Check Dams and the Promise of Renewing Groundwater Springs
When my family and I moved onto our farm a couple of years ago, the small creek that ran through the bottom part of our land had been essentially abandoned for several decades. While we could hear the creek, it was all but impossible to make our way down to where the water actually ran due to a mess of vines, thorns, and thick underbrush. An invasive vine (similar to kudzu) had choked out some of the cedar saplings that somehow had managed to take root in that mess of brush.
When the dry season finally came around, we were able to machete our way down to the creek and see firsthand the steady flow of water that we hoped to one day use for our domestic water supply. The dry season here in Central America, however, lasts at least half the year. In March (nearing the end of the dry season), our small creek had slowed to a trickle, and by April there was nothing but murky soil along the creek bed. Once the rains began again in May, the creek reappeared, but we realized that we would be left with several months of water shortage each year.
An Experiment with Check Dams
A couple weeks of intense machete hacking that dry season allowed us to plant several hundred cedar saplings along the creek´s edge. While our reforestation effort would hopefully contribute to protecting and maybe even strengthening the small creek, we knew it would take years to see any sort of progress towards a developing forest ecosystem.
After reading about the success of check dams on dry creek beds in certain parts of Africa, we decided to build a couple of small check dams along our slow flowing creek during the height of the next dry season to see if we could perhaps increase the rate of flow of the creek during the worst
parts of the dry season.
Check dams are simply some sort of permeable barrier placed perpendicularly to flows of transient waterways. In our case, we had an abundance of rock left over from the construction of our cob home. While it was a rather large task to haul several cubic meters of rock towards the river, it was a one-time task for an earthwork that we hoped would last a lifetime.
The check dams we built were simply made from rocks that were stacked two to three layers thick. During heavy rains in the rainy season, the flow of the small creek can become rather fast, so we wanted to make sure that the check dams were sufficiently strong to hold up during these brief, heavy rains without having to use any sort of cement or concrete.
We chose three different areas along the creek bed to build the check dams. In these areas, we widened the creek bed which in most places was only 50 to 75 centimeters wide. Above the check dam, we also excavated a small pond or pooling area and made 75 cm mounds of dirt (reinforced with rock) on the sides of these makeshift ponds.
We hoped that when the rains came, the water pooled up behind the check dams would form a series of miniature ponds which besides being beautiful additions to our future cedar forests, would also considerably increment the amount of water infiltrating the soil and thus replenishing the underground water table.
Lessons that Came with the First Rain
As with most things in life, trial and error is the best teacher. While two of our check dams worked pretty close to perfection with nice pools of water neatly contained within our makeshift banks and the excess water flowing through the open, low area within the rock check dam, the first check dam we built on the upper part of our land where the creek entered our farm, suffered mightily during several intense rains. The water coming down the creek after a hard night of rain scoured around the check dam itself as it wore away a few places in the banks we had built.
While the water still pooled up behind the check dam, we did have to repair the banks three times during that first rainy season. The second and third check dam, however, functioned perfectly most likely due to the fact that the flow rate of water had slowed considerably due to the first check dam.
The next dry season we built a small check dam (without a pooling area) in a wide area of the creek bed where it first enters our land. This check dam significantly slowed the flow of water during high rain event and allowed the other three check dams and pools to function without problems.
The Effects of our Check Dams
Three and a half years after building our series of check dams, during the most recent dry season we maintained a slow flow of water throughout the entire year. Even during the last weeks of April, we had a steady stream of water that we hope will only increase in coming years as our cedar forest continues to get established.
Furthermore, our neighbor downstream of us recently told us that she recently noticed a new spring of water flowing from an offshoot of our creek that runs through her land. While that branch of the creek had been dry for decades except during the most torrential downpours, our check dams had replenished the ground water reserves enough to help resurrect a stream that had been “dead” for years.