Eco-economic Background of Hilly-Gullied Loess Region and Optimized Eco-productive Paradigm of Small Watersheds

A thorough analysis on its natural environment as well as social economic status of the hilly-gullied loess region is presented. A small watershed, the dominant landscape unit of the region, has been singled out for further and specific study on landscape pattern and function, its social and economic distinctions. The authors proposed several principles based on its eco-economic background study, which includes water balance and efficient use principle, co-development of grass and agro-forestry principle, location optimization principle. Integrated with detailed analysis of a small watershed, an eco-productive paradigm for the loess land's development based on a small watershed scale was worked out. It consists of circle pattern with villages at core for high efficient agriculture production, hierarchical pattern along the slope for eco-economic development, point-axis pattern for commodity production and circulation in small watersheds and core-margin pattern for exchanges among watersheds.

Application of SCS Model in Estimation of Runoff from Small Watershed in Loess Plateau of China

Soil Conservation Service (SCS) model, developed by U. S. Soil Conservation Service in 1972, has been widely applied in the estimation of runoff from an small watershed. In this paper, based on the remote sensing geo-information data of land use and soil classification all obtained from Landsat images in 1996 and 1997 and con-ventional data of hydrology and meteorology, the SCS model was investigated for simulating the surface runoff for single rainstorm in Wangdonggou watershed, a typical small watershed in the Loess Plateau, located in Changwu County of Shaanxi Province of China. Wangdonggou watershed was compartmentalized into 28 sub-units according to natural draining division,and the table of curve number (CN) values fitting for Wangdonggou watershed was also presented. During the flood period from 1996 to 1997, the hydrograph of calculated runoff process using the SCS model and the hydrograph of observed runoff process coincided very well in height as well as shape, and the model was of high precision above 75%. It is indicated that the SCS model is legitimate and can be successfully used to simulate the runoff generation and the runoff process of typical small watershed based on the remote sensing geo-information in the Loess Plateau.

Simulating the vegetation-producing process in small watersheds in the Loess Plateau of China

Small watersheds are the basic composition unit of the Loess Plateau in China. An accurate estimation of vegetation net primary productivity （NPP） is of great significance for eco-benefit evaluation in small watershed management in this region. Here we describe the development and testing of a vegetation-producing process model （VPP） of a small watershed in the Loess Plateau. The model couples three modules： radiation adjustment; soil hydrological processes; and vegetation carbon assimilation. Model validation indicates that the VPP model can be used to estimate the NPP of small watersheds in the region. With the VPP model, we estimated the spatial NPP distributions in the Yangou watershed for 2007. The results show that in the Yangou watershed the NPP is relatively low, averaging 168 g C/（m^2.a）. Trees and shrubs have a higher NPP than crops and grasses. The NPP is larger on the partly shaded and shaded slopes than on the partly sunny and sunny slopes. The NPP on the slopes increases gradually on 0-20° slopes and decreases slightly on slopes steeper than 20°. Our simulation indicates that the vegetation type is the most important factor in determining the NPP distribution in small watersheds in the Loess Plateau.

Estimation of soil organic carbon storage and its fractions in a small karst watershed

With few available soil organic carbon(SOC)profiles and the heterogeneity of those that do exist, the estimation of SOC pools in karst areas is highly uncertain.Based on the spatial heterogeneity of SOC content of 23,536 samples in a karst watershed, a modified estimation method was determined for SOC storage that exclusively applies to karst areas. The method is a "soil-type method" based on revised calculation indexes for SOC storage. In the present study, the organic carbon contents of different soil types varied greatly, but generally decreased with increasing soil depth. The organic carbon content decreased nearly linearly to a depth of 0–50 cm and then varied at depths of 50–100 cm. Because of the large spatial variability in the karst area, we were able to determine that influences of the different indexes on the estimation of SOC storage decreased as follows: soil thickness > boulder content > rock fragment content > SOC content > bulk density. Using the modified formula, the SOC content in the Houzhai watershed in Puding was estimated to range from 3.53 to 5.44 kg m^(-2), with an average value of 1.24 kg m^(-2) to a depth of 20 cm, and from 4.44 to 14.50 kg m^(-2), with an average value of 12.12 kg m^(-2) to a depth of 100 cm. The total SOC content was estimated at 5.39*10^(5) t.

