
“Sand Dams” Are Transforming African Drylands - misnamed
https://weburbanist.com/2018/09/04/fertile-grounds-low-tech-sand-dams-breathe-new-life-into-african-drylands/
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Meph504
These 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-
I 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
Removing 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
The 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.

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theothermkn
One 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!

~~~
dredmorbius
Changing 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
> Changing an ecosystem changes an ecosystem.

The ecosystem is already in the process of changing via desertification.

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sj4nz
Additionally: 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/)

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vram22
Another related technique is imprinting:

[http://www.imprinting.org/mechanics1.htm](http://www.imprinting.org/mechanics1.htm)

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tobtoh
A 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.

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kristianp
Looks great, but it would be nice to see before and after photos, not an
animation. Satellite photos would be great.

~~~
sharkmerry
not 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-
exce...](https://knowledge.unccd.int/publications/1000-sand-dams-excellent-
milestone)

~~~
geezerjay
Those 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
Map/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.

~~~
PeterTWP
These 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&...](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)

~~~
camelite
Can you comment on what will happen to that community when the hand pumped
wells go dry? (assuming this is inevitable?) The best argument I've seen
against what you are doing is that you are moving farming from sustainable
areas to unsustainable areas. But I don't know much at all about the topic.

~~~
Jedd
> But I don't know much at all about the topic.

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.)

~~~
camelite
> Did you watch the video?

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.

~~~
Jedd
> 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?

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'.

~~~
camelite
Thank you for that.

> 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.

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downrightmike
I'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.

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TheBill
IIRC 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_co...](https://www.jstor.org/stable/40278311?seq=1#page_scan_tab_contents)

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Jedd
Seems 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.

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DoreenMichele
Desertification 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!)

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entee
Doesn't the "lake" get filled with sand eventually? Do you need to then
excavate/move it away to maintain effectiveness?

~~~
MayeulC
They 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.

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grogers
Over many years would the sand get compacted down to be less porous, making it
less effective at holding water?

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chungy
Is 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.

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wodenokoto
Do they dam up sand, or is the dam made of sand or why is called a sand dam?

~~~
olliej
It 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
Maybe 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
I 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
A 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.

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w0mbat
In Belgium they've got Jean-Claude Sand Dams.

~~~
w0mbat
You people are no fun.

