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2. Study area and data source
2.1. Study area
Chosen type Black Soil Area of Northeast China which locates in the Wuyuer river and Nemoer river
basin as study area, the study area is located in the middle of HeiLongJang Province in China and its
total area is about 23 thousands km
2
where the city of Wudalianchi in the north, and Mingshui county
in the South, and the city of Beian in the East ,and Fuyu County in the West. In geomorphology, it is
in the transition zone of lesser Hinggan Mountains and Songnen plain and the geomorphology
characteristic is Rolling Hilly. Slope is much more gentle, often lower 5°. The major agrotype is type
black soil, besides meadow soil and bog soils are mainly in the low-lying wetland plain. Black soil
has high organic matter, loose texture and big spacing and make it easy to accelerate erosion. The
altitude is 150-600m and the altitude in the northeast is 200-500m where is highland, and
corresponding, the southwest is rolling hilly plain. The study area falls into a temperate continental
monsoon climate. Its mean annual temperature is 0.2°C -1.5°C . Its mean annual rainfall is 550mm-
600mm and mean depth of runoff is about 75mm. Wuyuer river, Nemoer river,Shuangyang river,
Laolai river and Runjin river are the main rivers in this region. The vegetation has the characteristic
of interleaving of forest and meadow plain and it belongs the Mongolia vegetation zone.
2.2. Data source
Tweleve scenes cloud-free 2.5m resolution simulation true color SPOT5 images were as data source.
Then according to the image characteristic, such as tone and texture, with the help of expert
knowledge and about 20 days field survey, the gully interpretation signs were build. Then, taken
ArcView software as platform, combined with expert experience, reference to topographic maps and
other related information, the gully distribution data in 2005 were acquired. Then validation work
was undertaken from 12 November 2008 to 15 November 2008. At last, according validation results,
the gully data were modified, and the final results were get. It suggests that the gully interpretation
precision is greater than 95%.
For DEM data: First, contour and elevation spot were obtained by digiting the scale of 1:50
thousands topographic maps. Then with the digital contour and elevation spot, using TOPGRID
arithmetic, it created the 5m resolution DEM. Then the S and A were extracted.
3. Method
3.1. Model conception
Geomorphic threshold model is as follows:
S=aA
-b
(1)
Where S is slope of headcut; A is accumulation area; a,b are coefficient which are no units.
It can confirm the geomorphic threshold model by extracted the S and A .There are two important
application. One is that a parallel line below the lower limit of the scatter of the data defines the limit
below which valley floors are stable. Another is that the line of best fit through the data represents
the mean topographic threshold conditions for gullying. The first application is mainly used to gully
prediction and the other is used to the analysis of dominant gully process.
3.2. Model application
By the gully data and DEM , it get the S and A of the headcut. Then, it used the parallel line below
the lower limit of the scatter of the data to get the geomorphic threshold model (Figure 1). The model
was as follows:
S
=1.2482A
-0.0936
(2)
Prediction of Area Vulnerable to Gullying based on Geomorphic Threshold Theory
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