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“Sand Dams” Are Transforming African Drylands
- kristianp 8y agoLooks great, but it would be nice to see before and after photos, not an animation. Satellite photos would be great.
- sharkmerry 8y agonot satellite but more info https://thewaterproject.org/sand-dams https://thewaterproject.org/sand-dams theyve built 1000 of them at least https://knowledge.unccd.int/publications/1000-sand-dams-excellent-milestone https://knowledge.unccd.int/publications/1000-sand-dams-exce...
- geezerjay 8y agoThose links only show marketing content devised to ask for nore donations. If they've indeed buillt over 1000 sand dams over the past half dozen years then they should have plenty of info demonstrating their effectiveness. However, their sites show nothing.
- ronilan 8y agoMap/Satellite and dozens of face-level photos for each project: https://thewaterproject.org/our-water-projects https://thewaterproject.org/our-water-projects It's actually amazing in scope.
- smpetrey 8y agoPiggybacking to post this PDF. It's titled, "Practical Guide to Sand Dam Implementation." Very thorough. http://www.bebuffered.com/downloads/PracticalGuidetoSandDamImplementation_April_2011.pdf http://www.bebuffered.com/downloads/PracticalGuidetoSandDamI...
- PeterTWP 8y agoThese are without a doubt some of our most impressive and impactful work. I just returned from one of our mature (1.5yrs old) sand dam sites this past month. The community has huge terraced gardens up both sides and a hand pumped well that has not gone dry (it's sunk directly into the sand bed) for a year. This is in the middle of a desperate 3-yr drought. Everything else around is dry. They are not an anomaly. We hear similar news from the other sites as well. Here's a quick link to the 90 or so we've worked on with our local teams. Google Earth recently updated their SAT pics, so many of these are highly visible in great resolution from an objective observer. https://thewaterproject.org/water-project-catalog?q=&hPP=15&idx=Water_Projects&p=0&dFR%5BCountry%5D%5B0%5D=Kenya&dFR%5BProject%20Type%5D%5B0%5D=Sand%20Dam&dFR%5BStatus%5D%5B0%5D=Completed https://thewaterproject.org/water-project-catalog?q=&hPP=15&...
- TheSpiceIsLife 8y agoAre you familiar with Hügelkultur? I wonder if they'd be of any utility in conjunction with the sand damns. https://en.wikipedia.org/wiki/H%C3%BCgelkultur https://en.wikipedia.org/wiki/H%C3%BCgelkultur
- dwiel 8y agoThe problem is there isn't much biomass in the desert to bury.
- TheSpiceIsLife 8y agoGood point. I wonder if it is an input worth importing?
- Jedd 8y agoMy gut feeling is 'probably not'. A variety of reasons spring to mind. It's unproven (most support is anecdotal, with few if any rigorous studies available), possibly performs no better than bunds / swales / keyline, requires a lot of maintenance (rebuild every few years), is better for short-term crops than the preferred tree / forest crops for these sites that will be more resilient to regular droughts, risk of introducing non-native pest species.
- deleted 8y ago[deleted]
- aaron695 8y agoGiven the video is sooooo WTF, by default I'd be running away asap. Anyway, seems to just be a johad - http://www.ecotippingpoints.org/our-stories/indepth/india-rajasthan-rainwater-harvest-restoration-groundwater-johad.html http://www.ecotippingpoints.org/our-stories/indepth/india-ra... Johad's seem real? I'd like a cynic to comment on them. So you don't just get to add water and create a village, which you can look at johad's for more info of the social structure. But to then add to it using them in a sand environment would need an engineer to comment.
- wodenokoto 8y agoDo they dam up sand, or is the dam made of sand or why is called a sand dam?
- olliej 8y agoIt looks like a relatively light weight dam that blocks most of the sand in wet weather run off. Following is my interpretation: Basically the dam slows the flow of runoff enough to allow the sand content to sink. The bulk of the water flows over the dam, at that point containing mostly just silt (so nutrients for farming?). This results in the water being able to saturate the ground on the upstream side of the dam while also resulting in cleaner water down stream.
- jessaustin 8y agoMaybe in drier times when people use water from the reservoir it is recharged from the wet sand (wet because of the dam and reservoir; it would be dry otherwise) that surrounds it?
