Study On Evaporation By Field Test And Numerical Simulation In The YinChuan Plain

Presently methods of precipitation seepage coefficient and irrigation infiltrationcoefficient are mainly used to define the quantities of these two kinds of recharge, toobtain the coefficients more accurately, only by studying the law of soil moisturetransport in unsaturated zone, the recharge volume of precipitation and irrigation togroundwater can be more correctly computed and therefore, computation accuracy ofgroundwater resource quantity can be improved, which could better satisfy thedemand of industry and agriculture development. YinChuan Plain is located in semi-arid region of Northeast of China, groundwatercycle mostly appears as the vertical alternation, in which irrigation, channelinfiltration and precipitation seepage aggregation occupy 94 percent of total recharge,and evapotranspiration ,the main discharge way of groundwater in the plain,approaches 55 percent of total discharge. So it is of great importance to do theresearch on laws of groundwater vertical recharge and discharge, which can lay theground for correct evaluation of groundwater recharge amount and safe yield,reasonable development of groundwater resources, scientific management and etc. Based on the understanding of domestic and abroad achievements of researchon vadose zone, in this paper, the laws of evapotranspiraion and seepage, as well asother influence factors are discussed according to the combination of experimentanalysis and mathematical simulation. Devices like WM-1 vacuometer and SDM6rainfall gauge are used to build three experimental stations of vadose zone inYinChuan Plain, each which includes two conditions: vadose zone with vegetationcover and the other one without. As to all the six test stations, observation was donefrom July 2004 to Sep 2005 and especially, synchronized observation was done to thetimed weather data. Based on the practical observation data, soil moisture flux methodis used to compute surface evapotranspiration, so as to get the proximity of vegetationtranspiration quantity. Results are presented that the evapotranspiration of naked landin Luhuatai is 819 mm, grape farmland 1300 mm, Wanghong 994 mm, corn farmland1612 mm, Wuduqiao 690 mm. After that, comparing the calculated surfaceevapotranspiration in each month with the timed weather data, by fitting curves, theempirical formula can be acquired in the last. Six numerical models of moisturetransport in vadose zone under six kinds of conditions are subsequently built, andparticularly numerical modeling was done to part of months in observation periods,together with the fit of the measured data, conclusions can be obtained that the modelsare feasible. Finally, laws of evapotranspiration and seepage are detailed proved andanalyzed considering various weather conditions, litho logy, vegetation covering andgroundwater level.