Study On The Drought And Flood Disasters Formation Mechanism In Karst Area Of Southwest China

Drought and flood is a common environmental problem in bare and shallow bare type ofkarst environment. In southwestern China, the variation of natural conditions and thecomplicated geographical environment provide the hazard inducing environment of droughtsand floods disaster and form the special karst drought and karst Immersion-waterlogging. Theprevention for such droughts and floods is extremely difficult without knowing its geneticmechanism and evolution mechanism.Through comprehensive analysis of southwest China karst area drought and flooddisasters from1900to2012in contour map and meteorological disaster bulletin, the timesof disasters can be summed to pick up the worst-hit areas, Guizhou,Yunnan, Guangxi.Fromthe beginning of the21st century, Guizhou, Yunnan, Guangxi suffered severe drought andflood disasters.Precipitation is the direct factor leading to drought and flood disaster.firstly,taking thePrecipitation from1960to2012of southwest China karst area and Guizhou,Yunnan,Guangxias the study subject. Contrast analysis of the average precipitation and the multi-yearaverage precipitation in these areas Since2000. Results indicate that karst areas ofSouthwest China was entering into the most drought period in history from the beginning ofthe21st century, and in the next ten years, the precipitation of these areas would growsubstantially. But because of the abnormal change about the Monsoon and the water vaportransport in this years, the share of the summer monsoon rainfall will be increased and theshare of the winter monsoon rainfall will be reduced, so, flood season precipitation increaselead to the floods and non-flood season precipitation reduce lead to seasonal droughts. Wecan draw a conclusion that the floods and droughts in the karst areas of Southwest Chinawill not be reduced yet.To see which combination of factors will lead to the floods and droughts, make thesame rainfall as a precondition,pick up the karst topography, karst surface, sub-surface karstarea connectivity pipes，the complexity of the underground karst pipes, the buried depth ofthe underground karst pipes and the hydraulic gradient of the underground karst pipes asmain parameters. Taking the serious drought disaster area in the southwest part of the karstarea as an representative, this paper is using the geometric similarity and water conservancysimilarity to simulate the indoor physics experiment. under the same rainfall intensity, throughcomparative analysis the response of the precipitation in each combination of factors,taking the first max value of prior period and the first min value of decay period as quantitative data，then it is concluded the time and the speed of the Precipitation process under the sixcombination of factors.Finally, combining with rainfall condition, indoor physical simulation comparativeexperiment results and other factors(water storage project and lift irrigation project). Thispaper draws a conclusion about Formation mechanism of the disaster. Precipitation sourceplays a direct role in the formation of the disaster. Under the same precipitation,Karst PeakCluster-depression is easily to be flooded and droughts in peak-forest valley happen easily. Inthe same volume of karst depression, the shape of flat-bottom cylinder is easily drought thanthe shape of parabolic.Under the good connectivity conditions of the surface-undergroundkarst conduit,floods caused by grounder-water are happen easily,and under the badconnectivity conditions of the surface-underground karst conduit,floods caused by surfacewater are happen easily. The underground karst pipes with shallow buried depth and smallerhydraulic gradient easily take place floods, and the underground karst pipes with deeperburied depth and bigger hydraulic gradient easily take place droughts. The underground waterwhich near reservoir is more easy to cause floods in flood season. lift irrigation project is easyto cause partial droughts.