- landon32 8y agoI think if you have wet sand it's then possible to make a well and get clean water. Basically it seems like the water flows more slowly and then sinks into the water table, which can then be accessed by wells (also lets plant tap into the water in the water table). Could be wrong though
- DoubleCribble 8y agoA reservoir of wet sand seems like a great natural filtration medium. Line the reservoir basin with a french drain and just stick a tap on the downstream side of the damn to access some relatively clean water.
- entee 8y agoDoesn't the "lake" get filled with sand eventually? Do you need to then excavate/move it away to maintain effectiveness?
- war1025 8y agoI think the idea was the sand is there to start with and the dam is there to hold it back. And then the water gets soaked into the sand and settles into the water table before it evaporates or runs off somewhere else.
- MayeulC 8y agoThey explain in their videos that the dams are there to prevent the sand from running off, which then acts as a sponge/filter to retain water. Having such a huge water supply also helps vegetation, which prevents erosion and helps the soil absorb water, so I guess it's a virtuous circle, at least in theory. Very interesting concept.
- markdown 8y agothatsthepoint.jpg
- 394549 8y ago> Doesn't the "lake" get filled with sand eventually? Do you need to then excavate/move it away to maintain effectiveness? In the video, it seems like the dug wells (or laid piping) in the sand to allow the water to be pumped out from the sand when needed. It seems kinda like an artificial aquifer.
- deleted 8y ago[deleted]
- theothermkn 8y agoOne thing I like about this idea is that there doesn't seem to be the impact that, for example, a hydroelectric plant would have. In other words, because the streams are intermittent, and because most of the flow seems to be restored by overflow downstream, you don't interrupt things like migratory fish. It's a neat concept. It gets the water beneath a thermal mass, stabilizing its temperature and preventing evaporation. The water can become available to deep-rooted plants and trees, too. I wish I'd thought of it!
- black_puppydog 8y agofrom how the video and the real life pictures look, I wouldn't expect anything surviving in that "stream" so far that requires even seasonally stable water flow anyhow. so, probably no fish migrating there...
- gascan 8y agoThere are plenty of fish that don't need year round flows. One famous example that springs to mind is even from that region. https://www.nationalgeographic.org/media/west-african-lungfish/ https://www.nationalgeographic.org/media/west-african-lungfi...
- dredmorbius 8y agoChanging an ecosystem changes an ecosystem. Even, or especially, one you don't understandd. Mind: the concept is creative aand impressive. I'd still like to see a full benefits/impacts analysis, rather than the one-sided advocacy presented here.
- mcphage 8y ago> Changing an ecosystem changes an ecosystem. The ecosystem is already in the process of changing via desertification.
- TheBill 8y agoIIRC there was a post on something similar being done in the times prior to the British Raj - small valleys would be damed off to capture the monsoon rains & insure that rivers & springs flowed year round. https://www.jstor.org/stable/40278311?seq=1#page_scan_tab_contents https://www.jstor.org/stable/40278311?seq=1#page_scan_tab_co...
- vram22 8y agoAnother related technique is imprinting: http://www.imprinting.org/mechanics1.htm http://www.imprinting.org/mechanics1.htm
- sj4nz 8y agoAdditionally: Digging trenches and planting at the appropriate time have long been known to be useful in these arid places. https://permaculturenews.org/2008/11/19/desert-ways/ https://permaculturenews.org/2008/11/19/desert-ways/
- downrightmike 8y agoI've built these on the mountain I'm near after a fire stripped it of trees. Called them check dams, supposed to help raise the water table.
