Abstract:[Objective] We aimed to illustrate the roots distribution and tensile properties of three herbages on the hedge of sloping cultivated lands of purple soils in Three Gorges Reservoir region, in order to supply the theory evidence and data supports for hedge consolidation with hedge plants.[Methods] One natural herbage, Eulaliopsis binata, and two artificial herbages, Allium tuberosum and Vicia faba were selected and their root distributions and root tensile properties in different soil depths were compared.[Results] (1) Diameters of the three herbages in 0-40 cm soil depth ranked as:V. faba > A. tuberosum > E. binata. Exponential function can be used to described their relationship between their diameter and the distributed soil depth. (2) There existed obviously significant difference between the roots biomass of A. tuberosum and the root biomass of V. faba and E. binata in 0-40 cm soil depth(p<0.05). Root biomass of A. tuberosum and V. faba were both decreased with the downward distribution in soil, but the root biomass of E. binata firstly increased then decreased with the increase of soil depth. (3) Mean root tensile force of the three hedge herbages ranked as:V. faba(10.53 N) > E. binata(6.03 N) > A. tuberosum(4.51 N). And mean root tensile force was found dependent in power function upon root dimeter(p<0.05). Meanwhile, the rank of mean root tensile strength was E. binata(45.91 MPa) > V. faba(18.02 MPa) > A. tuberosum(12.20 MPa). (4) The mean root cohesion of the three herbages ranked as:E. binata(0.013 1 kPa) > V. faba(0.009 4 kPa) > A. tuberosum(0.005 5 kPa). And exponential relationship between mean root cohesion and soil depths was well fitted(p<0.01).[Conclusion] The natural hedge herbage of E. binata had better performances in soil reinforcement and soil conservation in this region, which could be used to effectively conserve soil and water from the sloping lands. And the herbage reinforcement of the hedge is a new idea for sloping cultivated land harness in the Three Gorges Reservoir region.

Abstract:A watershed model was established based on a field survey of a small watershed located in the Three Gorges Reservoir region, three simulated rainfall events which intensities were 60, 90 and 120 mm/h on the watershed to study the process of runoff and sediment yield. The results showed that the runoff and sediment yield increased with the increase of rainfall intensity, but the runoff yield increased much faster than sediment yield. In each of the three rainfalls, the runoff showed the tendency of increasing initially before tending to be stable, but the sediment yield changed quite complicated. In each rainfall, both the cumulative runoff and sediment yield varied in a linear function law with the increase of rainfall duration. A fluctuation change of sediment concentration was showed in three simulated rainfalls experiments.

Abstract:Based on 3 year(2007-2009) continuous observations, characteristics of woodland hydrological effects from the three typical models of converting cropland to forest were studied in Lanningxi small water- shed of the Three Gorges Reservoir region.Results are as follows:(1) Compared with sloping farmland,t he total soil porosity and non-capillary porosity increased from 4.2% to 11.5% and 69.1% to 162.6% , respec- tively. The maximum soil water capacity and non-capillary water capacity increased by 42.5% and 221.4% , respectively, after converting cropland to forest. (2)Initial infiltration rate and stable infiltration rate in A layer for each of the three models were between 2.73and 4.74mm / min and 1.30and 2.96mm /m in, respec-tively, which had no great differences from those on sloping farmland; and in B layer, between 0.14～0.87 mm/ min and 0.06～0.47mm/min, respectively, which were 0.85～5.21and 3.33～6.83times of those on sloping farmland. (3)The surface runoff depths for the three models were between 13.21 and 22.38mm, which were reduced by 74.7%～57.3% as compared with those on cropland.The average annual soil erosion modulus for the three models were between 137.1and 331.1t/km2, which were reduced by 92.4%～81.6% in contrast to CK.

