| In the loess plateau,the traditional silt arresters are no more appropriate,and moreover,it is more difficult to balance the occupancy and supply of arable land.However,the Yan'an region located in typical region of loess hilly and gully,includes abundant gully resources in store.It is no doubt gully remediation is an effective measure for transforming these gullies into fertile soil.Taking the Yan'an region as study area,this thesis adopts the technologies and methods of geographical information science(GIS),sensing(RS),global navigation satellite system(GNSS),mathematical statistics.In addition,this thesis is also guided by theories of sustainable development,regional differentiation and landscape ecology.To establish the evaluation system of gully remediation potentiality of Yan'an region,12 evaluation indexes are selected from the four potentiality factors i.e.,gully macro terrain,natural,ecological and economic society.This thesis employs several resources and environment indexes,e.g.,vegetation coverage,land utilization and meteorology,to study and analyze their changes,development trends and influence to gully remediation.The contributions are described as follows:(?)The comprehensive evaluation system of gully remediation and evaluation results are proposed.The level and spatial distribution of gully remediation potentiality of Yan'an region is obtained.(?)Based on the evaluation results concerning of micro topographic factor,the divisional gully remediation pattern is also presented.To achieve above mentioned two novel points,the major methodologies which are used in this thesis are summarized as follows:(1)On the basis of the connotation of gully remediation potentiality and special landform in Yan'an region,this thesis establishes the evaluation system of gully remediation potentiality.The evaluation system takes into account the external conditions change and the influence to gully remediation of economy,society,resource environment and ecological environment.According to the suitability and limitation of arable land and other interrelated elements,the evaluation system's selection principle is based on remediation target of agricultural production,indicator of arable land remediation influence and evaluation indicator of gully remediation potentiality.The evaluation system adopts the entropy method to identify the corresponding weight of each index.The method of weighted synthetically value of indexes is also employed to assess the potentiality of each unit.This thesis qualitatively analyzes the specific gully's capacity of remediation that is based on the gully's micro terrain factors.In addition,considering the region's macro and micro terrain factors,the evaluation of gully remediation potentiality in Yan'an region is analyzed quantitatively and qualitatively.(2)We extract gully network which is more than 1 km,and analyze its terrain features.D8 algorithm is utilized to extract the gully network of Yan'an region from TM remote sensing image and the digital elevation model(DEM).And then the physiognomy geometric mathematical model is employed to grade the extracted gullies.Through regression analysis,logarithmic function relationship is obtained between the length and grade of gully.Considering the DEM of Yan'an region,the macro and micro terrain factors,gradient,aspect and elevation have a relatively big influence to the formation,evolution and remediation of gully.Apart from the Luochuan county,it is noted that for each county of Yan'an region the percentage of slope between 10°-15° is highest,and next is between 15°-20° and the third percentage is between 5°-10°.The percentage of above three intervals reaches up to 60%.The distribution of aspect for each county of Yan'an region is relatively uniform,and the percentage for each aspect interval is approximately equal.The east slope has a little more priority,while the north slope has the most weaknesses.There are many gullies which are less than 1 km and make a tremendous contribution to the density of gullies.In the gully region of loess plateau,the percentage of gullies which are less than 1 km accounts for 67%,and even reaches up to 80%in the loess hilly region.(3)This thesis studies the land coverage change and its influence to gully remediation.Specifically,we take advantage of landscape pattern index to analyze landscape pattern characteristics in different temporal and spatial scales and reveal the potentiality landscape orders.This thesis extracts the land use classification data of Yan'an region to analyze the change of land utilization and rules of spatial distribution using the ways of spatial overlay analysis,the land use dynamic analysis and the space transfer matrix analysis.The areas of construction land and unused land in Yan'an region were increasing;however arable lands were decreasing from 2000 to 2010.It is noted that the ratio of forestry areas were increased in southwest and southeast of Yan'an region,and the areas of grassland was improved significantly.Since these are obvious contradiction between farmland decrease and population increase,it is necessary to supplement the farmland by gully remediation.In 2010,since the type of landscape was very complicated in Yan'an region,the number of landscape patches increased rapidly and the mean area of patch decreased,it was necessary to increase the mean patch area of arable land by gully remediation.Besides,although the degree of crushing of landscapes was greater,the heterogeneity and edge effect of landscapes were much more obvious,the connectivity of different landscapes was poor and the landscape was sensible to outside interferences.This connectivity was becoming better due to the increased areas of forestry and grass lands.The improvement of predominant landscapes can benefit the implementation of gully remediation.This