...more about flat channel terraces...
rainfall held in a newly constructed terrace
contour shape of the terrace
terrace in foreground - another in distance
rainfall held in terrace with wheat stubble (2 weeks after harvest)
The following explanation is an attempt to answer questions from the
geography students of King Yin Ng in Hong Kong.
Flat channel terraces are structures formed with existing soil to hold rain
water on fields. They are built on a contour starting at the upper (highest
elevation) of a field. They are placed every 350 feet to 600 feet horizontally
across the field (which represents a 3 foot to 7 foot vertical spacing or drop in
elevation for each one).
Each terrace consists of a 2 foot high dam or dike that is about 3 feet wide at the
top and 24 feet to 32 feet wide at the base with a flat channel approximately 45 feet to
60 feet wide behind the dike, depending on the slope of the field. The dam or
the dike is built using the soil from the channel. These structures are
wide enough and low enough that the farmer can plant and harvest
the top and the channel. Most times the best crop is in the channel or
"terrace bottom" because it has received more moisture.
The capacity of the
channel is designed to hold 3.5 inches to 3.75 inches of precipitation in a 24 hour
period. Not only do the channels hold the moisture, but they prevent what
would normally runoff from washing out the field.
diagram of a terrace
We have to be careful when farming the terraces, but we do use all our
equipment on them. We farm in the same direction of the terrace instead of
across the top - that way we are farming the whole field on the contour.
This also prevents erosion and aids in water conservation.
Our combines have 30 foot headers, but we still cut the wheat by traveling in
the direction of the contour; we do not fully utilize the whole width of the
header while cutting the steepest slope of the terrace. Other equipment,
for instance a 102 foot sprayer or a 60 foot drill, has some flex and is pulled in
the direction of the contour with just part of it lapped up onto the
terrace top. Farming terraces does require more time, but is economically efficient because of the
increase in production. The bottom of the terrace may yield any where from
1% to 100% more than the average of the rest of the field depending on the
amount of precipitation.
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