Introduction: What is a Sand Dam?
Concerns for water are growing globally on an almost daily
basis. Some consider water supply a greater potential
cause of conflict than oil. Certainly this is already true in
Kenya. Episodic drought causes frequent problems
regionally in that country, but for the last three years
drought has proven devastating almost everywhere.
Political instability and increasing population intensify the
impact of the water shortage. There were times on our
recent Kenya Study Abroad trip to the country we felt
nearly hopeless in the face of drought.
Sand Dams: A Successful and Expanding
Approach to Supplying Water in SemiArid Lands
Early sand dams used a sloping center to channel water to
the middle. As designs progressed it was found that this
created problems of erosion on the downstream side of
the dam, as well as some excavation of sand on the sides
of the upstream side of the dam as seen in Figure 5.
Newer designs by SASOL feature a rectangular spillway
design as in Figure 1 and often a pair of spurs on the
downstream side of the dam to deflect water and reduce
erosion damage.
Wayne S. Teel , ISAT
The final feature, and relatively new addition to all dams,
is the covered hand dug well on the upstream side of the
dam to provide clean water, shown in Figure 2 and 7.
Other dams had featured open wells, which became
contaminated by animals, or pipes put through the dam
itself to tap water on the downstream side. These clogged
occasionally and proved difficult to repair. Hand pump
technology and community skills in repairing these pumps
have improved enough to make them worthwhile
community investments on these projects.
Hope can take curious forms at times. The concept of sand
dams is one such curiosity, as well as being an effective
method of fighting the now chronic problems with water
supply. We generally associate sand with deserts or the
beach. Think of the times you have taken a bucket of water
from the ocean and poured it on the sand; how fast did it
disappear? Sand dams take advantage of the fact that sand
itself is not a solid, it is highly porous material with lots of
capacity to hold water if bounded by an impermeable
barrier.
What benefits do they provide?
A sand dam is essentially a small dam, usually between 1
and 3 meters tall, that is designed to both halt the flow of
water, sand and courser material carried by the stream.
The sand builds up behind the dam to the level of the spill
way usually in one to three years. Water remains behind
the dam as well, but is unseen below the surface. Though
the dam will only hold between30 and 40% of the water
found in an open reservoir, it has the added advantage of
reducing evaporation loses as the sand reflects light and
reduces energy input from the sun.
Figure 1: The women above are part of a team completing a sand dam in central Kitui District. They are mixing cement,
putting the final touches on a dam that will become their major water supply. Water for making the cement comes either
on their backs or by donkey cart 17 kilometers to reach this site. These women live within one kilometer of the dam. This
particular dam will start filling with sand and water as soon as the long awaited rainy season begins.
Most of the major benefits of sand dams have been
mentioned already, foremost among them being a clean,
local water supply. This supply reduces labor demand,
increases community interaction, reduces diseases like
childhood dysentery and other diarrheal problems, and
improves nutrition. This latter benefit comes in two
forms. First, the increased labor availability by the women
allows them to spend more time of their crops, increasing
yield. Second, the water available usually enables
irrigation of small vegetable plots, fruit and other
nutritionally dense foods as soon in Figure 8. Some
communities with sand dams allow the planting of crops
like elephant grass that is fed to cows or goats, improving
milk supply in the dry season.
Where are they found?
Though sand dams have been around for a long time, and
are direct technological descendents of sub-surface dams,
their more widespread adoption is a fairly recent
phenomenon that started in the Ukambani region of Kenya
in the 1980s. Ukambani means the land of the Kamba
people, who live to the east and south of Nairobi. The
landscape there is rolling hills, some reaching nearly 2000
meters elevation, but the majority of the landscape is
between 800 and 1500 meters above sea level. Some of
the higher elevations of the region get adequate rainfall for
maize and coffee production, but most of the land receives
between 250 and 800mm of rainfall per year, often coming
in 2 rainy seasons, given its equatorial location. Failure of
one or more rainy seasons is relatively frequent.
Gideon Mutiso has supervised construction of sand dams
in Kitui for nearly 15 years and has not lost any
enthusiasm for the effort. He claims that high value
vegetable crops like tomatoes are a part of the benefit he
did not anticipate. Most vegetables in the area are
imported from the wetter Kenyan highlands and sold in
the market at substantial cost. Even amidst the recent
drought local production from sand dam sites has cut into
this market, offering the same produce for lower cost, and
enabling more families to pay school fees for their
children. As times goes on it is likely that even more
benefits from sand dams will emerge.
Since their success in Kenya, the technology of sand dams
has spread more broadly in Africa, moving south to
Tanzania and Mozambique. There are also similar
techniques underway in the drier areas of India, including
Rajastan and Gujarat.
How do they affect hydrology?
Hydrology is basically the study of the movement of water,
both above and below ground. Sand dams are analogous
to beaver dams on streams in North America, though
perhaps more permanent structures. They slow water and
spread it out on either side. This gives water more contact
time with the land behind the dam enabling more to sink
underground. In both the Machakos and Kitui people have
noticed that springs that their grandparents had used, but
had dried up as the area was converted to agriculture, were
now re-emerging downstream from sand dam sites.
