Yin Guokang, Chen Qinluan
Located in the southeast Zhejiang Province along the seacoast,the lower reach FeiyunjiangRiver has a strong-tide affected river mouth with serious hazards in flood.waterlogging and stormtide.The level of both correction and development is lower in the area.By analysing its channelproperties,this paper predicts the renewal bed-forming processes of the lower reach caused by building key water control project at Shanxi and diversion works at Tanjiao at the upper and middlereaches of Feiyunjiang River as well as makes a comprehensive appraisal for feasibilities of the rivercutoff,the navigable channel regulation and the harbour construction at the strong-tide affectedreacher.1.River cut-off project can bring obvious socio-economic benefits,but it will exert a certain influence on the channel properties such as:①The limits of both tide currents and tide head will goupstream some 10 km.Consequently a transient aggradation in the river channel may occur and theriver bed will be filled up.So the flood control benefit coming from river cut-off will reduce.②After the cut-off,the channel length will be shorteded by 12.1km,with the channel storage decreaseand the gradient increase the flood peak discharge will increase and get down to the reach earlier.③Owing the expansion of the cut-off leading channel,there will be 1809×104m3 sediments in volumeinputting the channel,most of which will fill in the oxbow lake and other may deposit in the channelbelow the leading channel.This may exert an unfavourable influence on the navigable channel andharbour basin at some local reaches.2.Inside and outside the Feiyunjiang River mouth there are two places in which deepwaterberthes of 104 tonnage can be built:①Ruian new harbour area.②The water area southwest of Beilong island,and.38 km away from Ruian city.3.Building the key water control project at Shanxi and deversion works at Tanjiao.due to theregulated flow and the large amount drawn water out of the channel,will exert the following important influences on the downstream channel:①The channel runoff will reduce its transportability.②As both the tidel water and sediments discharge of the flood tide increase,aggradation in the streamchannel will be able to occur so that the average width,depth and sectional area will respectively decrease by 2.5%,3,0% and 4.0%.③The physical feature of the river channel as a whole willgradually be stable.④As the alterration range of the tidal current limit will obviously be shortened,with a more concentrated deposition in the limited range,a depositional body will occur.⑤The central bar and the riffle at the river reaches between new barbour area and the old one near Rulan citywill extend because of deposition and the movement of river-mouth bar into the mouth.⑥As thetidal current limit goes upstream,the salt-water encroachment will bring an unfavourable influenceto both the soil salinization and the fresh water supply in the flood plain region.
