Study On The Impact From Hydrological Processes Of Shahu Lake With Remote Sensing

Wetland plant is a very important component in the wetland ecosystem. Wetlandhydrological processes, such as water level, flooded time, flooding probability,submergence depth and other hydrological factors controlling the formation andevolution of the wetland, and plays a decisive role on the structure and the growth ofwetland plant. As China’s largest freshwater lake Poyang Lake, which is one of thelargest birds wintering in Asia, to clarify the relationship between the wetlandecosystem structure and hydrological processes has great important significance.This essay selects Shahu Lake as the research area, which is one of the sub lakeof Poyang Lake. Use both RS and GIS technology, to quantitative analysis thecharacteristics of water level, flood duration, probability of flooding, cumulativeinundation depth. Using the time series（2002-2010）EVI (Enhanced vegetation index)from MODIS and8months NDVI date extract from HJ satellites which quality grandabove9. Respectively analysis the space-time variation characteristics, and analysisthe relationship between wetland vegetation index and flooded time, submergencedepth.(1) The change of water level in Shahu lake is relatively stable, especially inautumn and winter season, the highest average water level was in July, and lowestaverage water level in January; The flooding area increase linearly as the rise of waterlevel, when the water level higher than15.2meters, the flooded area reaches themaximum value is10.11km2.(2) According to the average flooded time of Shahu Lake during2002-2013, theelevation of submerged area was between12.4-12.6m, it accounted for18percent ofthe total area, the flooded time changed by elevation, the lower elevation, flood lastedlonger; The higher elevation, flooded lasted shorter; According to the averageprobability of flooding in each quarter, in the first quarter the probability is the lowestand the elevation rate is bigger, water flooding probability increases gradually in thesecond quarter, the Shahu Lake almost whole flooded in third quarter, the floodingprobability reduced when the water level fall back in the fourth quarter, but due to theeffect of gate, the flooding probability reduce slow; according to the average dailysubmergence depth of Shahu Lake, the average daily submergence depth was theshallowest in the first quarter, in the third quarter the average daily submergence depth reaches the maximum value of the year, the deepest depth was4m. the averagedaily submergence depth decline in the fourth quarter, the deepest depth is between1to1.2m.(3) Each vertical band were changed by the fluctuate, the vegetation is dividedinto two growing season, the first growing season in the middle of April to may, thesecond growing season began in the middle of September; EVI decreases by the riseof water level; In spring and autumn EVI value is higher than summer and winter. Thechange tendency of EVI values is consistent by different elevation, on the whole theEVI values was obvious upward with the increase of the rising of elevation.(4) According to the NDVI value extracted by HJ satellite in2012, the NDVIvalue in the scope above13.2m height showed an obvious bimodal characteristics,vegetation began to sprout in March, and with time gradually the grass growcompleted in one month; In mid-September, the grass enter into the second growingseason, NDVI value increased rapidly; within the scope of14.4-15m height theincrease speed of NDVI was faster in spring and the ends of autumn, has a rapidspeed up speed and settling up, the NDVI decline rapidly along with the rainy seasoncoming and in winter when the temperature decrease.(5) Analysis the relationship between EVI value and flooded time, submergencedepth in October. and besides the year2006, the average of flooded time in the restyear were had significantly negative correlation with EVI value. This obviouslyshows the flooded time had a linear relationship with the EVI; submergence depthwere significantly negative with EVI value, EVI value decreased with by thedeepening of cumulative flooding depth In the year2006and2010, this trend werenot obvious, so it showed that the submergence depth is not the only limiting factoraffecting the EVI values.