Evidence indicates that groundwater is being recharged by
the sand dams and water is flowing through new or newly
recharged underground systems.
Who started the present sand dam
construction efforts?
The first of the recent wave of sand dam construction
began in Machakos District near the town of Utooni by a
local development work named Joshua Mukusya, founder
of the Utooni Development Group. He began on a small
scale in 1979, with one locally designed and constructed
sand dam to complement other development work he
coordinated. The sand dam proved a keystone
development effort. The increased water supply enabled
other development activities, but more importantly it
freed up women of the community to spend more labor
on agriculture and household projects. As a result
Mukusya changed his focus to developing more sand dams
in his immediate area.
Figure 4: Terracing is an essential part of the community sand dam construction effort. These terraces were built by hand
using an adapted construction technique known throughout Kenya as “fanya juu”, or raise up. The idea is relatively straight
forward. First a trench is dug following a contour line and the soil dug out and thrown up the hill just above the terrace final
location. In many places there is little stone. Here on the rocky, side slopes of the Yatta Plateau, stones are placed at the base
of the terrace so that the lean back into the hill. When the stones are all set along the contour line the piled soil is then pulled
back completing the terrace. Sasol requires terracing all agricultural fields near the sand dam sites to reduce erosion and
prevent heavy siltation. Silt and clay are porous, like sand, but water takes much longer to move through the pore spaces
giving less daily yield in the well and in hand dug open well used for irrigating vegetables.
Two other crucial needs were apparent along with the
water supply issue. The first was soil conservation. Food
supply presented annual problems in Ukambani due to
frequent drought and soil loss. By terracing fields (see
Figure 4) soil loss is halted and water is retained in soil
instead of lost through surface runoff. At the same time
the other big labor drain, especially for women, was
addressed, the collection of firewood. Like water, women
commonly spent many hours per day collecting wood.
Tree planting became possible in Utooni because
enhanced water supply enabled seedling survival. As the
trees grew, trimmings became part of the fuel wood
supply and the unexpected benefit of microclimate
improvement was noticed. This three legged
development strategy then became the model for other
development groups, including Sahelian Solutions, or the
SASOL Foundation, a development group based in Kitui,
Kenya.
Figure 2: A critical need in Kitui District, and nearly 90% of Kenya, is clean drinking water. This dam in the Yatta plateau area will
supply approximately 25 families with drinking water. Though they can get water from holes dug in the sand behind the dam, the
SASOL group has found that digging a shallow covered well just upstream from the dam itself takes advantage of the ability of
sand to filter water and prevent contamination by animals. The hole itself is over 3 meters deep and is dug into bedrock using a
sledgehammer and chisels. A trench was dug from the well through rock and filled with sand in order to speed the filtration
process. An example of the covered well with a pump is shown in Figure 7.
Slowing runoff has numerous benefits. It does not mean
that downstream supply will be limited. In fact anecdotal
evidence is mounting that downstream supplies are
increasing. The recent drought has hidden some of the
evidence of this, and more documentation is needed to
prove the positive impact on annual stream flow, but
slower flow of water off landscapes does have long term
watershed wide benefits.
Figure 3: Sand dam construction is a community effort and takes a lot of labor. SASOL provides the two major physical
inputs, cement and rebar, as well as a construction supervisor, pictured just to the right of the dam. Don’t be fooled by the
young woman on the left of the dam, looking at the camera. She is the chair of the community committee organizing the
construction of three sand dams and multiple kilometers of terracing accompanying the sand dams (see Figure 4). She
organizes work crews for the dam site three days a week and the one day a week the terracing effort. Normally this Yatta
Plateau community has between 12 and 25 workers on site, a majority of them women, and have proven very efficient in
their work given everything is done entirely by hand. Water for this site work comes from a dry river bed 4 miles away,
carried by donkey cart or on the women's backs. Men in this area are fewer in number because many of them have gone
seeking work in the cities, such as Nairobi or Thika. Their major contribution is splitting the rock used in construction and
digging the well, the edge of which is on the left of the photo.
Perhaps the best evidence of hydrologic change is seen if
Figure 7. The banana plants located behind the hand pump
are significantly uphill from the dam itself. These plants are
not irrigated, indicating that the water behind the dam has
backed up water on the slope, underground, to a point
where the banana roots can tap the water. This process
would take time. Given that this particular dam is now 13
years old the process of hydrologic shift may be complete,
but it strongly indicates that these sand dams have impact
beyond the sand itself.
What more do we need to learn about
them?
Figure 5: The sand dam above was completed in 1996, one of the earliest dams completed by SASOL. It is located about 8
kilometers (5 miles) south of the District headquarters town of Kitui, but not in the watershed that drains the town itself. The
dam is built just below the confluence of two ephemeral streams at a narrow location of the bedrock. Just upstream the area
widens considerably. According to Dr. Gideon Mutiso, Director of SASOL, wearing black on the left, it took three years for the
dam to fill with sand. Although you can see some cracking clay deposited close to the dam, most of the material behind the
dam, to a depth of nearly 2 meters (just over 6 feet) is sand. Total area of sand deposition is about 1.2 hectares (3 acres).
