“Sand Dams” Are Transforming African Drylands
weburbanist.com
weburbanist.com
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.
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.
It clearly won't. The article/video discusses how a) the dams are low profile and allow most water to flow over the top -- they are designed to trap sand while allowing alluvial material over / through, and b) they're also designed to fill within a few years which means the bulk of alluvial material in subsequent events will bypass the site entirely.
> There is a reason that much of this planets life comes from delta regions ...
Can you explain what you mean by this please?
> 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.
I appreciate your point of view here, though I'm now curious where you happen to live and how you'd feel about being forcibly relocated if/when climate change renders your home unlivable without being modified.
I'd suggest that much of this work is trying to recover recently ruined, or maintain currently precarious human habitations, and perhaps halt the desertification of currently habitable regions.
Sand dams may very well improve downstream conditions. Because anything that holds, slows down the surface water is a good thing.
I'm reminded of a widespread mitigation project where simply removing non-native plants and replanting native trees restored water ways.
These man made oases may do the same.
Think of them as beaver dams, without the beavers.
Many places where this technique is used were once more lush but humans degraded the environment, often through overgrazing. So, the degraded landscape of today may not be the "natural" state.
Take China's efforts to restore the Loess Plateau, probably the largest restoration effort ever undertaken.
https://en.m.wikipedia.org/wiki/Loess_Plateau
I've not heard of concerns you raised about the impact on deltas. I'm not a scholar but I've done some research on the issue. Can you point me to any papers that address your concerns?
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!
https://www.nationalgeographic.org/media/west-african-lungfi...
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.
The ecosystem is already in the process of changing via desertification.
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.
https://thewaterproject.org/sand-dams
theyve built 1000 of them at least https://knowledge.unccd.int/publications/1000-sand-dams-exce...
It's actually amazing in scope.
http://www.bebuffered.com/downloads/PracticalGuidetoSandDamI...
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&...
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.
For bang-for-back (or bang per kilogram, as transport may be the biggest expense in these environments) something like biochar would be a good import. Guaranteed pest-free, lightweight, hard to make on-site, etc. Nutrient loss won't be as severe as in a heavy rainfall environment, but what little there is here you'd want to lock up before the next big rains.
Did you watch the video?
> Can you comment on what will happen to that community when the hand pumped wells go dry? (assuming this is inevitable?)
Why do you assume this is inevitable? Was there something in the video that made you think these will go dry?
> The best argument I've seen against what you are doing is that you are moving farming from sustainable areas to unsustainable areas.
Are you under the impression that people are moving into the areas that these things are being built?
What does sustainable farming mean for you? (For a lot of westerners it means (nearly) free energy being used to produce synthetic fertilisers combined with broad pesticides, servicing large monocultures with little to no attention to improving soil quality, severe erosion from bare soil practices, etc.)
Yes, and I still don't know much about the topic. Hence, the questions.
> Why do you assume this is inevitable? Was there something in the video that made you think these will go dry?
Dude, I don't know much, so I'm signposting the potentially incorrect assumptions I might be making, to help out whoever wants to answer my questions. You have a smug attitude, but I don't see you attempting an answer. What's up with that?
> Are you under the impression that people are moving into the areas that these things are being built?
No, and you appear to be missing my point if you think that is necessary for the criticism to hold.
> What does sustainable farming mean for you?
For the purposes of this discussion, enough water in perpetuity.
Okay, that's my fault. What you interpreted as smug should have come across as frustration. Most comments in this thread are evidently from people who didn't watch the video, threw in some assumptions, and declined to do a brief web search.
If you look elsewhere in the comments you'll see an earlier comment from me that likely fills in your gaps.
Can I suggest that rather than loading your questions like 'What happens when these fail- I assume they fail' you could ask 'How long will these last?'
Wikipedia's 'sand dam' article would answer that question. They're designed to go for 50+ years. (I expect they'd actually be serviceable a fair while longer.) In any case, you'd presumably be building others up or down stream.
Noting that the problem here is not what happens in 50 years (assuming what you're doing now doesn't jeopardise 2 gens forward) but rather what happens in the next few years -- specifically providing sustainable water, food, health, societal benefits to people who need those things now.
You suggested I was missing your point, but to be candid I wasn't sure what that was -- do you mean your criticism of the project because you didn't know if it was sustainable?
Sustainable farming is about a lot more than 'enough water in perpetuity' - it's about nutrient capture / cycles / management, resilience, minimising external inputs (f.e. pesticides, town water, fertilisers etc -- while insects, birds, dust, wind, rain, sun, nutrients from retrieved by grazing animals are usually considered freebies).
Note that most conventional / western / broad acre / industrial / monoculture farming by definition is not sustainable, regardless of water abundance.
It's fun to consider just how sustainable are the practices of generating the food you eat, especially in 'the west'.
> You suggested I was missing your point, but to be candid I wasn't sure what that was -- do you mean your criticism of the project because you didn't know if it was sustainable?
More or less, yes.
https://www.jstor.org/stable/40278311?seq=1#page_scan_tab_co...
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.
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!)
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.
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.
At least in the northwest US, damming has been devastating to the natural ecosystem.
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.
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