Saturday, May 6, 2017

April rains, and evaluating sand dams

Life for most East Africans revolves around the cycles of rainy and dry seasons.  April is the height of the "short rains" in Kenya, one of the two rainy seasons here.  It was good to again be out in Kitui for the week, where rains have transformed this semi-arid region into a beautifully green landscape.  The rains are spotty though, and it remains to be seen if it is enough to break the drought with enough rain that crops will grow well this wet season.

Kitui East - an area with ruggedly beautiful countryside where we visiting some newer dams.  Good thing for the MCC landcruiser, which got us through some rough roads.
The week was spent in the field finishing our evaluation of sand dams.  As an MCCer, the experience of spending a good deal of time with our partners, and the farmers and other community members that benefit from them, has been a valuable way of learning what benefits or challenges are associated with sand dams.  In the tradition of recent efforts for more "evidence-based" development, this study was an attempt to step back and see if I could apply some scientific approaches that would add to what we know from experience.  There was is a lot that comes out of that work, below is a taste of the things we learned that will hopefully help our partners as they work with sand dams.

One part of our study investigating water quality - is the water clean to drink?  

A summary of our test results are below: the tests at the top show bacteria in the water samples.  In short, results vary, but scoop holes do have bacteria and are not necessarily cleaner than other water that is present.
Not surprisingly, more protected sources of water like pump wells and roof rainwater are much cleaner sources of water.  While pump wells had lower levels of fecal colifiorms, they are not without their challenges.  The one in the left picture below is functioning, but they can suffer from vandalism (for scrap metal), flood damage, or general mechanical failure (such as broken base).  Members often then use them as open wells, but these then get more contamination.

Most users of sand dams don't realize the water has bacteria and is a health risk.  Our surveys below show that in both perception and practice, users generally view the water as clean.  (Interviewees reported on how the people in their communities perceive water cleanliness, and whether they treat water).  MCC is now working with partners on how to encourage water treatment and other sanitation and hygiene practices.  


The major part of the evaluation was looking at how successful dams have been, both in actually collecting water, and in communities using the available water.

At each of 97 dams, we assessed various aspects of dam function, and then rated them on how successful they were.  The bar graph below shows the dams as their "functionality index" (essentially how successful the dams have been at holding water, and being used by the community).  The scale is 0 (the 5 broken dams at left) to 1 (most functional, at right).  Individual pictures of dams can be seen better here.

The lesson from this was that dams vary in their functionality, with relatively few being essential "failures", and relatively few being the nearly ideal situation of having lots of water that is being used well.  Most dams have some good functions, but are not perfect.

One of the big questions about sand dams is silt buildup impedes their funciton.  The dams must have sand, rather than silt or clay, to function well.  If a bunch of fine silt washes into the dam, water cannot be effectively extracted.  We measured how much sand and silt was present in the dams.  The short answer as shown in the graph below - silting causes some issues, but does not severely limit the function of most dams in the area.

This graph shows how much (in percentage) less water is stored in dams because of siltation, compared with a "perfect" accumulation of sand.  Estimates of how much water is stored in sand and silt vary, so we made two calculations, the low and high estimates.  So dams in categories with low percentages (left side of graph) are not impacted much by siltation, and most of the dams in fact fall in the categories of low percentages.

So if dams vary considerably in their functionality, why is this?  What are the main reasons that some dams are judged more functional than others?

Below is one example of how we try to determine what makes dams function better.  The level of silt problems at dams (colors of the stars on the maps - green is better and red is worse) varied.  There was some tendency for dams with more silt to be in areas with steeper hills (red background is steeper, grey/black is flatter).  Choosing watersheds that aren't too steep could help keep siltation problems down.

That's some of the science behind what we've been doing with sand dams.  It's gratifying to identify some areas that can help the sand dams better serve the people who struggle with availability of water.


On a personal note for our family, April has been a fantastic month for birding at and around Nairobi. 

The sunbirds around our place have been amazing lately.  Here a bronze sunbird is taking advantage of the many flowers out right now.
Collared Sunbird on the blooming loquat tree outside the kitchen.

Several Spotted Eagle Owls were resident up at Brackenhurst when we were there over Easter.

The loquat tree outside our kitchen balcony is in full bloom, attracting all sorts of birds.  The Slaty Flycatchers like all of the insects that are in the tree.

Silvery-cheeked Hornbills have been seen frequently around our apartment too.  Their squawks are easily recognized.

Occasionally we find chameleons around our place.  This guy had crawled into our house, we found him hanging out near the dining room table one afternoon.

Tiny flowerpot snakes are fascinating, they look like worms, but are in fact just very small snakes.
Walking around sand dams in Kitui we stumbled on a couple of bushbabies (Greater Galagos), one with a baby.  While not uncommon, they're hard to see as they're nocturnal.  So this was a nice sighting in the middle of the day!

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