Abstract:Cultivated slopes are the major soil loss area and the major river sediment source in the Three Gorges Reservoir region. However, reliable studies of soil erosion and sedimentation in the region are limited and the fundamental research on soil erosion is inefficient. A study was carried out to investigate soil erosion on a cultivated slope in the region using 137Cs technique. Preliminary results showed that the 137 Cs reference inventory of the study catchment was estimated to be 1 420.9 Bq/ m2. The 137 Cs inventories of gentle cultivated slope with a mean degree of 11.4°ranged between 398.5 and 1649.6 Bq/ m2 and the average value of slopelengt weighted was 816.0 Bq/ m2. Soil erosion rate on the cultivated slope was estimated by revised simplified mass balance model. Soil erosion rate on he study slope ranged between - 3358.8 and 4937.4 t/(km2·a) and the average value of slope length weighted was 1 294. 6 t/ (km2·a) . Influenced by the tillage, soil erosion rates in two slope segments decreased downslope and deposition occurred at the bottom of slope. The lower soil erosion rate is because the cultivated slope has a gentle gradient. On the other hand, a series of tillage method are adopted by the local farmers for preventing soil and water loss efficiently, which greatly reduces soil erosion.

Abstract:Annualized Agricultural Non-Point Source model (AnnA GN PS),a continuous-simulation water-shed-scale model ,is widely used to evaluate non-point source pollution in agricultural watersheds in a number of countries. The Daning River watershed in the Three Gorges Reservoir Region was selected as a case stud-y. The model was parameterized based on landuse,soil,topographic data,and eight-year climatic data. Di-rect runoff was derived from the observed runoff using the baseflow filter method. Then indicators such as percent error (PE) , Nash2Sutcliffe coefficient (NS) , determination coefficient r2,and gradientk were used to evaluate the performance of AnnA GNPS. The calibration result for runoff is very satisfactory ( PE =-3.71%,r2=0.94,k=1.04,and NS=0.94).The validation result also matches well with the observed data,with PE=-6.37%,r2=0.93,k=0.93,and NS =0.94 for runoff and PE=-16.5% for sedi-ment yield. Alternative scenario simulations show that converting cultivated land into forest is promising BMPs (Best Management Practices) for sediment reduction. The results demonstrate that the model is suit-able for prediction and assessment of runoff and sediment from the watershed.

Abstract:Annualized Agricultural Non Point Source model(AnnA GN PS),a continuo us simulation model at water shed scale,simulates surface water,sediment,nut rients,and pesticides leaving the cells and their transport through watershed.The Daning River water shed is selected as a study case.The characteristics of sediment delivery are studied based on landuse,soil,topographic data,and eight year climatic data from 11 meteorological stations.Averaged annual sediment load is 1.25×106t/a at the Wuxing station,rapidly rises up to 1.81×106t/a at the Dachang station,and reaches 1.95×106t/a at the water shed outlet.Xixi River,one of the biggest tributaries in the Daning River watershed,has the largest volume of water discharge up to 20.97%of the total at the watershed outlet.Dongxi River,the second tributary,has the most sediment load up to 26.88%of the total at the watershed outlet.In addition,the area of left bank in the middle watershed(from Wuxi station to Dachang station)is another large sediment source.The sediment delivery ratio(SDR)of the whole watershed is 0.30 in accordance with published references.Viewed from four main stream stations,i.e.Do ngxi river outlet,Wuxi station,Dachang station,and the watershed outlet,the SDR is positively correlated with the watershed area.However,the relation is not significant in the six tributaries owing to the high variatio ns of drainage area,slope,runoff rainfall facto rs,land use/ land cover,etc.

Abstract:With the aid of the rainfall erosivity model using daily rainfall and geographic information system ( GIS) software , ArcGIS 9.0 ,daily rainfall data from 21 weather stations in Da’ ning River watershed and its adjacent area , the Three Gorges Reservoir Region , were used to analyze the temporal2spatial variations of rainfall erosivity(R factor) for the watershed.R factor varied consistently with watershed elevation.R factor decreased rapidly in the upper reaches of the watershed from Gaolou station to Wuxi station , trended towards gentleness in the middle reaches from Wuxi station to Dachang station , and increased gradually in the down reaches from Dachang station to Wushang station(watershed outlet) .There was a great variation in year-toyear R factor with the maximum being three times greater than the minimum.The distribution of rainfall erosivity was highly seasonal with a single peak.Summer months from May to early September typically contributed 90.4 % of the yearly R factor.July and early August were the peak months with more than 38 % of the yearly R factor.