| Aimed at the strong gully erosion and the prediction requirement for erosionfeatures in Pisha sandstone area of Middle reaches of Yellow River, based on theresult of gully erosion research on the Loess Plateau, using the Remote sensing andGIS technology, the author analysed characteristics of gully shoulder lines movingbackward and erosion styles in the typical zone of Pisha sandstone, and constructedthe database including shoulder lines and all the effecting factors. Based on theProbability and Statistics theories, the effect factors on the shoulder lines movingbackward were analyzed singlely, and erosion risk modes about the shoulder linesfrom gentle slope surface erosion and from steep slop surface erosion wereconstructed respectively. This research improved the application references on theland features of the Pisha sandstone area, and provided beneficial inquiry for relevantwater and soil conservation rules.The present study came to make important results and achievements as thefollowing.1. Using the method of Area and altitued, the land topographic features of studyarea were analyzed. According to the Strahler integral value S in 0.441, this area wasin the period of maturity phase. This proved that the erosion would last a long time tillPeneplain formed.2. Based on two stages of high spatial resolution remote sensing images, thecharacteristics of gully shoulder lines moving backward and their erosion types in thestudy area were summarized. In the study area, both the frequency and the amount oferosion on the steep slope surface were larger than that of the gentle slope surface.Nevertheless, the erosion occurint on the gentle slope surface makes the shoulderlines move backward for a longer distance.3. Effect of factors, including terrain features, surface soil type, land utilizationtype and gully stratum structures on gully shoulder lines moving backward wereanalyzed. The results were as follows: (1) With the increasement of gully slope, theprobability of gentle slope erosion was smaller, and that of steep slop erosion wasbigger. (2) The gentle slop erosion was inclined to appear on the sunny slopes, but thesteep slop erosion with the gravitational erosion was inclined to appear on the shadyslopes. (3) The flow length determined shoulder lines moving backward for the gentleslope erosion, but for the steep slop erosion, its effect was not distinctly. (4) For thegentle slop surface erosion, the series of soil erodibility is aeolian sand, sandy loessand Pisha sandstone. But the steep slop erosion tended to occur on sandy loess andnaked pisha sandstone fractures, furthermore, the Aeolian sand can prevent theoccurrence of steep slop erosion. (5) Sparse shrubbery cover could not prevent the water and soil loess both for the gentle slope eroion and steep erosion, even under acertain condition, the medium shrubbery cover could not prevent them too. On thecultivate land and natural land, it is earsier to occur the steep slope gravity erosion,and the probability of gentle slope water erosion is small. (6) On the shallow gullieswithout mudstone layer, the probability of gentle slop erosion is high, but more layersof mudstone could increase the probability of steep slop erosion.4. Based on the information mode, modes of erosion risk on shoulder lines forgentle slope erosion and steep slope erosion were constructed separately. According tothese modes, shoulder lines of 1987 and 2006 were all divided to four types of erosionrisks. Comparaing to the erosion riskes of 1987 shoulder lines, the capability of 2006shoulder lines resisting gentle slop erosion decreased, but the capability for steepslope erosion increased.5. The method of risk assessment has certain applicabilities, and can provice"nuts-and-bolts" suggestions for those water and soil conservation rule makers.Because the effecting factors were overall in som extent and they were easily toobtain. Lastely, the mode was easy to construct.
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