Spatial Variability Of Precipitation And Groundwater Response Behavior Of Small Watershed In Mountainous Area

Heavy rainfall in mountainous watershed is always followed by development of vegetated slopes instability,Rainfall infiltration into groundwater is the main cause of the slope deformation and destruction, Finding out the groundwater runoff process with accumulation-preservation-dissipation in the study area,response of the groundwater level to intense rain process lagging and water-circulation progress.And response mechanisms of the groundwater in vegetated slopes to intense rain process and its hazard effect,constructing precipitation landslide early warning model is important.Taking typical parent-rock slopes covered by vegetation of Touzhai for research objects, by means of in situ inspections, experiments, indoor test, numerical analysis.and so forth.the following problems will be probed into:The regional geological characteristics,the chemical and physical properties of soil, physical-hydraulic parameter of unsaturated soil, macropore network,and the response process of groundwater. The following conclusions are obtained.(1) Making analysis on the geological survey and physical properties of the soils in vegetated slopes, we can draw such conclusions:The natural moisture content of the soil is very high in the study area, Moisture content of soil is close to saturated moisture content during the rainy season:The natural density, dry density and specific gravity of soil are small,the porosity is large and decreaseing with the depth.(2) According to setting up weather station in two different altitude height position in study area respectively, this paper observated precipitation for one year and compared characteris of precipitation.The results show that precipitation gradient in the study area is up to 190 mm/100 m, the precipitation of the two positions varies significantly with altitude; the main contribution factor of the difference of precipitation between 1# and 2# of the area is the difference of the duration of precipitation;the difference of the precipitation between 1# and 2# are very small when it rains lightly, but when it moderate rains and above that in the 1#, precipitation in the 2# is higher than in the 1# by 1-2 levels and there is 59%probability it will rains heavily or rainstorm in the 2#;when there is a rainstorm in the 1#, the probability of heavy rain and even rainstorm in the 2# is 100%;the precipitation at night is greater than during the day no matter 1# or 2#, Most of heavy precipitation events occurred in the night;There is a large number of regional landslide early warning of critical precipitation standard of different scales,but still existing some problems like warning extension space and time precision, critical precipitation threshold is not scientific.(3) Istalling four triangle weir in main channel section,all of which are aiming at monitoring the whole year’s water level,flow discharge(more than once a week),the real-time precipitation and chemical analysis of water.we draw the such conclusion: the soil in the slope of the vegetation development will not appear surface runoff. The soil of precipitation presents a totally absorb behavior, This is extremely unfavorable to the stability of the slope;River water is formed by groundwater discharge rather than surface runoff, and the water level and quantity of water in the short time changes dramatical ly;Under the influence of natural water content and topography, rainfall in a short time quickly transformed into groundwater and the formation of supply channel flow measurement, groundwater discharge relative precipitation process has no obvious delay. The soil’s ability to regulate precipitation is low. Through the water storage in the dry season and water release to adjust annual runoff is limited.(4)According to the Slope infiltration experiment, which show that the soil saturated infiltration coefficient is very high, the soil can simultaneously absorb most of the precipitation precipitation without surface runoff;The presence of large pores allows water to migrate in the form of preferential flow, and participate in the groundwater cycle. The water flow in the large pore can penetrate the wall of the hole and enter the surrounding matrix area, and accelerate the speed of the downward migration of rainfall;The characteristics of the two element structure of soil and rock can form a partial barrier, the water transfer process is blocked by the transient saturated zone, and the soil matrix suction is decreased, which is easy to cause the slope deformation and failure or shallow landslide.