| Today is :
Archives (2004)
Getting a head start in the battle against soil erosion
by Ma. Lizbeth J. Baroņa |
January-March
2004
|
 |
| Heavily eroded soil |
Aside from having to deal with the innate problems
in farming, like high production input costs, calamities,
and insect pests, our farmers have one more dilemma to face:
soil erosion.
There is more in the attempt to understand
soil erosion than meets the eye. It is a complex process that
integrates different factors like climate, terrain, and the
sideway, or lateral interaction of the piece of land with
its adjacent lands. The latter, was studied by the Central
Luzon State University(CLSU) and the University of the Philippines
Los Baños (UPLB) using Geographic Information System(GIS)
technology. Specifically, the study conducted by Drs. Nenita
dela Cruz and Eduardo Paningbatan, sought to validate the
positive paybacks to using GIS technology in predicting catchment's
runoff and soil erosion.
Soil erosion
Although soil erosion can be considered a natural process,
the negative effect of this phenomenon on human livelihood
and on the environment must be studied. But time and time
again, it has proven itself to be a natural occurrence that
we have to contend with. The Food and Agriculture Organization
(FAO), of the United Nations estimates that the global loss
of productive land through erosion is 5-7 million ha/year.
Erosion removes the topsoil first. This is where most of
the soil nutrients are entrenched. Once this nutrient-rich
layer of soil is gone, few plants will grow in the soil again.
This soil becomes desert-like and unable to support life -
this process is called desertification. It is difficult and
often impossible to restore desertified land.
Can GIS help?
Simply, GIS combines layers of information about a place to
give you a better understanding of that area. What layers
of information can be combined depends on the purpose, finding
the best location for a new store, analyzing environmental
damage, or viewing similar crimes in a city to detect a pattern.
In the case of mapping soil erosion and runoff,
the study tested the accuracy of a GIS-based soil erosion
model, the PCARES or Predicting Catchments Runoff and Soil
Erosion for Sustainability. This model can describe and integrate
the different hydrological and biophysical processes occurring
in a watershed.
The study focused on an intensively farmed
area in one of the micro catchments of the Mapawa watershed
located at Barangay Sungco, Lantapan, Bukidnon. The watershed
was characterized in terms of soil characteristics, river
and tributary system, climate, topography, slope, land use,
cropping pattern, and cropping system.
Testing the PCARES was done through computer
simulation using three actual major rainfall events which
generated a major stream flow in the Mapawa creek. These rainfalls
occurred within the duration of the study. To measure the
capability of PCARES, the "predicted values", or
the simulation inputs were compared to the actual observed
values using three actual major rainfall events which generated
a major stream flow in the Mapawa creek. These rainfalls occurred
within the duration of the study. To measure the capability
of PCARES, the "predicted values", or the simulation
inputs were compared to the actual observed values.
The three rainfall events considered in the
study were on July 14, where the rainfall lasted for 183 minutes
with 46mm; July 18 which lasted for 120 minutes and produced
134 mm; and the August 13 rainfall event that lasted for 50
minutes producing 39 mm.
The July 18 rainfall gave the highest peak
of predicted runoff depth, and the highest simulated volume
of runoff water. This prediction decreased in the August 13
event. This variation in runoff volume is explained by the
varying antecedent soil moisture regime as a result of the
varying intensities of rainfall.
The same trend was observed in soil loss. The
highest value of soil loss at 23,052 kg was predicted in the
July 18 rainfall. The prediction for July 14 was 20,947 kg,
and 17,185 kg of soil loss was predicted for the August 13
rainfall event. The predictions of the model were found to
be accurate after they were compared to the actual observations.
As to predicting the erosion hotspots, it was
found that the areas in the steeper slopes, agricultural lands,
and areas with less vegetation are considered prone to soil
erosion. The areas in the catchments where erosion was minimally
expected were on the vegetation areas. The ability of the
PCARES to predict soil erosion is one of its main features.
Given the accuracy of the predictions of the model, pointing
out the areas where measures can be made to avert soil erosion
is almost guaranteed.
The study showed that PCARES is a useful tool
in accurately predicting the runoffs, soil loss, and erosion
hotspots. In the process, one can zero in on the high-risk
erosion spots with precision, and at the same time, can prepare
for possible magnitude damages from soil loss and water run-off
in the event of a torrential rainfall.
Sources:
“Guaranteed catchment runoff and soil erosion using
Geographic Information System (GIS)-assisted soil erosion
model” by Nenita de la Cruz and Eduardo Paningbatan,
Jr of Central Luzon State University (CLSU) and University
of the Philippines at Los Baños (UPLB)
www.botany.uwc.ac.za
www.gis.com
[More
2004 Articles]
|