This area has seen below normal rainfall for the past three years. None of the 6 rainy seasons in this biannual rainfall region
has produced a normal crop.
There is much to learn. Though SASOL and the Utooni
Develop Group and many other have learned a lot about
construction and design of sand dams, every new site
requires new evaluation and design changes. Many
questions can be asked: Are the dams the correct height?
How does placement of a dam in a stream affect overall
flow? How many dams can be placed in a watershed?
Where does the water go? Are all the hydrologic changes
positive? Can design enhance the positive changes while
limiting negative ones? Are there places where sand
dams do not work well even though conditions look right?
We do know this much: sand dams increase water supply
and improve water quality and demand for sand dams is
rising in local communities. This in itself makes the
technology a good one. The real question is, “Can they be
even better?”
SASOL was founded by Gideon Mutiso, Ph.D. and his
brother Sam Mutiso in 1990 primarily as a response to
drought and relief efforts among Somali refugees. After 5
years they realized that events were pushing them to
focus on water as the major development constraint in
Kitui District. In 1995 they started dam construction with
startup monies from Wateraid UK, the Mennonite Central
Committee, and the Canadian Food Grains Bank. To date
they have constructed 700 dams, mostly in Kitui District.
All the photographs on this poster were taken at SASOL
project sites.
How are they built?
Sand dams do require certain conditions before
construction. They function best when the landscape is
sloped but the stream itself has only a slight overall
slope, between 0.5 and 2%. They also require bedrock
relatively close to the surface, and it is better if the valley
is pinched with bedrock on the side to shorten the width
of the dam, while maximizing the upstream area of sand.
What are the resources for learning more?
Excellent Development Kenya’s website is the major
source for Joshua Mukusya’s work in Machakos District.
http://www.excellent development.com/kenya.php
Mutiso, Gideon. 2002. Kitui Sand Dams: Social and
Economic Impacts. Muticon. Nairobi, Kenya
Once these conditions are met, and a site found, work
begins on the dam’s foundation, which means
penetrating to bedrock along the entire perimeter of the
dam to a width of 50-75 cm, about 2 feet. Holes are then
drilled by hand into the bedrock and reinforcing rod is
cemented into these holes to provide structural support.
If form material is available it will be used to shape the
hand split rock and cement of the dam. If not SASOL’s
construction supervisor will guide the building of thin,
twin stone walls which will then be filled in with stone,
cement and more rebar as seen in Figure 3.
Figure 6: The extent of the drought and the rocky nature of the dam shown in Figure 5, are clearly seen in this photo looking
downstream from the dam. The Kitui District site is in what is considered a zone 4 climate, relatively dry, between 500 and 800
mm of rainfall annually, and mostly warm or hot temperatures leading to high evapotranspiration rates. The trees seen here
are primarily drought tolerant acacia species, with a few drought tolerant figs or Combretum species. Most farmers in the
area keep goats and cattle, which keep the trees neatly trimmed underneath. There is little or no soil cover left.
Mutiso, Sam. 2005. The Significance of Sub Surface Water
Storage in Kenya. SASOL, Kenya.
Mutiso, Sam M. & Prof. G-C.M. Mutiso. 2004. Kitui Sand
Dams: A Development Paradigm. SASOL Foundation. P.O.
Box 85, Kitui, Kenya
Mutiso, Gideon. 2009 SASOL Milestones (unpublished)
Figure 7: When originally built in 1996 the dam featured in Figures 5 and 6 did not have a well. SASOL recognized later the
value of incorporating a well to keep water protected for human consumption, as is shown in Figure 2. In 2008 this
community established a committee to design, dig and protect the well and install the pump pictured here. The water is
filtered through sand and comes out clear and almost completely free of bacteria and parasites, which has reduced instances
of diarrheal diseases. A notable aspect of this photo are the banana plants behind and uphill from the pump. These bananas
are not irrigated. They get their water from the water table raised behind the sand dam. Sand dams are now known to not
only increase water supply, they also change the hydrology of a stream in a way that changes the entire riparian ecosystem.
Rempel, Henry. 2005 A socio-economic assessment of
SASOL Foundations Kitui Sand Dams project.
SASOL Foundation. Mennonite Central Committee.
Canadian Food Grains Bank. October 2005
Figure 8: The benefits of sand dams go beyond water supply. Once that need is met labor is free to take advantage of
irrigation. The above picture is taken about 70 meters upstream from the sand dam in Figures 5 and 6. Tomatoes, sikuma
wiki ( a collard green relative), onions, cassava, maize, and elephant grass for fodder are all pictured above. The farmer dug a
1.5 meter pit to collect water for the crops. At least 4 other open wells like this were sited behind this dam. Tomatoes and
sikuma wiki are cash crops. Dr. Mutiso stated that tomato imports to Kitui from the wetter Kenya highlands have dropped to
near zero because of locally available sand dam tomatoes. Clean water, increased labor supply and alternative income
generation have enabled more children to attend school. SASOL has no shortage of demand for more sand dams.