Study On Processes And Controlling Of Runoff, Sediment And Nutrient Losses In A Watershed Of The Middle Reaches Of Han River

According to the monitoring and experiments in flood seasons during2011-2012in the Hougou agricultural watershed, we carried out the transport mechanisms andmodelling studies of water and sediment erosion and non-point source pollution，discussing the interception of soil and water conservation measures and reduceeffectively of agricultural non-point source pollution for the South-North WaterDiversion Project. By the method of combining theoretical analysis and experimentsstudy, the main results were as follows:（1） Clarify the characteristic of runoff and spatial and temporal distribution ofsediment yield. During the flood season, there is in highly significant correlation withrainfall and runoff in runoff plot, among there was a highly significant linear correlationin the9°plot，there existed very significant curve function correlation in14°-25°plots.Moreover, the rainfall of critical runoff yield decline with slope degree increase.Stored-full runoff was the main pattern of runoff yield in slope farmland in theHougou agricultural watershed, and the subsurface flow accounted for a largerpercentage of total runoff. Moreover, the subsurface flow ratio is1.14-1.35times at theseedling stage and the vigorous stage.Runoff rate is increase with volume of runoff increase; there is power function andlinear relation between runoff velocity and runoff volume in the early and the later offlood season. There are power functions and linear relation between runoff kineticenergy and sediment loss in the early and the later of flood season, however, powerfunction relation in the middle of flood season.（2） The SCS model not only reflects the runoff yield conditions under differentsoil types and vegetation covers in the Hougou agricultural watershed, but also fullyconsidered the soil moisture impacts runoff. When loss parameter is0.3, and CN value is58, monitored runoff and calculated runoff is very closer in runoff plot in the Hougouagricultural watershed.（3） Clarify the change laws of soil erodibility under different land use andelevations. The study of slope indicated that soil erodibility of woodland，abandonedland and cornfield is drop off over increasing elevation, the maximum soil erodibility atthe point of309m, then declines gradually，the minimum soil erodibility of terracedfield at elevation between420m and430m, the value is tending towards stability.（4） Clarify the effect of the rainfall erosivity and soil erosion modulus underdifferent land use, and reveal the relation between runoff and sediment yield. Themaximum rainfall erosivity in July, average R value is3403.66MJ·mm（/hm²·h·a）, andaverage soil erosion amount is15587.41t/a, soil erosion modulus is2013.877t/（km2·a）,which in the scope of middle soil erosion intensity in the Hougou agriculturalwatershed. However, average soil erosion amount of slope land is9853.47t/a, whichtakes up of more than63.2%in total soil erosion amount.The order of soil erosion amount in different land use is: garden field＞slope land＞abandoned land＞orchard field.The results showed that the maximum soil erosionamount of slope land, abandoned land, garden field, orchard field in July, which takesup of more than31.76%,32.78%,39.05%,11.44%in total soil erosion amount in a rainevent during flood season, respectively.The best regression equation is cubic curve-fitting equation between soil lossamounts and runoff of orchard field, however, the best regression equation is S curveequation between soil loss amounts and runoff of slope land, abandoned land, gardenfield.（5） The N and P loss processes shows in stages obviously in flood sesons during2011-2012. N and P loss predictions done stage-by-stage can have improved accuracy.Although the fitted equations between the amount of N and P loss between runoff andsediment yield were N=aR^bS^c assessed stage-by-stage, the method was supported by thestudy for predicting the amount of N and P loss in the Hougou agricultural watershed.The process of N and P loss in runoff and sediment is different obviously underdifferent land use. The N and P loss concentrations in orchard field and garden fieldhave exceeded surface water Class Ⅱ water standard more than15and1.25times. For four land uses, the order of N and P loss is garden field＞abandoned land＞slope land＞orchard field. According to the monitored results, average TN amount loss of gardenfield, abandoned land, slope land, orchard field are15.29,7.20,4.92,1.37kg/（hm²·a）,however, average TP amount loss of garden field, abandoned land, slope land, orchardfield are0.25,0.22,0.09,0.05kg/（hm²·a）, respectively.（6） Reveal the relation between runoff, sediment and TN, TP concentration. Thecubic function can express relation between the TN concentration in runoff and runofffrom slopeland, abandoned land, garden field, orchard fields, especially orchard field.The cubic function can express relation between the TP concentration and sedimentfrom slopeland, abandoned land, garden field; however, S curve equation; powerfunction and logistic equation can express the relation in orchard fields.（7） Ditch water of different sections was monitored at different times to study theecological effectiveness of ditch. The results showed that ditch and aquatic plant hadfunction of interception and purification water. N and P concentration of waterdecreased when water flow through the ditch. Generally reduction range of TN and washigher than that of TP. Moreover, reduction range of NH₄⁺-N was higher than that ofTN. However, NO₃^--N concentration had slight fluctuated incremental trend in ditchafter rains. The coefficient of variation of TN, NH₄⁺-N, NO₃^--N and TP in differentsections is downstream＞upstream＞midstream. The coefficient of variation of TP isthe highest; the range is48.32-113.66%, and the coefficient of variation of NO₃^--N isthe smallest; the range is9.71-20.24%.