Calculating the sediment flux of the small coastal watersheds:a modification of global equations

Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder and Syvitski(1996),Syvitski et al.(2003),and Syvitski and Milliman(2007).The second kind is the modified equations revised by the characteristics of the coastal watersheds,including the drainage area,mean water discharge,and mean sediment discharge.Compared with the observations of the hydrometric stations,the global equations overestimate the sediment flux by 1–2 orders of magnitude.By using the modified equations,the accuracy of the estimated sediment flux is significantly improved,with the relative error in the range of 7%–24%.The reason for the overestimation mainly caused by different parameters’domain and regression coefficients between global rivers and study coastal watersheds.This study demonstrates that modification needs to be considered when using global regression equations to reproduce the sediment flux of the small coastal watersheds in southeastern China.

Benefit Evaluation Model of Small Watershed Control Based on Projection Pursuit

A projection pursuit model is presented in this paper for comprehensive evaluation of benefits of small watershed control.By using the model,small watershed control samples with many benefit evaluation indexes can be synthesized projective values with one dimension.The samples can be naturally evaluated according to the projective values.The parameters of the model is optimized by using real coding beased accelerating genetic aglrothm,which overcomes the shortcomings of large computation amount and difficulty of computer programming in traditional projection prusuit methods,and provides a new way for wide applications of projection pursuit technique to different evaluation problems in agricultural systems engineering.

Study on the Topographic Effect on Soil Erosion Using RUSLE Model for Small Size Watershed

Soil erosion and subsequent sedimentation have caused serious environmental and soil degradation problems in Okinawa Prefecture,Japan.This research aims at evaluating an availability of the Revised Universal Soil loss Equation（RUSLE） for predicting the range of soil loss values for the Nago watershed in Okinawa.It shows that climatic conditions substantially influence the rainfall amount as a function of the I30 of the rainfall event.The rate of soil loss is higher with increasing in altitude due to greater slope steepness.By rainfall data analysis,it is concluded that the large difference in soil loss between 2000 and 2001 was due to concentrated heavy rainfall in the rainy season or the typhoon season.

A Study on Description Methods of Sediment Transport Modulus in Small Watersheds

[Objective]This study aimed to clear the advantages,disadvantages and applicability of various analysis methods to assess sediment transport modulus in small watersheds using the multi-year observation data. [Method]Four methods,including the statistical eigenvalues,depolarized arithmetic mean,frequency of erosion intensity and box-whisker plots were applied into calculation of sediment transport modulus in four small watersheds,and then the results of the methods were compared to to filter a method with the widest applicability and scientific validity. [Result] The statistical arithmetic mean and median could hardly represent the concentration and general level of multi-year sediment transport modulus. Although the depolarized arithmetic mean had the tendency of reflecting the general level of data,it lost the extreme value and its information for making decision. The frequency of erosion intensity grade reflected the distribution of data in intensity classification. Box-whisker plot could show the concentration,dispersion and the number of abnormal data. [Conclusion] Multiple methods can be combined to comprehensively and objectively characterize the multi-year sand transport modulus due to their advantages and disadvantages. Additionally,box-whisker plot has good objectivity and applicability in displaying the multi-year data of small watershed.

The Influence of Land Use and Fish Farming on the Contents of Ca²⁺, Mg²⁺, K⁺and Na⁺in Pond and Reservoir Ecosystems in an Agricultural Small Watershed, China

It is not understood well that how the effects of land use and fish farming on the contents of alkali metals (Ca2+, Mg2+, K+ and Na+) in small water bodies of pond and reservoir ecosystems at the watershed scale. In this study, the concentrations of Ca2+, Mg2+, K+ and Na+ in water bodies were measured for 103 ponds and reservoirs used as fish farming or surrounded by different agricultural land use types in the subtropical hilly watershed of Jinjing (105 km2), China. The two important environmental factors of fishing farming and agricultural land use influenced the spatial variation the contents of alkali metals. The ponds and reservoirs in residential area had significantly higher concentrations of Ca2+ and Na+ than those with other land use types, reflecting the influence of domestic wastewater. Compared with those of natural ponds with non-fish farming, no significant increase of alkali metal contents occurred in fish farming ponds, due to the regular cleaning of ponds by farmers. However, the effect of fish culture on alkali metal contents was still supported indirectly by the fact that the alkali metal contents significantly correlated with nitrate contents in fish farming ponds and but high related with that of DIP in natural ponds. The suitability assessment for irrigation on the pond water indicated that almost all of ponds were suitable for irrigation except some ponds surrounded by residential area and tea plantation. Generally, our results demonstrated that fish farming and agricultural land use affected the contents of alkali metals in ponds and reservoirs. The agricultural water irrigation would be with caution from the ponds with tea plantation and residential area in the subtropical hilly watershed.

