggestion here?) So on this path you can build rolling berms or "water bars" that redirect the flow of water down the road back into the hill side or maybe off of the the road down hill into a orchard with a small ditch system, or wherever.
What I'm getting at here is make your access road that you want into your snaking water retention system! Could have a lot of potential for the site.
The most important thing I have learned is to avoid roads in low-lying areas that tend to collect water, and to limit the length of roads going up and downhill unless you include plenty of water bars as mentioned by Tate above. Water bars built of soil tend to wear down and stop working, so ditches/swales and culverts are probably a better solution on dirt roads. Our main driveway is compacted gravel and we recently had water bars added and they're helping a great deal. Much easier to design these things in at the very beginning.
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