Preliminary Study On The Hydrological Relationship Between River And Reparian Wetlands

Research on wetland hydrology is the prerequisite for wetland protection and restoration. It is one of the most important branches of wetland scicncc.The ripafian wetland is a special type of wetlands because of its geographical location.The hydrology of reparian wetlands is affected not only by precipation,but also by interactions between fiver and the floodplain. Generally speaking,there are two types of interactions that include surface connection and subsurface connection.These connections are linked by over-bank flooding and groundwater water exchange.Taking the Jingwei riparian wetland for example,this research studied the effect of the Wei River on the hydrology of the Jingwei wetland.First,statistical analisis was performed on the variation of the over-bank floods and the cause of change was postulated based on historical records of hydrological data.The hydrology model-MODFLOW was then used to study groungwater interactions between river and the riparian wetland.Last,the importance of over-bank flood on restoration of the Jingwei wetland was studied from the pointview of monthly water banlance of different hydrological year.Major findings of this research are as follows:1)The number of annual over-bank flooding reduced sharply from 1950s to 1990s by 80%. The duration of over-bank flooding,which is mainly controlled by precipation and shapes of the river cross section , declined slightly between 1950 and 2000 . The number of floodingoccurrence has decreased,and the decrease in May and June has the most impact on growth of wetland vegetation.The reduced precipation has major impact on hydrological change of the wetland,and construction of hydraulic projects enhanced such impact by prolonging the duration of drought period.2)The changes in flooding process,duration,river bed hydraulic conductivity and evaporation rate have great impact on the interactions between river and groundwater.The hydraulic conductivity of the floodplain has significant impact on the range of river stage influence.3)The over-bank flooding is the major driving force of the Jingwei wetland hydrology. Groundwater recharge from the Wei River could affect wetness of the reparian wetland within a range of 400m from the river.4)The surface recharge,including over-bank floods and precipation,is the main water sourcefor the Jingwei riparian wetland. It consists of about 60% of the total water supply to the wetland. The effect of groundwater recharge from river is limited,taking part of no more than 30%of the total water supply.The main discharge of the Jingwei riparian wetland is through ET,which is about more than 60%of its total water loss.The annual water balance components change greatly with the large variation of monthly hydrologic factors.