Applied Geography formerly Rural Training Center, Thailand

2009 Dec 27 RTC-TH Programs: S.O.W. --- Save Our Water

Dec 27, 2009

Water is essential to life and to the life of a farm. In many parts of the world, water is limited and the lack of water precludes the existence of a farm. Sustainable agriculture requires effective management and use of water resources for the family farm.

S.O.W. begins with a careful understanding of the farm?’s topography and climate. In the Geographic Systems Model, the Lithosphere and Atmosphere are the primary focus. Water is affected by gravity. Rainfall is the primary source of water for most farms. Once the rain reaches the ground, it flows ?“downward?”: flowing down the slope and percolating down into the soil.

Careful study of the topography (the shape of the land) lets you see where the surface flow will go. Water will flow from higher elevation to lower elevation. The steeper the slope of the land, the faster the water can flow down the slope. The idea is to slow the flow as much as possible. This can be done by terracing the land. So rather having a continuous slope downward, the land is shaped into a series of steps. This can give the water more time to soak into the soil.

Mulching (putting cut grass or other vegetative materials) the terrace covers the bare soil and protects the surface from the impact of rain drops. A typical rain drop might strike the surface at a velocity of 22.53 km/hr or ~14 mph. The impact loosens soil particles from the surface and makes them ready to be carried by water flowing down slope. We suggest mulching to a depth of 20-23 cm / 8-9 inches. With this layer of mulch, no rain drop can reach the soil surface. At the same time, mulching protects the soil surface from direct sunlight, reducing soil temperatures and soil evapotranspiration. We also plant squash, cucumbers, pumpkins and other vine crops to climb onto overhead trellises and armadas. This provides more shaded garden beds for growing while keeping the produce off the ground. The net result is increased soil moisture retention. Also, the natural shade produced by the vines and leaves eliminated the need to buy commercial shading fabric to protect the garden beds from the intense, hot dry season sun.

The combination of terracing and mulching also slows the movement of water on the surface. Adding a swale (a shallow pan shaped depression) to the terrace lets the water accumulate on the terrace rather than flowing off the terrace. This also gives the soil more time to soak into the soil.

Eventually the mulch decomposes and becomes compost. Compost improves the soil structure and provides food for soil organisms (e.g. earthworms, etc.). The net result is increasing the capacity of soil to retain moisture and to resist erosion. Thus, S.O.S. is an integral part of S.O.W.

Planted flow paths are another way to reduce the velocity of water flowing down slope. The plant stems slow the surface water velocity and catch larger particles. The plant roots for a network to retain soil. And, whenever water velocity is reduced, the water has more time to soak into the soil.

Check dams were a key part of early RTC-TH training in Chiang Rai. A few years ago (before we terraced the upper farm), we used check dams in the central gully. A check dam isn?’t designed to hold water. It is intended to slow the flow of the water in a gully. It traps debris and soil particles behind the check dam. This also give water more time to soak into the soil. Eventually it can help to fill a gully. Fortunately, we don?’t have gully erosion problems on our farm.

Rainwater harvesting is also a part of S.O.W. Effective rainwater harvesting requires knowing how much rainfall might be available, when it rains, and having ways to capture and store the water. Typically any structure with a roof should be fitted with gutters and rain water storage tanks. Harvesting rain is not new in Thailand. In fact, Thailand is one of the world leaders in this practice. Gutters direct rainwater into storage tanks. When full, the storage tanks overflow to a fish pond, surface holding pond, ground water recharge area, or cultivated field. The low-cost approach relies on using gravity as much as possible to move the water from storage areas/containers to where it will be used. We also plan garden beds near water tank faucets so any wash runoff goes to the garden. Cleaning drains for water tanks are planned so flush water is used to irrigate gardens.

Accurate or useful rainfall data for a particular farm is not readily available. Government weather stations, even if only a few kilometers away, may not provide rainfall data pertinent to your farm. Many of you have seen rain falling on one side of a valley and not the other. But in many cases, the government data may be all you have to use for rain water harvesting calculations. [Note: To overcome this lack of data, we developed the G.R.O.W. (Getting Real On-farm Weather) program to teach farmers to measure and collect weather data for rainwater harvesting and other farm management calculations. G.R.O.W. will be featured in another article in this series.]

The long range climate forecasts for northern Thailand call for longer, hotter dry seasons with increased drought potential. The total annual rainfall may remain the same or decrease slightly. However, the rainy season will be shorter and more intense. This is akin to getting the same annual salary, but instead of being paid monthly, you get paid during only 3 consecutive months a year. So with the current 5-6 month rainy season may get shorter, rainwater storage will be more important. More intense rains also raise the potential for increase soil erosion.

Future activities on our wish list include:
?•Build a passive solar water distillation as a means to purify drinking water;
?•Build a waterless composting toilets (to reduce water consumption);
?•Build biogas digester to process solid and liquid organic wastes (to reduce waste water generated on the farm and produce more compost and an alternative fuel from wastes);
?•Use planted ?“pavement?” for parking and roadway areas (a paving methods allowing grass to grow through planned openings in the pavement surface to allow rain water to infiltrate into the soil while shading the paved surface to reduce surface temperature and evapotranspiration);
?•Install a gray water distribution system to garden beds and orchards;
?•Expand the use of subsurface drip irrigation systems;
?•Increase composting and inter-cropping in the orchards and terraces;
?•Redirect runoff from any new farm roads into catchment basins, swales, and ?“green?” firebreaks;
?•Start selective trials of crops requiring less water and tolerant of warmer temperatures.

In conclusion, water is similar to money; we never seem to have enough of it. So we encourage people to save as much of it as possible.

[Note: This was a brief description of SOW. For the lessons to be meaningful, they are all adapted to local site conditions prior to training. A typical scenario for off-farm training involves time to pre-view the area for the training (about ?½ to 1 day prior to the training). This lets us tailor the lessons to be as site specific as possible. Relevance is critical to making the lessons useful. Thus, there isn?’t a ?“standard?” lesson booklet as such. Included with the training is the ?“teach back?” model. This encourages the participants to share the knowledge with others, just as we are freely sharing our knowledge with them. Payment for the training consists of covering our costs to get to and from the training site, and room/board for the duration of the training. Although we are not a formal / legal non-profit organization, we conduct ourselves in that manner. We are not doing this to make a profit. This is primarily a ?“give back to the community?” activity.]