Study On Measurement Methodology Of Soil Infiltration And Preferential Flow

Soil infiltration capacity and preferential flow determines the amount of water storing in soil,the quantity of underground water and runoff,which affects the design of irrigation system,no-point pollution,and pollution transforming in vodase zone.A ring infiltrometer is the most commonly applied method to measure soil infiltration capacity.The study focused on the new method for calculating infiltration rate,improved device of ring infiltrometer and the method for partition soil matrix infiltration and preferential flow.The main research contents and results are as follows:Numerous reports indicated that the most reliable results measured by a ring infiltrometer were remarkably distinct from those measured by a rainfall simulator.Calculating method and installation of a ring infiltrometer may be the reasons for the higher results of infiltration rate.The hypotheses were verified by lab experiments.The optimal positioning location and time step length was advanced to accurately measure soil infiltration rate curves.A specially constructed ring and soil container was applied to produce a soil profile that could visually display water movement in the soil.The wetted soil profile inside the ring indicated that the actually infiltration consisted of vertical infiltration from the ground surface and horizontal infiltration caused by the gaps between the ring wall and soil,which caused that the initial infiltration rate measured by a single-ring infiltrometer was 3 times of one-dimensional vertical infiltration rate.In the steady infiltration stage,the lateral flow increased the measured the infiltration rates.Mathematical models based on Green-Ampt model were derived to correct the measured infiltration rates affected by preferential and lateral flows during the initial and steady infiltration stages.The corrected infiltration rates agreed well with one-dimensional infiltration rates,with the proportional coefficients very close to 1(0.983 and 0.996).A surfaced-positioned double-ring infiltrometer that was placed on the soil surface to avoid preferential flow was suggested to measure soil infiltration rate.Lab experiments and numerical simulations indicated that the infiltration rates from the surfaced-positioned double-ring infiltrometer agreed well with one-dimensional vertical ones,with the maximum error of 18.95%.A method was developed to measure soil matrix infiltration by sprinkling a layer of fine sand on ring infiltrometer to shelter the macropores and to ensure that water infiltrates the soil through the matrix only.The experimental method and algorithm model was developed.Based on the fact that the total cumulative infiltration amount consisted of the preferential flow and soil matrix infiltration,a new method was advanced to partition preferential flow rate and matrix infiltration with two surface-positioned double-ring infiltrometers.Field experiments were conducted to evaluate the quantitative relationship between the soil matrix infiltration and preferential flow.The preferential flow rate was 2.0-7.2 times of soil matrix infiltration rate and cumulative infiltration of preferential flow was 2.3-10.2 times of that of soil matrix.Preferential flow played an important role in the hydrological cycle in forest soils.A mathematics methodology was suggested to calculate the whole infiltration process.The calculated infiltration curves agreed well with the entire measured curves,with the proportional coefficients ranging from 1.004 to 1.050(R~2>0.95).The method could reduce measurement time to 30 min and improve measurement efficiency.These measurement methods overcome the disadvantages of the traditional double-ring infiltrometer and partition preferential flow and soil matrix infiltration.The study supplies very helpful tools and methods to the study on the hydrologic process of rainfall-runoff,no-point solution control,soil erosion,irrigation design and management.