thesis analyzes and calculates the annual average vegetation coverage from 2000 to 2010 in Yan'an region.First,the vegetation index NDVI will be produced through maximum value compositing(MVC)on the data of MODIS.Second,the Savitzky-Golay is immediately used to smooth NDVI.Finally,we obtain the annual average and yearly maximum vegetation coverage by normalized NDVI.On the one hand,from the view of temporal scale,the vegetation coverage in Yan'an region was increased slowly.On the other hand,from the view of spatial scale,distribution of vegetation coverage is high in east and south and relatively low in west and north.The areas of relatively high vegetation coverage is distributed in southwest and southeast of Yan'an region,however,the vegetation coverage is relatively low in west,north and northeast of Yan'an region.But the growing rate of vegetation coverage is much more obviously in northeast of Yan'an region.There is not obvious increased in west and north regions,and even exists land degradation.It is noted that regional ecological carrying capacity can be significantly improved by vegetation coverage increasing,which is benefit to gully remediation,even though the difficulties exits due to spatial differences.This thesis extracts and analyzes the change rules of average annual temperature and amount of precipitation from 1980 to 2010 in Yan'an region.The method will be taken as follows.Firstly,the spatial interpolation method is employed by using the interrelated weather stations data and thus the annual precipitation and average annual temperature between 1980 and 2010 in Yan'an region can be obtained.Then,we will obtain the change rules of temperature and amount of precipitation by taking advantage of trend analysis,wavelet analysis and extreme change analysis.With the climate becoming warmer in Yan'an region,the annual temperature is continuing to rise and the total growing range exceeds one degree.While the amount of precipitation is declining slowly,and the amount of precipitation has rebounded since the 21st centuries.There is largely similarity between temperature and precipitation in the long run,but there is obvious difference in short period changing rules referring to 5-10 years.On the contrary,the temperature changing rule is more stable and orderable than the precipitation changing rule.It is benefit for gully remediation with a modest increasing of precipitation.(4)We propose evaluation method of the gully remediation potentiality by using gully network data,terrain feature data,land utilization data,vegetation coverage data,meteorological data as well as the social and economic statistical data.The range of evaluated units is defined by 30(m)×30(m).The gully remediation potentiality indexes can be derived from literature consultation and comparative analysis methods.The corresponding weighs were also determined by entropy method.The potentiality indexes for each unit can be well evaluated by the weighted comprehensive assessment methods.In 2010,the possibility for gully remediation is generally low.The half areas of Yan'an region belongs to the small remediation supplement areas.The high remediation potentiality areas only account for 12.7%.The potentiality of gully remediation is concluded as follows:The potentiality in the south central and southeast is high.In the west,north and northeast,it is relatively low.The distribution tendency shows that the potentiality is declined from south to north and from east to west in Yan'an region.The spatial differences of remediation potentiality are much more obvious.By analyzing conditions of each county,it is obviously that the potentiality of gully remediation is very small for Wuqi,Zichang and Yanchuan counties,located in west and northeast of the Yan'an region in 2010.For Luochuan,Baota,Ansai,and Zhidan counties located in northern middle and southern of Yan'an region,the potentiality is relatively small.However,the potentiality of gully remediation for south central and southeast of Yan'an region is relatively high.Huanglong is the highest county.Fuxian and Ganquan are relatively high countries.Huangling,Yichuan and Yanchang are the middle potentiality countries.In Yan'an region,it is difficult to remediate gullies in a fragile ecological environment region and it is urgent that the gully remediation is the effective way to improve the ecological environment.(5)The gully remediation potentiality grades which are divided on the basis of its evaluation results can identify the priority remediation area,the reserved remediation area,the ecological maintain area and the ecological control area by synthetically taking gully macro terrain feature,nature factors,ecological factors and social economic factors into account.For the priority remediation area and the reserved remediation area,we propose the remediation project to control the gully head extension,prevent ditch expansion and gully bottom remediation.Furthermore,considering the gullies' shape,vertical,plane modality,etc.micro terrain factors,we propose three kinds of gully bottom remediation patterns that are the detention reservoir sedimentation type,the gully bottom filling type(the sluiceway stretched out type)and gully platform remediation type.Environmental sensitivity and ecological frangibility of Yan'an region is contributes to the complicated resource environment and the social economics,which directly results in the spatial different of gully remediation potentiality.Quantitative evaluation and analysis of gully remediation can significantly provide theoretical basis and development decisions for gully remediation and restoration of ecological environment.Moreover,it can also supply technical support for evaluation of loess plateau and ecological environment investigation. |
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