- Jedd 8y agoSeems to be a few comments from people who didn't watch TFV. Yes, the idea is that you build a concrete wall that stays there forever. You don't just build one per stream - but place them every so often. Behind the dam the sand builds up after a few rains / years. Most silt, they say, flows over the top, so your downstream nutrient refresh still happens. Before you build the dam you lay down a network of pipes with small holes or slits that then acts as a horizontal spear / well with filtering of larger (sand) particles. In subsequent seasons the sand retains more rainwater for longer after each rain event, and that water can be recovered via that pipe network. Damming also has the benefit of slowing rain water down -- which reduces erosion and improves infiltration down and sideways from the reservoir. The idea isn't new - low-head weirs have been popular (though not as popular as I'd like) for a very long time. Placement distances are determined by bed width, height, flow rate, seasonality, available funds, geography, etc -- so it could be every few hundred metres. Obviously concrete and earth moving aren't cheap, but waterways that only flow a month out of the year are much easier (and much more useful) to do this work on. People worried about the fish - for non-permanent waterways it's moot. For low-head weirs on waterways that tend to always have flow, there's ways to allow fish movement in both direction. Maintenance of the pipework could be an issue, but the nice thing about this approach is you put it in place, and it backfills and gets support during the next rain(s). I've looked at doing this on a low-flow / periodic creek bed before, and it'd involve some major earthworks to excavate down to below the normal water table (a couple of metres) and then the laying down of some very carefully constructed PVC piping - the big risk there is movement and cracking of same as you back-fill. PVC pipes are typically used as they're easier to work with, and reasonably safe in that use case. Very small slits - 1 or 2mm - are made along as much of the pipes as possible, that allow water infiltration but should prevent sand. You need to pump-flush for a while to remove the proximal silt, but after that you've got an effective horizontal spear / well that is kind of self-filtering. In this case there's nothing stopping you building another sand dam, a few hundred metres away, a decade later and repeating the whole process. EDIT: Oh, for non-rendered images of the benefits of even just slowing seasonal water down in arid lands, search for "Geoff Lawton greening the desert" -- he's a permaculturist that's done some spectacular work in Jordan, with proven sustained / sustainable results.
- DoreenMichele 8y agoDesertification has been going on a long time in Africa. Reversing that seems like a good thing to me. This is a brilliant strategy and, also, the "illustrations" (some kind of time lapse stuff) in the article are great. (Former environmental science major. Squee!)
- tobtoh 8y agoA very interesting concept. IIRC one of the problems of traditional (water) dams is when they silt up since it reduces the water storage capacity. However, in this case, the 'silting up' (or sanding up) is the whole intent. So basically they are creating an artificial aquifer. Simple yet effective.
- picsao 8y agoIt's still depending on people to build, finance and upkeep it. Imagine a Mars rover building and maintaining these in remote wadis on its own.
- w0mbat 8y agoIn Belgium they've got Jean-Claude Sand Dams.
- w0mbat 8y agoYou people are no fun.
- chungy 8y agoIs there consideration for what impact it might have on the environment? At least in the northwest US, damming has been devastating to the natural ecosystem.
- Meph504 8y agoThese may be greatly helpful for those near where they will be built. But this technique does have a cost, it will kill the downstream deltas By stripping off the alluvial soil, and depositing it at the dams, it never reaches it original destination. There is a reason that much of this planets life comes from delta regions, and robbing them of the minerals and fresh water they need to thrive is costing a lot more than providing people the ability to create farms in areas where they shouldn't. This isn't terraforming, it's shifting resources to a place that can't sustain themselves naturally, and killing an ecosystem that could without interferences. It also seems to not mention that natural waterways including rivers, streams, and tributaries shift and move overtime, largely because once a water way fills up with deposits and debris its no longer the path of least resistance.
- quixoticelixer- 8y agoI would argue that the cost of this is worth it, these aren't first world alluvial plains where you can afford to farm and buy food from elsewhere, this is Africa.
- Meph504 8y agoRemoving the human factor from this, we are creating non-self sustaining environments at the cost of delta's which are sustainable, and play a vital role in survival in their regions. I assure you, if there are people living upstream of a delta in places that can't sustain life, there are people living in that delta region, who rely on it just as much. this isn't solving a problem, it's at best moving them, and at worst creating additional problems. Instead of attempting to make every region on the planet farm land, we should focus on solutions that take into account a balanced ecosystem, and where that can't be achieved, relocation the human population.
- yayana 8y agoThe same complaints can't be addressed along the Rio Grande with 80% diversion and no one is talking about relocation for the environmental catastrophe called Las Vegas. That is in a country that includes plenty of fertile land.
- grogers 8y agoOver many years would the sand get compacted down to be less porous, making it less effective at holding water?