Response of vegetation net primary productivity to climate change scenarios in the Loess Plateau of China--A case study of the Yangou watershed

Vegetation net primary productivity(NPP)is a sensitive indicator to characterize the response of terrestrial ecosystems to the climate change.Projections of the NPP changes of the Loess Plateau under future climate scenarios have great significances in revealing the interactions among terrestrial ecosystems and climatic systems,as well as instructing future vegetation construction of this region.Here,we carried out a case study on the Yangou watershed in the Loess Plateau.Using the vegetation-producing process model(VPP)established for such small watersheds,we simulated the NPP of the Yangou watershed under different scenarios of climate changes.The results showed that the NPP significandy increased with the precipitation increasing and evidently decreased with the temperature increasing where the climate change occurred in the whole year or in the summer half year.However,where the climate change occurred in the winter half year,the increased precipitation had little effect on the NPP,and the increased temperature significantly reduced the NPP.There were clear differences among the response sensitivities of different vegetation types with trees and shrubs were more sensitive to the changes in temperature and precipitation than crops and grasses.Currently,the most favourable climate change scenario to the NPP in the Yangou watershed was T0P15 under which the precipitation increased by 15%and the temperature did not changed,in the whole year;in the meantime,the most unfavourable climate change scenarios was T2P-15 under which the precipitation declined by 15%and the temperature increased by 2℃,in the whole year.

Critical Rainfall Analysis on Flash Flood Early Warning for South Branch of Censhui Watershed

Critical rainfall for flash flood early warning is a converse result of precipitation-runoffprocess based on warning discharge threshold for a warning station of interest in a watershed; the key aspects of critical rainfall include rainfall amount and rainfall duration Using hydrological modeling technique with detailed sub-basin delineation and manual for design precipitation-runoff computation, this study introduces basic concept and methods of analyzing critical rainfall for flash flood early warning. Taking South Branch of Censhui watershed in China as an example, typical critical rainfalls for flash flood dynamic early warning were estimated for 3 warning stations located in the watershed. This research illustrates that detailed watershed characteristics in the context of several warning stations can be modeled in-depth by further delineating the watershed into smaller sub-basins to simulate spatial distribution of various basin parameters. It further confirms that time of concentration of a watershed is an important factor to rainfall duration determination, and the antecedent soil moisture condition of a watershed has significant impact on critical rainfall for same rainfall duration.

Parameter evaluation for soil erosion estimation on small watersheds using SWAT model

This research was undertaken for the evaluation of soil erosion using the semi-distributed basin scale SWAT model for four subcatchments of the Dhrabi River Catchment(DRC),which is located in the Pothwar Plateau region.Two subcatchments(catchment-25 and-31)are characterized by gullies while the other two(catchment-27 and-32)are managed with terraced landuse system.The performance of the model was satisfactory with coefficient of determination(R^(2))=0.67 to 0.91 and Nash-Sutcliffe efficiency(ENS)=0.54 to 0.85 for both surface runoff and sediment yield during the calibration(2009-2010)and validation(2011)periods.The PUSLE factor was found to be the most sensitive parameter during model calibration.It was observed that all of the rainfall-runoff events occurred during the monsoon season(June to September).The estimated annual sediment loss ranged from 2.6 t/hm^(2) to 31.1 t/hm^(2) over the duration of the simulation period for the non-terraced catchments,in response to annual precipitation amounts that were between 194.8 mm to 579.3 mm.In contrast,the predicted annual sediment levels for the terraced catchments ranged from 0.52 t/hm^(2) to 10.10 t/hm^(2) due to similar precipitation amounts.The terraced catchments resulted in 4 to 5 times lower sediment yield as compared to non-terraced catchments.The results suggest that there is a huge potential for terraces to reduce soil erosion in the DRC specifically and Pothwar area generally,which have proven to be an efficient approach to establishing soil and water conservation structures in this region.

