珠江三角洲海平面上升对堤围防御能力的影响

The Influence ofSea LevelRising on the Em bankm ents in the Zhujiang Delta

珠江三角洲２０３０ 年海平面上升幅度约为３０ ｃｍ 。按此，由水力学模型计算了２４ 个站最高洪潮水位的升幅， 以５ ｃｍ 和２５ ｃｍ 等值线划分出影响很小区、影响较大区、影响最大区。由水文学方程计算了１７ 个站４ 种重现期的最高洪潮水位升幅， 得知现有堤围的防御标准在影响较大区将降低半个等级， 在影响最大区将降低一个半等级。受影响的堤围长度为２ ６０８ ｋｍ ， 维护工作量为１ ７５２×１０４ｍ ３， 需投资２１

Itisforecasted thattheam plitude ofsea levelriseforthenext40 years (1990～ 2030) isabout30 cm nearthe Zhujiang Delta. Based on the influence offlood ortide cur- rentthe delta can be divided into three areas, theflood, flood-tidaland tidal. Using a hy- draulicm odelundera typicalcondition ofcatastrophicstorm surge and sm alldischarge oc- curred atSeptem ber1993,therising am plitudesofthehighestflood-tidewaterlevelfor24 hydrom etric stations are calculated respectively, unter the assum ption that the rising is 30 cm . The calculated resultshow s thatthere willbe three influenced areas according to the two isolinesofthe rising am plitude of5 cm and 25 cm . Them axim um rising am plitude Willbe 31 cm in them ostinfluenced area, 25 cm in them edium area and 4 cm only in the uninfluenced area. Itis obvious thatthe influence ofrising 30 cm sea-levelwould be oc- cured m ainly in the tidaland flood-tidalareas. Being influenced by sea levelrise, the frequency ofthe highestflood-tide water level is increased, thatm eans the protection standard ofdyke againstcalam ties is notenough. Using a hydrom etric equation the rising am plitudes of the highist flood-tide w ater level corresponding to fourkindsoffrequencies, ofdischargefor17 stationsarecalculated. The calculated results arein accordancew ith thefrequency ofthehightestflood-tidew aterlev- el. The change ofreappearance periodsofflood-tidew aterlevalare show n in differentar- eas: in flood tide area, the reappearance period decreases by 1/2 class, thatis from 1/50 yrto 1/50～20 yr; in tide area, the decrease is 1.5 or2.0 class, thatis from 1/100 yrto 1/50～20yr. In otherw ords, itisnecessary to raisetheclassofdyke protection standard. There are 104 m u cultivating land orm ore underprotection ofover104 m u totallength of3 057 km dykes, w ithin which, 2 608 km willbeinfluenced by sea levelrise. However the dykesw hich arenotreached the design standard have1 126 km ; thatis43% oftheto- tallength. Therefore in order to pledge the protection ofem bankm ents in the future, it should be considered thatnotonly to reach the design standard butalso to raisethedykes to m eetw ith the rise am plitude offlood-tide w aterlevelifsea levelrise 30 cm are real. It is calculated thattheprojectofcubicm etreofsoiland stonefor2 608 km length dykesis1 752×104m 3 and the investm entis about21 hundred m illion yuan.