Structure regulation of land use and landscape pattern changes based on matter element analysis in a small watershed in Sichuan,China

The agricultural land suitability assessment based on the natural characteristics of land blocks is traditionally the basis for agricultural and/or land use planning.The assessment,however,is static and cannot be incorporated with potential land use changes.Recently,a dynamic approach,i.e.,matter element analysis,has been effectively applied for land use planning.In the present study,based on matter element analysis,we estab-lished a matter element analysis model for land use suitability assessment using the suitability grade of land use,evaluation indicators and their characteristic values as matter elements,and also using sutra field,controlled field,weight value and correlation degree from field survey,as well as an expert system.This model was applied to the structure regulation of the land use in the small Yuejiagou watershed of the Langzhong Municipality in Sichuan Province,China.Results show that the proportion among agriculture,forestry and animal husbandry tended to rationalize land use.The economic and eco-logical indices of the lands were increased from 1529.8 to 1719.99 and from 1460.94 to 1758.21 after the regulation,respectively.The regulation also caused changes in landscape patterns as follows:The indices of diversity and evenness were increased from 1.3028 to 2.0920 and from 0.6108 to 0.8463,or by 60.58%and 38.56%,respectively.However,the indices of dominance and contagion were decreased from 0.6431 to 0.2106 and from 0.7467 to 0.7125,respectively.This indicated that the land use in the small watershed was rational.The spatial distribution of patches tended to be uniform.The patch congregation was gradually dispersed.This study verified that the matter element analysis approach can not only overcome the factitious influences and improve the precision of land assessment,but also can be used for the structure regu-lation of specific patches.

黄丘五副区小流域水土流失的时空变化

本项研究以高泉沟流域为试验区，对黄丘五副区小流域水土流失的时空变化进行了研究。结果表明，小流域水土流失的时段分布不均匀，空间差异悬殊。从时间上看，一次降雨的水土流失在不同产流时段上差异较大，径流量、输沙量主要集中于某一产流时段内；年内各月间的水土流失在数量上变化较大，５～８月份分别集中了年径流总量、输沙总量的９０．９５％、９７．７９％；年际间的水土流失量各异，多年的水土流失量大小主要取决于暴雨次数多、雨强大的个别年份。从空间上看，梁峁坡面为主要产流区，沟谷为主要产沙区，沟坡沟底难利用地侵蚀最严重，梁峁坡面的产流量对沟谷产沙量的影响极显著。

Optimization Design of Warping Dam in Wangjiagou, Shanxi Province

This paper introduces the simulating design of warping dam in the Loess Plateau, western Shanxi province. On the basis of collected data, the digital elevation model in the studied area has been created. Utilizing GIS (geographical information system) technology, this paper achieves some environmental based results with the simulation method. Also based on the parameter model of precipitation, the tendency of warping sand has been calculated, aiming at providing academic basis for optimization design in the small watershed.

Benefit Evaluation on the Control Mode for Typical Karst Rocky Desertification in Guizhou Province,China

Control mode for typical karst rocky desertification in Guizhou Province,China is selected as the research object.The ecological benefit,the social and economic benefit and the popularization prospect of mode are selected as evaluation indices.Evaluation index system of control modebenefits for karst rocky desertification is established.The Dingtan mode and the Wangjiazhai-Yangchangdong small watershed control mode are se-lected as evaluation objects.Preliminary assessment on the two modes are carried out by Analytic Hierarchy Process,grading evaluation,and com-prehensive evaluation method.Result shows that comprehensive score of Dingtan mode is 3.81,which is higher than the score of Wangjiazhai-Yangchangdong small watershed control mode(3.11).In the aspects of ecological benefit and social and economic benefit,Dingtan mode(4.83and 3.258) is superior than the Wangjiazhai-Yangchangdong small watershed control mode(3.38 and 2.531).In the aspect of popularization pros-pect of mode,score of Dingtan mode(3) is lower than that of Wangjiazhai-Yangchangdong small watershed control mode(3.333).Therefore,theevaluation index system has certain science and offers reference and guidance for the karst rocky desertification control in southwest China.

Analysis of Sediment Source of Watershed in Western Shanxi of the Loess Plateau

The paper analyzes the sediment source of watershed by means of studying watershed in westernShanxi of the Losses Plateau. On the basis of watersheds classification, 7 typical watersheds were chosen andobserved for 11 years. The result shows that the sediment at the small watershed mainly comes from gullies,which is 60% of the total sediment. Erosion modulus of valley (including gully head, gully bed, valley side)is 1.28~2.48 times as that of the area between channels(including hill slope and mound of the Loess Plateau).The main sediment source of slope erosion is cultivated land on slope without water and soil conservationmeasures.